define([], function () {
    var Flat = {};

    var slice = function (coll) {
        return Array.prototype.slice.call(coll);
    };

    var getAttrs = function (el) {
        var i = 0;
        var l = el.attributes.length;
        var attr;
        var data = {};
        for (;i < l;i++) {
            attr = el.attributes[i];
            if (attr.name && attr.value) { data[attr.name] = attr.value; }
        }
        return data;
    };

    var identity = function (x) { return x; };
    Flat.fromDOM = function (dom) {
        var data = {
            map: {},
        };

        var i = 1; // start from 1 so we're always truthey
        var uid = function () { return i++; };

        var process = function (el) {
            var id;
            if (!el.tagName && el.nodeType === Node.TEXT_NODE) {
                id = uid();
                data.map[id] = el.textContent;
                return id;
            }
            if (!el || !el.attributes) { return void console.error(el); }
            id = uid();
            data.map[id] = [
                el.tagName,
                getAttrs(el),
                slice(el.childNodes).map(function (e) {
                    return process(e);
                }).filter(identity)
            ];
            return id;
        };

        data.root = process(dom);
        return data;
    };

    Flat.toDOM = function (data) {
        var visited = {};
        var process = function (key) {
            if (!key) { return; } // ignore falsey keys
            if (visited[key]) {
                // TODO handle this more gracefully.
                throw new Error('duplicate id or loop detected');
            }
            visited[key] = true; // mark paths as visited.

            var hj = data.map[key];
            if (typeof(hj) === 'string') { return document.createTextNode(hj); }
            if (typeof(hj) === 'undefined') { return; }
            if (!Array.isArray(hj)) { console.error(hj); throw new Error('expected array'); }

            var e = document.createElement(hj[0]);
            for (var x in hj[1]) { e.setAttribute(x, hj[1][x]); }
            var child;
            for (var i = 0; i < hj[2].length; i++) {
                child = process(hj[2][i]);
                if (child) {
                    e.appendChild(child);
                }
            }
            return e;
        };

        return process(data.root);
    };

    return Flat;
});