/*
    * Copyright 2022 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty5.example.http2.file;
  
  import io.netty5.buffer.api.Buffer;
  import io.netty5.channel.ChannelHandler;
  import io.netty5.channel.ChannelHandlerContext;
  import io.netty5.handler.codec.http.HttpHeaderNames;
  import io.netty5.handler.codec.http.HttpResponseStatus;
  import io.netty5.handler.codec.http2.DefaultHttp2DataFrame;
  import io.netty5.handler.codec.http2.DefaultHttp2Headers;
  import io.netty5.handler.codec.http2.DefaultHttp2HeadersFrame;
  import io.netty5.handler.codec.http2.Http2DataChunkedInput;
  import io.netty5.handler.codec.http2.Http2DataFrame;
  import io.netty5.handler.codec.http2.Http2FrameStream;
  import io.netty5.handler.codec.http2.Http2Headers;
  import io.netty5.handler.codec.http2.Http2HeadersFrame;
  import io.netty5.handler.stream.ChunkedFile;
  import io.netty5.util.CharsetUtil;
  import io.netty5.util.concurrent.Future;
  import io.netty5.util.internal.SystemPropertyUtil;
  
  import javax.activation.MimetypesFileTypeMap;
  import java.io.File;
  import java.io.FileNotFoundException;
  import java.io.RandomAccessFile;
  import java.io.UnsupportedEncodingException;
  import java.net.URLDecoder;
  import java.nio.charset.StandardCharsets;
  import java.nio.file.Files;
  import java.nio.file.attribute.BasicFileAttributes;
  import java.text.SimpleDateFormat;
  import java.util.Calendar;
  import java.util.Date;
  import java.util.GregorianCalendar;
  import java.util.Locale;
  import java.util.TimeZone;
  import java.util.regex.Pattern;
  
  import static io.netty5.handler.codec.http.HttpMethod.GET;
  import static io.netty5.handler.codec.http.HttpResponseStatus.FORBIDDEN;
  import static io.netty5.handler.codec.http.HttpResponseStatus.FOUND;
  import static io.netty5.handler.codec.http.HttpResponseStatus.INTERNAL_SERVER_ERROR;
  import static io.netty5.handler.codec.http.HttpResponseStatus.METHOD_NOT_ALLOWED;
  import static io.netty5.handler.codec.http.HttpResponseStatus.NOT_FOUND;
  import static io.netty5.handler.codec.http.HttpResponseStatus.NOT_MODIFIED;
  import static io.netty5.handler.codec.http.HttpResponseStatus.OK;
  
  /**
   * A simple handler that serves incoming HTTP requests to send their respective
   * HTTP responses.  It also implements {@code 'If-Modified-Since'} header to
   * take advantage of browser cache, as described in
   * <a href="https://tools.ietf.org/html/rfc2616#section-14.25">RFC 2616</a>.
   *
   * <h3>How Browser Caching Works</h3>
   * <p>
   * Web browser caching works with HTTP headers as illustrated by the following
   * sample:
   * <ol>
   * <li>Request #1 returns the content of {@code /file1.txt}.</li>
   * <li>Contents of {@code /file1.txt} is cached by the browser.</li>
   * <li>Request #2 for {@code /file1.txt} does not return the contents of the
   *     file again. Rather, a 304 Not Modified is returned. This tells the
   *     browser to use the contents stored in its cache.</li>
   * <li>The server knows the file has not been modified because the
   *     {@code If-Modified-Since} date is the same as the file's last
   *     modified date.</li>
   * </ol>
   *
   * <pre>
   * Request #1 Headers
   * ===================
   * GET /file1.txt HTTP/1.1
   *
   * Response #1 Headers
   * ===================
   * HTTP/1.1 200 OK
   * Date:               Tue, 01 Mar 2011 22:44:26 GMT
   * Last-Modified:      Wed, 30 Jun 2010 21:36:48 GMT
   * Expires:            Tue, 01 Mar 2012 22:44:26 GMT
   * Cache-Control:      private, max-age=31536000
   *
   * Request #2 Headers
   * ===================
   * GET /file1.txt HTTP/1.1
   * If-Modified-Since:  Wed, 30 Jun 2010 21:36:48 GMT
  *
  * Response #2 Headers
  * ===================
  * HTTP/1.1 304 Not Modified
  * Date:               Tue, 01 Mar 2011 22:44:28 GMT
  *
  * </pre>
  */
 public class Http2StaticFileServerHandler implements ChannelHandler {
 
     public static final String HTTP_DATE_FORMAT = "EEE, dd MMM yyyy HH:mm:ss zzz";
     public static final String HTTP_DATE_GMT_TIMEZONE = "GMT";
     public static final int HTTP_CACHE_SECONDS = 60;
 
     private Http2FrameStream stream;
 
