/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.contacts;

import android.app.ActivityManager;
import android.content.ComponentCallbacks2;
import android.content.ContentResolver;
import android.content.ContentUris;
import android.content.Context;
import android.content.res.Configuration;
import android.content.res.Resources;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.ColorDrawable;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.TransitionDrawable;
import android.media.ThumbnailUtils;
import android.net.TrafficStats;
import android.net.Uri;
import android.net.Uri.Builder;
import android.os.Handler;
import android.os.Handler.Callback;
import android.os.HandlerThread;
import android.os.Message;
import android.provider.ContactsContract;
import android.provider.ContactsContract.Contacts;
import android.provider.ContactsContract.Contacts.Photo;
import android.provider.ContactsContract.Data;
import android.provider.ContactsContract.Directory;
import androidx.core.graphics.drawable.RoundedBitmapDrawable;
import androidx.core.graphics.drawable.RoundedBitmapDrawableFactory;
import android.text.TextUtils;
import android.util.Log;
import android.util.LruCache;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

import com.android.contacts.lettertiles.LetterTileDrawable;
import com.android.contacts.util.BitmapUtil;
import com.android.contacts.util.PermissionsUtil;
import com.android.contacts.util.TrafficStatsTags;
import com.android.contacts.util.UriUtils;
import com.android.contactsbind.util.UserAgentGenerator;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.Reference;
import java.lang.ref.SoftReference;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Iterator;
import java.util.List;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Asynchronously loads contact photos and maintains a cache of photos.
 */
public abstract class ContactPhotoManager implements ComponentCallbacks2 {
    static final String TAG = "ContactPhotoManager";
    static final boolean DEBUG = false; // Don't submit with true
    static final boolean DEBUG_SIZES = false; // Don't submit with true

    /** Contact type constants used for default letter images */
    public static final int TYPE_PERSON = LetterTileDrawable.TYPE_PERSON;
    public static final int TYPE_BUSINESS = LetterTileDrawable.TYPE_BUSINESS;
    public static final int TYPE_VOICEMAIL = LetterTileDrawable.TYPE_VOICEMAIL;
    public static final int TYPE_DEFAULT = LetterTileDrawable.TYPE_DEFAULT;

    /** Scale and offset default constants used for default letter images */
    public static final float SCALE_DEFAULT = 1.0f;
    public static final float OFFSET_DEFAULT = 0.0f;

    public static final boolean IS_CIRCULAR_DEFAULT = false;

    /** Uri-related constants used for default letter images */
    private static final String DISPLAY_NAME_PARAM_KEY = "display_name";
    private static final String IDENTIFIER_PARAM_KEY = "identifier";
    private static final String CONTACT_TYPE_PARAM_KEY = "contact_type";
    private static final String SCALE_PARAM_KEY = "scale";
    private static final String OFFSET_PARAM_KEY = "offset";
    private static final String IS_CIRCULAR_PARAM_KEY = "is_circular";
    private static final String DEFAULT_IMAGE_URI_SCHEME = "defaultimage";
    private static final Uri DEFAULT_IMAGE_URI = Uri.parse(DEFAULT_IMAGE_URI_SCHEME + "://");

    // Static field used to cache the default letter avatar drawable that is created
    // using a null {@link DefaultImageRequest}
    private static Drawable sDefaultLetterAvatar = null;

    private static ContactPhotoManager sInstance;

    /**
     * Given a {@link DefaultImageRequest}, returns a {@link Drawable}, that when drawn, will
     * draw a letter tile avatar based on the request parameters defined in the
     * {@link DefaultImageRequest}.
     */
    public static Drawable getDefaultAvatarDrawableForContact(Resources resources, boolean hires,
            DefaultImageRequest defaultImageRequest) {
        if (defaultImageRequest == null) {
            if (sDefaultLetterAvatar == null) {
                // Cache and return the letter tile drawable that is created by a null request,
                // so that it doesn't have to be recreated every time it is requested again.
                sDefaultLetterAvatar = LetterTileDefaultImageProvider.getDefaultImageForContact(
                        resources, null);
            }
            return sDefaultLetterAvatar;
        }
        return LetterTileDefaultImageProvider.getDefaultImageForContact(resources,
                defaultImageRequest);
    }

    /**
     * Given a {@link DefaultImageRequest}, returns an Uri that can be used to request a
     * letter tile avatar when passed to the {@link ContactPhotoManager}. The internal
     * implementation of this uri is not guaranteed to remain the same across application
     * versions, so the actual uri should never be persisted in long-term storage and reused.
     *
     * @param request A {@link DefaultImageRequest} object with the fields configured
     * to return a
     * @return A Uri that when later passed to the {@link ContactPhotoManager} via
     * {@link #loadPhoto(ImageView, Uri, int, boolean, DefaultImageRequest)}, can be
     * used to request a default contact image, drawn as a letter tile using the
     * parameters as configured in the provided {@link DefaultImageRequest}
     */
    public static Uri getDefaultAvatarUriForContact(DefaultImageRequest request) {
        final Builder builder = DEFAULT_IMAGE_URI.buildUpon();
        if (request != null) {
            if (!TextUtils.isEmpty(request.displayName)) {
                builder.appendQueryParameter(DISPLAY_NAME_PARAM_KEY, request.displayName);
            }
            if (!TextUtils.isEmpty(request.identifier)) {
                builder.appendQueryParameter(IDENTIFIER_PARAM_KEY, request.identifier);
            }
            if (request.contactType != TYPE_DEFAULT) {
                builder.appendQueryParameter(CONTACT_TYPE_PARAM_KEY,
                        String.valueOf(request.contactType));
            }
            if (request.scale != SCALE_DEFAULT) {
                builder.appendQueryParameter(SCALE_PARAM_KEY, String.valueOf(request.scale));
            }
            if (request.offset != OFFSET_DEFAULT) {
                builder.appendQueryParameter(OFFSET_PARAM_KEY, String.valueOf(request.offset));
            }
            if (request.isCircular != IS_CIRCULAR_DEFAULT) {
                builder.appendQueryParameter(IS_CIRCULAR_PARAM_KEY,
                        String.valueOf(request.isCircular));
            }

        }
        return builder.build();
    }

    /**
     * Adds a business contact type encoded fragment to the URL.  Used to ensure photo URLS
     * from Nearby Places can be identified as business photo URLs rather than URLs for personal
     * contact photos.
     *
     * @param photoUrl The photo URL to modify.
     * @return URL with the contact type parameter added and set to TYPE_BUSINESS.
     */
    public static String appendBusinessContactType(String photoUrl) {
        Uri uri = Uri.parse(photoUrl);
        Builder builder = uri.buildUpon();
        builder.encodedFragment(String.valueOf(TYPE_BUSINESS));
        return builder.build().toString();
    }

    /**
     * Removes the contact type information stored in the photo URI encoded fragment.
     *
     * @param photoUri The photo URI to remove the contact type from.
     * @return The photo URI with contact type removed.
     */
    public static Uri removeContactType(Uri photoUri) {
        String encodedFragment = photoUri.getEncodedFragment();
        if (!TextUtils.isEmpty(encodedFragment)) {
            Builder builder = photoUri.buildUpon();
            builder.encodedFragment(null);
            return builder.build();
        }
        return photoUri;
    }

    /**
     * Inspects a photo URI to determine if the photo URI represents a business.
     *
     * @param photoUri The URI to inspect.
     * @return Whether the URI represents a business photo or not.
     */
    public static boolean isBusinessContactUri(Uri photoUri) {
        if (photoUri == null) {
            return false;
        }

