/*
 * JGrapes Event Driven Framework
 * Copyright (C) 2016-2018 Michael N. Lipp
 * 
 * This program is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU Affero General Public License as published by 
 * the Free Software Foundation; either version 3 of the License, or 
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License 
 * for more details.
 * 
 * You should have received a copy of the GNU Affero General Public License along 
 * with this program; if not, see <http://www.gnu.org/licenses/>.
 */

package org.jgrapes.http.annotation;

import java.lang.annotation.Annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Method;
import java.text.ParseException;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;
import org.jgrapes.core.Channel;
import org.jgrapes.core.ComponentType;
import org.jgrapes.core.Components;
import org.jgrapes.core.Eligible;
import org.jgrapes.core.Event;
import org.jgrapes.core.HandlerScope;
import org.jgrapes.core.InvocationFilter;
import org.jgrapes.core.Self;
import org.jgrapes.core.annotation.Handler.NoChannel;
import org.jgrapes.core.annotation.Handler.NoEvent;
import org.jgrapes.core.annotation.HandlerDefinition;
import org.jgrapes.core.annotation.HandlerDefinition.ChannelReplacements;
import org.jgrapes.core.internal.EventBase;
import org.jgrapes.http.ResourcePattern;
import org.jgrapes.http.events.Request;
import org.jgrapes.http.events.Request.In;

/**
 * This annotation marks a method as handler for events. The method is 
 * invoked for events that have a type derived from {@link Request} and
 * are matched by one of the specified {@link ResourcePattern}s.
 * 
 * Note that matching uses a shortened request URI for reasons outlined
 * in {@link In#defaultCriterion()}. Specifying patterns with
 * more path components than are used by the event's default criterion
 * may therefore result in unexpected events. If the default criterion
 * of an event shortens a requested URI "/foo/bar" to "/foo/**" and
 * the {@link RequestHandler} annotation specifies "/foo/baz" as pattern,
 * the handler will be invoked.
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@HandlerDefinition(evaluator = RequestHandler.Evaluator.class)
public @interface RequestHandler {

    /**
     * Specifies classes of events that the handler is to receive.
     * 
     * @return the event classes
     */
    @SuppressWarnings("rawtypes")
    Class<? extends Event>[] events() default NoEvent.class;

    /**
     * Specifies classes of channels that the handler listens on.
     * 
     * @return the channel classes
     */
    Class<? extends Channel>[] channels() default NoChannel.class;

    /**
     * Specifies the patterns that the handler is supposed to handle
     * (see {@link ResourcePattern}).
     * 
     * @return the patterns
     */
    String[] patterns() default "";

    /**
     * Specifies a priority. The value is used to sort handlers.
     * Handlers with higher priority are invoked first.
     * 
     * @return the priority
     */
    int priority() default 0;

    /**
     * Returns {@code true} if the annotated annotation defines a
     * dynamic handler. A dynamic handler must be added to the set of
     * handlers of a component explicitly.
     * 
     * @return the result
     */
    boolean dynamic() default false;

    /**
     * This class provides the {@link Evaluator} for the {@link RequestHandler}
     * annotation. It implements the behavior as described for the annotation.
     */
    class Evaluator implements HandlerDefinition.Evaluator {

        /*
         * (non-Javadoc)
         * 
         * @see
         * org.jgrapes.core.annotation.HandlerDefinition.Evaluator#getPriority()
         */
        @Override
        public int priority(Annotation annotation) {
            return ((RequestHandler) annotation).priority();
        }

        @Override
        public HandlerScope scope(ComponentType component, Method method,
                ChannelReplacements channelReplacements) {
            RequestHandler annotation
                = method.getAnnotation(RequestHandler.class);
            if (annotation.dynamic()) {
                return null;
            }
            return new Scope(component, method, (RequestHandler) annotation,
                channelReplacements, null);
        }

        /**
         * Adds the given method of the given component as a 
         * dynamic handler for a specific pattern. Other informations
         * are taken from the annotation.
         * 
         * @param component the component
         * @param method the name of the method that implements the handler
         * @param pattern the pattern
         */
        public static void add(ComponentType component, String method,
                String pattern) {
            add(component, method, pattern, null);
        }

        /**
         * Adds the given method of the given component as a 
         * dynamic handler for a specific pattern with the specified
         * priority. Other informations are taken from the annotation.
         *
         * @param component the component
         * @param method the name of the method that implements the handler
         * @param pattern the pattern
         * @param priority the priority
         */
        public static void add(ComponentType component, String method,
                String pattern, int priority) {
            add(component, method, pattern, Integer.valueOf(priority));
        }

        @SuppressWarnings("PMD.AvoidBranchingStatementAsLastInLoop")
        private static void add(ComponentType component, String method,
                String pattern, Integer priority) {
            try {
                for (Method m : component.getClass().getMethods()) {
                    if (!m.getName().equals(method)) {
                        continue;
                    }
                    for (Annotation annotation : m.getDeclaredAnnotations()) {
                        Class<?> annoType = annotation.annotationType();
                        HandlerDefinition hda
                            = annoType.getAnnotation(HandlerDefinition.class);
                        if (hda == null
                            || !RequestHandler.class.isAssignableFrom(annoType)
                            || !((RequestHandler) annotation).dynamic()) {
                            continue;
                        }
                        @SuppressWarnings("PMD.AvoidInstantiatingObjectsInLoops")
                        Scope scope = new Scope(component, m,
                            (RequestHandler) annotation,
                            Collections.emptyMap(), pattern);
                        Components.manager(component)
                            .addHandler(m, scope, priority == null
                                ? ((RequestHandler) annotation).priority()
                                : priority);
                        return;
                    }
                }
                throw new IllegalArgumentException(
                    "No method named \"" + method + "\" with DynamicHandler"
                        + " annotation and correct parameter list.");
            } catch (SecurityException e) {
                throw (RuntimeException) (new IllegalArgumentException()
                    .initCause(e));
            }
        }

