/*
 * Copyright 2000-2014 JetBrains s.r.o.
 *
 * 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.intellij.util.containers;

import com.intellij.openapi.util.Condition;
import com.intellij.openapi.util.Conditions;
import com.intellij.util.Processor;
import com.intellij.util.concurrency.Semaphore;
import gnu.trove.Equality;
import org.jetbrains.annotations.NonNls;
import org.jetbrains.annotations.NotNull;

import javax.swing.*;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Allows to process elements in the EDT.
 * Processes elements in batches, no longer than 200ms (or maxUnitOfWorkThresholdMs constructor parameter) per batch,
 * and reschedules processing later for longer batches.
 * Usage: {@link TransferToEDTQueue#offer(Object)} } : schedules element for processing in EDT (via invokeLater)
 */
public class TransferToEDTQueue<T> {
  @SuppressWarnings({"FieldCanBeLocal", "UnusedDeclaration"})
  private final String myName;
  private final Processor<T> myProcessor;
  private volatile boolean stopped;
  private final Condition<?> myShutUpCondition;
  private final int myMaxUnitOfWorkThresholdMs; //-1 means indefinite

  private final Queue<T> myQueue = new Queue<T>(10); // guarded by myQueue
  private final AtomicBoolean invokeLaterScheduled = new AtomicBoolean();
  private final Runnable myUpdateRunnable = new Runnable() {
    @Override
    public void run() {
      boolean b = invokeLaterScheduled.compareAndSet(true, false);
      assert b;
      if (stopped || myShutUpCondition.value(null)) {
        stop();
        return;
      }
      long start = System.currentTimeMillis();
      int processed = 0;
      while (processNext()) {
        processed++;
        long finish = System.currentTimeMillis();
        if (myMaxUnitOfWorkThresholdMs != -1 && finish - start > myMaxUnitOfWorkThresholdMs) break;
      }
      if (!isEmpty()) {
        scheduleUpdate();
      }
    }
  };

  public TransferToEDTQueue(@NotNull @NonNls String name,
                            @NotNull Processor<T> processor,
                            @NotNull Condition<?> shutUpCondition,
                            int maxUnitOfWorkThresholdMs) {
    myName = name;
    myProcessor = processor;
    myShutUpCondition = shutUpCondition;
    myMaxUnitOfWorkThresholdMs = maxUnitOfWorkThresholdMs;
  }
  
  public static TransferToEDTQueue<Runnable> createRunnableMerger(@NotNull @NonNls String name, int maxUnitOfWorkThresholdMs) {
    return new TransferToEDTQueue<Runnable>(name, new Processor<Runnable>() {
      @Override
      public boolean process(Runnable runnable) {
        runnable.run();
        return true;
      }
    }, Conditions.alwaysFalse(), maxUnitOfWorkThresholdMs);
  }

  private boolean isEmpty() {
    synchronized (myQueue) {
      return myQueue.isEmpty();
    }
  }

  // return true if element was pulled from the queue and processed successfully
  private boolean processNext() {
    T thing = pullFirst();
    if (thing == null) return false;
    if (!myProcessor.process(thing)) {
      stop();
      return false;
    }
    return true;
  }

  protected T pullFirst() {
    synchronized (myQueue) {
      return myQueue.isEmpty() ? null : myQueue.pullFirst();
    }
  }

  public boolean offer(@NotNull T thing) {
    synchronized (myQueue) {
      myQueue.addLast(thing);
    }
    scheduleUpdate();
    return true;
  }

  public boolean offerIfAbsent(@NotNull final T thing, @NotNull final Equality<T> equality) {
    synchronized (myQueue) {
      boolean absent = myQueue.process(new Processor<T>() {
        @Override
        public boolean process(T t) {
          return !equality.equals(t, thing);
        }
      });
      if (absent) {
        myQueue.addLast(thing);
        scheduleUpdate();
      }
      return absent;
    }
  }

  private void scheduleUpdate() {
    if (!stopped && invokeLaterScheduled.compareAndSet(false, true)) {
      schedule(myUpdateRunnable);
    }
  }

  protected void schedule(@NotNull Runnable updateRunnable) {
    SwingUtilities.invokeLater(updateRunnable);
  }

  public void stop() {
    stopped = true;
    synchronized (myQueue) {
      myQueue.clear();
    }
  }

  public int size() {
    synchronized (myQueue) {
      return myQueue.size();
    }
  }

  // process all queue in current thread
  public void drain() {
    int processed = 0;
    long start = System.currentTimeMillis();
    while (processNext()) {
      processed++;
    }
    long finish = System.currentTimeMillis();
  }

  // blocks until all elements in the queue are processed
  public void waitFor() {
    final Semaphore semaphore = new Semaphore();
    semaphore.down();
    schedule(new Runnable() {
      @Override
      public void run() {
        semaphore.up();
      }
    });
    semaphore.waitFor();
  }

}