        String encodedFragment = photoUri.getEncodedFragment();
        return !TextUtils.isEmpty(encodedFragment)
                && encodedFragment.equals(String.valueOf(TYPE_BUSINESS));
    }

    protected static DefaultImageRequest getDefaultImageRequestFromUri(Uri uri) {
        final DefaultImageRequest request = new DefaultImageRequest(
                uri.getQueryParameter(DISPLAY_NAME_PARAM_KEY),
                uri.getQueryParameter(IDENTIFIER_PARAM_KEY), false);
        try {
            String contactType = uri.getQueryParameter(CONTACT_TYPE_PARAM_KEY);
            if (!TextUtils.isEmpty(contactType)) {
                request.contactType = Integer.valueOf(contactType);
            }

            String scale = uri.getQueryParameter(SCALE_PARAM_KEY);
            if (!TextUtils.isEmpty(scale)) {
                request.scale = Float.valueOf(scale);
            }

            String offset = uri.getQueryParameter(OFFSET_PARAM_KEY);
            if (!TextUtils.isEmpty(offset)) {
                request.offset = Float.valueOf(offset);
            }

            String isCircular = uri.getQueryParameter(IS_CIRCULAR_PARAM_KEY);
            if (!TextUtils.isEmpty(isCircular)) {
                request.isCircular = Boolean.valueOf(isCircular);
            }
        } catch (NumberFormatException e) {
            Log.w(TAG, "Invalid DefaultImageRequest image parameters provided, ignoring and using "
                    + "defaults.");
        }

        return request;
    }

    protected boolean isDefaultImageUri(Uri uri) {
        return DEFAULT_IMAGE_URI_SCHEME.equals(uri.getScheme());
    }

    /**
     * Contains fields used to contain contact details and other user-defined settings that might
     * be used by the ContactPhotoManager to generate a default contact image. This contact image
     * takes the form of a letter or bitmap drawn on top of a colored tile.
     */
    public static class DefaultImageRequest {
        /**
         * The contact's display name. The display name is used to
         */
        public String displayName;

        /**
         * A unique and deterministic string that can be used to identify this contact. This is
         * usually the contact's lookup key, but other contact details can be used as well,
         * especially for non-local or temporary contacts that might not have a lookup key. This
         * is used to determine the color of the tile.
         */
        public String identifier;

        /**
         * The type of this contact. This contact type may be used to decide the kind of
         * image to use in the case where a unique letter cannot be generated from the contact's
         * display name and identifier. See:
         * {@link #TYPE_PERSON}
         * {@link #TYPE_BUSINESS}
         * {@link #TYPE_PERSON}
         * {@link #TYPE_DEFAULT}
         */
        public int contactType = TYPE_DEFAULT;

        /**
         * The amount to scale the letter or bitmap to, as a ratio of its default size (from a
         * range of 0.0f to 2.0f). The default value is 1.0f.
         */
        public float scale = SCALE_DEFAULT;

        /**
         * The amount to vertically offset the letter or image to within the tile.
         * The provided offset must be within the range of -0.5f to 0.5f.
         * If set to -0.5f, the letter will be shifted upwards by 0.5 times the height of the canvas
         * it is being drawn on, which means it will be drawn with the center of the letter starting
         * at the top edge of the canvas.
         * If set to 0.5f, the letter will be shifted downwards by 0.5 times the height of the
         * canvas it is being drawn on, which means it will be drawn with the center of the letter
         * starting at the bottom edge of the canvas.
         * The default is 0.0f, which means the letter is drawn in the exact vertical center of
         * the tile.
         */
        public float offset = OFFSET_DEFAULT;

        /**
         * Whether or not to draw the default image as a circle, instead of as a square/rectangle.
         */
        public boolean isCircular = false;

        /**
         * Used to indicate that a drawable that represents a contact without any contact details
         * should be returned.
         */
        public static DefaultImageRequest EMPTY_DEFAULT_IMAGE_REQUEST = new DefaultImageRequest();

        /**
         * Used to indicate that a drawable that represents a business without a business photo
         * should be returned.
         */
        public static DefaultImageRequest EMPTY_DEFAULT_BUSINESS_IMAGE_REQUEST =
                new DefaultImageRequest(null, null, TYPE_BUSINESS, false);

        /**
         * Used to indicate that a circular drawable that represents a contact without any contact
         * details should be returned.
         */
        public static DefaultImageRequest EMPTY_CIRCULAR_DEFAULT_IMAGE_REQUEST =
                new DefaultImageRequest(null, null, true);

        /**
         * Used to indicate that a circular drawable that represents a business without a business
         * photo should be returned.
         */
        public static DefaultImageRequest EMPTY_CIRCULAR_BUSINESS_IMAGE_REQUEST =
                new DefaultImageRequest(null, null, TYPE_BUSINESS, true);

        public DefaultImageRequest() {
        }

        public DefaultImageRequest(String displayName, String identifier, boolean isCircular) {
            this(displayName, identifier, TYPE_DEFAULT, SCALE_DEFAULT, OFFSET_DEFAULT, isCircular);
        }

        public DefaultImageRequest(String displayName, String identifier, int contactType,
                boolean isCircular) {
            this(displayName, identifier, contactType, SCALE_DEFAULT, OFFSET_DEFAULT, isCircular);
        }

        public DefaultImageRequest(String displayName, String identifier, int contactType,
                float scale, float offset, boolean isCircular) {
            this.displayName = displayName;
            this.identifier = identifier;
            this.contactType = contactType;
            this.scale = scale;
            this.offset = offset;
            this.isCircular = isCircular;
        }
    }

    public static abstract class DefaultImageProvider {
        /**
         * Applies the default avatar to the ImageView. Extent is an indicator for the size (width
         * or height). If darkTheme is set, the avatar is one that looks better on dark background
         *
         * @param defaultImageRequest {@link DefaultImageRequest} object that specifies how a
         * default letter tile avatar should be drawn.
         */
        public abstract void applyDefaultImage(ImageView view, int extent, boolean darkTheme,
                DefaultImageRequest defaultImageRequest);
    }

    /**
     * A default image provider that applies a letter tile consisting of a colored background
     * and a letter in the foreground as the default image for a contact. The color of the
     * background and the type of letter is decided based on the contact's details.
     */
    private static class LetterTileDefaultImageProvider extends DefaultImageProvider {
        @Override
        public void applyDefaultImage(ImageView view, int extent, boolean darkTheme,
                DefaultImageRequest defaultImageRequest) {
            final Drawable drawable = getDefaultImageForContact(view.getResources(),
                    defaultImageRequest);
            view.setImageDrawable(drawable);
        }

        public static Drawable getDefaultImageForContact(Resources resources,
                DefaultImageRequest defaultImageRequest) {
            final LetterTileDrawable drawable = new LetterTileDrawable(resources);
            if (defaultImageRequest != null) {
                // If the contact identifier is null or empty, fallback to the
                // displayName. In that case, use {@code null} for the contact's
                // display name so that a default bitmap will be used instead of a
                // letter
                if (TextUtils.isEmpty(defaultImageRequest.identifier)) {
                    drawable.setLetterAndColorFromContactDetails(null,
                            defaultImageRequest.displayName);
                } else {
                    drawable.setLetterAndColorFromContactDetails(defaultImageRequest.displayName,
                            defaultImageRequest.identifier);
                }
                drawable.setContactType(defaultImageRequest.contactType);
                drawable.setScale(defaultImageRequest.scale);
                drawable.setOffset(defaultImageRequest.offset);
                drawable.setIsCircular(defaultImageRequest.isCircular);
            }
            return drawable;
        }
    }

    private static class BlankDefaultImageProvider extends DefaultImageProvider {
        private static Drawable sDrawable;

