/*
 * Copyright (C) 2015 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.example.android.confirmdevicecredentials;

import android.app.Activity;
import android.app.KeyguardManager;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.security.keystore.KeyGenParameterSpec;
import android.security.keystore.KeyProperties;
import android.security.keystore.UserNotAuthenticatedException;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import java.io.IOException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.UnrecoverableKeyException;
import java.security.cert.CertificateException;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;

/**
 * Main entry point for the sample, showing a backpack and "Purchase" button.
 */
public class MainActivity extends Activity {

    /** Alias for our key in the Android Key Store. */
    private static final String KEY_NAME = "my_key";
    private static final byte[] SECRET_BYTE_ARRAY = new byte[] {1, 2, 3, 4, 5, 6};

    private static final int REQUEST_CODE_CONFIRM_DEVICE_CREDENTIALS = 1;

    /**
     * If the user has unlocked the device Within the last this number of seconds,
     * it can be considered as an authenticator.
     */
    private static final int AUTHENTICATION_DURATION_SECONDS = 30;

    private KeyguardManager mKeyguardManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button purchaseButton = (Button) findViewById(R.id.purchase_button);
        if (!createKey()) {
            // Failed to create a key due to probably the user hasn't set up a lock screen yet.
            purchaseButton.setEnabled(false);
            return;
        }
        findViewById(R.id.purchase_button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Test to encrypt something. It might fail if the timeout expired (30s).
                tryEncrypt();
            }
        });
        mKeyguardManager = (KeyguardManager) getSystemService(Context.KEYGUARD_SERVICE);
    }

    /**
     * Tries to encrypt some data with the generated key in {@link #createKey} which is
     * only works if the user has just authenticated via device credentials.
     */
    private void tryEncrypt() {
        try {
            KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
            keyStore.load(null);
            SecretKey secretKey = (SecretKey) keyStore.getKey(KEY_NAME, null);
            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");

            // Try encrypting something, it will only work if the user authenticated within
            // the last AUTHENTICATION_DURATION_SECONDS seconds.
            cipher.init(Cipher.ENCRYPT_MODE, secretKey);
            cipher.doFinal(SECRET_BYTE_ARRAY);

            // If the user has recently authenticated, you will reach here.
            showAlreadyAuthenticated();
        } catch (UserNotAuthenticatedException e) {
            // User is not authenticated, let's authenticate with device credentials.
            showAuthenticationScreen();
        } catch (BadPaddingException | IllegalBlockSizeException | KeyStoreException |
                CertificateException | UnrecoverableKeyException | IOException
                | NoSuchPaddingException | NoSuchAlgorithmException | InvalidKeyException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Creates a symmetric key in the Android Key Store which can only be used after the user has
     * authenticated with device credentials within the last X seconds.
     *
     * @return {@code true} when a key is created successfully, {@code false} otherwise.
     */
    private boolean createKey() {
        // Generate a key to decrypt payment credentials, tokens, etc.
        // This will most likely be a registration step for the user when they are setting up your app.
        try {
            KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
            keyStore.load(null);
            KeyGenerator keyGenerator = KeyGenerator.getInstance("AES", "AndroidKeyStore");

            // Set the alias of the entry in Android KeyStore where the key will appear
            // and the constrains (purposes) in the constructor of the Builder
            keyGenerator.init(new KeyGenParameterSpec.Builder(KEY_NAME,
                            KeyProperties.PURPOSE_ENCRYPT |
                            KeyProperties.PURPOSE_DECRYPT)
                    .setBlockModes("CBC")
                    .setUserAuthenticationRequired(true)
                            // Require that the user has unlocked in the last 30 seconds
                    .setUserAuthenticationValidityDurationSeconds(AUTHENTICATION_DURATION_SECONDS)
                    .setEncryptionPaddings("PKCS7Padding")
                    .build());
            keyGenerator.generateKey();
            return true;
        } catch (IllegalStateException e) {
            // Show a message that the user hasn't set up a lock screen.
            Toast.makeText(this,
                    "Go to 'Settings -> Security -> Screenlock' to set up device screenlock\n" +
                            e.getMessage(), Toast.LENGTH_LONG).show();
            return false;
        } catch (NoSuchAlgorithmException | NoSuchProviderException
                | InvalidAlgorithmParameterException | KeyStoreException
                | CertificateException | IOException e) {
            throw new RuntimeException("Failed to create a symmetric key", e);
        }
    }

    private void showAuthenticationScreen() {
        // Create the Confirm Credentials screen. You can customize the title and description. Or
        // we will provide a generic one for you if you leave it null
        Intent intent = mKeyguardManager.createConfirmDeviceCredentialIntent(null, null);
        if (intent != null) {
            startActivityForResult(intent, REQUEST_CODE_CONFIRM_DEVICE_CREDENTIALS);
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_CODE_CONFIRM_DEVICE_CREDENTIALS) {
            // Challenge completed, proceed with using cipher
            if (resultCode == RESULT_OK) {
                showPurchaseConfirmation();
            } else {
                // The user canceled or didn’t complete the lock screen
                // operation. Go to error/cancellation flow.
            }
        }
    }

    private void showPurchaseConfirmation() {
        findViewById(R.id.confirmation_message).setVisibility(View.VISIBLE);
        findViewById(R.id.purchase_button).setEnabled(false);
    }

    private void showAlreadyAuthenticated() {
        TextView textView = (TextView) findViewById(
                R.id.already_has_valid_device_credential_message);
        textView.setVisibility(View.VISIBLE);
        textView.setText(getString(
                R.string.already_confirmed_device_credentials_within_last_x_seconds,
                AUTHENTICATION_DURATION_SECONDS));
        findViewById(R.id.purchase_button).setEnabled(false);
    }

}