package com.mapbox.mapboxsdk.style.sources;

import android.support.annotation.Keep;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.UiThread;
import android.support.annotation.WorkerThread;

import com.mapbox.geojson.Feature;
import com.mapbox.geojson.FeatureCollection;
import com.mapbox.mapboxsdk.geometry.LatLngBounds;
import com.mapbox.mapboxsdk.style.expressions.Expression;

import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Custom Vector Source, allows using FeatureCollections.
 * <p>
 * CustomGeometrySource uses a coalescing model for frequent data updates targeting the same tile id,
 * which means, that the in-progress request as well as the last scheduled request are guaranteed to finish.
 * Any requests scheduled meanwhile can be canceled.
 */
public class CustomGeometrySource extends Source {
  public static final String THREAD_PREFIX = "CustomGeom";
  public static final int THREAD_POOL_LIMIT = 4;
  private static final AtomicInteger poolCount = new AtomicInteger();
  private final Lock executorLock = new ReentrantLock();
  private ThreadPoolExecutor executor;
  private GeometryTileProvider provider;
  private final Map<TileID, GeometryTileRequest> awaitingTasksMap = new HashMap<>();

  /**
   * A map containing in-progress requests targeting distinct tiles.
   * A request is considered in-progress when it's started by the ThreadPoolExecutor.
   * A request is marked as done when the data is passed from the JNI layer to the core, after the features conversion.
   */
  private final Map<TileID, AtomicBoolean> inProgressTasksMap = new HashMap<>();

  /**
   * Create a CustomGeometrySource
   *
   * @param id       The source id.
   * @param provider The tile provider that returns geometry data for this source.
   */
  @UiThread
  public CustomGeometrySource(String id, GeometryTileProvider provider) {
    this(id, new CustomGeometrySourceOptions(), provider);
  }

  /**
   * Create a CustomGeometrySource with non-default {@link CustomGeometrySourceOptions}.
   *
   * @param id       The source id.
   * @param options  CustomGeometrySourceOptions.
   * @param provider The tile provider that returns geometry data for this source.
   */
  @UiThread
  public CustomGeometrySource(String id, CustomGeometrySourceOptions options,
                              GeometryTileProvider provider) {
    super();
    this.provider = provider;
    initialize(id, options);
  }

  /**
   * Invalidate previously provided features within a given bounds at all zoom levels.
   * Invoking this method will result in new requests to `GeometryTileProvider` for regions
   * that contain, include, or intersect with the provided bounds.
   *
   * @param bounds The region in which features should be invalidated at all zoom levels
   */
  public void invalidateRegion(LatLngBounds bounds) {
    nativeInvalidateBounds(bounds);
  }

  /**
   * Invalidate the geometry contents of a specific tile. Invoking this method will result
   * in new requests to `GeometryTileProvider` for visible tiles.
   *
   * @param zoomLevel Tile zoom level.
   * @param x         Tile X coordinate.
   * @param y         Tile Y coordinate.
   */
  public void invalidateTile(int zoomLevel, int x, int y) {
    nativeInvalidateTile(zoomLevel, x, y);
  }

  /**
   * Set or update geometry contents of a specific tile. Use this method to update tiles
   * for which `GeometryTileProvider` was previously invoked. This method can be called from
   * background threads.
   *
   * @param zoomLevel Tile zoom level.
   * @param x         Tile X coordinate.
   * @param y         Tile Y coordinate.
   * @param data      Feature collection for the tile.
   */
  public void setTileData(int zoomLevel, int x, int y, FeatureCollection data) {
    nativeSetTileData(zoomLevel, x, y, data);
  }

  /**
   * Queries the source for features.
   *
   * @param filter an optional filter expression to filter the returned Features
   * @return the features
   */
  @NonNull
  public List<Feature> querySourceFeatures(@Nullable Expression filter) {
    checkThread();
    Feature[] features = querySourceFeatures(filter != null ? filter.toArray() : null);
    return features != null ? Arrays.asList(features) : new ArrayList<Feature>();
  }

  @Keep
  protected native void initialize(String sourceId, Object options);

  @NonNull
  @Keep
  private native Feature[] querySourceFeatures(Object[] filter);

  @Keep
  private native void nativeSetTileData(int z, int x, int y, FeatureCollection data);

  @Keep
  private native void nativeInvalidateTile(int z, int x, int y);

  @Keep
  private native void nativeInvalidateBounds(LatLngBounds bounds);

  @Override
  @Keep
  protected native void finalize() throws Throwable;

  private void setTileData(TileID tileId, FeatureCollection data) {
    nativeSetTileData(tileId.z, tileId.x, tileId.y, data);
  }

  /**
   * Tile data request can come from a number of different threads.
   * To remove race condition for requests targeting the same tile id we are first checking if there is a request
   * already enqueued, if yes, we are replacing it.
   * Otherwise, we are checking if there is an in-progress request, if yes,
   * we are creating or replacing an awaiting request.
   * If none of the above, we are enqueueing the request.
   */
  @WorkerThread
  @Keep
  private void fetchTile(int z, int x, int y) {
    AtomicBoolean cancelFlag = new AtomicBoolean(false);
    TileID tileID = new TileID(z, x, y);
    GeometryTileRequest request =
      new GeometryTileRequest(tileID, provider, awaitingTasksMap, inProgressTasksMap, this, cancelFlag);

    synchronized (awaitingTasksMap) {
      synchronized (inProgressTasksMap) {
        if (executor.getQueue().contains(request)) {
          executor.remove(request);
          executeRequest(request);
        } else if (inProgressTasksMap.containsKey(tileID)) {
          awaitingTasksMap.put(tileID, request);
        } else {
          executeRequest(request);
        }
      }
    }
  }

  private void executeRequest(@NonNull GeometryTileRequest request) {
    executorLock.lock();
    try {
      if (executor != null && !executor.isShutdown()) {
        executor.execute(request);
      }
    } finally {
      executorLock.unlock();
    }
  }

