package com.comphenix.protocol.utility;

import java.lang.reflect.Method;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.TimeUnit;

import com.comphenix.protocol.reflect.FieldAccessException;
import com.google.common.base.Ticker;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.RemovalListener;

/**
 * Represents a Guava CacheBuilder that is compatible with both Guava 10 and 13.
 * 
 * @author Kristian
 */
public class SafeCacheBuilder<K, V> {
    private CacheBuilder<K, V> builder;

    private static Method BUILD_METHOD;
    private  static Method AS_MAP_METHOD;
    
    @SuppressWarnings("unchecked")
    private SafeCacheBuilder() {
        builder = (CacheBuilder<K, V>) CacheBuilder.newBuilder();
    }

    /**
     * Construct a new safe cache builder.
     * @param <K> Key type
     * @param <V> Value type
     * 
     * @return A new cache builder.
     */
    public static <K, V> SafeCacheBuilder<K, V> newBuilder() {
        return new SafeCacheBuilder<K, V>();
    }

    /**
     * Guides the allowed concurrency among update operations. Used as a hint
     * for internal sizing. The table is internally partitioned to try to permit
     * the indicated number of concurrent updates without contention. Because
     * assignment of entries to these partitions is not necessarily uniform, the
     * actual concurrency observed may vary. Ideally, you should choose a value
     * to accommodate as many threads as will ever concurrently modify the
     * table. Using a significantly higher value than you need can waste space
     * and time, and a significantly lower value can lead to thread contention.
     * But overestimates and underestimates within an order of magnitude do not
     * usually have much noticeable impact. A value of one permits only one
     * thread to modify the cache at a time, but since read operations can
     * proceed concurrently, this still yields higher concurrency than full
     * synchronization. Defaults to 4.
     * 
     * <p>
     * <b>Note:</b>The default may change in the future. If you care about this
     * value, you should always choose it explicitly.
     * 
     * @param concurrencyLevel New concurrency level
     * @return This for chaining
     * 
     * @throws IllegalArgumentException if {@code concurrencyLevel} is
     *         nonpositive
     * @throws IllegalStateException if a concurrency level was already set
     */
    public SafeCacheBuilder<K, V> concurrencyLevel(int concurrencyLevel) {
        builder.concurrencyLevel(concurrencyLevel);
        return this;
    }

    /**
     * Specifies that each entry should be automatically removed from the cache
     * once a fixed duration has elapsed after the entry's creation, or last
     * access. Access time is reset by {@link com.google.common.cache.Cache#get Cache.get()},
     * but not by operations on the view returned by
     * {@link com.google.common.cache.Cache#asMap() Cache.asMap()}.
     * 
     * <p>
     * When {@code duration} is zero, elements will be evicted immediately after
     * being loaded into the cache. This has the same effect as invoking
     * {@link #maximumSize maximumSize}{@code (0)}. It can be useful in testing,
     * or to disable caching temporarily without a code change.
     * 
     * <p>
     * Expired entries may be counted by {@link com.google.common.cache.Cache#size Cache.size()}, but will never be
     * visible to read or write operations. Expired entries are currently
     * cleaned up during write operations, or during occasional read operations
     * in the absense of writes; though this behavior may change in the future.
     * 
     * @param duration the length of time after an entry is last accessed that
     *            it should be automatically removed
     * @param unit the unit that {@code duration} is expressed in
     * @return This for chaining
     * 
     * @throws IllegalArgumentException if {@code duration} is negative
     * @throws IllegalStateException if the time to idle or time to live was
     *             already set
     */
    public SafeCacheBuilder<K, V> expireAfterAccess(long duration, TimeUnit unit) {
        builder.expireAfterAccess(duration, unit);
        return this;
    }

    /**
     * Specifies that each entry should be automatically removed from the cache
     * once a fixed duration has elapsed after the entry's creation, or the most
     * recent replacement of its value.
     * 
     * <p>
     * When {@code duration} is zero, elements will be evicted immediately after
     * being loaded into the cache. This has the same effect as invoking
     * {@link #maximumSize maximumSize}{@code (0)}. It can be useful in testing,
     * or to disable caching temporarily without a code change.
     * 
     * <p>
     * Expired entries may be counted by {@link com.google.common.cache.Cache#size Cache.size()}, but will never be
     * visible to read or write operations. Expired entries are currently
     * cleaned up during write operations, or during occasional read operations
     * in the absense of writes; though this behavior may change in the future.
     * 
     * @param duration the length of time after an entry is created that it
     *            should be automatically removed
     * @param unit the unit that {@code duration} is expressed in
     * @return This for chaining
     * 
     * @throws IllegalArgumentException if {@code duration} is negative
     * @throws IllegalStateException if the time to live or time to idle was
     *             already set
     */
    public SafeCacheBuilder<K, V> expireAfterWrite(long duration, TimeUnit unit) {
        builder.expireAfterWrite(duration, unit);
        return this;
    }