        @Override
        public void applyDefaultImage(ImageView view, int extent, boolean darkTheme,
                DefaultImageRequest defaultImageRequest) {
            if (sDrawable == null) {
                Context context = view.getContext();
                sDrawable = new ColorDrawable(context.getResources().getColor(
                        R.color.image_placeholder));
            }
            view.setImageDrawable(sDrawable);
        }
    }

    public static DefaultImageProvider DEFAULT_AVATAR = new LetterTileDefaultImageProvider();

    public static final DefaultImageProvider DEFAULT_BLANK = new BlankDefaultImageProvider();

    public static ContactPhotoManager getInstance(Context context) {
        if (sInstance == null) {
            Context applicationContext = context.getApplicationContext();
            sInstance = createContactPhotoManager(applicationContext);
            applicationContext.registerComponentCallbacks(sInstance);
            if (PermissionsUtil.hasContactsPermissions(context)) {
                sInstance.preloadPhotosInBackground();
            }
        }
        return sInstance;
    }

    public static synchronized ContactPhotoManager createContactPhotoManager(Context context) {
        return new ContactPhotoManagerImpl(context);
    }

    @VisibleForTesting
    public static void injectContactPhotoManagerForTesting(ContactPhotoManager photoManager) {
        sInstance = photoManager;
    }

    /**
     * Load thumbnail image into the supplied image view. If the photo is already cached,
     * it is displayed immediately.  Otherwise a request is sent to load the photo
     * from the database.
     */
    public abstract void loadThumbnail(ImageView view, long photoId, boolean darkTheme,
            boolean isCircular, DefaultImageRequest defaultImageRequest,
            DefaultImageProvider defaultProvider);

    /**
     * Calls {@link #loadThumbnail(ImageView, long, boolean, DefaultImageRequest,
     * DefaultImageProvider)} using the {@link DefaultImageProvider} {@link #DEFAULT_AVATAR}.
     */
    public final void loadThumbnail(ImageView view, long photoId, boolean darkTheme,
            boolean isCircular, DefaultImageRequest defaultImageRequest) {
        loadThumbnail(view, photoId, darkTheme, isCircular, defaultImageRequest, DEFAULT_AVATAR);
    }


    /**
     * Load photo into the supplied image view. If the photo is already cached,
     * it is displayed immediately. Otherwise a request is sent to load the photo
     * from the location specified by the URI.
     *
     * @param view The target view
     * @param photoUri The uri of the photo to load
     * @param requestedExtent Specifies an approximate Max(width, height) of the targetView.
     * This is useful if the source image can be a lot bigger that the target, so that the decoding
     * is done using efficient sampling. If requestedExtent is specified, no sampling of the image
     * is performed
     * @param darkTheme Whether the background is dark. This is used for default avatars
     * @param defaultImageRequest {@link DefaultImageRequest} object that specifies how a default
     * letter tile avatar should be drawn.
     * @param defaultProvider The provider of default avatars (this is used if photoUri doesn't
     * refer to an existing image)
     */
    public abstract void loadPhoto(ImageView view, Uri photoUri, int requestedExtent,
            boolean darkTheme, boolean isCircular, DefaultImageRequest defaultImageRequest,
            DefaultImageProvider defaultProvider);

    /**
     * Calls {@link #loadPhoto(ImageView, Uri, int, boolean, DefaultImageRequest,
     * DefaultImageProvider)} with {@link #DEFAULT_AVATAR} and {@code null} display names and
     * lookup keys.
     *
     * @param defaultImageRequest {@link DefaultImageRequest} object that specifies how a default
     * letter tile avatar should be drawn.
     */
    public final void loadPhoto(ImageView view, Uri photoUri, int requestedExtent,
            boolean darkTheme, boolean isCircular, DefaultImageRequest defaultImageRequest) {
        loadPhoto(view, photoUri, requestedExtent, darkTheme, isCircular,
                defaultImageRequest, DEFAULT_AVATAR);
    }

    /**
     * Calls {@link #loadPhoto(ImageView, Uri, boolean, boolean, DefaultImageRequest,
     * DefaultImageProvider)} with {@link #DEFAULT_AVATAR} and with the assumption, that
     * the image is a thumbnail.
     *
     * @param defaultImageRequest {@link DefaultImageRequest} object that specifies how a default
     * letter tile avatar should be drawn.
     */
    public final void loadDirectoryPhoto(ImageView view, Uri photoUri, boolean darkTheme,
            boolean isCircular, DefaultImageRequest defaultImageRequest) {
        loadPhoto(view, photoUri, -1, darkTheme, isCircular, defaultImageRequest, DEFAULT_AVATAR);
    }

    /**
     * Remove photo from the supplied image view. This also cancels current pending load request
     * inside this photo manager.
     */
    public abstract void removePhoto(ImageView view);

    /**
     * Cancels all pending requests to load photos asynchronously.
     */
    public abstract void cancelPendingRequests(View fragmentRootView);

    /**
     * Temporarily stops loading photos from the database.
     */
    public abstract void pause();

    /**
     * Resumes loading photos from the database.
     */
    public abstract void resume();

    /**
     * Marks all cached photos for reloading.  We can continue using cache but should
     * also make sure the photos haven't changed in the background and notify the views
     * if so.
     */
    public abstract void refreshCache();

    /**
     * Stores the given bitmap directly in the LRU bitmap cache.
     * @param photoUri The URI of the photo (for future requests).
     * @param bitmap The bitmap.
     * @param photoBytes The bytes that were parsed to create the bitmap.
     */
    public abstract void cacheBitmap(Uri photoUri, Bitmap bitmap, byte[] photoBytes);

    /**
     * Initiates a background process that over time will fill up cache with
     * preload photos.
     */
    public abstract void preloadPhotosInBackground();

    // ComponentCallbacks2
    @Override
    public void onConfigurationChanged(Configuration newConfig) {
    }

    // ComponentCallbacks2
    @Override
    public void onLowMemory() {
    }

    // ComponentCallbacks2
    @Override
    public void onTrimMemory(int level) {
    }
}

class ContactPhotoManagerImpl extends ContactPhotoManager implements Callback {
    private static final String LOADER_THREAD_NAME = "ContactPhotoLoader";

    private static final int FADE_TRANSITION_DURATION = 200;

    /**
     * Type of message sent by the UI thread to itself to indicate that some photos
     * need to be loaded.
     */
    private static final int MESSAGE_REQUEST_LOADING = 1;

    /**
     * Type of message sent by the loader thread to indicate that some photos have
     * been loaded.
     */
    private static final int MESSAGE_PHOTOS_LOADED = 2;

    private static final String[] EMPTY_STRING_ARRAY = new String[0];

    private static final String[] COLUMNS = new String[] { Photo._ID, Photo.PHOTO };

    /**
     * Placeholder object used to indicate that a bitmap for a given key could not
     * be stored in the cache.
     */
    private static final BitmapHolder BITMAP_UNAVAILABLE;

    static {
        BITMAP_UNAVAILABLE = new BitmapHolder(new byte[0], 0);
        BITMAP_UNAVAILABLE.bitmapRef = new SoftReference<Bitmap>(null);
    }

    /**
     * Maintains the state of a particular photo.
     */
    private static class BitmapHolder {
        final byte[] bytes;
        final int originalSmallerExtent;

        volatile boolean fresh;
        Bitmap bitmap;
        Reference<Bitmap> bitmapRef;
        int decodedSampleSize;

        public BitmapHolder(byte[] bytes, int originalSmallerExtent) {
            this.bytes = bytes;
            this.fresh = true;
            this.originalSmallerExtent = originalSmallerExtent;
        }
    }

    private final Context mContext;

    /**
     * An LRU cache for bitmap holders. The cache contains bytes for photos just
     * as they come from the database. Each holder has a soft reference to the
     * actual bitmap.
     */
    private final LruCache<Object, BitmapHolder> mBitmapHolderCache;

    /**
     * {@code true} if ALL entries in {@link #mBitmapHolderCache} are NOT fresh.
     */
    private volatile boolean mBitmapHolderCacheAllUnfresh = true;

    /**
     * Cache size threshold at which bitmaps will not be preloaded.
     */
    private final int mBitmapHolderCacheRedZoneBytes;

    /**
     * Level 2 LRU cache for bitmaps. This is a smaller cache that holds
     * the most recently used bitmaps to save time on decoding
     * them from bytes (the bytes are stored in {@link #mBitmapHolderCache}.
     */
    private final LruCache<Object, Bitmap> mBitmapCache;

