/*
 * This file is part of Araknemu.
 *
 * Araknemu is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Araknemu is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with Araknemu.  If not, see <https://www.gnu.org/licenses/>.
 *
 * Copyright (c) 2017-2019 Vincent Quatrevieux
 */

package fr.quatrevieux.araknemu.game.exploration.interaction.action;

import org.checkerframework.checker.nullness.qual.Nullable;

import java.util.ArrayDeque;
import java.util.NoSuchElementException;
import java.util.Queue;

/**
 * Queue for game actions
 *
 * A new action will be pushed at the end of the queue
 * The action will be started when the last action will be finished, or the queue is empty
 *
 * Example :
 *
 * recv  GA001
 * recv  GA500
 * push  MOVE
 * start MOVE
 * send  GA001
 * push  IO_ACTION
 * ... Wait for move end...
 * GKK001
 * end   MOVE
 * pop   MOVE
 * start IO_ACTION
 * ... Wait for end...
 *
 * The action have 2 different types of ending :
 * - {@link BlockingAction#end()}  When an action is successfully ended
 * - {@link BlockingAction#cancel(String)} When an error occurs during the action, and should be stopped prematurely
 */
public final class ActionQueue {
    private final Queue<Action> actions = new ArrayDeque<>();

    private @Nullable BlockingAction current;
    private byte lastActionId = 0;

    /**
     * Check if the queue is not empty
     */
    public boolean isBusy() {
        return current != null || !actions.isEmpty();
    }

    /**
     * Push the action to the queue, and start it if not busy
     */
    public void push(Action action) {
        actions.add(action);

        runNextAction();
    }

    /**
     * End an action which is successfully terminated
     *
     * @param actionId The action to end
     *
     * @return true if the action was ended, false if there is no pending action with this id
     */
    public boolean end(int actionId) {
        final BlockingAction current = this.current;

        if (current == null || current.id() != actionId) {
            return false;
        }

        current.end();
        this.current = null;

        runNextAction();
        return true;
    }

    /**
     * Cancel an action in the queue
     *
     * @param actionId Action to cancel
     * @param argument The cancel argument
     */
    public void cancel(int actionId, String argument) {
        final BlockingAction current = this.current;

        if (current == null || current.id() != actionId) {
            throw new NoSuchElementException("The action ID do not corresponds");
        }

        try {
            current.cancel(argument);
        } finally {
            this.current = null;
            actions.clear();
        }
    }

    /**
     * Remove all pending actions and cancel the current action
     *
     * This method MUST not throws exceptions
     * If a blocking action receive NULL as argument for cancel, no error must be raised
     */
    public void stop() {
        actions.clear();

        if (current != null) {
            try {
                current.cancel(null);
            } finally {
                current = null;
            }
        }
    }

    /**
     * The action waits for a Game action end and blocks the action queue
     * A unique action id will be generated
     *
     * @param pending The pending action
     */
    public void setPending(BlockingAction pending) {
        pending.setId(generateId());

        this.current = pending;
    }

    /**
     * Generate a new action id
     */
    private int generateId() {
        return ++lastActionId;
    }

    /**
     * Run the next pending action
     *
     * If an error occurs during the action, it will be removed
     */
    private void runNextAction() {
        RuntimeException error = null;

        while (this.current == null && !actions.isEmpty()) {
            final Action action = actions.remove();

            try {
                action.start(this);
            } catch (RuntimeException e) {
                this.current = null;
                error = e;
            }
        }

        if (error != null) {
            throw error;
        }
    }
}