        /**
         * The scope implementation.
         */
        public static class Scope implements HandlerScope, InvocationFilter {

            private final Set<Object> handledEventTypes = new HashSet<>();
            private final Set<Object> handledChannels = new HashSet<>();
            private final Set<ResourcePattern> handledPatterns
                = new HashSet<>();

            /**
             * Instantiates a new scope.
             *
             * @param component the component
             * @param method the method
             * @param annotation the annotation
             * @param channelReplacements the channel replacements
             * @param pattern the pattern
             */
            @SuppressWarnings({ "PMD.CyclomaticComplexity",
                "PMD.NPathComplexity", "PMD.AvoidDeeplyNestedIfStmts",
                "PMD.CollapsibleIfStatements", "PMD.CognitiveComplexity",
                "PMD.AvoidInstantiatingObjectsInLoops" })
            public Scope(ComponentType component,
                    Method method, RequestHandler annotation,
                    Map<Class<? extends Channel>, Object> channelReplacements,
                    String pattern) {
                if (!HandlerDefinition.Evaluator.checkMethodSignature(method)) {
                    throw new IllegalArgumentException("Method "
                        + method.toString() + " cannot be used as"
                        + " handler (wrong signature).");
                }
                // Get all event keys from the handler annotation.
                if (annotation.events()[0] != NoEvent.class) {
                    handledEventTypes
                        .addAll(Arrays.asList(annotation.events()));
                }
                // If no event types are given, try first parameter.
                if (handledEventTypes.isEmpty()) {
                    Class<?>[] paramTypes = method.getParameterTypes();
                    if (paramTypes.length > 0) {
                        if (Event.class.isAssignableFrom(paramTypes[0])) {
                            handledEventTypes.add(paramTypes[0]);
                        }
                    }
                }

                // Get channel keys from the annotation.
                boolean addDefaultChannel = false;
                if (annotation.channels()[0] != NoChannel.class) {
                    for (Class<?> c : annotation.channels()) {
                        if (c == Self.class) {
                            if (!(component instanceof Channel)) {
                                throw new IllegalArgumentException(
                                    "Canot use channel This.class in "
                                        + "annotation of " + method
                                        + " because " + getClass().getName()
                                        + " does not implement Channel.");
                            }
                            // Will be added anyway, see below
                        } else if (c == Channel.Default.class) {
                            addDefaultChannel = true;
                        } else {
                            handledChannels.add(channelReplacements == null
                                ? c
                                : channelReplacements.getOrDefault(c, c));
                        }
                    }
                }
                if (handledChannels.isEmpty() || addDefaultChannel) {
                    handledChannels.add(Components.manager(component)
                        .channel().defaultCriterion());
                }
                // Finally, a component always handles events
                // directed at it directly.
                if (component instanceof Channel) {
                    handledChannels.add(
                        ((Channel) component).defaultCriterion());
                }

                try {
                    // Get all paths from the annotation.
                    if (!annotation.patterns()[0].isEmpty()) {
                        for (String p : annotation.patterns()) {
                            handledPatterns.add(new ResourcePattern(p));
                        }
                    }

                    // Add additionally provided path
                    if (pattern != null) {
                        handledPatterns.add(new ResourcePattern(pattern));
                    }
                } catch (ParseException e) {
                    throw new IllegalArgumentException(e.getMessage(), e);
                }
            }

            @Override
            @SuppressWarnings({ "PMD.DataflowAnomalyAnalysis",
                "PMD.NPathComplexity", "PMD.CognitiveComplexity" })
            public boolean includes(Eligible event, Eligible[] channels) {
                boolean match = false;
                for (Object eventType : handledEventTypes) {
                    if (Class.class.isInstance(eventType)
                        && ((Class<?>) eventType)
                            .isAssignableFrom(event.getClass())) {
                        match = true;
                        break;
                    }

                }
                if (!match) {
                    return false;
                }
                match = false;
                // Try channels
                for (Eligible channel : channels) {
                    for (Object channelValue : handledChannels) {
                        if (channel.isEligibleFor(channelValue)) {
                            match = true;
                            break;
                        }
                    }
                }
                if (!match) {
                    return false;
                }
                if (!(event instanceof Request.In)) {
                    return false;
                }
                for (ResourcePattern rp : handledPatterns) {
                    if (((Request.In) event).isEligibleFor(
                        Request.In.createMatchValue(Request.In.class, rp))) {
                        return true;
                    }
                }
                return false;
            }

            @Override
            public boolean includes(EventBase<?> event) {
                for (ResourcePattern rp : handledPatterns) {
                    if (rp.matches(((Request.In) event).requestUri()) >= 0) {
                        return true;
                    }
                }
                return false;
            }

            /*
             * (non-Javadoc)
             * 
             * @see java.lang.Object#toString()
             */
            @Override
            public String toString() {
                StringBuilder builder = new StringBuilder();
                builder.append("Scope [");
                if (handledEventTypes != null) {
                    builder.append("handledEventTypes=")
                        .append(handledEventTypes.stream().map(value -> {
                            if (value instanceof Class) {
                                return Components.className((Class<?>) value);
                            }
                            return value.toString();
                        }).collect(Collectors.toSet()));
                    builder.append(", ");
                }
                if (handledChannels != null) {
                    builder.append("handledChannels=");
                    builder.append(handledChannels);
                    builder.append(", ");
                }
                if (handledPatterns != null) {
                    builder.append("handledPatterns=");
                    builder.append(handledPatterns);
                }
                builder.append(']');
                return builder.toString();
            }

        }
    }
}