    /**
     * A map from ImageView to the corresponding photo ID or uri, encapsulated in a request.
     * The request may swapped out before the photo loading request is started.
     */
    private final ConcurrentHashMap<ImageView, Request> mPendingRequests =
            new ConcurrentHashMap<ImageView, Request>();

    /**
     * Handler for messages sent to the UI thread.
     */
    private final Handler mMainThreadHandler = new Handler(this);

    /**
     * Thread responsible for loading photos from the database. Created upon
     * the first request.
     */
    private LoaderThread mLoaderThread;

    /**
     * A gate to make sure we only send one instance of MESSAGE_PHOTOS_NEEDED at a time.
     */
    private boolean mLoadingRequested;

    /**
     * Flag indicating if the image loading is paused.
     */
    private boolean mPaused;

    /** Cache size for {@link #mBitmapHolderCache} for devices with "large" RAM. */
    private static final int HOLDER_CACHE_SIZE = 2000000;

    /** Cache size for {@link #mBitmapCache} for devices with "large" RAM. */
    private static final int BITMAP_CACHE_SIZE = 36864 * 48; // 1728K

    /** Height/width of a thumbnail image */
    private static int mThumbnailSize;

    /** For debug: How many times we had to reload cached photo for a stale entry */
    private final AtomicInteger mStaleCacheOverwrite = new AtomicInteger();

    /** For debug: How many times we had to reload cached photo for a fresh entry.  Should be 0. */
    private final AtomicInteger mFreshCacheOverwrite = new AtomicInteger();

    /**
     * The user agent string to use when loading URI based photos.
     */
    private String mUserAgent;

    public ContactPhotoManagerImpl(Context context) {
        mContext = context;

        final ActivityManager am = ((ActivityManager) context.getSystemService(
                Context.ACTIVITY_SERVICE));

        final float cacheSizeAdjustment = (am.isLowRamDevice()) ? 0.5f : 1.0f;

        final int bitmapCacheSize = (int) (cacheSizeAdjustment * BITMAP_CACHE_SIZE);
        mBitmapCache = new LruCache<Object, Bitmap>(bitmapCacheSize) {
            @Override protected int sizeOf(Object key, Bitmap value) {
                return value.getByteCount();
            }

            @Override protected void entryRemoved(
                    boolean evicted, Object key, Bitmap oldValue, Bitmap newValue) {
                if (DEBUG) dumpStats();
            }
        };
        final int holderCacheSize = (int) (cacheSizeAdjustment * HOLDER_CACHE_SIZE);
        mBitmapHolderCache = new LruCache<Object, BitmapHolder>(holderCacheSize) {
            @Override protected int sizeOf(Object key, BitmapHolder value) {
                return value.bytes != null ? value.bytes.length : 0;
            }

            @Override protected void entryRemoved(
                    boolean evicted, Object key, BitmapHolder oldValue, BitmapHolder newValue) {
                if (DEBUG) dumpStats();
            }
        };
        mBitmapHolderCacheRedZoneBytes = (int) (holderCacheSize * 0.75);
        Log.i(TAG, "Cache adj: " + cacheSizeAdjustment);
        if (DEBUG) {
            Log.d(TAG, "Cache size: " + btk(mBitmapHolderCache.maxSize())
                    + " + " + btk(mBitmapCache.maxSize()));
        }

        mThumbnailSize = context.getResources().getDimensionPixelSize(
                R.dimen.contact_browser_list_item_photo_size);

        // Get a user agent string to use for URI photo requests.
        mUserAgent = UserAgentGenerator.getUserAgent(context);
        if (mUserAgent == null) {
            mUserAgent = "";
        }
    }

    /** Converts bytes to K bytes, rounding up.  Used only for debug log. */
    private static String btk(int bytes) {
        return ((bytes + 1023) / 1024) + "K";
    }

    private static final int safeDiv(int dividend, int divisor) {
        return (divisor  == 0) ? 0 : (dividend / divisor);
    }

    /**
     * Dump cache stats on logcat.
     */
    private void dumpStats() {
        if (!DEBUG) return;
        {
            int numHolders = 0;
            int rawBytes = 0;
            int bitmapBytes = 0;
            int numBitmaps = 0;
            for (BitmapHolder h : mBitmapHolderCache.snapshot().values()) {
                numHolders++;
                if (h.bytes != null) {
                    rawBytes += h.bytes.length;
                }
                Bitmap b = h.bitmapRef != null ? h.bitmapRef.get() : null;
                if (b != null) {
                    numBitmaps++;
                    bitmapBytes += b.getByteCount();
                }
            }
            Log.d(TAG, "L1: " + btk(rawBytes) + " + " + btk(bitmapBytes) + " = "
                    + btk(rawBytes + bitmapBytes) + ", " + numHolders + " holders, "
                    + numBitmaps + " bitmaps, avg: "
                    + btk(safeDiv(rawBytes, numHolders))
                    + "," + btk(safeDiv(bitmapBytes,numBitmaps)));
            Log.d(TAG, "L1 Stats: " + mBitmapHolderCache.toString()
                    + ", overwrite: fresh=" + mFreshCacheOverwrite.get()
                    + " stale=" + mStaleCacheOverwrite.get());
        }

        {
            int numBitmaps = 0;
            int bitmapBytes = 0;
            for (Bitmap b : mBitmapCache.snapshot().values()) {
                numBitmaps++;
                bitmapBytes += b.getByteCount();
            }
            Log.d(TAG, "L2: " + btk(bitmapBytes) + ", " + numBitmaps + " bitmaps"
                    + ", avg: " + btk(safeDiv(bitmapBytes, numBitmaps)));
            // We don't get from L2 cache, so L2 stats is meaningless.
        }
    }

    @Override
    public void onTrimMemory(int level) {
        if (DEBUG) Log.d(TAG, "onTrimMemory: " + level);
        if (level >= ComponentCallbacks2.TRIM_MEMORY_MODERATE) {
            // Clear the caches.  Note all pending requests will be removed too.
            clear();
        }
    }

    @Override
    public void preloadPhotosInBackground() {
        ensureLoaderThread();
        mLoaderThread.requestPreloading();
    }

    @Override
    public void loadThumbnail(ImageView view, long photoId, boolean darkTheme, boolean isCircular,
            DefaultImageRequest defaultImageRequest, DefaultImageProvider defaultProvider) {
        if (photoId == 0) {
            // No photo is needed
            defaultProvider.applyDefaultImage(view, -1, darkTheme, defaultImageRequest);
            mPendingRequests.remove(view);
        } else {
            if (DEBUG) Log.d(TAG, "loadPhoto request: " + photoId);
            loadPhotoByIdOrUri(view, Request.createFromThumbnailId(photoId, darkTheme, isCircular,
                    defaultProvider, defaultImageRequest));
        }
    }

    @Override
    public void loadPhoto(ImageView view, Uri photoUri, int requestedExtent, boolean darkTheme,
            boolean isCircular, DefaultImageRequest defaultImageRequest,
            DefaultImageProvider defaultProvider) {
        if (photoUri == null) {
            // No photo is needed
            defaultProvider.applyDefaultImage(view, requestedExtent, darkTheme,
                    defaultImageRequest);
            mPendingRequests.remove(view);
        } else {
            if (DEBUG) Log.d(TAG, "loadPhoto request: " + photoUri);
            if (isDefaultImageUri(photoUri)) {
                createAndApplyDefaultImageForUri(view, photoUri, requestedExtent, darkTheme,
                        isCircular, defaultProvider);
            } else {
                loadPhotoByIdOrUri(view, Request.createFromUri(photoUri, requestedExtent,
                        darkTheme, isCircular, defaultProvider, defaultImageRequest));
            }
        }
    }

    private void createAndApplyDefaultImageForUri(ImageView view, Uri uri, int requestedExtent,
            boolean darkTheme, boolean isCircular, DefaultImageProvider defaultProvider) {
        DefaultImageRequest request = getDefaultImageRequestFromUri(uri);
        request.isCircular = isCircular;
        defaultProvider.applyDefaultImage(view, requestedExtent, darkTheme, request);
    }

    private void loadPhotoByIdOrUri(ImageView view, Request request) {
        boolean loaded = loadCachedPhoto(view, request, false);
        if (loaded) {
            mPendingRequests.remove(view);
        } else {
            mPendingRequests.put(view, request);
            if (!mPaused) {
                // Send a request to start loading photos
                requestLoading();
            }
        }
    }

