package  nextrek.imagecache;

/*
 * Copyright (C) 2011 The Android Open Source Project
 * 
 * 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.
 */

import java.util.Map;

import nextrek.lib.SIC;
import android.os.Debug;
import android.util.Log;

/**
 * A cache that holds strong references to a limited number of values. Each time
 * a value is accessed, it is moved to the head of a queue. When a value is
 * added to a full cache, the value at the end of that queue is evicted and may
 * become eligible for garbage collection.
 * 
 * <p>
 * If your cached values hold resources that need to be explicitly released, override {@link #entryRemoved}.
 * 
 * <p>
 * If a cache miss should be computed on demand for the corresponding keys, override {@link #create}. This simplifies the calling code, allowing it to assume a value will always be returned, even when there's a cache miss.
 * 
 * <p>
 * By default, the cache size is measured in the number of entries. Override {@link #sizeOf} to size the cache in different units. For example, this cache is limited to 4MiB of bitmaps:
 * 
 * <pre>
 * {@code
 *   int cacheSize = 4 * 1024 * 1024; // 4MiB
 *   LruCache<String, Bitmap> bitmapCache = new LruCache<String, Bitmap>(cacheSize) {
 *       protected int sizeOf(String key, Bitmap value) {
 *           return value.getByteCount();
 *       }
 *   }}
 * </pre>
 * 
 * <p>
 * This class is thread-safe. Perform multiple cache operations atomically by synchronizing on the cache:
 * 
 * <pre>
 * {@code
 *   synchronized (cache) {
 *     if (cache.get(key) == null) {
 *         cache.put(key, value);
 *     }
 *   }}
 * </pre>
 * 
 * <p>
 * This class does not allow null to be used as a key or value. A return value of null from {@link #get}, {@link #put} or {@link #remove} is unambiguous: the key was not in the cache.
 */
public class LruCache<K, V> {
    private int createCount;

    private int evictionCount;
    private int hitCount;

    private final ICSLinkedHashMap<K, V> map;
    private final int maxSize;
    private int missCount;
    private int putCount;
    /** Size of this cache in units. Not necessarily the number of elements. */
    private int size;

    private String TAG;

    /**
     * @param maxSize
     *            for caches that do not override {@link #sizeOf}, this is
     *            the maximum number of entries in the cache. For all other caches,
     *            this is the maximum sum of the sizes of the entries in this cache.
     */
    public LruCache(final String name, final int maxSize) {
        TAG = name;
        if (maxSize <= 0) {
            throw new IllegalArgumentException("maxSize <= 0");
        }
        this.maxSize = maxSize;
        this.map = new ICSLinkedHashMap<K, V>(8, 0.75f, true);
    }

    /**
     * Called after a cache miss to compute a value for the corresponding key.
     * Returns the computed value or null if no value can be computed. The
     * default implementation returns null.
     * 
     * <p>
     * The method is called without synchronization: other threads may access the cache while this method is executing.
     * 
     * <p>
     * If a value for {@code key} exists in the cache when this method returns, the created value will be released with {@link #entryRemoved} and discarded. This can occur when multiple threads request the same key at the same time (causing multiple values
     * to be created), or when one thread calls {@link #put} while another is creating a value for the same key.
     */
    protected V create(final K key) {
        return null;
    }

    /**
     * Returns the number of times {@link #create(Object)} returned a value.
     */
    public synchronized final int createCount() {
        return createCount;
    }

    /**
     * Called for entries that have been evicted or removed. This method is
     * invoked when a value is evicted to make space, removed by a call to {@link #remove}, or replaced by a call to {@link #put}. The default
     * implementation does nothing.
     * 
     * <p>
     * The method is called without synchronization: other threads may access the cache while this method is executing.
     * 
     * @param evicted
     *            true if the entry is being removed to make space, false
     *            if the removal was caused by a {@link #put} or {@link #remove}.
     * @param newValue
     *            the new value for {@code key}, if it exists. If non-null,
     *            this removal was caused by a {@link #put}. Otherwise it was caused by
     *            an eviction or a {@link #remove}.
     */
    protected void entryRemoved(final boolean evicted, final K key, final V oldValue, final V newValue) {
    }

    /**
     * Clear the cache, calling {@link #entryRemoved} on each removed entry.
     */
    public final void evictAll() {
        trimToSize(-1); // -1 will evict 0-sized elements
    }

    /**
     * Returns the number of values that have been evicted.
     */
    public synchronized final int evictionCount() {
        return evictionCount;
    }

    /**
     * Returns the value for {@code key} if it exists in the cache or can be
     * created by {@code #create}. If a value was returned, it is moved to the
     * head of the queue. This returns null if a value is not cached and cannot
     * be created.
     */
    public final V get(final K key) {
        if (key == null) {
            throw new NullPointerException("key == null");
        }

        V mapValue;
        synchronized (this) {
            mapValue = map.get(key);
            if (mapValue != null) {
                if (SIC.DEBUG)
                    Log.d(TAG, "get " + key);
                hitCount++;
                return mapValue;
            }
            missCount++;
        }

