(function (tree) {
//
// CSS @import node
//
// The general strategy here is that we don't want to wait
// for the parsing to be completed, before we start importing
// the file. That's because in the context of a browser,
// most of the time will be spent waiting for the server to respond.
//
// On creation, we push the import path to our import queue, though
// `import,push`, we also pass it a callback, which it'll call once
// the file has been fetched, and parsed.
//
tree.Import = function (path, imports) {
    var that = this;

    this._path = path;

    // The '.mess' extension is optional
    if (path instanceof tree.Quoted) {
        this.path = /\.(le?|c)ss$/.test(path.value) ? path.value : path.value + '.mess';
    } else {
        this.path = path.value.value || path.value;
    }

    this.css = /css$/.test(this.path);

    // Only pre-compile .mess files
    if (! this.css) {
        imports.push(this.path, function (root) {
            if (! root) {
                throw new(Error)("Error parsing " + that.path);
            }
            that.root = root;
        });
    }
};

//
// The actual import node doesn't return anything, when converted to CSS.
// The reason is that it's used at the evaluation stage, so that the rules
// it imports can be treated like any other rules.
//
// In `eval`, we make sure all Import nodes get evaluated, recursively, so
// we end up with a flat structure, which can easily be imported in the parent
// ruleset.
//
tree.Import.prototype = {
    toCSS: function () {
        if (this.css) {
            return "@import " + this._path.toCSS() + ';\n';
        } else {
            return "";
        }
    },
    eval: function (env) {
        var ruleset;

        if (this.css) {
            return this;
        } else {
            ruleset = new(tree.Ruleset)(null, this.root.rules.slice(0));

            for (var i = 0; i < ruleset.rules.length; i++) {
                if (ruleset.rules[i] instanceof tree.Import) {
                    Array.prototype
                         .splice
                         .apply(ruleset.rules,
                                [i, 1].concat(ruleset.rules[i].eval(env)));
                }
            }
            return ruleset.rules;
        }
    }
};

})(require('mess/tree'));