/*
 * Copyright (C) 2025 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.google.android.libraries.mobiledatadownload.testing;

import static com.google.common.util.concurrent.Futures.immediateFailedFuture;
import static com.google.common.util.concurrent.Futures.immediateVoidFuture;

import android.net.Uri;

import androidx.test.core.app.ApplicationProvider;

import com.google.android.libraries.mobiledatadownload.DownloadException;
import com.google.android.libraries.mobiledatadownload.DownloadException.DownloadResultCode;
import com.google.android.libraries.mobiledatadownload.downloader.DownloadRequest;
import com.google.android.libraries.mobiledatadownload.downloader.FileDownloader;
import com.google.android.libraries.mobiledatadownload.file.Opener;
import com.google.android.libraries.mobiledatadownload.file.SynchronousFileStorage;
import com.google.android.libraries.mobiledatadownload.file.openers.WriteStreamOpener;
import com.google.android.libraries.mobiledatadownload.internal.logging.LogUtil;
import com.google.common.io.ByteStreams;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.concurrent.Executor;

/**
 * A {@link FileDownloader} that "downloads" by copying the file from the application's assets.
 *
 * <p>This downloader retrieves files by matching the filename in the provided `urlToDownload` with
 * a file in the assets. For example, to "download" a file named "image.png" located in the assets,
 * you would use a URL like "https://example.com/images/image.png".
 *
 * <p><b>Note:</b> This implementation ignores DownloadConditions.
 */
public final class LocalFileDownloader implements FileDownloader {

    private static final String TAG = "LocalFileDownloader";

    private final Executor backgroudExecutor;
    private final SynchronousFileStorage fileStorage;

    public LocalFileDownloader(
            SynchronousFileStorage fileStorage, ListeningExecutorService executor) {
        this.fileStorage = fileStorage;
        this.backgroudExecutor = executor;
    }

    @Override
    public ListenableFuture<Void> startDownloading(DownloadRequest downloadRequest) {
        return Futures.submitAsync(
                () -> startDownloadingInternal(downloadRequest), backgroudExecutor);
    }

    private ListenableFuture<Void> startDownloadingInternal(DownloadRequest downloadRequest) {
        Uri fileUri = downloadRequest.fileUri();
        String urlToDownload = downloadRequest.urlToDownload();
        LogUtil.d(
                "%s: startDownloadingInternal;  urlToDownload: %s; fileUri: %s;",
                TAG, urlToDownload, fileUri);

        try {
            Opener<OutputStream> writeStreamOpener = WriteStreamOpener.create();
            long writtenBytes;
            try (InputStream in =
                            ApplicationProvider.getApplicationContext()
                                    .getAssets()
                                    .open(urlToDownload);
                    OutputStream out = fileStorage.open(fileUri, writeStreamOpener)) {
                writtenBytes = ByteStreams.copy(in, out);
            }
            LogUtil.d(
                    "%s: File URI %s download complete, writtenBytes: %d",
                    TAG, fileUri, writtenBytes);
        } catch (IOException e) {
            LogUtil.e(e, "%s: startDownloading got exception", TAG);
            return immediateFailedFuture(
                    DownloadException.builder()
                            .setDownloadResultCode(DownloadResultCode.ANDROID_DOWNLOADER_HTTP_ERROR)
                            .build());
        }

        return immediateVoidFuture();
    }
}