package net.roarsoftware.lastfm.cache;

import java.io.InputStream;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

import net.roarsoftware.util.StringUtilities;

/**
 * The <code>Cache</code> handles storing and loading to a permanent storage for last.fm api requests. This could be
 * a file system or a sql database.
 *
 * @author Janni Kovacs
 * @see net.roarsoftware.lastfm.Caller#setCache(Cache)
 * @see net.roarsoftware.lastfm.cache.ExpirationPolicy
 */
public abstract class Cache {

	private static boolean hashCacheEntryNames = true;

	private ExpirationPolicy expirationPolicy;

	protected Cache() {
		expirationPolicy = new DefaultExpirationPolicy();
	}

	/**
	 * Returns the active {@link net.roarsoftware.lastfm.cache.ExpirationPolicy}
	 *
	 * @return the ExpirationPolicy
	 */
	public ExpirationPolicy getExpirationPolicy() {
		return expirationPolicy;
	}

	/**
	 * Sets the active {@link net.roarsoftware.lastfm.cache.ExpirationPolicy}.
	 *
	 * @param expirationPolicy An ExpirationPolicy, not <code>null</code>
	 */
	public void setExpirationPolicy(ExpirationPolicy expirationPolicy) {
		if (expirationPolicy == null)
			throw new NullPointerException("policy == null");
		this.expirationPolicy = expirationPolicy;
	}

	/**
	 * Checks if the cache contains an entry with the given name.
	 *
	 * @param cacheEntryName An entry name
	 * @return <code>true</code> if the cache contains this entry
	 */
	public abstract boolean contains(String cacheEntryName);

	/**
	 * Loads the specified entry from the cache and returns an InputStream to be read from. Returns <code>null</code>
	 * if the cache does not contain the specified cacheEntryName.
	 *
	 * @param cacheEntryName An entry name
	 * @return an InputStream or <code>null</code>
	 */
	public abstract InputStream load(String cacheEntryName);

	/**
	 * Removes the specified entry from the cache if available. Does nothing if no such entry is
	 * available.
	 *
	 * @param cacheEntryName An entry name
	 */
	public abstract void remove(String cacheEntryName);

	/**
	 * Stores a request in the cache.
	 *
	 * @param cacheEntryName The entry name to be stored to
	 * @param inputStream An InputStream containing the data to be cached
	 * @param expirationDate The date of expiration represented in milliseconds since 1.1.1970
	 */
	public abstract void store(String cacheEntryName, InputStream inputStream, long expirationDate);

	/**
	 * Checks if the specified entry is expired.
	 *
	 * @param cacheEntryName An entry name
	 * @return <code>true</code> if the entry is expired
	 */
	public abstract boolean isExpired(String cacheEntryName);

	/**
	 * Clears the cache by effectively removing all cached data.
	 */
	public abstract void clear();

	/**
	 * Creates a unique entry name string for a request. It consists of the method name and all the parameter names
	 * and values concatenated in alphabetical order. It is used to identify cache entries in the backend storage.
	 * If <code>hashCacheEntryNames</code> is set to <code>true</code> this method will return a MD5 hash of
	 * the generated name.
	 *
	 * @param method The request method
	 * @param params The request parameters
	 * @return a cache entry name
	 */
	public static String createCacheEntryName(String method, Map<String, String> params) {
		if (!(params instanceof SortedMap)) {
			params = new TreeMap<String, String>(params);
		}
		StringBuilder b = new StringBuilder(100);
		b.append(method.toLowerCase());
		b.append('.');
		for (Map.Entry<String, String> e : params.entrySet()) {
			b.append(e.getKey());
			b.append(e.getValue());
		}
		String name = b.toString();
		if (hashCacheEntryNames)
			return StringUtilities.md5(name);
		return StringUtilities.cleanUp(name);
	}

	/**
	 * If <code>hashCacheEntryNames</code> is set to true the {@link #createCacheEntryName} method  will
	 * return a hash of the original entry name instead of the name itself.
	 *
	 * @param hashCacheEntryNames <code>true</code> to generate hashes
	 */
	public static void setHashCacheEntryNames(boolean hashCacheEntryNames) {
		Cache.hashCacheEntryNames = hashCacheEntryNames;
	}
}