var _ = require("underscore");


exports.Element = Element;
exports.element = function(name, attributes, children) {
    return new Element(name, attributes, children);
};
exports.text = function(value) {
    return {
        type: "text",
        value: value
    };
};


var emptyElement = {
    first: function() {
        return null;
    },
    firstOrEmpty: function() {
        return emptyElement;
    },
    attributes: {}
};

function Element(name, attributes, children) {
    this.type = "element";
    this.name = name;
    this.attributes = attributes || {};
    this.children = children || [];
}

Element.prototype.first = function(name) {
    return _.find(this.children, function(child) {
        return child.name === name;
    });
};

Element.prototype.firstOrEmpty = function(name) {
    return this.first(name) || emptyElement;
};

Element.prototype.getElementsByTagName = function(name) {
    var elements = _.filter(this.children, function(child) {
        return child.name === name;
    });
    return toElementList(elements);
};

Element.prototype.text = function() {
    if (this.children.length === 0) {
        return "";
    } else if (this.children.length !== 1 || this.children[0].type !== "text") {
        throw new Error("Not implemented");
    }
    return this.children[0].value;
};

var elementListPrototype = {
    getElementsByTagName: function(name) {
        return toElementList(_.flatten(this.map(function(element) {
            return element.getElementsByTagName(name);
        }, true)));
    }
};

function toElementList(array) {
    return _.extend(array, elementListPrototype);
}