var iterate = require('./lib/iterate.js')
    , initState = require('./lib/state.js')
    , terminator = require('./lib/terminator.js')
    ;

// Public API
module.exports = serialOrdered;
// sorting helpers
module.exports.ascending = ascending;
module.exports.descending = descending;

/**
 * Runs iterator over provided sorted array elements in series
 *
 * @param   {array|object} list - array or object (named list) to iterate over
 * @param   {function} iterator - iterator to run
 * @param   {function} sortMethod - custom sort function
 * @param   {function} callback - invoked when all elements processed
 * @returns {function} - jobs terminator
 */
function serialOrdered(list, iterator, sortMethod, callback) {
    var state = initState(list, sortMethod);

    iterate(list, iterator, state, function iteratorHandler(error, result) {
        if (error) {
            callback(error, result);
            return;
        }

        state.index++;

        // are we there yet?
        if (state.index < (state['keyedList'] || list).length) {
            iterate(list, iterator, state, iteratorHandler);
            return;
        }

        // done here
        callback(null, state.results);
    });

    return terminator.bind(state, callback);
}

/*
 * -- Sort methods
 */

/**
 * sort helper to sort array elements in ascending order
 *
 * @param   {mixed} a - an item to compare
 * @param   {mixed} b - an item to compare
 * @returns {number} - comparison result
 */
function ascending(a, b) {
    return a < b ? -1 : a > b ? 1 : 0;
}

/**
 * sort helper to sort array elements in descending order
 *
 * @param   {mixed} a - an item to compare
 * @param   {mixed} b - an item to compare
 * @returns {number} - comparison result
 */
function descending(a, b) {
    return -1 * ascending(a, b);
}
