/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 *
 * 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.badlogic.gdx.utils;

/** A pool of objects that can be reused to avoid allocation.
 * @see Pools
 * @author Nathan Sweet */
abstract public class Pool<T> {
    /** The maximum number of objects that will be pooled. */
    public final int max;
    /** The highest number of free objects. Can be reset any time. */
    public int peak;

    private final Array<T> freeObjects;

    /** Creates a pool with an initial capacity of 16 and no maximum. */
    public Pool () {
        this(16, Integer.MAX_VALUE);
    }

    /** Creates a pool with the specified initial capacity and no maximum. */
    public Pool (int initialCapacity) {
        this(initialCapacity, Integer.MAX_VALUE);
    }

    /** @param initialCapacity The initial size of the array supporting the pool. No objects are created/pre-allocated. Use
     *           {@link #fill(int)} after instantiation if needed.
     * @param max The maximum number of free objects to store in this pool. */
    public Pool (int initialCapacity, int max) {
        freeObjects = new Array(false, initialCapacity);
        this.max = max;
    }

    abstract protected T newObject ();

    /** Returns an object from this pool. The object may be new (from {@link #newObject()}) or reused (previously
     * {@link #free(Object) freed}). */
    public T obtain () {
        synchronized (freeObjects) {
            return freeObjects.size == 0 ? newObject() : freeObjects.pop();
        }
    }

    /** Puts the specified object in the pool, making it eligible to be returned by {@link #obtain()}. If the pool already contains
     * {@link #max} free objects, the specified object is {@link #discard(Object) discarded}, it is not reset and not added to the
     * pool.
     * <p>
     * The pool does not check if an object is already freed, so the same object must not be freed multiple times. */
    public void free (T object) {
        synchronized (freeObjects) {
            if (object == null) throw new IllegalArgumentException("object cannot be null.");
            if (freeObjects.size < max) {
                freeObjects.add(object);
                peak = Math.max(peak, freeObjects.size);
                reset(object);
            } else
                discard(object);
        }
    }

    /** Adds the specified number of new free objects to the pool. Usually called early on as a pre-allocation mechanism but can be
     * used at any time.
     *
     * @param size the number of objects to be added */
    public void fill (int size) {
        synchronized (freeObjects) {
            for (int i = 0; i < size; i++)
                if (freeObjects.size < max) freeObjects.add(newObject());
            peak = Math.max(peak, freeObjects.size);
        }
    }

    /** Called when an object is freed to clear the state of the object for possible later reuse. The default implementation calls
     * {@link Poolable#reset()} if the object is {@link Poolable}. */
    protected void reset (T object) {
        if (object instanceof Poolable) ((Poolable)object).reset();
    }

    /** Called when an object is discarded. This is the case when an object is freed, but the maximum capacity of the pool is
     * reached, and when the pool is {@link #clear() cleared} */
    protected void discard (T object) {
        reset(object);
    }

    /** Puts the specified objects in the pool. Null objects within the array are silently ignored.
     * <p>
     * The pool does not check if an object is already freed, so the same object must not be freed multiple times.
     * @see #free(Object) */
    public void freeAll (Array<T> objects) {
        synchronized (freeObjects) {
            if (objects == null) throw new IllegalArgumentException("objects cannot be null.");
            Array<T> freeObjects = this.freeObjects;
            int max = this.max;
            for (int i = 0, n = objects.size; i < n; i++) {
                T object = objects.get(i);
                if (object == null) continue;
                if (freeObjects.size < max) {
                    freeObjects.add(object);
                    reset(object);
                } else {
                    discard(object);
                }
            }
            peak = Math.max(peak, freeObjects.size);
        }
    }

    /** Removes and discards all free objects from this pool. */
    public void clear () {
        synchronized (freeObjects) {
            Array<T> freeObjects = this.freeObjects;
            for (int i = 0, n = freeObjects.size; i < n; i++)
                discard(freeObjects.get(i));
            freeObjects.clear();
        }
    }

    /** The number of objects available to be obtained. */
    public int getFree () {
        synchronized (freeObjects) {
            return freeObjects.size;
        }
    }

    /** Objects implementing this interface will have {@link #reset()} called when passed to {@link Pool#free(Object)}. */
    static public interface Poolable {
        /** Resets the object for reuse. Object references should be nulled and fields may be set to default values. */
        public void reset ();
    }
}
