/*
    * Licensed to The Apereo Foundation under one or more contributor license
    * agreements. See the NOTICE file distributed with this work for additional
    * information regarding copyright ownership.
    *
    *
    * The Apereo Foundation licenses this file to you under the Educational
    * Community 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://opensource.org/licenses/ecl2.txt
   *
   * 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.opencastproject.subtitleparser.webvttparser;
  
  import org.opencastproject.subtitleparser.SubtitleParsingException;
  
  import org.apache.commons.io.input.BOMInputStream;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.nio.charset.Charset;
  import java.nio.charset.StandardCharsets;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  /**
   * Parses WebVTT from a file into a datastructure to allow for easy modification.
   * Throws exceptions if the read WebVTT is invalid.
   *
   * TODO: Comments are currently ignored and discarded. Find a good way to keep comments
   *  without compromising easy editing.
   */
  public class WebVTTParser {
  
    private static final String WEBVTT_METADATA_HEADER_STRING = "\\S*[:=]\\S*";
    private static final Pattern WEBVTT_METADATA_HEADER =
            Pattern.compile(WEBVTT_METADATA_HEADER_STRING);
  
    // Regex checks if not a time interval
    private static final String WEBVTT_CUE_IDENTIFIER_STRING = "^(?!.*(-->)).*$";
    private static final Pattern WEBVTT_CUE_IDENTIFIER =
            Pattern.compile(WEBVTT_CUE_IDENTIFIER_STRING);
  
    // Timestamp from time interval
    private static final String WEBVTT_TIMESTAMP_STRING = "(\\d+:)?[0-5]\\d:[0-5]\\d\\.\\d{3}";
    private static final Pattern WEBVTT_TIMESTAMP = Pattern.compile(WEBVTT_TIMESTAMP_STRING);
  
    private Charset charset; // Charset of the input files
  
    public WebVTTParser() {
      this.charset = StandardCharsets.UTF_8;
    }
  
    public WebVTTParser(Charset charset) {
      this.charset = charset;
    }
  
    public WebVTTSubtitle parse(InputStream is) throws IOException, SubtitleParsingException {
      // Wrap input stream into Apache Commons IO BOMInputStream
      BOMInputStream bomIn = new BOMInputStream(is, false);
  
      // Create subtitle object
      WebVTTSubtitle subtitle = new WebVTTSubtitle();
  
      // Read each line
      BufferedReader webvttReader = new BufferedReader(new InputStreamReader(bomIn, this.charset));
      String line = "";
  
      // File should start with "WEBVTT" on the first line
      line = webvttReader.readLine();
      if (line == null) {
        throw new SubtitleParsingException("WEBVTT Header line is null");
      }
  
      if (!line.startsWith("WEBVTT")) {
        throw new SubtitleParsingException("Header line did not start with WEBVTT. Got " + line);
      }
  
      subtitle.addHeaderLine(line);
  
      // While this is not mentioned in the W3C specs, it seems to be common practice to have additional lines after
      // the header containing metadata information on the file.
      while ((line = webvttReader.readLine()) != null && !line.isEmpty()) {
        subtitle.addHeaderLine(line);
      }
  
      // Process the cues
      while ((line = webvttReader.readLine()) != null) {
        WebVTTSubtitleCue cue = new WebVTTSubtitleCue();
 
       // Skip additional newlines
       if (line.isEmpty()) {
         continue;
       }
 
       if (line.startsWith("REGION")) {
         WebVTTSubtitleRegion region = new WebVTTSubtitleRegion();
         region.addLine(line);
         while ((line = webvttReader.readLine()) != null && !line.isEmpty()) {
           region.addLine(line);
         }
         subtitle.addRegion(region);
         continue;
       }
 
       if (line.startsWith("STYLE")) {
         WebVTTSubtitleStyle style = new WebVTTSubtitleStyle();
         style.addLine(line);
         while ((line = webvttReader.readLine()) != null && !line.isEmpty()) {
           style.addLine(line);
         }
         subtitle.addStyle(style);
         continue;
       }
 
       if (line.startsWith("NOTE")) {
         while ((line = webvttReader.readLine()) != null && !line.isEmpty()) {
           // do nothing
         }
         continue;
       }
 
       // Parse the cue identifier (if present)
       Matcher matcher = WEBVTT_CUE_IDENTIFIER.matcher(line);
       if (matcher.find()) {
         cue.setId(line);
         line = webvttReader.readLine();
       }
 
       // Parse the cue timestamps
       matcher = WEBVTT_TIMESTAMP.matcher(line);
 
       // Parse start timestamp
       if (!matcher.find()) {
         throw new SubtitleParsingException("Expected cue start time: " + line);
       } else {
         cue.setStartTime(parseTimestamp(matcher.group()));
       }
 
       // Parse end timestamp
       if (!matcher.find()) {
         throw new SubtitleParsingException("Expected cue end time: " + line);
       } else {
         cue.setEndTime(parseTimestamp(matcher.group()));
       }
 
       // Parse cue settings list
       String cueSettings = line.substring(matcher.end()).trim();
       if (!cueSettings.isEmpty()) {
         cue.setCueSettingsList(cueSettings);
       }
 
 
       // Parse text
       while (((line = webvttReader.readLine()) != null) && (!line.isEmpty())) {
         cue.addLine(line);
       }
 
       subtitle.addCue(cue);
     }
 
     webvttReader.close();
     is.close();
 
     return subtitle;
   }
 
   private static long parseTimestamp(String s) throws NumberFormatException {
     if (!s.matches(WEBVTT_TIMESTAMP_STRING)) {
       throw new NumberFormatException("has invalid format");
     }
 
     String[] parts = s.split("\\.", 2);
     long value = 0;
     for (String group : parts[0].split(":")) {
       value = value * 60 + Long.parseLong(group);
     }
     return (value * 1000 + Long.parseLong(parts[1]));
   }
 }