    /**
     * Sets the minimum total size for the internal hash tables. For example, if
     * the initial capacity is {@code 60}, and the concurrency level is
     * {@code 8}, then eight segments are created, each having a hash table of
     * size eight. Providing a large enough estimate at construction time avoids
     * the need for expensive resizing operations later, but setting this value
     * unnecessarily high wastes memory.
     * 
     * @param initialCapacity - initial capacity
     * @return This for chaining
     * 
     * @throws IllegalArgumentException if {@code initialCapacity} is negative
     * @throws IllegalStateException if an initial capacity was already set
     */
    public SafeCacheBuilder<K, V> initialCapacity(int initialCapacity) {
        builder.initialCapacity(initialCapacity);
        return this;
    }

    /**
     * Specifies the maximum number of entries the cache may contain. Note that
     * the cache <b>may evict an entry before this limit is exceeded</b>. As the
     * cache size grows close to the maximum, the cache evicts entries that are
     * less likely to be used again. For example, the cache may evict an entry
     * because it hasn't been used recently or very often.
     * 
     * <p>
     * When {@code size} is zero, elements will be evicted immediately after
     * being loaded into the cache. This has the same effect as invoking
     * {@link #expireAfterWrite expireAfterWrite}{@code (0, unit)} or
     * {@link #expireAfterAccess expireAfterAccess}{@code (0,
     * unit)}. It can be useful in testing, or to disable caching temporarily
     * without a code change.
     * 
     * @param size the maximum size of the cache
     * @return This for chaining
     * 
     * @throws IllegalArgumentException if {@code size} is negative
     * @throws IllegalStateException if a maximum size was already set
     */

    public SafeCacheBuilder<K, V> maximumSize(int size) {
        builder.maximumSize(size);
        return this;
    }

    /**
     * Specifies a listener instance, which all caches built using this
     * {@code CacheBuilder} will notify each time an entry is removed from the
     * cache by any means.
     * 
     * <p>
     * Each cache built by this {@code CacheBuilder} after this method is called
     * invokes the supplied listener after removing an element for any reason
     * (see removal causes in {@link com.google.common.cache.RemovalCause RemovalCause}). It will invoke the listener
     * during invocations of any of that cache's public methods (even read-only
     * methods).
     * 
     * <p>
     * <b>Important note:</b> Instead of returning <em>this</em> as a
     * {@code CacheBuilder} instance, this method returns
     * {@code CacheBuilder<K1, V1>}. From this point on, either the original
     * reference or the returned reference may be used to complete configuration
     * and build the cache, but only the "generic" one is type-safe. That is, it
     * will properly prevent you from building caches whose key or value types
     * are incompatible with the types accepted by the listener already
     * provided; the {@code CacheBuilder} type cannot do this. For best results,
     * simply use the standard method-chaining idiom, as illustrated in the
     * documentation at top, configuring a {@code CacheBuilder} and building
     * your {@link com.google.common.cache.Cache Cache} all in a single statement.
     * 
     * <p>
     * <b>Warning:</b> if you ignore the above advice, and use this
     * {@code CacheBuilder} to build a cache whose key or value type is
     * incompatible with the listener, you will likely experience a
     * {@link ClassCastException} at some <i>undefined</i> point in the future.
     * 
     * @param <K1> Key type
     * @param <V1> Value type
     * @param listener - removal listener
     * @return This for chaining
     * 
     * @throws IllegalStateException if a removal listener was already set
     */
    @SuppressWarnings("unchecked")
    public <K1 extends K, V1 extends V> SafeCacheBuilder<K1, V1> removalListener(RemovalListener<? super K1, ? super V1> listener) {
        builder.removalListener(listener);
        return (SafeCacheBuilder<K1, V1>) this;
    }

