package moe.nekojimi.friendcloud;

import moe.nekojimi.friendcloud.objects.NetworkFile;
import moe.nekojimi.friendcloud.tasks.FileDownloadTask;

import java.util.*;
import java.util.concurrent.CompletableFuture;

public class DownloadManager
{
	private static DownloadManager instance = null;
	public static DownloadManager getInstance()
	{
		if(instance == null)
			instance = new DownloadManager();
		return instance;
	}
	private DownloadManager()
	{

	}

	public Map<FileDownloadTask, CompletableFuture<Void>> activeDownloads = new HashMap<>();

	public CompletableFuture<?> downloadPieces(NetworkFile file, SortedSet<Integer> pieces)
	{
		cullCompletedDownloads();

		Set<CompletableFuture<Void>> tasksToWaitFor = new HashSet<>();
		SortedSet<Integer> inactivePieces = new TreeSet<>(pieces);
		for (Map.Entry<FileDownloadTask, CompletableFuture<Void>> e : activeDownloads.entrySet())
		{
			if (!Collections.disjoint(inactivePieces, e.getKey().getMissingPieceIndices()))
			{
				inactivePieces.removeAll(e.getKey().getMissingPieceIndices());
				tasksToWaitFor.add(e.getValue());
			}
		}

		if (!inactivePieces.isEmpty())
		{
			FileDownloadTask downloadTask = new FileDownloadTask(file, Main.getInstance().getConnectionManager(), pieces);
			CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(downloadTask,Main.getInstance().getExecutor());
			activeDownloads.put(downloadTask,completableFuture);
			return completableFuture;
		}

		return CompletableFuture.allOf(tasksToWaitFor.toArray(new CompletableFuture[0]));

	}

	private void cullCompletedDownloads()
	{
		Set<FileDownloadTask> toRemove = new HashSet<>();
		for (Map.Entry<FileDownloadTask, CompletableFuture<Void>> e : activeDownloads.entrySet())
		{
			if (e.getValue().isDone())
				toRemove.add(e.getKey());
		}
		for (FileDownloadTask t: toRemove)
			activeDownloads.remove(t);
	}

	public Map<FileDownloadTask, CompletableFuture<Void>> getActiveDownloads()
	{
		return Collections.unmodifiableMap(activeDownloads);
	}
}