package java.util.concurrent;

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.NoSuchElementException;

public class LinkedBlockingQueue<T> implements BlockingQueue<T> {
  private final Object collectionLock;
  private final LinkedList<T> storage;
  private final int capacity;
  
  public LinkedBlockingQueue() {
    this(Integer.MAX_VALUE);
  }
  
  public LinkedBlockingQueue(int capacity) {
    collectionLock = new Object();
    this.capacity = capacity;
    storage = new LinkedList<T>();
  }
  
  // should be synchronized on collectionLock before calling
  private void handleRemove() {
    collectionLock.notifyAll();
  }
  
  // should be synchronized on collectionLock before calling
  private void handleAdd() {
    collectionLock.notifyAll();
  }

  // should be synchronized on collectionLock before calling
  private void blockTillNotFull() throws InterruptedException {
    blockTillNotFull(Long.MAX_VALUE);
  }

  // should be synchronized on collectionLock before calling
  private void blockTillNotFull(long maxWaitInMillis) throws InterruptedException {
    if (capacity > storage.size()) {
      return;
    }
    
    long startTime = 0;
    if (maxWaitInMillis != Long.MAX_VALUE) {
      startTime = System.currentTimeMillis();
    }
    long remainingWait = maxWaitInMillis;
    while (remainingWait > 0) {
      collectionLock.wait(remainingWait);
      
      if (capacity > storage.size()) {
        return;
      } else if (maxWaitInMillis != Long.MAX_VALUE) {
        remainingWait = maxWaitInMillis - (System.currentTimeMillis() - startTime);
      }
    }
  }

  // should be synchronized on collectionLock before calling
  private void blockTillNotEmpty() throws InterruptedException {
    blockTillNotEmpty(Long.MAX_VALUE);
  }

  // should be synchronized on collectionLock before calling
  private void blockTillNotEmpty(long maxWaitInMillis) throws InterruptedException {
    if (! storage.isEmpty()) {
      return;
    }
    
    long startTime = 0;
    if (maxWaitInMillis != Long.MAX_VALUE) {
      startTime = System.currentTimeMillis();
    }
    long remainingWait = maxWaitInMillis;
    while (remainingWait > 0) {
      collectionLock.wait(remainingWait);
      
      if (! storage.isEmpty()) {
        return;
      } else if (maxWaitInMillis != Long.MAX_VALUE) {
        remainingWait = maxWaitInMillis - (System.currentTimeMillis() - startTime);
      }
    }
  }

  @Override
  public boolean add(T element) {
    if (! offer(element)) {
      throw new IllegalStateException("At capacity");
    }
    
    return true;
  }

  @Override
  public boolean offer(T element) {
    synchronized (collectionLock) {
      if (capacity > storage.size()) {
        storage.addLast(element);
        
        handleAdd();
        
        return true;
      } else {
        return false;
      }
    }
  }

  @Override
  public boolean offer(T e, long timeout, TimeUnit unit) throws InterruptedException {
    long timeoutInMillis = unit.toMillis(timeout);
    synchronized (collectionLock) {
      // block till we can add or have reached timeout
      blockTillNotFull(timeoutInMillis);
      
      return offer(e);
    }
  }

  @Override
  public void put(T e) throws InterruptedException {
    synchronized (collectionLock) {
      // block till we have space
      blockTillNotFull();
      
      storage.add(e);
      handleAdd();
    }
  }

  @Override
  public boolean addAll(Collection<? extends T> c) {
    synchronized (collectionLock) {
      if (storage.size() + c.size() > capacity) {
        throw new IllegalStateException("Not enough space");
      }
      
      if (c.isEmpty()) {
        return false;
      } else {
        storage.addAll(c);
        
        return true;
      }
    }
  }

  @Override
  public T peek() {
    synchronized (collectionLock) {
      if (storage.isEmpty()) {
        return null;
      } else {
        return storage.getFirst();
      }
    }
  }

  @Override
  public T element() {
    T result = peek();
    
    if (result == null) {
      throw new NoSuchElementException();
    }
    
    return result;
  }

  // should be synchronized on collectionLock before calling
  private T removeFirst() {
    T result = storage.removeFirst();
    handleRemove();
    
    return result;
  }

  @Override
  public T poll() {
    synchronized (collectionLock) {
      if (storage.isEmpty()) {
        return null;
      } else {
        return removeFirst();
      }
    }
  }

  @Override
  public T poll(long timeout, TimeUnit unit) throws InterruptedException {
    long timeoutInMillis = unit.toMillis(timeout);
    synchronized (collectionLock) {
      // block till we available or timeout
      blockTillNotEmpty(timeoutInMillis);
      
      return poll();
    }
  }

  @Override
  public T take() throws InterruptedException {
    synchronized (collectionLock) {
      // block till we available
      blockTillNotEmpty();
      
      return removeFirst();
    }
  }

  @Override
  public T remove() {
    T result = poll();
    
    if (result == null) {
      throw new NoSuchElementException();
    }
    
    return result;
  }

  @Override
  public int drainTo(Collection<? super T> c) {
    return drainTo(c, Integer.MAX_VALUE);
  }

  @Override
  public int drainTo(Collection<? super T> c, int maxElements) {
    int remainingElements = maxElements;
    synchronized (collectionLock) {
      while (remainingElements > 0 && ! storage.isEmpty()) {
        c.add(storage.removeFirst());
        remainingElements--;
      }
      
      if (remainingElements != maxElements) {
        handleRemove();
      }
      
      return maxElements - remainingElements;
    }
  }

  @Override
  public int remainingCapacity() {
    synchronized (collectionLock) {
      return capacity - storage.size();
    }
  }

  @Override
  public int size() {
    synchronized (collectionLock) {
      return storage.size();
    }
  }

  @Override
  public boolean isEmpty() {
    return size() == 0;
  }

  @Override
  public boolean contains(Object element) {
    synchronized (collectionLock) {
      return storage.contains(element);
    }
  }

  @Override
  public boolean containsAll(Collection<?> c) {
    synchronized (collectionLock) {
      return storage.containsAll(c);
    }
  }

  @Override
  public boolean remove(Object element) {
    synchronized (collectionLock) {
      if (storage.remove(element)) {
        handleRemove();
        return true;
      } else {
        return false;
      }
    }
  }

  @Override
  public boolean removeAll(Collection<?> c) {
    synchronized (collectionLock) {
      if (storage.removeAll(c)) {
        handleRemove();
        return true;
      } else {
        return false;
      }
    }
  }

  @Override
  public void clear() {
    synchronized (collectionLock) {
      storage.clear();
    }
  }

  @Override
  public Object[] toArray() {
    synchronized (collectionLock) {
      return storage.toArray();
    }
  }

  @Override
  public <S> S[] toArray(S[] array) {
    synchronized (collectionLock) {
      return storage.toArray(array);
    }
  }

  @Override
  public Iterator<T> iterator() {
    throw new UnsupportedOperationException("Not implemented yet");
  }
}