gnavalesi/music-tag

var _ = require('underscore'),
        fs = require('fs'),
        Buffer = require('buffer').Buffer,
        Q = require('q');


(function () {
    'use strict';

    var read = function (path) {
        var deferred = Q.defer();

        openFile(path).then(function (fileHandle) {
            readHeaderBuffer(fileHandle)
                .then(loadHeader)
                .then(_.partial(readTagBuffer, fileHandle))
                .then(function (tagBuffer) {
                    closeFile(fileHandle).then(function () {
                        deferred.resolve(tagBuffer);
                    }).catch(deferred.reject);
                }).catch(deferred.reject);
        }).catch(deferred.reject);

        return deferred.promise;
    };

    var openFile = function (path) {
        var deferred = Q.defer();

        fs.open(path, 'r', function (err, fileHandle) {
            if (err) {
                deferred.reject(err);
            } else {
                deferred.resolve(fileHandle);
            }
        });

        return deferred.promise;
    };

    var readHeaderBuffer = function (fileHandle) {
        var deferred = Q.defer();
        var buffer = new Buffer(10);

        fs.read(fileHandle, buffer, 0, 10, 0, function (err) {
            if (err) {
                deferred.reject(err);
            } else {
                deferred.resolve(buffer);
            }
        });

        return deferred.promise;
    };

    var loadHeader = function (buffer) {
        var deferred = Q.defer();
        var header = buffer.slice(0, 10);

        if (header.slice(0, 3).toString() === 'ID3') {
            var dataSize = id3Size(header.slice(6, 10)) + 10;
            deferred.resolve(dataSize);
        } else {
            deferred.reject('NO_ID3');
        }

        return deferred.promise;
    };

    var readTagBuffer = function (fileHandle, tagSize) {
        var deferred = Q.defer();
        var tagBuffer = new Buffer(tagSize);

        fs.read(fileHandle, tagBuffer, 0, tagSize, 0, function (err) {
            if (err) {
                deferred.reject(new Error("Unable to read file"));
            } else {
                deferred.resolve(tagBuffer);
            }
        });

        return deferred.promise;
    };

    var closeFile = function (fileHandle) {
        var deferred = Q.defer();

        fs.close(fileHandle, function (err) {
            if (err) {
                deferred.reject(err);
            } else {
                deferred.resolve();
            }
        });

        return deferred.promise;
    };

    var id3Size = function (buffer) {
        return ((buffer[0] & 0x7F) << 21 ) |
            ((buffer[1] & 0x7F) << 14) |
            ((buffer[2] & 0x7F) << 7) |
            (buffer[3] & 0x7F);
    };

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