/*
 * Copyright 2002-2013 the original author or authors.
 *
 * 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 org.springframework.security.core.parameters;

import java.lang.annotation.Annotation;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

import org.springframework.core.BridgeMethodResolver;
import org.springframework.core.ParameterNameDiscoverer;
import org.springframework.core.PrioritizedParameterNameDiscoverer;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.security.access.method.P;
import org.springframework.util.Assert;
import org.springframework.util.ReflectionUtils;

/**
 * Allows finding parameter names using the value attribute of any number of
 * {@link Annotation} instances. This is useful when needing to discover the parameter
 * names of interfaces with Spring Security's method level security. For example, consider
 * the following:
 *
 * <pre>
 * import org.springframework.security.access.method.P;
 *
 * {@code @PostAuthorize("#to == returnObject.to")}
 * public Message findMessageByTo(@P("to") String to);
 * </pre>
 *
 * We can make this possible using the following {@link AnnotationParameterNameDiscoverer}
 * :
 *
 * <pre>
 * ParameterAnnotationsNameDiscoverer discoverer = new ParameterAnnotationsNameDiscoverer(
 * 		&quot;org.springframework.security.access.method.P&quot;);
 * </pre>
 *
 * <p>
 * It is common for users to use {@link AnnotationParameterNameDiscoverer} in conjuction
 * with {@link PrioritizedParameterNameDiscoverer}. In fact, Spring Security's
 * {@link DefaultSecurityParameterNameDiscoverer} (which is used by default with method
 * level security) extends {@link PrioritizedParameterNameDiscoverer} and will
 * automatically support both {@link P} and Spring Data's Param annotation if it is found
 * on the classpath.
 * </p>
 *
 * <p>
 * It is important to note that if a single parameter name has a supported annotation on
 * it then all methods are resolved using {@link AnnotationParameterNameDiscoverer}. For
 * example, consider the following:
 * </p>
 *
 * <pre>
 * import org.springframework.security.access.method.P;
 *
 * {@code @PostAuthorize("#to == returnObject.to")}
 * public Message findMessageByToAndFrom(@P("to") User to, User from);
 * </pre>
 *
 * <p>
 * The result of finding parameters on the previous sample will be
 * <code>new String[] { "to", null}</code> since only a single parameter contains an
 * annotation. This is mostly due to the fact that the fallbacks for
 * {@link PrioritizedParameterNameDiscoverer} are an all or nothing operation.
 * </p>
 *
 * @see DefaultSecurityParameterNameDiscoverer
 *
 * @author Rob Winch
 * @since 3.2
 */
public class AnnotationParameterNameDiscoverer implements ParameterNameDiscoverer {

	private final Set<String> annotationClassesToUse;

	public AnnotationParameterNameDiscoverer(String... annotationClassToUse) {
		this(new HashSet<String>(Arrays.asList(annotationClassToUse)));
	}

	public AnnotationParameterNameDiscoverer(Set<String> annotationClassesToUse) {
		Assert.notEmpty(annotationClassesToUse,
				"annotationClassesToUse cannot be null or empty");
		this.annotationClassesToUse = annotationClassesToUse;
	}

	/*
	 * (non-Javadoc)
	 *
	 * @see org.springframework.core.ParameterNameDiscoverer#getParameterNames(java
	 * .lang.reflect.Method)
	 */
	public String[] getParameterNames(Method method) {
		Method originalMethod = BridgeMethodResolver.findBridgedMethod(method);
		String[] paramNames = lookupParameterNames(METHOD_METHODPARAM_FACTORY,
				originalMethod);
		if (paramNames != null) {
			return paramNames;
		}
		Class<?> declaringClass = method.getDeclaringClass();
		Class<?>[] interfaces = declaringClass.getInterfaces();
		for (Class<?> intrfc : interfaces) {
			Method intrfcMethod = ReflectionUtils.findMethod(intrfc, method.getName(),
					method.getParameterTypes());
			if (intrfcMethod != null) {
				return lookupParameterNames(METHOD_METHODPARAM_FACTORY, intrfcMethod);
			}
		}
		return paramNames;
	}

	/*
	 * (non-Javadoc)
	 *
	 * @see org.springframework.core.ParameterNameDiscoverer#getParameterNames(java
	 * .lang.reflect.Constructor)
	 */
	public String[] getParameterNames(Constructor<?> constructor) {
		return lookupParameterNames(CONSTRUCTOR_METHODPARAM_FACTORY, constructor);
	}

	/**
	 * Gets the parameter names or null if not found.
	 *
	 * @param parameterNameFactory the {@link ParameterNameFactory} to use
	 * @param t the {@link AccessibleObject} to find the parameter names on (i.e. Method
	 * or Constructor)
	 * @return the parameter names or null
	 */
	private <T extends AccessibleObject> String[] lookupParameterNames(
			ParameterNameFactory<T> parameterNameFactory, T t) {
		Annotation[][] parameterAnnotations = parameterNameFactory.findParameterAnnotations(t);
		int parameterCount = parameterAnnotations.length;
		String[] paramNames = new String[parameterCount];
		boolean found = false;
		for (int i = 0; i < parameterCount; i++) {
			Annotation[] annotations = parameterAnnotations[i];
			String parameterName = findParameterName(annotations);
			if (parameterName != null) {
				found = true;
				paramNames[i] = parameterName;
			}
		}
		return found ? paramNames : null;
	}

	/**
	 * Finds the parameter name from the provided {@link Annotation}s or null if it could
	 * not find it. The search is done by looking at the value property of the
	 * {@link #annotationClassesToUse}.
	 *
	 * @param parameterAnnotations the {@link Annotation}'s to search.
	 * @return
	 */
	private String findParameterName(Annotation[] parameterAnnotations) {
		for (Annotation paramAnnotation : parameterAnnotations) {
			if (annotationClassesToUse.contains(paramAnnotation.annotationType()
					.getName())) {
				return (String) AnnotationUtils.getValue(paramAnnotation, "value");
			}
		}
		return null;
	}

	private static final ParameterNameFactory<Constructor<?>> CONSTRUCTOR_METHODPARAM_FACTORY = new ParameterNameFactory<Constructor<?>>() {

		public Annotation[][] findParameterAnnotations(Constructor<?> constructor) {
			return constructor.getParameterAnnotations();
		}
	};

	private static final ParameterNameFactory<Method> METHOD_METHODPARAM_FACTORY = new ParameterNameFactory<Method>() {

		public Annotation[][] findParameterAnnotations(Method method) {
			return method.getParameterAnnotations();
		}
	};

	/**
	 * Strategy interface for looking up the parameter names.
	 *
	 * @author Rob Winch
	 * @since 3.2
	 *
	 * @param <T> the type to inspect (i.e. {@link Method} or {@link Constructor})
	 */
	private interface ParameterNameFactory<T extends AccessibleObject> {

		/**
		 * Gets the {@link Annotation}s at a specified index
		 * @param t
		 * @param index
		 * @return
		 */
		Annotation[][] findParameterAnnotations(T t);
	}
}