    /**
     * Specifies a nanosecond-precision time source for use in determining when
     * entries should be expired. By default, {@link System#nanoTime} is used.
     * 
     * <p>
     * The primary intent of this method is to facilitate testing of caches
     * which have been configured with {@link #expireAfterWrite} or
     * {@link #expireAfterAccess}.
     * 
     * @param ticker - ticker
     * @return This for chaining
     * 
     * @throws IllegalStateException if a ticker was already set
     */
    public SafeCacheBuilder<K, V> ticker(Ticker ticker) {
        builder.ticker(ticker);
        return this;
    }

    /**
     * Specifies that each value (not key) stored in the cache should be wrapped
     * in a {@link java.lang.ref.SoftReference SoftReference} (by default, strong references are used).
     * Softly-referenced objects will be garbage-collected in a <i>globally</i>
     * least-recently-used manner, in response to memory demand.
     * 
     * <p>
     * <b>Warning:</b> in most circumstances it is better to set a per-cache
     * {@linkplain #maximumSize maximum size} instead of using soft references.
     * You should only use this method if you are well familiar with the
     * practical consequences of soft references.
     * 
     * <p>
     * <b>Note:</b> when this method is used, the resulting cache will use
     * identity ({@code ==}) comparison to determine equality of values.
     * 
     * @return This for chaining
     * 
     * @throws IllegalStateException if the value strength was already set
     */
    public SafeCacheBuilder<K, V> softValues() {
        builder.softValues();
        return this;
    }

    /**
     * Specifies that each key (not value) stored in the cache should be wrapped
     * in a {@link java.lang.ref.WeakReference WeakReference} (by default, strong references are used).
     * 
     * <p>
     * <b>Warning:</b> when this method is used, the resulting cache will use
     * identity ({@code ==}) comparison to determine equality of keys.
     * 
     * @return This for chaining
     * 
     * @throws IllegalStateException if the key strength was already set
     */
    public SafeCacheBuilder<K, V> weakKeys() {
        builder.weakKeys();
        return this;
    }

    /**
     * Specifies that each value (not key) stored in the cache should be wrapped
     * in a {@link java.lang.ref.WeakReference WeakReference} (by default, strong references are used).
     * 
     * <p>
     * Weak values will be garbage collected once they are weakly reachable.
     * This makes them a poor candidate for caching; consider
     * {@link #softValues} instead.
     * 
     * <p>
     * <b>Note:</b> when this method is used, the resulting cache will use
     * identity ({@code ==}) comparison to determine equality of values.
     * 
     * @return This for chaining
     * 
     * @throws IllegalStateException if the value strength was already set
     */
    public SafeCacheBuilder<K, V> weakValues() {
        builder.weakValues();
        return this;
    }
    
    /**
     * Returns the cache wrapped as a ConcurrentMap.
     * <p>
     * We can't return the direct Cache instance as it changed in Guava 13.
     * @param <K1> Key type
     * @param <V1> Value type
     * @param loader - cache loader
     * @return The cache as a a map.
     */
    @SuppressWarnings("unchecked")
    public <K1 extends K, V1 extends V> ConcurrentMap<K1, V1> build(CacheLoader<? super K1, V1> loader) {
        Object cache = null;
        
        if (BUILD_METHOD == null) {
            try {
                BUILD_METHOD = builder.getClass().getDeclaredMethod("build", CacheLoader.class);
                BUILD_METHOD.setAccessible(true);
            } catch (Exception e) {
                throw new FieldAccessException("Unable to find CacheBuilder.build(CacheLoader)", e);
            }
        }
        
        // Attempt to build the Cache
        try {
            cache = BUILD_METHOD.invoke(builder, loader);
        } catch (Exception e) {
            throw new FieldAccessException("Unable to invoke " + BUILD_METHOD + " on " + builder, e);
        }
        
        if (AS_MAP_METHOD == null) {
            try {
                AS_MAP_METHOD = cache.getClass().getMethod("asMap");
                AS_MAP_METHOD.setAccessible(true);
            } catch (Exception e) {
                throw new FieldAccessException("Unable to find Cache.asMap() in " + cache, e);
            }
        }
        
        // Retrieve it as a map
        try {
            return (ConcurrentMap<K1, V1>) AS_MAP_METHOD.invoke(cache);
        } catch (Exception e) {
            throw new FieldAccessException("Unable to invoke " + AS_MAP_METHOD + " on " + cache, e);
        }
    }
}