     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
         if (msg instanceof Http2HeadersFrame) {
             Http2HeadersFrame headersFrame = (Http2HeadersFrame) msg;
             this.stream = headersFrame.stream();
 
             if (!GET.toString().equals(headersFrame.headers().method().toString())) {
                 sendError(ctx, METHOD_NOT_ALLOWED);
                 return;
             }
 
             final String uri = headersFrame.headers().path().toString();
             final String path = sanitizeUri(uri);
             if (path == null) {
                 sendError(ctx, FORBIDDEN);
                 return;
             }
 
             File file = new File(path);
             if (file.isHidden() || !file.exists()) {
                 sendError(ctx, NOT_FOUND);
                 return;
             }
 
             BasicFileAttributes readAttributes = Files.readAttributes(file.toPath(), BasicFileAttributes.class);
             if (readAttributes.isDirectory()) {
                 if (uri.endsWith("/")) {
                     sendListing(ctx, file, uri);
                 } else {
                     sendRedirect(ctx, uri + '/');
                 }
                 return;
             }
 
             if (!readAttributes.isRegularFile()) {
                 sendError(ctx, FORBIDDEN);
                 return;
             }
 
             // Cache Validation
             CharSequence ifModifiedSince = headersFrame.headers().get(HttpHeaderNames.IF_MODIFIED_SINCE);
             if (ifModifiedSince != null && !ifModifiedSince.toString().isEmpty()) {
                 SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
                 Date ifModifiedSinceDate = dateFormatter.parse(ifModifiedSince.toString());
 
                 // Only compare up to the second because the datetime format we send to the client
                 // does not have milliseconds
                 long ifModifiedSinceDateSeconds = ifModifiedSinceDate.getTime() / 1000;
                 long fileLastModifiedSeconds = readAttributes.lastModifiedTime().toMillis() / 1000;
                 if (ifModifiedSinceDateSeconds == fileLastModifiedSeconds) {
                     sendNotModified(ctx);
                     return;
                 }
             }
 
             RandomAccessFile raf;
             try {
                 raf = new RandomAccessFile(file, "r");
             } catch (FileNotFoundException ignore) {
                 sendError(ctx, NOT_FOUND);
                 return;
             }
             long fileLength = raf.length();
 
             Http2Headers headers = new DefaultHttp2Headers();
             headers.status("200");
             headers.setLong(HttpHeaderNames.CONTENT_LENGTH, fileLength);
 
             setContentTypeHeader(headers, file);
             setDateAndCacheHeaders(headers, file);
 
             // Write the initial line and the header.
             ctx.writeAndFlush(new DefaultHttp2HeadersFrame(headers).stream(stream));
 
             // Write the content.
             Future<Void> sendFileFuture = ctx.writeAndFlush(new Http2DataChunkedInput(
                     new ChunkedFile(raf, 0, fileLength, 8192), stream));
 
             sendFileFuture.addListener(f -> System.err.println(ctx.channel() + " Transfer complete."));
         } else {
             // Unsupported message type
             System.out.println("Unsupported message type: " + msg);
         }
     }
 
     @Override
     public void channelExceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
         cause.printStackTrace();
         if (ctx.channel().isActive()) {
             sendError(ctx, INTERNAL_SERVER_ERROR);
         }
     }
 
     private static final Pattern INSECURE_URI = Pattern.compile(".*[<>&\"].*");
 
     private static String sanitizeUri(String uri) throws UnsupportedEncodingException {
         // Decode the path.
         uri = URLDecoder.decode(uri, StandardCharsets.UTF_8);
 
         if (uri.isEmpty() || uri.charAt(0) != '/') {
             return null;
         }
 
         // Convert file separators.
         uri = uri.replace('/', File.separatorChar);
 
         // Simplistic dumb security check.
         // You will have to do something serious in the production environment.
         if (uri.contains(File.separator + '.') ||
                 uri.contains('.' + File.separator) ||
                 uri.charAt(0) == '.' || uri.charAt(uri.length() - 1) == '.' ||
                 INSECURE_URI.matcher(uri).matches()) {
             return null;
         }
 
         // Convert to absolute path.
         return SystemPropertyUtil.get("user.dir") + File.separator + uri;
     }
 
     private static final Pattern ALLOWED_FILE_NAME = Pattern.compile("[^-\\._]?[^<>&\\\"]*");
 
     private void sendListing(ChannelHandlerContext ctx, File dir, String dirPath) {
         StringBuilder buf = new StringBuilder()
                 .append("<!DOCTYPE html>\r\n")
                 .append("<html><head><meta charset='utf-8' /><title>")
                 .append("Listing of: ")
                 .append(dirPath)
                 .append("</title></head><body>\r\n")
 
                 .append("<h3>Listing of: ")
                 .append(dirPath)
                 .append("</h3>\r\n")
 
