package br.ufrgs.inf.prosoft.adaptivecaching.cachemanager.extensions.ehcache;

import br.ufrgs.inf.prosoft.adaptivecaching.cachemanager.model.Cache;
import br.ufrgs.inf.prosoft.adaptivecaching.cachemanager.model.ValueWrapper;
import br.ufrgs.inf.prosoft.adaptivecaching.cachemanager.model.support.SimpleValueWrapper;
import net.sf.ehcache.Ehcache;
import net.sf.ehcache.Element;
import net.sf.ehcache.Status;

import java.util.concurrent.Callable;

//import org.springframework.util.Assert;

/**
 * {@link Cache} implementation on top of an {@link Ehcache} instance.
 */
public class EhCacheCache implements Cache {

    private final Ehcache cache;


    /**
     * Create an {@link EhCacheCache} instance.
     *
     * @param ehcache backing Ehcache instance
     */
    public EhCacheCache(Ehcache ehcache) {
        Status status = ehcache.getStatus();
        if (!Status.STATUS_ALIVE.equals(status)) {
            throw new IllegalStateException(
                    "An 'alive' EhCache CacheManager is required - current cache is " + status.toString());
        }
        this.cache = ehcache;
    }


    @Override
    public final String getName() {
        return this.cache.getName();
    }

    @Override
    public final Ehcache getNativeCache() {
        return this.cache;
    }

    @Override
    public ValueWrapper get(Object key) {
        Element element = lookup(key);
        return toValueWrapper(element);
    }

    @SuppressWarnings("unchecked")
    @Override
    public <T> T get(Object key, Callable<T> valueLoader) {
        Element element = lookup(key);
        if (element != null) {
            return (T) element.getObjectValue();
        } else {
            this.cache.acquireWriteLockOnKey(key);
            try {
                element = lookup(key); // One more attempt with the write lock
                if (element != null) {
                    return (T) element.getObjectValue();
                } else {
                    return loadValue(key, valueLoader);
                }
            } finally {
                this.cache.releaseWriteLockOnKey(key);
            }
        }

    }

    private <T> T loadValue(Object key, Callable<T> valueLoader) {
        T value;
        try {
            value = valueLoader.call();
        } catch (Throwable ex) {
            throw new ValueRetrievalException(key, valueLoader, ex);
        }
        put(key, value);
        return value;
    }

    @Override
    @SuppressWarnings("unchecked")
    public <T> T get(Object key, Class<T> type) {
        Element element = this.cache.get(key);
        Object value = (element != null ? element.getObjectValue() : null);
        if (value != null && type != null && !type.isInstance(value)) {
            throw new IllegalStateException("Cached value is not of required type [" + type.getName() + "]: " + value);
        }
        return (T) value;
    }

    @Override
    public void put(Object key, Object value) {
        this.cache.put(new Element(key, value));
    }

    @Override
    public ValueWrapper putIfAbsent(Object key, Object value) {
        Element existingElement = this.cache.putIfAbsent(new Element(key, value));
        return toValueWrapper(existingElement);
    }

    @Override
    public void evict(Object key) {
        this.cache.remove(key);
    }

    @Override
    public void clear() {
        this.cache.removeAll();
    }


    private Element lookup(Object key) {
        return this.cache.get(key);
    }

    private ValueWrapper toValueWrapper(Element element) {
        return (element != null ? new SimpleValueWrapper(element.getObjectValue()) : null);
    }

}
