/**
 * Copyright (C) 2011 rwoo@gmx.de
 *
 * 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.
 */
package com.googlecode.catchexception.throwable;

import org.assertj.core.internal.cglib.proxy.MethodInterceptor;

import com.googlecode.catchexception.throwable.internal.DelegatingInterceptor;
import com.googlecode.catchexception.throwable.internal.InterfaceOnlyProxyFactory;
import com.googlecode.catchexception.throwable.internal.SubclassProxyFactory;
import com.googlecode.catchexception.throwable.internal.ThrowableHolder;
import com.googlecode.catchexception.throwable.internal.ThrowableProcessingInterceptor;

/**
 * 
 * @author rwoo
 * @since 1.2.0
 * 
 */
public class CatchThrowable {

    /**
     * Returns the throwable caught during the last call on the proxied object in the current thread.
     * 
     * @param <E>
     *            This type parameter makes some type casts redundant.
     * @return Returns the throwable caught during the last call on the proxied object in the current thread - if the
     *         call was made through a proxy that has been created via {@link #verifyThrowable(Object, Class)
     *         verifyThrowable()} or {@link #catchThrowable(Object, Class) catchThrowable()}. Returns null the proxy has
     *         not caught an throwable. Returns null if the caught throwable belongs to a class that is no longer
     *         {@link ClassLoader loaded}.
     */
    public static <E extends Throwable> E caughtThrowable() {
        return ThrowableHolder.<E> get();
    }

    /**
     * Use it to verify that an throwable is thrown and to get access to the thrown throwable (for further
     * verifications).
     * <p>
     * The following example verifies that obj.doX() throws a Throwable:
     * <code><pre class="prettyprint lang-java">verifyThrowable(obj).doX(); // catch and verify
assert "foobar".equals(caughtThrowable().getMessage()); // further analysis
</pre></code>
     * <p>
     * If <code>doX()</code> does not throw a <code>Throwable</code>, then a {@link ThrowableNotThrownAssertionError} is
     * thrown. Otherwise the thrown throwable can be retrieved via {@link #caughtThrowable()}.
     * <p>
     * 
     * @param <T>
     *            The type of the given <code>obj</code>.
     * 
     * @param obj
     *            The instance that shall be proxied. Must not be <code>null</code>.
     * @return Returns an object that verifies that each invocation on the underlying object throws an throwable.
     */
    public static <T> T verifyThrowable(T obj) {
        return verifyThrowable(obj, Throwable.class);
    }

    /**
     * Use it to verify that an throwable of specific type is thrown and to get access to the thrown throwable (for
     * further verifications).
     * <p>
     * The following example verifies that obj.doX() throws a MyThrowable:
     * <code><pre class="prettyprint lang-java">verifyThrowable(obj, MyThrowable.class).doX(); // catch and verify
assert "foobar".equals(caughtThrowable().getMessage()); // further analysis
</pre></code>
     * <p>
     * If <code>doX()</code> does not throw a <code>MyThrowable</code>, then a {@link ThrowableNotThrownAssertionError}
     * is thrown. Otherwise the thrown throwable can be retrieved via {@link #caughtThrowable()}.
     * <p>
     * 
     * @param <T>
     *            The type of the given <code>obj</code>.
     * 
     * @param <E>
     *            The type of the throwable that shall be caught.
     * @param obj
     *            The instance that shall be proxied. Must not be <code>null</code>.
     * @param clazz
     *            The type of the throwable that shall be thrown by the underlying object. Must not be <code>null</code>
     *            .
     * @return Returns an object that verifies that each invocation on the underlying object throws an throwable of the
     *         given type.
     */
    public static <T, E extends Throwable> T verifyThrowable(T obj, Class<E> clazz) {