    @Override
    public void removePhoto(ImageView view) {
        view.setImageDrawable(null);
        mPendingRequests.remove(view);
    }


    /**
     * Cancels pending requests to load photos asynchronously for views inside
     * {@param fragmentRootView}. If {@param fragmentRootView} is null, cancels all requests.
     */
    @Override
    public void cancelPendingRequests(View fragmentRootView) {
        if (fragmentRootView == null) {
            mPendingRequests.clear();
            return;
        }
        final Iterator<Entry<ImageView, Request>> iterator = mPendingRequests.entrySet().iterator();
        while (iterator.hasNext()) {
            final ImageView imageView = iterator.next().getKey();
            // If an ImageView is orphaned (currently scrap) or a child of fragmentRootView, then
            // we can safely remove its request.
            if (imageView.getParent() == null || isChildView(fragmentRootView, imageView)) {
                iterator.remove();
            }
        }
    }

    private static boolean isChildView(View parent, View potentialChild) {
        return potentialChild.getParent() != null && (potentialChild.getParent() == parent || (
                potentialChild.getParent() instanceof ViewGroup && isChildView(parent,
                        (ViewGroup) potentialChild.getParent())));
    }

    @Override
    public void refreshCache() {
        if (mBitmapHolderCacheAllUnfresh) {
            if (DEBUG) Log.d(TAG, "refreshCache -- no fresh entries.");
            return;
        }
        if (DEBUG) Log.d(TAG, "refreshCache");
        mBitmapHolderCacheAllUnfresh = true;
        for (BitmapHolder holder : mBitmapHolderCache.snapshot().values()) {
            if (holder != BITMAP_UNAVAILABLE) {
                holder.fresh = false;
            }
        }
    }

    /**
     * Checks if the photo is present in cache.  If so, sets the photo on the view.
     *
     * @return false if the photo needs to be (re)loaded from the provider.
     */
    private boolean loadCachedPhoto(ImageView view, Request request, boolean fadeIn) {
        BitmapHolder holder = mBitmapHolderCache.get(request.getKey());
        if (holder == null) {
            // The bitmap has not been loaded ==> show default avatar
            request.applyDefaultImage(view, request.mIsCircular);
            return false;
        }

        if (holder.bytes == null || holder.bytes.length == 0) {
            request.applyDefaultImage(view, request.mIsCircular);
            return holder.fresh;
        }

        Bitmap cachedBitmap = holder.bitmapRef == null ? null : holder.bitmapRef.get();
        if (cachedBitmap == null) {
            if (holder.bytes.length < 8 * 1024) {
                // Small thumbnails are usually quick to inflate. Let's do that on the UI thread
                inflateBitmap(holder, request.getRequestedExtent());
                cachedBitmap = holder.bitmap;
                if (cachedBitmap == null) return false;
            } else {
                // This is bigger data. Let's send that back to the Loader so that we can
                // inflate this in the background
                request.applyDefaultImage(view, request.mIsCircular);
                return false;
            }
        }

        final Drawable previousDrawable = view.getDrawable();
        if (fadeIn && previousDrawable != null) {
            final Drawable[] layers = new Drawable[2];
            // Prevent cascade of TransitionDrawables.
            if (previousDrawable instanceof TransitionDrawable) {
                final TransitionDrawable previousTransitionDrawable =
                        (TransitionDrawable) previousDrawable;
                layers[0] = previousTransitionDrawable.getDrawable(
                        previousTransitionDrawable.getNumberOfLayers() - 1);
            } else {
                layers[0] = previousDrawable;
            }
            layers[1] = getDrawableForBitmap(mContext.getResources(), cachedBitmap, request);
            TransitionDrawable drawable = new TransitionDrawable(layers);
            view.setImageDrawable(drawable);
            drawable.startTransition(FADE_TRANSITION_DURATION);
        } else {
            view.setImageDrawable(
                    getDrawableForBitmap(mContext.getResources(), cachedBitmap, request));
        }

        // Put the bitmap in the LRU cache. But only do this for images that are small enough
        // (we require that at least six of those can be cached at the same time)
        if (cachedBitmap.getByteCount() < mBitmapCache.maxSize() / 6) {
            mBitmapCache.put(request.getKey(), cachedBitmap);
        }

        // Soften the reference
        holder.bitmap = null;

        return holder.fresh;
    }

    /**
     * Given a bitmap, returns a drawable that is configured to display the bitmap based on the
     * specified request.
     */
    private Drawable getDrawableForBitmap(Resources resources, Bitmap bitmap, Request request) {
        if (request.mIsCircular) {
            final RoundedBitmapDrawable drawable =
                    RoundedBitmapDrawableFactory.create(resources, bitmap);
            drawable.setAntiAlias(true);
            drawable.setCornerRadius(bitmap.getHeight() / 2);
            return drawable;
        } else {
            return new BitmapDrawable(resources, bitmap);
        }
    }

    /**
     * If necessary, decodes bytes stored in the holder to Bitmap.  As long as the
     * bitmap is held either by {@link #mBitmapCache} or by a soft reference in
     * the holder, it will not be necessary to decode the bitmap.
     */
    private static void inflateBitmap(BitmapHolder holder, int requestedExtent) {
        final int sampleSize =
                BitmapUtil.findOptimalSampleSize(holder.originalSmallerExtent, requestedExtent);
        byte[] bytes = holder.bytes;
        if (bytes == null || bytes.length == 0) {
            return;
        }

        if (sampleSize == holder.decodedSampleSize) {
            // Check the soft reference.  If will be retained if the bitmap is also
            // in the LRU cache, so we don't need to check the LRU cache explicitly.
            if (holder.bitmapRef != null) {
                holder.bitmap = holder.bitmapRef.get();
                if (holder.bitmap != null) {
                    return;
                }
            }
        }

        try {
            Bitmap bitmap = BitmapUtil.decodeBitmapFromBytes(bytes, sampleSize);

            // TODO: As a temporary workaround while framework support is being added to
            // clip non-square bitmaps into a perfect circle, manually crop the bitmap into
            // into a square if it will be displayed as a thumbnail so that it can be cropped
            // into a circle.
            final int height = bitmap.getHeight();
            final int width = bitmap.getWidth();

            // The smaller dimension of a scaled bitmap can range from anywhere from 0 to just
            // below twice the length of a thumbnail image due to the way we calculate the optimal
            // sample size.
            if (height != width && Math.min(height, width) <= mThumbnailSize * 2) {
                final int dimension = Math.min(height, width);
                bitmap = ThumbnailUtils.extractThumbnail(bitmap, dimension, dimension);
            }
            // make bitmap mutable and draw size onto it
            if (DEBUG_SIZES) {
                Bitmap original = bitmap;
                bitmap = bitmap.copy(bitmap.getConfig(), true);
                original.recycle();
                Canvas canvas = new Canvas(bitmap);
                Paint paint = new Paint();
                paint.setTextSize(16);
                paint.setColor(Color.BLUE);
                paint.setStyle(Style.FILL);
                canvas.drawRect(0.0f, 0.0f, 50.0f, 20.0f, paint);
                paint.setColor(Color.WHITE);
                paint.setAntiAlias(true);
                canvas.drawText(bitmap.getWidth() + "/" + sampleSize, 0, 15, paint);
            }

            holder.decodedSampleSize = sampleSize;
            holder.bitmap = bitmap;
            holder.bitmapRef = new SoftReference<Bitmap>(bitmap);
            if (DEBUG) {
                Log.d(TAG, "inflateBitmap " + btk(bytes.length) + " -> "
                        + bitmap.getWidth() + "x" + bitmap.getHeight()
                        + ", " + btk(bitmap.getByteCount()));
            }
        } catch (OutOfMemoryError e) {
            // Do nothing - the photo will appear to be missing
        }
    }

    public void clear() {
        if (DEBUG) Log.d(TAG, "clear");
        mPendingRequests.clear();
        mBitmapHolderCache.evictAll();
        mBitmapCache.evictAll();
    }

