/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.sling.engine.impl.request;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.sling.api.SlingConstants;
import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.request.RequestDispatcherOptions;
import org.apache.sling.api.request.RequestProgressTracker;
import org.apache.sling.api.resource.Resource;
import org.apache.sling.api.resource.ResourceWrapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class SlingRequestDispatcher implements RequestDispatcher {

    /** default log */
    private final Logger log = LoggerFactory.getLogger(getClass());

    private Resource resource;

    private RequestDispatcherOptions options;

    private String path;

    public SlingRequestDispatcher(String path, RequestDispatcherOptions options) {
        this.path = path;
        this.options = options;
        this.resource = null;
    }

    public SlingRequestDispatcher(Resource resource,
            RequestDispatcherOptions options) {

        this.resource = resource;
        this.options = options;
        this.path = resource.getPath();
    }

    @Override
    public void include(ServletRequest request, ServletResponse sResponse)
            throws ServletException, IOException {

        // guard access to the request and content data: If the request is
        // not (wrapping) a SlingHttpServletRequest, accessing the request Data
        // throws an IllegalArgumentException and we cannot continue
        final ContentData cd;
        try {
            cd = RequestData.getRequestData(request).getContentData();
        } catch (IllegalArgumentException iae) {
            throw new ServletException(iae.getMessage());
        }

        // ClassCastException is not expected here because we operate in
        // HTTP requests only (it cannot be excluded though if some client
        // code uses a ServletRequestWrapper rather than an
        // HttpServletRequestWrapper ...)
        final HttpServletRequest hRequest = (HttpServletRequest) request;

        // set the inclusion request attributes from the current request
        final Object v1 = setAttribute(request,
            SlingConstants.ATTR_REQUEST_CONTENT, cd.getResource());
        final Object v2 = setAttribute(request,
            SlingConstants.ATTR_REQUEST_SERVLET, cd.getServlet());
        final Object v3 = setAttribute(request,
            SlingConstants.ATTR_REQUEST_PATH_INFO, cd.getRequestPathInfo());
        final Object v4 = setAttribute(request,
            SlingConstants.ATTR_INCLUDE_CONTEXT_PATH, hRequest.getContextPath());
        final Object v5 = setAttribute(request,
            SlingConstants.ATTR_INCLUDE_PATH_INFO, hRequest.getPathInfo());
        final Object v6 = setAttribute(request,
            SlingConstants.ATTR_INCLUDE_QUERY_STRING, hRequest.getQueryString());
        final Object v7 = setAttribute(request,
            SlingConstants.ATTR_INCLUDE_REQUEST_URI, hRequest.getRequestURI());
        final Object v8 = setAttribute(request,
            SlingConstants.ATTR_INCLUDE_SERVLET_PATH, hRequest.getServletPath());

        try {

            dispatch(request, sResponse, true);

        } finally {

            // reset inclusion request attributes to previous values
            request.setAttribute(SlingConstants.ATTR_REQUEST_CONTENT, v1);
            request.setAttribute(SlingConstants.ATTR_REQUEST_SERVLET, v2);
            request.setAttribute(SlingConstants.ATTR_REQUEST_PATH_INFO, v3);
            request.setAttribute(SlingConstants.ATTR_INCLUDE_CONTEXT_PATH, v4);
            request.setAttribute(SlingConstants.ATTR_INCLUDE_PATH_INFO, v5);
            request.setAttribute(SlingConstants.ATTR_INCLUDE_QUERY_STRING, v6);
            request.setAttribute(SlingConstants.ATTR_INCLUDE_REQUEST_URI, v7);
            request.setAttribute(SlingConstants.ATTR_INCLUDE_SERVLET_PATH, v8);

        }
    }

    @Override
    public void forward(ServletRequest request, ServletResponse response)
            throws ServletException, IOException {

        // fail forwarding if the response has already been committed
        if (response.isCommitted()) {
            throw new IllegalStateException("Response already committed");
        }

        // reset the response, will throw an IllegalStateException
        // if already committed, which will not be the case because
        // we already tested for this condition
        response.resetBuffer();

        // ensure inclusion information attributes are not set
        request.removeAttribute(SlingConstants.ATTR_REQUEST_CONTENT);
        request.removeAttribute(SlingConstants.ATTR_REQUEST_SERVLET);
        request.removeAttribute(SlingConstants.ATTR_REQUEST_PATH_INFO);
        request.removeAttribute(SlingConstants.ATTR_INCLUDE_CONTEXT_PATH);
        request.removeAttribute(SlingConstants.ATTR_INCLUDE_PATH_INFO);
        request.removeAttribute(SlingConstants.ATTR_INCLUDE_QUERY_STRING);
        request.removeAttribute(SlingConstants.ATTR_INCLUDE_REQUEST_URI);
        request.removeAttribute(SlingConstants.ATTR_INCLUDE_SERVLET_PATH);