  /**
   * We want to cancel only the oldest request, therefore, we are first checking if it's in progress,
   * if not or if the currently in progress request has already been canceled,
   * we are searching for any request in the executor's queue.
   * Otherwise, we are removing an awaiting request targeting this tile id.
   * <p>
   * {@link GeometryTileRequest#equals(Object)} is overridden to cover only the tile id,
   * therefore, we can use an empty request to search the executor's queue.
   */
  @WorkerThread
  @Keep
  private void cancelTile(int z, int x, int y) {
    TileID tileID = new TileID(z, x, y);

    synchronized (awaitingTasksMap) {
      synchronized (inProgressTasksMap) {
        AtomicBoolean cancelFlag = inProgressTasksMap.get(tileID);
        // check if there is an in progress task
        if (!(cancelFlag != null && cancelFlag.compareAndSet(false, true))) {
          // if there is no tasks in progress or the in progress task was already cancelled, check the executor's queue
          GeometryTileRequest emptyRequest =
            new GeometryTileRequest(tileID, null, null, null, null, null);
          if (!executor.getQueue().remove(emptyRequest)) {
            // if there was no tasks in queue, remove from the awaiting map
            awaitingTasksMap.remove(tileID);
          }
        }
      }
    }
  }

  @Keep
  private void startThreads() {
    executorLock.lock();
    try {
      if (executor != null && !executor.isShutdown()) {
        executor.shutdownNow();
      }

      executor = new ThreadPoolExecutor(THREAD_POOL_LIMIT, THREAD_POOL_LIMIT,
        0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>(),
        new ThreadFactory() {
          final AtomicInteger threadCount = new AtomicInteger();
          final int poolId = poolCount.getAndIncrement();

          @NonNull
          @Override
          public Thread newThread(@NonNull Runnable runnable) {
            return new Thread(
              runnable,
              String.format(Locale.US, "%s-%d-%d", THREAD_PREFIX, poolId, threadCount.getAndIncrement()));
          }
        });
    } finally {
      executorLock.unlock();
    }
  }

  @Keep
  private void releaseThreads() {
    executorLock.lock();
    try {
      executor.shutdownNow();
    } finally {
      executorLock.unlock();
    }
  }

  @Keep
  private boolean isCancelled(int z, int x, int y) {
    return inProgressTasksMap.get(new TileID(z, x, y)).get();
  }

  static class TileID {
    public int z;
    public int x;
    public int y;

    TileID(int _z, int _x, int _y) {
      z = _z;
      x = _x;
      y = _y;
    }

    public int hashCode() {
      return Arrays.hashCode(new int[] {z, x, y});
    }

    public boolean equals(@Nullable Object object) {
      if (object == this) {
        return true;
      }

      if (object == null || getClass() != object.getClass()) {
        return false;
      }

      if (object instanceof TileID) {
        TileID other = (TileID) object;
        return this.z == other.z && this.x == other.x && this.y == other.y;
      }
      return false;
    }
  }

  static class GeometryTileRequest implements Runnable {
    private final TileID id;
    private final GeometryTileProvider provider;
    private final Map<TileID, GeometryTileRequest> awaiting;
    private final Map<TileID, AtomicBoolean> inProgress;
    @NonNull
    private final WeakReference<CustomGeometrySource> sourceRef;
    private final AtomicBoolean cancelled;

    GeometryTileRequest(TileID _id, GeometryTileProvider p,
                        Map<TileID, GeometryTileRequest> awaiting,
                        Map<TileID, AtomicBoolean> m,
                        CustomGeometrySource _source, AtomicBoolean _cancelled) {
      id = _id;
      provider = p;
      this.awaiting = awaiting;
      inProgress = m;
      sourceRef = new WeakReference<>(_source);
      cancelled = _cancelled;
    }

    public void run() {
      synchronized (awaiting) {
        synchronized (inProgress) {
          if (inProgress.containsKey(id)) {
            // request targeting this tile id is already being processed,
            // scenario that should occur only if the tile is being requested when
            // another request is switching threads to execute
            if (!awaiting.containsKey(id)) {
              awaiting.put(id, this);
            }
            return;
          } else {
            inProgress.put(id, cancelled);
          }
        }
      }

      if (!isCancelled()) {
        FeatureCollection data = provider.getFeaturesForBounds(LatLngBounds.from(id.z, id.x, id.y), id.z);
        CustomGeometrySource source = sourceRef.get();
        if (!isCancelled() && source != null && data != null) {
          source.setTileData(id, data);
        }
      }

      synchronized (awaiting) {
        synchronized (inProgress) {
          inProgress.remove(id);

          // executing the next request targeting the same tile
          if (awaiting.containsKey(id)) {
            GeometryTileRequest queuedRequest = awaiting.get(id);
            CustomGeometrySource source = sourceRef.get();
            if (source != null && queuedRequest != null) {
              source.executor.execute(queuedRequest);
            }

            awaiting.remove(id);
          }
        }
      }
    }

    private Boolean isCancelled() {
      return cancelled.get();
    }

    @Override
    public boolean equals(@Nullable Object o) {
      if (this == o) {
        return true;
      }
      if (o == null || getClass() != o.getClass()) {
        return false;
      }
      GeometryTileRequest request = (GeometryTileRequest) o;
      return id.equals(request.id);
    }
  }
}