define(["backbone", "underscore"], function(Backbone, _) {
    var LicenseModel = Backbone.Model.extend({
        defaults: {
            "type": null,
            "options": {},
            "custom": false // either `false`, or a string
        },

        initialize: function(attributes) {
            if(attributes && attributes.asString) {
                this.setFromString(attributes.asString);
                this.unset("asString");
            }
        },

        toString: function() {
            var custom = this.get("custom");
            if (custom) {
                return custom;
            }

            var type = this.get("type"),
                options = this.get("options");

            if (_.isEmpty(options)) {
                return type || "";
            }

            // options are where it gets tricky
            var optionStrings = _.map(options, function (value, key) {
                if(_.isBoolean(value)) {
                    return value ? key : null
                } else {
                    return key + "=" + value
                }
            });
            // filter out nulls
            optionStrings = _.filter(optionStrings, _.identity);
            // build license string and return
            return type + ": " + optionStrings.join(" ");
        },

        setFromString: function(string, options) {
            if (!string) {
                // reset to defaults
                return this.set(this.defaults, options);
            }

            var colonIndex = string.indexOf(":"),
                spaceIndex = string.indexOf(" ");

            // a string without a colon could be a custom license, or a license
            // type without options
            if (colonIndex == -1) {
                if (spaceIndex == -1) {
                    // if there's no space, it's a license type without options
                    return this.set({
                        "type": string,
                        "options": {},
                        "custom": false
                    }, options);
                } else {
                // if there is a space, it's a custom license
                    return this.set({
                        "type": null,
                        "options": {},
                        "custom": string
                    }, options);
                }
            }

            // there is a colon, which indicates a license type with options.
            var type = string.substring(0, colonIndex),
                optionsObj = {},
                optionsString = string.substring(colonIndex + 1);

                _.each(optionsString.split(" "), function(optionString) {
                    if (_.isEmpty(optionString)) {
                        return;
                    }
                    var eqIndex = optionString.indexOf("=");
                    if(eqIndex == -1) {
                        // this is a boolean flag
                        optionsObj[optionString] = true;
                    } else {
                        // this is a key-value pair
                        var optionKey = optionString.substring(0, eqIndex);
                        var optionVal = optionString.substring(eqIndex + 1);
                        optionsObj[optionKey] = optionVal;
                    }
                });

            return this.set({
                "type": type, "options": optionsObj, "custom": false,
            }, options);
        }
    });

    return LicenseModel;
});