    @Override
    public void pause() {
        mPaused = true;
    }

    @Override
    public void resume() {
        mPaused = false;
        if (DEBUG) dumpStats();
        if (!mPendingRequests.isEmpty()) {
            requestLoading();
        }
    }

    /**
     * Sends a message to this thread itself to start loading images.  If the current
     * view contains multiple image views, all of those image views will get a chance
     * to request their respective photos before any of those requests are executed.
     * This allows us to load images in bulk.
     */
    private void requestLoading() {
        if (!mLoadingRequested) {
            mLoadingRequested = true;
            mMainThreadHandler.sendEmptyMessage(MESSAGE_REQUEST_LOADING);
        }
    }

    /**
     * Processes requests on the main thread.
     */
    @Override
    public boolean handleMessage(Message msg) {
        switch (msg.what) {
            case MESSAGE_REQUEST_LOADING: {
                mLoadingRequested = false;
                if (!mPaused) {
                    ensureLoaderThread();
                    mLoaderThread.requestLoading();
                }
                return true;
            }

            case MESSAGE_PHOTOS_LOADED: {
                if (!mPaused) {
                    processLoadedImages();
                }
                if (DEBUG) dumpStats();
                return true;
            }
        }
        return false;
    }

    public void ensureLoaderThread() {
        if (mLoaderThread == null) {
            mLoaderThread = new LoaderThread(mContext.getContentResolver());
            mLoaderThread.start();
        }
    }

    /**
     * Goes over pending loading requests and displays loaded photos.  If some of the
     * photos still haven't been loaded, sends another request for image loading.
     */
    private void processLoadedImages() {
        final Iterator<Entry<ImageView, Request>> iterator = mPendingRequests.entrySet().iterator();
        while (iterator.hasNext()) {
            final Entry<ImageView, Request> entry = iterator.next();
            // TODO: Temporarily disable contact photo fading in, until issues with
            // RoundedBitmapDrawables overlapping the default image drawables are resolved.
            final boolean loaded = loadCachedPhoto(entry.getKey(), entry.getValue(), false);
            if (loaded) {
                iterator.remove();
            }
        }

        softenCache();

        if (!mPendingRequests.isEmpty()) {
            requestLoading();
        }
    }

    /**
     * Removes strong references to loaded bitmaps to allow them to be garbage collected
     * if needed.  Some of the bitmaps will still be retained by {@link #mBitmapCache}.
     */
    private void softenCache() {
        for (BitmapHolder holder : mBitmapHolderCache.snapshot().values()) {
            holder.bitmap = null;
        }
    }

    /**
     * Stores the supplied bitmap in cache.
     * bytes should be null to indicate a failure to load the photo. An empty byte[] signifies
     * a successful load but no photo was available.
     */
    private void cacheBitmap(Object key, byte[] bytes, boolean preloading, int requestedExtent) {
        if (DEBUG) {
            BitmapHolder prev = mBitmapHolderCache.get(key);
            if (prev != null && prev.bytes != null) {
                Log.d(TAG, "Overwriting cache: key=" + key + (prev.fresh ? " FRESH" : " stale"));
                if (prev.fresh) {
                    mFreshCacheOverwrite.incrementAndGet();
                } else {
                    mStaleCacheOverwrite.incrementAndGet();
                }
            }
            Log.d(TAG, "Caching data: key=" + key + ", " +
                    (bytes == null ? "<null>" : btk(bytes.length)));
        }
        BitmapHolder holder = new BitmapHolder(bytes,
                bytes == null ? -1 : BitmapUtil.getSmallerExtentFromBytes(bytes));

        // Unless this image is being preloaded, decode it right away while
        // we are still on the background thread.
        if (!preloading) {
            inflateBitmap(holder, requestedExtent);
        }

        if (bytes != null) {
            mBitmapHolderCache.put(key, holder);
            if (mBitmapHolderCache.get(key) != holder) {
                Log.w(TAG, "Bitmap too big to fit in cache.");
                mBitmapHolderCache.put(key, BITMAP_UNAVAILABLE);
            }
        } else {
            mBitmapHolderCache.put(key, BITMAP_UNAVAILABLE);
        }

        mBitmapHolderCacheAllUnfresh = false;
    }

    @Override
    public void cacheBitmap(Uri photoUri, Bitmap bitmap, byte[] photoBytes) {
        final int smallerExtent = Math.min(bitmap.getWidth(), bitmap.getHeight());
        // We can pretend here that the extent of the photo was the size that we originally
        // requested
        Request request = Request.createFromUri(photoUri, smallerExtent, false /* darkTheme */,
                false /* isCircular */ , DEFAULT_AVATAR);
        BitmapHolder holder = new BitmapHolder(photoBytes, smallerExtent);
        holder.bitmapRef = new SoftReference<Bitmap>(bitmap);
        mBitmapHolderCache.put(request.getKey(), holder);
        mBitmapHolderCacheAllUnfresh = false;
        mBitmapCache.put(request.getKey(), bitmap);
    }

    /**
     * Populates an array of photo IDs that need to be loaded. Also decodes bitmaps that we have
     * already loaded
     */
    private void obtainPhotoIdsAndUrisToLoad(Set<Long> photoIds,
            Set<String> photoIdsAsStrings, Set<Request> uris) {
        photoIds.clear();
        photoIdsAsStrings.clear();
        uris.clear();

        boolean jpegsDecoded = false;

        /*
         * Since the call is made from the loader thread, the map could be
         * changing during the iteration. That's not really a problem:
         * ConcurrentHashMap will allow those changes to happen without throwing
         * exceptions. Since we may miss some requests in the situation of
         * concurrent change, we will need to check the map again once loading
         * is complete.
         */
        Iterator<Request> iterator = mPendingRequests.values().iterator();
        while (iterator.hasNext()) {
            Request request = iterator.next();
            final BitmapHolder holder = mBitmapHolderCache.get(request.getKey());
            if (holder == BITMAP_UNAVAILABLE) {
                continue;
            }
            if (holder != null && holder.bytes != null && holder.fresh &&
                    (holder.bitmapRef == null || holder.bitmapRef.get() == null)) {
                // This was previously loaded but we don't currently have the inflated Bitmap
                inflateBitmap(holder, request.getRequestedExtent());
                jpegsDecoded = true;
            } else {
                if (holder == null || !holder.fresh) {
                    if (request.isUriRequest()) {
                        uris.add(request);
                    } else {
                        photoIds.add(request.getId());
                        photoIdsAsStrings.add(String.valueOf(request.mId));
                    }
                }
            }
        }

        if (jpegsDecoded) mMainThreadHandler.sendEmptyMessage(MESSAGE_PHOTOS_LOADED);
    }

    /**
     * The thread that performs loading of photos from the database.
     */
    private class LoaderThread extends HandlerThread implements Callback {
        private static final int BUFFER_SIZE = 1024*16;
        private static final int MESSAGE_PRELOAD_PHOTOS = 0;
        private static final int MESSAGE_LOAD_PHOTOS = 1;

        /**
         * A pause between preload batches that yields to the UI thread.
         */
        private static final int PHOTO_PRELOAD_DELAY = 1000;

        /**
         * Number of photos to preload per batch.
         */
        private static final int PRELOAD_BATCH = 25;