                 .append("<ul>")
                 .append("<li><a href=\"../\">..</a></li>\r\n");
 
         File[] files = dir.listFiles();
         if (files != null) {
             for (File f : files) {
                 if (f.isHidden() || !f.canRead()) {
                     continue;
                 }
 
                 String name = f.getName();
                 if (!ALLOWED_FILE_NAME.matcher(name).matches()) {
                     continue;
                 }
 
                 buf.append("<li><a href=\"")
                         .append(name)
                         .append("\">")
                         .append(name)
                         .append("</a></li>\r\n");
             }
         }
 
         buf.append("</ul></body></html>\r\n");
 
         Buffer buffer = ctx.bufferAllocator().allocate(buf.length());
         buffer.writeCharSequence(buf.toString(), CharsetUtil.UTF_8);
 
         Http2Headers headers = new DefaultHttp2Headers();
         headers.status(OK.toString());
         headers.add(HttpHeaderNames.CONTENT_TYPE, "text/html; charset=UTF-8");
 
         ctx.write(new DefaultHttp2HeadersFrame(headers).stream(stream));
         ctx.writeAndFlush(new DefaultHttp2DataFrame(buffer.send(), true).stream(stream));
     }
 
     private void sendRedirect(ChannelHandlerContext ctx, String newUri) {
         Http2Headers headers = new DefaultHttp2Headers();
         headers.status(FOUND.toString());
         headers.add(HttpHeaderNames.LOCATION, newUri);
 
         ctx.writeAndFlush(new DefaultHttp2HeadersFrame(headers, true).stream(stream));
     }
 
     private void sendError(ChannelHandlerContext ctx, HttpResponseStatus status) {
         Http2Headers headers = new DefaultHttp2Headers();
         headers.status(status.toString());
         headers.add(HttpHeaderNames.CONTENT_TYPE, "text/plain; charset=UTF-8");
 
         Http2HeadersFrame headersFrame = new DefaultHttp2HeadersFrame(headers);
         headersFrame.stream(stream);
 
         Http2DataFrame dataFrame = new DefaultHttp2DataFrame(
                 ctx.bufferAllocator().copyOf(("Failure: " + status + "\r\n").getBytes(CharsetUtil.UTF_8)).send(), true);
         dataFrame.stream(stream);
 
         ctx.write(headersFrame);
         ctx.writeAndFlush(dataFrame);
     }
 
     /**
      * When file timestamp is the same as what the browser is sending up, send a "304 Not Modified"
      *
      * @param ctx Context
      */
     private void sendNotModified(ChannelHandlerContext ctx) {
         Http2Headers headers = new DefaultHttp2Headers();
         headers.status(NOT_MODIFIED.toString());
         setDateHeader(headers);
 
         ctx.writeAndFlush(new DefaultHttp2HeadersFrame(headers, true).stream(stream));
     }
 
     /**
      * Sets the Date header for the HTTP response
      *
      * @param headers Http2 Headers
      */
     private static void setDateHeader(Http2Headers headers) {
         SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
         dateFormatter.setTimeZone(TimeZone.getTimeZone(HTTP_DATE_GMT_TIMEZONE));
 
         Calendar time = new GregorianCalendar();
         headers.set(HttpHeaderNames.DATE, dateFormatter.format(time.getTime()));
     }
 
     /**
      * Sets the Date and Cache headers for the HTTP Response
      *
      * @param headers     Http2 Headers
      * @param fileToCache file to extract content type
      */
     private static void setDateAndCacheHeaders(Http2Headers headers, File fileToCache) {
         SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
         dateFormatter.setTimeZone(TimeZone.getTimeZone(HTTP_DATE_GMT_TIMEZONE));
 
         // Date header
         Calendar time = new GregorianCalendar();
         headers.set(HttpHeaderNames.DATE, dateFormatter.format(time.getTime()));
 
         // Add cache headers
         time.add(Calendar.SECOND, HTTP_CACHE_SECONDS);
         headers.set(HttpHeaderNames.EXPIRES, dateFormatter.format(time.getTime()));
         headers.set(HttpHeaderNames.CACHE_CONTROL, "private, max-age=" + HTTP_CACHE_SECONDS);
         headers.set(HttpHeaderNames.LAST_MODIFIED, dateFormatter.format(new Date(fileToCache.lastModified())));
     }
 
     /**
      * Sets the content type header for the HTTP Response
      *
      * @param headers Http2 Headers
      * @param file    file to extract content type
      */
     private static void setContentTypeHeader(Http2Headers headers, File file) {
         MimetypesFileTypeMap mimeTypesMap = new MimetypesFileTypeMap();
         headers.set(HttpHeaderNames.CONTENT_TYPE, mimeTypesMap.getContentType(file.getPath()));
     }
 }