        /*
         * Attempt to create a value. This may take a long time, and the map
         * may be different when create() returns. If a conflicting value was
         * added to the map while create() was working, we leave that value in
         * the map and release the created value.
         */

        final V createdValue = create(key);
        if (createdValue == null) {
            return null;
        }

        synchronized (this) {
            createCount++;
            mapValue = map.put(key, createdValue);

            if (mapValue != null) {
                // There was a conflict so undo that last put
                map.put(key, mapValue);
            } else {
                size += safeSizeOf(key, createdValue);
            }
        }

        if (mapValue != null) {
            entryRemoved(false, key, createdValue, mapValue);
            return mapValue;
        } else {
            trimToSize(maxSize);
            return createdValue;
        }
    }

    /**
     * Returns the number of times {@link #get} returned a value that was
     * already present in the cache.
     */
    public synchronized final int hitCount() {
        return hitCount;
    }

    /**
     * For caches that do not override {@link #sizeOf}, this returns the maximum
     * number of entries in the cache. For all other caches, this returns the
     * maximum sum of the sizes of the entries in this cache.
     */
    public synchronized final int maxSize() {
        return maxSize;
    }

    /**
     * Returns the number of times {@link #get} returned null or required a new
     * value to be created.
     */
    public synchronized final int missCount() {
        return missCount;
    }

    /**
     * Caches {@code value} for {@code key}. The value is moved to the head of
     * the queue.
     * 
     * @return the previous value mapped by {@code key}.
     */
    public final V put(final K key, final V value) {

        if (SIC.DEBUG)
            Log.d(TAG, "put " + key);
        if ((key == null) || (value == null)) {
            throw new NullPointerException("key == null || value == null");
        }

        V previous;
        synchronized (this) {
            putCount++;
            size += safeSizeOf(key, value);
            previous = map.put(key, value);
            if (previous != null) {
                size -= safeSizeOf(key, previous);
            }
        }

        if (previous != null) {
            entryRemoved(false, key, previous, value);
        }

        trimToSize(maxSize);
        return previous;
    }

    /**
     * Returns the number of times {@link #put} was called.
     */
    public synchronized final int putCount() {
        return putCount;
    }

    /**
     * Removes the entry for {@code key} if it exists.
     * 
     * @return the previous value mapped by {@code key}.
     */
    public final V remove(final K key) {
        if (key == null) {
            throw new NullPointerException("key == null");
        }

        V previous;
        synchronized (this) {
            previous = map.remove(key);
            if (previous != null) {
                size -= safeSizeOf(key, previous);
            }
        }

        if (previous != null) {
            entryRemoved(false, key, previous, null);
        }

        return previous;
    }

    private int safeSizeOf(final K key, final V value) {
        final int result = sizeOf(key, value);
        if (result < 0) {
            throw new IllegalStateException("Negative size: " + key + "=" + value);
        }
        return result;
    }

    /**
     * For caches that do not override {@link #sizeOf}, this returns the number
     * of entries in the cache. For all other caches, this returns the sum of
     * the sizes of the entries in this cache.
     */
    public synchronized final int size() {
        return size;
    }

    /**
     * Returns the size of the entry for {@code key} and {@code value} in
     * user-defined units. The default implementation returns 1 so that size
     * is the number of entries and max size is the maximum number of entries.
     * 
     * <p>
     * An entry's size must not change while it is in the cache.
     */
    protected int sizeOf(final K key, final V value) {
        return 1;
    }

    @Override
    public synchronized final String toString() {
        final int accesses = hitCount + missCount;
        final int hitPercent = accesses != 0 ? ((100 * hitCount) / accesses) : 0;
        return String.format("LruCache[maxSize=%d,hits=%d,misses=%d,hitRate=%d%%]", maxSize, hitCount, missCount, hitPercent);
    }

    /**
     * @param maxSize
     *            the maximum size of the cache before returning. May be -1
     *            to evict even 0-sized elements.
     */
    private void trimToSize(final int maxSize) {

        final int initialSize = size;

        while (true) {
            K key;
            V value;
            synchronized (this) {
                if ((size < 0) || (map.isEmpty() && (size != 0))) {
                    throw new IllegalStateException(getClass().getName() + ".sizeOf() is reporting inconsistent results!");
                }

                if (size <= maxSize) {
                    break;
                }

                final Map.Entry<K, V> toEvict = map.eldest();
                if (toEvict == null) {
                    break;
                }

                key = toEvict.getKey();
                value = toEvict.getValue();
                map.remove(key);
                size -= safeSizeOf(key, value);
                evictionCount++;
            }

            entryRemoved(true, key, value, null);
        }
        if (initialSize > maxSize) {
            System.gc();
            Log.i(TAG, "MEM cache size: " + size + " (" + map.size() + " elements) free mem:" + Runtime.getRuntime().freeMemory() + " ext-heap alloc:" + Debug.getNativeHeapAllocatedSize());
        }
    }
}