package io.trygvis.async;

import io.trygvis.queue.QueueExecutor;
import io.trygvis.queue.QueueService;
import io.trygvis.queue.QueueSystem;
import io.trygvis.queue.SqlEffect;
import io.trygvis.queue.SqlEffectExecutor;
import io.trygvis.queue.Task;
import io.trygvis.queue.TaskEffect;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledThreadPoolExecutor;

import static io.trygvis.queue.QueueExecutor.TaskExecutionResult;
import static io.trygvis.queue.QueueService.TaskExecutionRequest;
import static io.trygvis.queue.Task.TaskState.NEW;

public class QueueController {
    private final Logger log = LoggerFactory.getLogger(getClass());

    private final QueueSystem queueSystem;

    private final SqlEffectExecutor sqlEffectExecutor;

    private final TaskEffect taskEffect;

    private final TaskExecutionRequest req;

    public final QueueExecutor queue;

    private boolean shouldRun = true;

    private boolean checkForNewTasks;

    private boolean running;

    private Thread thread;

    private ScheduledThreadPoolExecutor executor;

    public QueueController(QueueSystem queueSystem, TaskExecutionRequest req, TaskEffect taskEffect, QueueExecutor queue) {
        this.queueSystem = queueSystem;
        this.req = req;
        this.sqlEffectExecutor = queueSystem.sqlEffectExecutor;
        this.taskEffect = taskEffect;
        this.queue = queue;
    }

    public void executeTasks(final QueueService.TaskExecutionRequest req, final TaskEffect effect, final List<Task> tasks,
                             ScheduledThreadPoolExecutor executor) {
        ExecutorCompletionService<TaskExecutionResult> completionService = new ExecutorCompletionService<>(executor);

        List<Future<TaskExecutionResult>> results = new ArrayList<>(tasks.size());

        for (final Task task : tasks) {
            results.add(completionService.submit(new Callable<TaskExecutionResult>() {
                @Override
                public TaskExecutionResult call() throws Exception {
                    return queue.applyTask(effect, task);
                }
            }));
        }

        for (Future<TaskExecutionResult> result : results) {
            while(!result.isDone()) {
                try {
                    result.get();
                    break;
                } catch (InterruptedException e) {
                    if(shouldRun) {
                        continue;
                    }
                } catch (ExecutionException e) {
                    log.error("Unexpected exception.", e);
                    break;
                }
            }
        }
    }

    private class QueueThread implements Runnable {
        public void run() {
            while (shouldRun) {
                List<Task> tasks = null;

                try {
                    tasks = sqlEffectExecutor.transaction(new SqlEffect<List<Task>>() {
                        public List<Task> doInConnection(Connection c) throws SQLException {
                            return queueSystem.createTaskDao(c).findByQueueAndState(queue.queue.name, NEW, req.chunkSize);
                        }
                    });

                    log.info("Found {} tasks on queue {}", tasks.size(), queue.queue.name);

                    if (tasks.size() > 0) {
                        executeTasks(req, taskEffect, tasks, executor);
                    }
                } catch (Throwable e) {
                    if (shouldRun) {
                        log.warn("Error while executing tasks.", e);
                    }
                }

                // If we found exactly the same number of tasks that we asked for, there is most likely more to go.
                if (tasks != null && tasks.size() == req.chunkSize) {
                    log.info("Got a full chunk, continuing directly.");
                    continue;
                }

                synchronized (this) {
                    if (checkForNewTasks) {
                        log.info("Ping received!");
                        checkForNewTasks = false;
                    } else {
                        try {
                            wait(queue.queue.interval);
                        } catch (InterruptedException e) {
                            // ignore
                        }
                    }
                }
            }

            log.info("Thread for queue {} has stopped.", queue.queue.name);
            running = false;
            synchronized (this) {
                this.notifyAll();
            }
        }
    }

    public synchronized void start(ScheduledThreadPoolExecutor executor) {
        if (running) {
            throw new IllegalStateException("Already running");
        }

        log.info("Starting thread for queue {} with poll interval = {}ms", queue.queue.name, queue.queue.interval);

        running = true;
        this.executor = executor;

        thread = new Thread(new QueueThread(), "queue: " + queue.queue.name);
        thread.setDaemon(true);
        thread.start();
    }

    public synchronized void stop() {
        if (!running) {
            return;
        }

        log.info("Stopping thread for queue {}", queue.queue.name);

        shouldRun = false;

        // TODO: empty out the currently executing tasks.

        thread.interrupt();
        while (running) {
            try {
                wait(1000);
            } catch (InterruptedException e) {
                // continue
            }
            thread.interrupt();
        }
        thread = null;
        executor.shutdownNow();
    }
}