package org.hamcrest;

import org.hamcrest.internal.ReflectiveTypeFinder;

/**
 * Convenient base class for Matchers that require a non-null value of a specific type and that will report why the received value has been
 * rejected. This implements the null check, checks the type and then casts. To use, implement
 * 
 * <pre>
 * matchesSafely()
 * </pre>
 * 
 * .
 *
 * @author Neil Dunn
 * @author Nat Pryce
 * @author Steve Freeman
 */
public abstract class TypeSafeDiagnosingMatcher<T> extends BaseMatcher<T> {
	private static final ReflectiveTypeFinder TYPE_FINDER = new ReflectiveTypeFinder("matchesSafely", 2, 0);
	private final Class<?> expectedType;

	/**
	 * Subclasses should implement this. The item will already have been checked for the specific type and will never be null.
	 */
	protected abstract boolean matchesSafely(T item, Description mismatchDescription);

	/**
	 * Use this constructor if the subclass that implements <code>matchesSafely</code> is <em>not</em> the class that binds <T> to a
	 * type.
	 * 
	 * @param expectedType
	 *            The expectedType of the actual value.
	 */
	protected TypeSafeDiagnosingMatcher(final Class<?> expectedType) {
		this.expectedType = expectedType;
	}

	/**
	 * Use this constructor if the subclass that implements <code>matchesSafely</code> is <em>not</em> the class that binds <T> to a
	 * type.
	 * 
	 * @param typeFinder
	 *            A type finder to extract the type
	 */
	protected TypeSafeDiagnosingMatcher(final ReflectiveTypeFinder typeFinder) {
		this.expectedType = typeFinder.findExpectedType(getClass());
	}

	/**
	 * The default constructor for simple sub types
	 */
	protected TypeSafeDiagnosingMatcher() {
		this(TYPE_FINDER);
	}

	@Override
	@SuppressWarnings("unchecked")
	public final boolean matches(final Object item) {
		return item != null && expectedType.isInstance(item) && matchesSafely((T) item, new Description.NullDescription());
	}

	@SuppressWarnings("unchecked")
	@Override
	public final void describeMismatch(final Object item, final Description mismatchDescription) {
		if (item == null || !expectedType.isInstance(item)) {
			super.describeMismatch(item, mismatchDescription);
		} else {
			matchesSafely((T) item, mismatchDescription);
		}
	}
}