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

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 (Minecraft 1.7.X) and 13
 */
public class CompatibleCacheBuilder<K, V> {

    private static Method BUILD_METHOD;
    private static Method AS_MAP_METHOD;

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

    private final CacheBuilder<K, V> builder;

    @SuppressWarnings("unchecked")
    private CompatibleCacheBuilder() {
        builder = (CacheBuilder<K, V>) CacheBuilder.newBuilder();
    }

    /**
     * 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 CompatibleCacheBuilder<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 CompatibleCacheBuilder<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 CompatibleCacheBuilder<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 CompatibleCacheBuilder<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 CompatibleCacheBuilder<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> CompatibleCacheBuilder<K1, V1> removalListener(RemovalListener<? super K1, ? super V1> listener) {
        builder.removalListener(listener);
        return (CompatibleCacheBuilder<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 CompatibleCacheBuilder<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 CompatibleCacheBuilder<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 CompatibleCacheBuilder<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 CompatibleCacheBuilder<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 IllegalStateException("Unable to find CacheBuilder.build(CacheLoader)", e);
            }
        }

        // Attempt to build the Cache
        try {
            cache = BUILD_METHOD.invoke(builder, loader);
        } catch (Exception e) {
            throw new IllegalStateException("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 IllegalStateException("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 IllegalStateException("Unable to invoke " + AS_MAP_METHOD + " on " + cache, e);
        }
    }
}