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assets/webapps/music-oga.gaiamobile.org/js/metadata/id3v1.js

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+/* global BlobView */
+/* exported ID3v1Metadata */
+'use strict';
+
+/**
+ * Parse files with ID3v1 metadata. Metadata includes title, artist, album,
+ * and possibly the track number. Year, comment and genre are ignored.
+ *
+ * Format information:
+ *   http://www.id3.org/ID3v1
+ *   http://en.wikipedia.org/wiki/ID3
+ */
+var ID3v1Metadata = (function() {
+  /**
+   * Parse a file and return a Promise with the metadata.
+   *
+   * @param {BlobView} blobview The audio file to parse.
+   * @return {Promise} A Promise returning the parsed metadata object.
+   */
+  function parse(blobview) {
+    return new Promise(function(resolve, reject) {
+      var blob = blobview.blob;
+      BlobView.get(blob, blob.size - 128, 128, function(footer, error) {
+        if (error) {
+          reject(error);
+          return;
+        }
+
+        try {
+          var magic = footer.getBinaryText(0, 3);
+          if (magic === 'TAG') {
+            // It's an MP3 file with an ID3v1 tag.
+            resolve(parseID3v1Metadata(footer));
+          } else {
+            // It's an MP3 file with no metadata. Just resolve to an empty
+            // metatada object.
+            resolve({});
+          }
+        } catch (e) {
+          reject(e);
+        }
+      });
+    });
+  }
+
+  /**
+   * Parse ID3v1 metadata from the 128 bytes footer at the end of a file.
+   *
+   * @param {BlobView} footer The last 128 bytes of the file.
+   * @return {Metadata} The parsed metadata object.
+   */
+  function parseID3v1Metadata(footer) {
+    footer.seek(3); // Skip the "TAG" prefix.
+    var title = footer.readNullTerminatedLatin1Text(30, true);
+    var artist = footer.readNullTerminatedLatin1Text(30, true);
+    var album = footer.readNullTerminatedLatin1Text(30, true);
+
+    footer.advance(32); // Skip year and comment.
+    var zerobyte = footer.readUnsignedByte();
+    var track = footer.readUnsignedByte();
+
+    var metadata = {
+      tag_format: 'id3v1',
+      title: title || undefined,
+      artist: artist || undefined,
+      album: album || undefined
+    };
+    if (zerobyte === 0 && track !== 0) {
+      metadata.tracknum = track;
+    }
+
+    return metadata;
+  }
+
+  return {
+    parse: parse
+  };
+
+})();