package moe.nekojimi.friendcloud;

import moe.nekojimi.friendcloud.network.PeerConnection;
import moe.nekojimi.friendcloud.network.requests.FilePiecesRequest;
import moe.nekojimi.friendcloud.objects.NetworkFile;
import moe.nekojimi.friendcloud.objects.Peer;
import moe.nekojimi.friendcloud.objects.PeerFileState;

import java.io.File;
import java.io.IOException;
import java.util.*;
import java.util.concurrent.*;

public class FileDownloadTask implements Callable<File>
{
	private final NetworkFile file;
	private final ConnectionManager manager;

	private final long timeoutPerPieceMs = 10_000;
	private static final int MAX_DOWNLOAD_PIECES_PER_ROUND = 128;

	private final SortedSet<Integer> missingPieceIndices = new TreeSet<>();

	public FileDownloadTask(NetworkFile file, ConnectionManager manager)
	{
		this.file = file;
		this.manager = manager;
		for (int i = 0; i < file.getPieceCount(); i++)
		{
			missingPieceIndices.add(i);
		}
	}

	public FileDownloadTask(NetworkFile file, ConnectionManager manager, List<Integer> missingPieces)
	{
		this.file = file;
		this.manager = manager;
		missingPieceIndices.addAll(missingPieces);
	}

	public NetworkFile getFile()
	{
		return file;
	}

	@Override
	public File call() throws Exception
	{
		System.out.println("Starting download of file " + file.getName());

		while (!missingPieceIndices.isEmpty())
		{
			System.out.println("Need to get " + missingPieceIndices.size() + " missing pieces.");

			Map<Peer, PeerFileState> fileStates = file.getFileStates();

			// determine what nodes we can connect to
			List<PeerConnection> connections = new ArrayList<>();
			for (PeerFileState peerFileState : fileStates.values())
			{
				if (peerFileState.getProgress() >= 100.0)
				{
					try
					{
						PeerConnection connection = manager.getNodeConnection(peerFileState.getNode());
						System.out.println("FileDownloadTask: Will download from " + peerFileState.getNode().getNodeName());
						connections.add(connection);
					} catch (IOException ex)
					{
						System.err.println("Failed to connect to peer " + peerFileState.getNode().getNodeName() + ": " + ex.getMessage());
					}
				}
			}


			if (connections.isEmpty())
			{
				System.err.println("FileDownloadTask: No peers have the file, download failed!");
				return null;
			}

			// find a continuous run of pieces to download
			// TODO: allow for runs with regular gaps (e.g. every 2) to account for previous failed download attempts
			int runStart = -1;
			int runEnd = -1;
			for (int pieceIdx: missingPieceIndices)
			{
				int runLength = runEnd - runStart;
				if (runLength >= MAX_DOWNLOAD_PIECES_PER_ROUND)
					break;
				else if (runStart == -1)
				{
					runStart = pieceIdx;
					runEnd = pieceIdx;
				}
				else if (pieceIdx == runEnd + 1)
					runEnd = pieceIdx;
				else
					break;
			}
			System.out.println("FileDownloadTask: Will download pieces from " + runStart + " to " + runEnd);

			// make one request per connectable peer, striping the needed pieces among them
			List<CompletableFuture<List<Integer>>> fileFutures = new ArrayList<>();
			int offset = 0;
			for (PeerConnection connection : connections)
			{
				CompletableFuture<List<Integer>> future = connection.makeRequest(new FilePiecesRequest(file, runStart+offset, (runEnd-runStart)+1, connections.size()));
				fileFutures.add(future);
				offset++;
			}

			long timeout = timeoutPerPieceMs * (missingPieceIndices.size() / connections.size());

			// wait for all the requests to complete
			for (CompletableFuture<List<Integer>> future : fileFutures)
			{
				try
				{
					List<Integer> receivedPieces = future.get(timeout, TimeUnit.MILLISECONDS);
					receivedPieces.forEach(missingPieceIndices::remove);
				} catch (InterruptedException e)
				{
					future.cancel(true);
					timeout = 1_000;
					System.err.println("FileDownloadTask: Request timed out.");
				} catch (ExecutionException | TimeoutException e)
				{
					e.printStackTrace(System.err);
				}
			}
		}

		System.out.println("FileDownloadTask: finished downloading " + file.getName() + "!");
		return file.getLocalFile();
	}
}