photopicker/src/com/android/photopicker/extensions/Flow.kt

/*
 * Copyright 2024 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.photopicker.extensions

import androidx.paging.PagingData
import androidx.paging.insertSeparators
import androidx.paging.map
import com.android.photopicker.core.components.MediaGridItem
import com.android.photopicker.data.model.Group
import com.android.photopicker.data.model.Media
import java.time.LocalDateTime
import java.time.ZoneOffset
import java.time.format.DateTimeFormatter
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.map

/**
 * An extension function to prepare a flow of [PagingData<Media>] to be provided to the [MediaGrid]
 * composable, by wrapping all of the [Media] objects in a [MediaGridItem.MediaItem].
 *
 * @return A [PagingData<MediaGridItem.MediaItem] that can be processed further, or provided to the
 *   [MediaGrid].
 */
fun Flow<PagingData<Media>>.toMediaGridItemFromMedia(): Flow<PagingData<MediaGridItem.MediaItem>> {
    return this.map { pagingData -> pagingData.map { MediaGridItem.MediaItem(it) } }
}

/**
 * An extension function to prepare a flow of [PagingData<Album>] to be provided to the [MediaGrid]
 * composable, by wrapping all of the [Album] objects in a [MediaGridItem].
 *
 * @return A [PagingData<MediaGridItem>] that can be processed further, or provided to the
 *   [MediaGrid].
 */
fun Flow<PagingData<Group.Album>>.toMediaGridItemFromAlbum(): Flow<PagingData<MediaGridItem>> {
    return this.map { pagingData -> pagingData.map { MediaGridItem.AlbumItem(it) } }
}

/**
 * An extension function which accepts a flow of [PagingData<MediaGridItem.MediaItem] (the actual
 * [Media] grid representation wrappers) and processes them inserting month separators in between
 * items that have different month.
 *
 * TODO(b/323830434): Update logic for separators after 4th row when UX finalizes.
 * Note: This does not include a separator for the first month of data.
 *
 * @return A [PagingData<MediaGridItem] that can be processed further, or provided to the
 *   [MediaGrid].
 */
fun Flow<PagingData<MediaGridItem.MediaItem>>.insertMonthSeparators():
    Flow<PagingData<MediaGridItem>> {
    return this.map {
        it.insertSeparators { before, after ->

            // If this is the first or last item in the list, no separators are required.
            if (after == null || before == null) {
                return@insertSeparators null
            }

            // ZoneOffset.UTC is used here because all timestamps are expected to be millisecionds
            // since epoch in UTC. See [CloudMediaProviderContract#MediaColumns.DATE_TAKEN_MILLIS]
            val beforeLocalDateTime =
                LocalDateTime.ofEpochSecond((before.media.getTimestamp() / 1000), 0, ZoneOffset.UTC)
            val afterLocalDateTime =
                LocalDateTime.ofEpochSecond((after.media.getTimestamp() / 1000), 0, ZoneOffset.UTC)

            if (beforeLocalDateTime.getMonth() != afterLocalDateTime.getMonth()) {
                val format =
                    // If the current calendar year is different from the items year, append the
                    // year to to the month string.
                    if (afterLocalDateTime.getYear() != LocalDateTime.now().getYear()) "MMMM YYYY"

                    // The year is the same, so just use the month's name.
                    else "MMMM"

                // The months are different, so insert a separator between [before] and [after]
                // by returning it here.
                MediaGridItem.SeparatorItem(
                    afterLocalDateTime.format(DateTimeFormatter.ofPattern(format))
                )
            } else {
                // Both Media have the same month, so no separator needed between the two.
                null
            }
        }
    }
}