        /**
         * Maximum number of photos to preload.  If the cache size is 2Mb and
         * the expected average size of a photo is 4kb, then this number should be 2Mb/4kb = 500.
         */
        private static final int MAX_PHOTOS_TO_PRELOAD = 100;

        private final ContentResolver mResolver;
        private final StringBuilder mStringBuilder = new StringBuilder();
        private final Set<Long> mPhotoIds = Sets.newHashSet();
        private final Set<String> mPhotoIdsAsStrings = Sets.newHashSet();
        private final Set<Request> mPhotoUris = Sets.newHashSet();
        private final List<Long> mPreloadPhotoIds = Lists.newArrayList();

        private Handler mLoaderThreadHandler;
        private byte mBuffer[];

        private static final int PRELOAD_STATUS_NOT_STARTED = 0;
        private static final int PRELOAD_STATUS_IN_PROGRESS = 1;
        private static final int PRELOAD_STATUS_DONE = 2;

        private int mPreloadStatus = PRELOAD_STATUS_NOT_STARTED;

        public LoaderThread(ContentResolver resolver) {
            super(LOADER_THREAD_NAME);
            mResolver = resolver;
        }

        public void ensureHandler() {
            if (mLoaderThreadHandler == null) {
                mLoaderThreadHandler = new Handler(getLooper(), this);
            }
        }

        /**
         * Kicks off preloading of the next batch of photos on the background thread.
         * Preloading will happen after a delay: we want to yield to the UI thread
         * as much as possible.
         * <p>
         * If preloading is already complete, does nothing.
         */
        public void requestPreloading() {
            if (mPreloadStatus == PRELOAD_STATUS_DONE) {
                return;
            }

            ensureHandler();
            if (mLoaderThreadHandler.hasMessages(MESSAGE_LOAD_PHOTOS)) {
                return;
            }

            mLoaderThreadHandler.sendEmptyMessageDelayed(
                    MESSAGE_PRELOAD_PHOTOS, PHOTO_PRELOAD_DELAY);
        }

        /**
         * Sends a message to this thread to load requested photos.  Cancels a preloading
         * request, if any: we don't want preloading to impede loading of the photos
         * we need to display now.
         */
        public void requestLoading() {
            ensureHandler();
            mLoaderThreadHandler.removeMessages(MESSAGE_PRELOAD_PHOTOS);
            mLoaderThreadHandler.sendEmptyMessage(MESSAGE_LOAD_PHOTOS);
        }

        /**
         * Receives the above message, loads photos and then sends a message
         * to the main thread to process them.
         */
        @Override
        public boolean handleMessage(Message msg) {
            switch (msg.what) {
                case MESSAGE_PRELOAD_PHOTOS:
                    preloadPhotosInBackground();
                    break;
                case MESSAGE_LOAD_PHOTOS:
                    loadPhotosInBackground();
                    break;
            }
            return true;
        }

        /**
         * The first time it is called, figures out which photos need to be preloaded.
         * Each subsequent call preloads the next batch of photos and requests
         * another cycle of preloading after a delay.  The whole process ends when
         * we either run out of photos to preload or fill up cache.
         */
        private void preloadPhotosInBackground() {
            if (mPreloadStatus == PRELOAD_STATUS_DONE) {
                return;
            }

            if (mPreloadStatus == PRELOAD_STATUS_NOT_STARTED) {
                queryPhotosForPreload();
                if (mPreloadPhotoIds.isEmpty()) {
                    mPreloadStatus = PRELOAD_STATUS_DONE;
                } else {
                    mPreloadStatus = PRELOAD_STATUS_IN_PROGRESS;
                }
                requestPreloading();
                return;
            }

            if (mBitmapHolderCache.size() > mBitmapHolderCacheRedZoneBytes) {
                mPreloadStatus = PRELOAD_STATUS_DONE;
                return;
            }

            mPhotoIds.clear();
            mPhotoIdsAsStrings.clear();

            int count = 0;
            int preloadSize = mPreloadPhotoIds.size();
            while(preloadSize > 0 && mPhotoIds.size() < PRELOAD_BATCH) {
                preloadSize--;
                count++;
                Long photoId = mPreloadPhotoIds.get(preloadSize);
                mPhotoIds.add(photoId);
                mPhotoIdsAsStrings.add(photoId.toString());
                mPreloadPhotoIds.remove(preloadSize);
            }

            loadThumbnails(true);

            if (preloadSize == 0) {
                mPreloadStatus = PRELOAD_STATUS_DONE;
            }

            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "Preloaded " + count + " photos.  Cached bytes: "
                        + mBitmapHolderCache.size());
            }

            requestPreloading();
        }

        private void queryPhotosForPreload() {
            Cursor cursor = null;
            try {
                Uri uri = Contacts.CONTENT_URI.buildUpon().appendQueryParameter(
                        ContactsContract.DIRECTORY_PARAM_KEY, String.valueOf(Directory.DEFAULT))
                        .appendQueryParameter(ContactsContract.LIMIT_PARAM_KEY,
                                String.valueOf(MAX_PHOTOS_TO_PRELOAD))
                        .build();
                cursor = mResolver.query(uri, new String[] { Contacts.PHOTO_ID },
                        Contacts.PHOTO_ID + " NOT NULL AND " + Contacts.PHOTO_ID + "!=0",
                        null,
                        Contacts.STARRED + " DESC, " + Contacts.LAST_TIME_CONTACTED + " DESC");

                if (cursor != null) {
                    while (cursor.moveToNext()) {
                        // Insert them in reverse order, because we will be taking
                        // them from the end of the list for loading.
                        mPreloadPhotoIds.add(0, cursor.getLong(0));
                    }
                }
            } finally {
                if (cursor != null) {
                    cursor.close();
                }
            }
        }

        private void loadPhotosInBackground() {
            if (!PermissionsUtil.hasPermission(mContext,
                    android.Manifest.permission.READ_CONTACTS)) {
                return;
            }
            obtainPhotoIdsAndUrisToLoad(mPhotoIds, mPhotoIdsAsStrings, mPhotoUris);
            loadThumbnails(false);
            loadUriBasedPhotos();
            requestPreloading();
        }

        /** Loads thumbnail photos with ids */
        private void loadThumbnails(boolean preloading) {
            if (mPhotoIds.isEmpty()) {
                return;
            }

            // Remove loaded photos from the preload queue: we don't want
            // the preloading process to load them again.
            if (!preloading && mPreloadStatus == PRELOAD_STATUS_IN_PROGRESS) {
                for (Long id : mPhotoIds) {
                    mPreloadPhotoIds.remove(id);
                }
                if (mPreloadPhotoIds.isEmpty()) {
                    mPreloadStatus = PRELOAD_STATUS_DONE;
                }
            }

            mStringBuilder.setLength(0);
            mStringBuilder.append(Photo._ID + " IN(");
            for (int i = 0; i < mPhotoIds.size(); i++) {
                if (i != 0) {
                    mStringBuilder.append(',');
                }
                mStringBuilder.append('?');
            }
            mStringBuilder.append(')');

            Cursor cursor = null;
            try {
                if (DEBUG) Log.d(TAG, "Loading " + TextUtils.join(",", mPhotoIdsAsStrings));
                cursor = mResolver.query(Data.CONTENT_URI,
                        COLUMNS,
                        mStringBuilder.toString(),
                        mPhotoIdsAsStrings.toArray(EMPTY_STRING_ARRAY),
                        null);

                if (cursor != null) {
                    while (cursor.moveToNext()) {
                        Long id = cursor.getLong(0);
                        byte[] bytes = cursor.getBlob(1);
                        if (bytes == null) {
                            bytes = new byte[0];
                        }
                        cacheBitmap(id, bytes, preloading, -1);
                        mPhotoIds.remove(id);
                    }
                }
            } finally {
                if (cursor != null) {
                    cursor.close();
                }
            }

