index.js

var extend = require('extend');

var defaultOptions = {
    propName: "links"
};

function hateoas(options) {
    options = extend({}, defaultOptions, options);
    if (!options.baseUrl) {
        throw Error("Missing required argument 'baseUrl'");
    }

    if (options.baseUrl[options.baseUrl.length-1] == "/") {
        options.baseUrl = options.baseUrl.substring(0, options.baseUrl.length-1);
    }

    var linkHandlers = {};
    var collectionLinkHandlers = {};

    function registerLinkHandler(type, handler) {
        if (!linkHandlers[type]) {
            linkHandlers[type] = [];
        }
        linkHandlers[type].push(handler);
    }

    function registerCollectionLinkHandler(type, handler) {
        if (!collectionLinkHandlers[type]) {
            collectionLinkHandlers[type] = [];
        }

        collectionLinkHandlers[type].push(handler);
    }

    function prefix(link) {
        if (!link.length || link[0] !== "/") {
            return link;
        }

        return options.baseUrl + link;
    }

    function getLinksGeneric(handlers, type, data) {
        if (handlers[type]) {
            var links = handlers[type].reduce(function(links, handler) {
                return extend({}, links, handler(data, type, links));
            }, {});

            return Object.keys(links).reduce(function(prefixedLinks, linkName) {
                prefixedLinks[linkName] = prefix(links[linkName]);
                return prefixedLinks;
            }, {});
        } else {
            return [];
        }
    }

    var getLinks = getLinksGeneric.bind(null, linkHandlers);
    var getCollectionLinks = getLinksGeneric.bind(null, collectionLinkHandlers);

    function linkCollection(type, collection) {
        var result = {
            data: collection.map(link.bind(null, type))
        };

        var links = getCollectionLinks(type, collection);

        if (options.propName) {
            result[options.propName] = links;
        } else {
            extend(result, links);
        }

        return result;
    }

    function link(type, data) {
        if (Array.isArray(data)) {
            return linkCollection(type, data);
        }

        if (linkHandlers[type]) {
            var links = getLinks(type, data);

            if (options.propName) {
                data[options.propName] = links;
            } else {
                extend(data, links);
            }

            return data;
        } else {
            return data;
        }
    }


    return {
        registerLinkHandler: registerLinkHandler,
        registerCollectionLinkHandler: registerCollectionLinkHandler,
        getLinks: getLinks,
        link: link
    };
}

module.exports = hateoas;