        return processThrowable(obj, clazz, true);
    }

    /**
     * Use it to catch an throwable and to get access to the thrown throwable (for further verifications).
     * <p>
     * In the following example you catch throwables that are thrown by obj.doX():
     * <code><pre class="prettyprint lang-java">catchThrowable(obj).doX(); // catch
if (caughtThrowable() != null) {
    assert "foobar".equals(caughtThrowable().getMessage()); // further analysis
}</pre></code> If <code>doX()</code>
     * throws a throwable, then {@link #caughtThrowable()} will return the caught throwable. If <code>doX()</code> does
     * not throw a throwable, then {@link #caughtThrowable()} will return <code>null</code>.
     * <p>
     * 
     * @param <T>
     *            The type of the given <code>obj</code>.
     * 
     * @param obj
     *            The instance that shall be proxied. Must not be <code>null</code>.
     * @return Returns a proxy for the given object. The proxy catches throwables of the given type when a method on the
     *         proxy is called.
     */
    public static <T> T catchThrowable(T obj) {

        return processThrowable(obj, Throwable.class, false);
    }

    /**
     * Use it to catch an throwable of a specific type and to get access to the thrown throwable (for further
     * verifications).
     * <p>
     * In the following example you catch throwables of type MyThrowable that are thrown by obj.doX():
     * <code><pre class="prettyprint lang-java">catchThrowable(obj, MyThrowable.class).doX(); // catch
if (caughtThrowable() != null) {
    assert "foobar".equals(caughtThrowable().getMessage()); // further analysis
}</pre></code> If <code>doX()</code>
     * throws a <code>MyThrowable</code>, then {@link #caughtThrowable()} will return the caught throwable. If
     * <code>doX()</code> does not throw a <code>MyThrowable</code>, then {@link #caughtThrowable()} will return
     * <code>null</code>. If <code>doX()</code> throws an throwable of another type, i.e. not a subclass but another
     * class, then this throwable is not thrown and {@link #caughtThrowable()} will return <code>null</code>.
     * <p>
     * 
     * @param <T>
     *            The type of the given <code>obj</code>.
     * 
     * @param <E>
     *            The type of the throwable that shall be caught.
     * @param obj
     *            The instance that shall be proxied. Must not be <code>null</code>.
     * @param clazz
     *            The type of the throwable that shall be caught. Must not be <code>null</code>.
     * @return Returns a proxy for the given object. The proxy catches throwables of the given type when a method on the
     *         proxy is called.
     */
    public static <T, E extends Throwable> T catchThrowable(T obj, Class<E> clazz) {

        return processThrowable(obj, clazz, false);
    }

    /**
     * Creates a proxy that processes throwables thrown by the underlying object.
     * <p>
     * Delegates to {@link SubclassProxyFactory#createProxy(Class, MethodInterceptor)} which itself might delegate to
     * {@link InterfaceOnlyProxyFactory#createProxy(Class, MethodInterceptor)}.
     */
    @SuppressWarnings("javadoc")
    private static <T, E extends Throwable> T processThrowable(T obj, Class<E> throwableClazz, boolean assertThrowable) {

        if (obj == null) {
            throw new IllegalArgumentException("obj must not be null");
        }

        return new SubclassProxyFactory().<T> createProxy(obj.getClass(), new ThrowableProcessingInterceptor<E>(obj,
                throwableClazz, assertThrowable));

    }

    /**
     * Returns a proxy that implements all interfaces of the underlying object.
     * 
     * @param <T>
     *            must be an interface the object implements
     * @param obj
     *            the object that created proxy will delegate all calls to
     * @return Returns a proxy that implements all interfaces of the underlying object and delegates all calls to that
     *         underlying object.
     */
    public static <T> T interfaces(T obj) {

        if (obj == null) {
            throw new IllegalArgumentException("obj must not be null");
        }

        return new InterfaceOnlyProxyFactory().<T> createProxy(obj.getClass(), new DelegatingInterceptor(obj));
    }

    /**
     * Sets the {@link #caughtThrowable() caught throwable} to null. This does not affect throwables saved at threads
     * other than the current one.
     * <p>
     * Actually you probably never need to call this method because each method call on a proxied object in the current
     * thread resets the caught throwable. But if you want to improve test isolation or if you want to 'clean up' after
     * testing (to avoid memory leaks), call the method before or after testing.
     */
    public static void resetCaughtThrowable() {
        ThrowableHolder.set(null);
    }

}