            // Remaining photos were not found in the contacts database (but might be in profile).
            for (Long id : mPhotoIds) {
                if (ContactsContract.isProfileId(id)) {
                    Cursor profileCursor = null;
                    try {
                        profileCursor = mResolver.query(
                                ContentUris.withAppendedId(Data.CONTENT_URI, id),
                                COLUMNS, null, null, null);
                        if (profileCursor != null && profileCursor.moveToFirst()) {
                            byte[] bytes = profileCursor.getBlob(1);
                            if (bytes == null) {
                                bytes = new byte[0];
                            }
                            cacheBitmap(profileCursor.getLong(0), bytes, preloading, -1);
                        } else {
                            // Couldn't load a photo this way either.
                            cacheBitmap(id, null, preloading, -1);
                        }
                    } finally {
                        if (profileCursor != null) {
                            profileCursor.close();
                        }
                    }
                } else {
                    // Not a profile photo and not found - mark the cache accordingly
                    cacheBitmap(id, null, preloading, -1);
                }
            }

            mMainThreadHandler.sendEmptyMessage(MESSAGE_PHOTOS_LOADED);
        }

        /**
         * Loads photos referenced with Uris. Those can be remote thumbnails
         * (from directory searches), display photos etc
         */
        private void loadUriBasedPhotos() {
            for (Request uriRequest : mPhotoUris) {
                // Keep the original URI and use this to key into the cache.  Failure to do so will
                // result in an image being continually reloaded into cache if the original URI
                // has a contact type encodedFragment (eg nearby places business photo URLs).
                Uri originalUri = uriRequest.getUri();

                // Strip off the "contact type" we added to the URI to ensure it was identifiable as
                // a business photo -- there is no need to pass this on to the server.
                Uri uri = ContactPhotoManager.removeContactType(originalUri);

                if (mBuffer == null) {
                    mBuffer = new byte[BUFFER_SIZE];
                }
                try {
                    if (DEBUG) Log.d(TAG, "Loading " + uri);
                    final String scheme = uri.getScheme();
                    InputStream is = null;
                    if (scheme.equals("http") || scheme.equals("https")) {
                        TrafficStats.setThreadStatsTag(TrafficStatsTags.CONTACT_PHOTO_DOWNLOAD_TAG);
                        final HttpURLConnection connection =
                                (HttpURLConnection) new URL(uri.toString()).openConnection();

                        // Include the user agent if it is specified.
                        if (!TextUtils.isEmpty(mUserAgent)) {
                            connection.setRequestProperty("User-Agent", mUserAgent);
                        }
                        try {
                            is = connection.getInputStream();
                        } catch (IOException e) {
                            connection.disconnect();
                            is = null;
                        }
                        TrafficStats.clearThreadStatsTag();
                    } else {
                        is = mResolver.openInputStream(uri);
                    }
                    if (is != null) {
                        ByteArrayOutputStream baos = new ByteArrayOutputStream();
                        try {
                            int size;
                            while ((size = is.read(mBuffer)) != -1) {
                                baos.write(mBuffer, 0, size);
                            }
                        } finally {
                            is.close();
                        }
                        cacheBitmap(originalUri, baos.toByteArray(), false,
                                uriRequest.getRequestedExtent());
                        mMainThreadHandler.sendEmptyMessage(MESSAGE_PHOTOS_LOADED);
                    } else {
                        if (Log.isLoggable(TAG, Log.VERBOSE)) {
                            Log.v(TAG, "Cannot load photo " + uri);
                        }
                        cacheBitmap(originalUri, null, false, uriRequest.getRequestedExtent());
                    }
                } catch (final Exception | OutOfMemoryError ex) {
                    if (Log.isLoggable(TAG, Log.VERBOSE)) {
                        Log.v(TAG, "Cannot load photo " + uri, ex);
                    }
                    cacheBitmap(originalUri, null, false, uriRequest.getRequestedExtent());
                }
            }
        }
    }

    /**
     * A holder for either a Uri or an id and a flag whether this was requested for the dark or
     * light theme
     */
    private static final class Request {
        private final long mId;
        private final Uri mUri;
        private final boolean mDarkTheme;
        private final int mRequestedExtent;
        private final DefaultImageProvider mDefaultProvider;
        private final DefaultImageRequest mDefaultRequest;
        /**
         * Whether or not the contact photo is to be displayed as a circle
         */
        private final boolean mIsCircular;

        private Request(long id, Uri uri, int requestedExtent, boolean darkTheme,
                boolean isCircular, DefaultImageProvider defaultProvider,
                DefaultImageRequest defaultRequest) {
            mId = id;
            mUri = uri;
            mDarkTheme = darkTheme;
            mIsCircular = isCircular;
            mRequestedExtent = requestedExtent;
            mDefaultProvider = defaultProvider;
            mDefaultRequest = defaultRequest;
        }

        public static Request createFromThumbnailId(long id, boolean darkTheme, boolean isCircular,
                DefaultImageProvider defaultProvider, DefaultImageRequest defaultRequest) {
            return new Request(id, null /* no URI */, -1, darkTheme, isCircular, defaultProvider,
                    defaultRequest);
        }

        public static Request createFromUri(Uri uri, int requestedExtent, boolean darkTheme,
                boolean isCircular, DefaultImageProvider defaultProvider) {
            return createFromUri(uri, requestedExtent, darkTheme, isCircular, defaultProvider,
                    /* defaultRequest */ null);
        }

        public static Request createFromUri(Uri uri, int requestedExtent, boolean darkTheme,
                boolean isCircular, DefaultImageProvider defaultProvider,
                DefaultImageRequest defaultRequest) {
            return new Request(0 /* no ID */, uri, requestedExtent, darkTheme, isCircular,
                    defaultProvider, defaultRequest);
        }

        public boolean isUriRequest() {
            return mUri != null;
        }

        public Uri getUri() {
            return mUri;
        }

        public long getId() {
            return mId;
        }

        public int getRequestedExtent() {
            return mRequestedExtent;
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + (int) (mId ^ (mId >>> 32));
            result = prime * result + mRequestedExtent;
            result = prime * result + ((mUri == null) ? 0 : mUri.hashCode());
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) return true;
            if (obj == null) return false;
            if (getClass() != obj.getClass()) return false;
            final Request that = (Request) obj;
            if (mId != that.mId) return false;
            if (mRequestedExtent != that.mRequestedExtent) return false;
            if (!UriUtils.areEqual(mUri, that.mUri)) return false;
            // Don't compare equality of mDarkTheme because it is only used in the default contact
            // photo case. When the contact does have a photo, the contact photo is the same
            // regardless of mDarkTheme, so we shouldn't need to put the photo request on the queue
            // twice.
            return true;
        }

        public Object getKey() {
            return mUri == null ? mId : mUri;
        }

        /**
         * Applies the default image to the current view. If the request is URI-based, looks for
         * the contact type encoded fragment to determine if this is a request for a business photo,
         * in which case we will load the default business photo.
         *
         * @param view The current image view to apply the image to.
         * @param isCircular Whether the image is circular or not.
         */
        public void applyDefaultImage(ImageView view, boolean isCircular) {
            final DefaultImageRequest request;

            if (mDefaultRequest == null) {
                if (isCircular) {
                    request = ContactPhotoManager.isBusinessContactUri(mUri)
                            ? DefaultImageRequest.EMPTY_CIRCULAR_BUSINESS_IMAGE_REQUEST
                            : DefaultImageRequest.EMPTY_CIRCULAR_DEFAULT_IMAGE_REQUEST;
                } else {
                    request = ContactPhotoManager.isBusinessContactUri(mUri)
                            ? DefaultImageRequest.EMPTY_DEFAULT_BUSINESS_IMAGE_REQUEST
                            : DefaultImageRequest.EMPTY_DEFAULT_IMAGE_REQUEST;
                }
            } else {
                request = mDefaultRequest;
            }
            mDefaultProvider.applyDefaultImage(view, mRequestedExtent, mDarkTheme, request);
        }
    }
}