gnavalesi/music-tag

var _ = require('underscore');
var config = require('../../config/config.json');

(function () {
    'use strict';

    var extract = function (tags) {
        return processTags(tags);
    };

    var getUserData = function (tag_text) {
        return {
            label: tag_text.substr(0, tag_text.lastIndexOf('\u0000')),
            text: tag_text.substr(tag_text.lastIndexOf('\u0000') + 1)
        };
    };

    var getTag = function (content, pos) {
        return {
            size: content.readUInt32BE(pos + 4),
            label: content.slice(pos, pos + 4).toString('ascii')
        };
    };

    var getTagData = function (content, tag, pos) {
        return {
            label: config.labels[tag.label].toLowerCase().replace(/\s/g, '_'),
            text: content.slice(pos + 10, pos + 10 + tag.size).toString('UTF-8').replace(/^[\u0000-\u0009]+/, '')
        };
    };

    var processTags = function (content) {
        var tags = {};

        var pos = 10;

        while (pos < content.length - 10) {
            var tag = getTag(content, pos);

            if (_.isUndefined(config.labels[tag.label]) === false) {
                var data = getTagData(content, tag, pos);

                // is this some user defined tag?
                if (data.label === "user_defined_text_information_frame") {
                    data = getUserData(data.text);
                }

                // if we have something in the text then put it in
                if (!_.isUndefined(data.label) && !_.isUndefined(data.text) && data.text !== "") {
                    tags[data.label] = data.text;
                }
            }

            pos += (tag.size + 10);
        }

        return tags;
    };

    module.exports = {
        extract: extract
    };
}());