package org.simantics.db.impl.query;

import java.util.ArrayList;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicInteger;

import org.simantics.db.Session;
import org.simantics.db.common.SessionThread;
import org.simantics.db.impl.query.QueryProcessor.SessionTask;
import org.simantics.db.impl.query.QueryProcessor.ThreadState;
import org.slf4j.LoggerFactory;

class QueryThread extends Thread implements SessionThread {

	private static final org.slf4j.Logger LOGGER = LoggerFactory.getLogger(QueryThread.class);

	boolean disposed = false;
	private Semaphore exited = new Semaphore(0);

	final int index;

	private Session session;
	private QuerySupport querySupport;
	private final QueryProcessor processor;
	private final Semaphore requests;

	final private ArrayList<SessionTask> tasks = new ArrayList<SessionTask>();
//	final private ArrayList<SessionTask> own;
//	final private ArrayList<SessionTask> ownSync;
//	final private ArrayList<SessionTask> queue;
//	final private ReentrantLock lock;
//	final private Condition condition;
	final private Object querySupportLock;
	final private int THREADS;
	final private AtomicInteger sleepers;
	final private ThreadState[] threadStates;
//	final private ArrayList<SessionTask>[] delayQueues;
//	final private QueryThread[] executors;
//	final private ReentrantLock[] threadLocks;
//	final private ArrayList<SessionTask>[] queues;
//	final private ArrayList<SessionTask>[] ownSyncTasks;

	public QueryThread(Session session, QueryProcessor processor, int index, String name) {
		super(QueryProcessor.QueryThreadGroup, null, name);
		this.session = session;
		this.processor = processor;
		this.index = index;
//		own = processor.ownTasks[index];
//		ownSync = processor.ownSyncTasks[index];
//		queue = processor.queues[index];
//		lock = processor.threadLocks[index];
//		condition = processor.threadConditions[index];
		querySupportLock = processor.querySupportLock;
		THREADS = processor.THREADS;
		sleepers = processor.sleepers;
		querySupport = processor.querySupport;
		threadStates = processor.threadStates;
		requests = processor.requests;
//		delayQueues = processor.delayQueues;
//		executors = processor.executors;
//		threadLocks = processor.threadLocks;
//		queues = processor.queues;
//		ownSyncTasks = processor.ownSyncTasks;
	}

	synchronized void dispose() {

//		System.err.println("qt dispose");

		disposed = true;
//		lock.lock();
//		condition.signalAll();
//		lock.unlock();
		
		try {
			exited.acquire();
		} catch (InterruptedException e) {
			LOGGER.error("dispose was interrupted", e);
		}

		session = null;
		querySupport = null;

//		System.err.println("qt disposed");

	}

	boolean isDisposed() { 

		return disposed;

	}

	public Session getSession() {

		return session;

	}

	private boolean pumpTask() {
		if(!processor.freeScheduling.isEmpty()) {
			tasks.add(processor.freeScheduling.removeFirst());
			processor.queueLength.decrementAndGet();
			return true;
		}
		return false;
	}
	
	ArrayList<SessionTask> newTasks(boolean doWait, ArrayList<SessionTask> tasks) {

		try {

			while(true) {

				// Return tasks if some were found
				if(!tasks.isEmpty()) return tasks;
				
				if(!doWait) return null;

				synchronized (querySupportLock) {

					if(pumpTask())
						return tasks;

//					lock.lock();

					// We are the last one awake
					if(sleepers.incrementAndGet() == THREADS) {

						// Do not indicate sleeping yet
						sleepers.decrementAndGet();
						// Ceased can create new own tasks
						if(querySupport == null) System.err.println("null qs");
						querySupport.ceased(index);

						if(pumpTask()) {
//							lock.unlock();
							return tasks;
						}

						// OK, now we are going to sleep
						sleepers.incrementAndGet();

					}

				}

				// Nope nothing. Sleep & wait
				// Whoever releases this calls sleepers.decrementAndGet()

				// We are done
				if(isDisposed()) {
					threadStates[index] = ThreadState.DISPOSED;
//					lock.unlock();
					return null;
				}

				
				threadStates[index] = ThreadState.SLEEP;
				
				requests.acquire();

				sleepers.decrementAndGet();

				// We are done
				if(isDisposed()) {
					threadStates[index] = ThreadState.DISPOSED;
					//lock.unlock();
					return null;
				}

				threadStates[index] = ThreadState.RUN;

				//lock.unlock();

			}

		} catch (InterruptedException e) {

			LOGGER.error("Query handling (newTasks) was interrupted", e);
			throw new RuntimeException("Querying was interrupted.", e);

		}

	}

	public boolean runSynchronized() {

		boolean didExecute = false;

//		for(int performer=0;performer<THREADS;performer++) {
//			if(!delayQueues[index * THREADS + performer].isEmpty()) {
//				synchronized(executors[performer]) {
//					threadLocks[performer].lock();
//					queues[performer].addAll(delayQueues[index * THREADS + performer]);
//					delayQueues[index * THREADS + performer].clear();
//					executors[performer].notify();
//					threadLocks[performer].unlock();
//				}
//			}
//		}

		if(tasks.isEmpty()) {
			ArrayList<SessionTask> finished = newTasks(false, tasks);
			if(finished == null) return didExecute;	
		}

		while(!tasks.isEmpty()) {

			SessionTask task = tasks.remove(tasks.size() - 1);

//			if(task.syncCaller == index) {
//				ownSyncTasks[index].add(task);
//			} else {
				task.run(index);
//				System.err.println("QT(s) " + index + " runs " + task);
				didExecute = true;
//			}

		}

		return didExecute;

	}

	@Override
	public void run() {

		processor.thread.set(index);
		
		QuerySupport support = this.querySupport;

		try {

			while (true) {

				boolean finished = newTasks(true, tasks) == null;
				if(finished) {
					return;
				}
				
				while(!tasks.isEmpty()) {

					SessionTask task = tasks.remove(tasks.size()-1);
//					System.err.println("QT " + index + " runs " + task);
					task.run(index);

				}

//				for(int performer=0;performer<THREADS;performer++) {
//					if(!delayQueues[index * THREADS + performer].isEmpty()) {
//						synchronized(executors[performer]) {
//							threadLocks[performer].lock();
//							queues[performer].addAll(delayQueues[index * THREADS + performer]);
//							delayQueues[index * THREADS + performer].clear();
//							executors[performer].notify();
//							threadLocks[performer].unlock();
//						}
//					}
//				}

			}

		} catch (Throwable t) {

			LOGGER.error("FATAL BUG: QueryThread task processing caused unexpected exception.", t);
			support.exit(t);

		} finally {
			
			exited.release();

		}

	}

}