        // now just include as normal
        dispatch(request, response, false);

        // finally, we would have to ensure the response is committed
        // and closed. Let's just flush the buffer and thus commit the
        // response for now
        response.flushBuffer();
    }

    private String getAbsolutePath(SlingHttpServletRequest request, String path) {
        // path is already absolute
        if (path.startsWith("/")) {
            return path;
        }

        // get parent of current request
        String uri = request.getResource().getPath();
        int lastSlash = uri.lastIndexOf('/');
        if (lastSlash >= 0) {
            uri = uri.substring(0, lastSlash);
        }

        // append relative path to parent
        return uri + '/' + path;
    }

    private void dispatch(ServletRequest request, ServletResponse sResponse,
            boolean include) throws ServletException, IOException {
        SlingHttpServletRequest cRequest = RequestData.unwrap(request);
        RequestData rd = RequestData.getRequestData(cRequest);
        String absPath = getAbsolutePath(cRequest, path);
        RequestProgressTracker requestProgressTracker = cRequest.getRequestProgressTracker();

        // if the response is not an HttpServletResponse, fail gracefully not
        // doing anything
        if (!(sResponse instanceof HttpServletResponse)) {
            log.error("include: Failed to include {}, response has wrong type",
                absPath);
            return;
        }

        if (resource == null) {
            String timerName = "resolveIncludedResource(" + absPath + ")";
            requestProgressTracker.startTimer(timerName);

            // resolve the absolute path in the resource resolver, using
            // only those parts of the path as if it would be request path
            resource = cRequest.getResourceResolver().resolve(absPath);

            // if the resource could not be resolved, fail gracefully
            if (resource == null) {
                log.error(
                    "include: Could not resolve {} to a resource, not including",
                    absPath);
                return;
            }

            requestProgressTracker.logTimer(timerName,
                    "path={0} resolves to Resource={1}",
                    absPath, resource);
        }

        // ensure request path info and optional merges
        SlingRequestPathInfo info = getMergedRequestPathInfo(cRequest);
        requestProgressTracker.log(
            "Including resource {0} ({1})", resource, info);
        rd.getSlingRequestProcessor().dispatchRequest(request, sResponse, resource,
            info, include);
    }

    /**
     * Returns a {@link SlingRequestPathInfo} object to use to select the
     * servlet or script to call to render the resource to be dispatched to.
     * <p>
     * <b>Note:</b> If this request dispatcher has been created with resource
     * type overwriting request dispatcher options, the resource to dispatch to
     * may be wrapped with a {@link TypeOverwritingResourceWrapper} as a result
     * of calling this method.
     */
    private SlingRequestPathInfo getMergedRequestPathInfo(
            final SlingHttpServletRequest cRequest) {
        SlingRequestPathInfo info = new SlingRequestPathInfo(resource);
        info = info.merge(cRequest.getRequestPathInfo());

        // merge request dispatcher options and resource type overwrite
        if (options != null) {
            info = info.merge(options);

            // ensure overwritten resource type
            String rtOverwrite = options.getForceResourceType();
            if (rtOverwrite != null
                && !rtOverwrite.equals(resource.getResourceType())) {
                resource = new TypeOverwritingResourceWrapper(resource,
                    rtOverwrite);
            }
        }

        return info;
    }

    private Object setAttribute(final ServletRequest request,
            final String name, final Object value) {
        final Object oldValue = request.getAttribute(name);
        request.setAttribute(name, value);
        return oldValue;
    }

    private static class TypeOverwritingResourceWrapper extends ResourceWrapper {

        private final String resourceType;

        TypeOverwritingResourceWrapper(Resource delegatee, String resourceType) {
            super(delegatee);
            this.resourceType = resourceType;
        }

        @Override
        public String getResourceType() {
            return resourceType;
        }

        /**
         * Overwrite this here because the wrapped resource will return null as
         * a super type instead of the resource type overwritten here
         */
        @Override
        public String getResourceSuperType() {
            return null;
        }

        @Override
        public boolean isResourceType(final String resourceType) {
            return this.getResourceResolver().isResourceType(this, resourceType);
        }

    }
}