// ==UserScript==
// @name          Hacker News Highlighter: See new posts and comments
// @namespace     http://mschade.me/userscripts
// @description   Improve [Hacker News](http://news.ycombinator.com/) by highlighting new and updated posts.
// @match         http://news.ycombinator.com/*
// @match         https://news.ycombinator.com/*
// @include       http://news.ycombinator.com/*
// @include       https://news.ycombinator.com/*
// ==/UserScript==

// URL to jQuery Library
var jqURL = "https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js";

function main() {
    /* Options */
    var   C_NEW_POST     = 'lightgreen'
        , C_UPDATED_POST = 'yellow'
        , C_NEW_COMMENT  = 'yellow'
        ;

    /* Add ability to compute difference between two arrays.

       Snippet via http://stackoverflow.com/q/4026828
     */
    Array.prototype.diff = function(a) {
        return this.filter(function(i) {return !(a.indexOf(i) > -1);});
    };

    /* Strips the prefix of query string to retrieve the intended id. */
    function getId(s) {
        return s.replace("item", "").replace("?id=", "");
    }

    /* Makes text plural only if count is not one. For example:

       pluralizeText("new post", 0) => "0 new posts"
       pluralizeText("new post", 1) => "1 new post"
       pluralizeText("new post", 2) => "2 new posts"
     */
    function pluralizeText(text, count) {
        var ntext  = count ? count : "No";
        ntext     += ' ' + text;
        if (count != 1) {
            ntext += 's';
        }
        return ntext;
    }

    /* Processes the comments on page to determine which, if any, are new,
       marking the new comments accordingly.
     */
    function processComments() {
        var   post        = getId(window.location.search)
            , comments    = []
            , oldComments = []
            , comheads    = {}
            ;

        // Populate comments
        $(".comhead a:last-child").each(function(index) {
            var cid = getId($(this).attr('href'));
            comments.push(cid);
            comheads[cid] = $(this).parent();
        });

        // Try to retrieve existing set of comments for this page
        if (post in localStorage) {
            oldComments = JSON.parse(localStorage.getItem(post));

            // Determine new comments and mark them visually
            var newComments = comments.diff(oldComments);
            $.each(newComments, function(index, cid) {
                comheads[cid].css('background-color', C_NEW_COMMENT);
            });

            /* Update top of page to reflect number of new comments. */
            var nspot = $("center > table > tbody > tr > td > br:first");
            var ntext = '<div style="margin-left: 25px; color: black;">'
                      + '<p><strong>'
                      + pluralizeText("new comment", newComments.length)
                      + '</strong></p></div>'
                      ;
            nspot.replaceWith(ntext);
        }

        // Save to browser storage
        localStorage.setItem(post, JSON.stringify(comments));
        localStorage.setItem("_" + post, comments.length);
    }

    function processPosts() {
        var newPosts = 0, updatedPosts = 0;

        $(".subtext a:last-child").each(function(index) {
            var   pid   = "_" + getId($(this).attr('href'))
                , count = 0
                , ctext = $(this).text()
                ;

            if (ctext.search(/\d+/) == 0) { // "# comments" on post
                count = JSON.parse(ctext.split(" ")[0]);
            }

            /* Determine if new or existing post; mark status */
            if (pid in localStorage) { // already seen
                var ocount = JSON.parse(localStorage.getItem(pid));

                // Add notice if there are new comments ("updated post")
                if (count > ocount) {
                    updatedPosts += 1;
                    $(this).append(' <span>').children().each(function(index) {
                        var t = '('
                              + pluralizeText("new comment", count - ocount)
                              + ')'
                              ;
                        $(this).text(t).css('background-color', C_UPDATED_POST);
                    });
                }
            } else { // new post
                newPosts += 1;
                $(this).css('background-color', C_NEW_POST);
            }

            // Save post count to browser storage
            localStorage.setItem(pid, count);
        });

        /* Update top of page to reflect number of new/updated posts. */
        var   nspot  = $("center > table > tbody > tr:nth-child(2)")
            , nstyle = "color: black; padding: 10px; padding-left: 35px;"
            , ntext  = '<td><p style="' + nstyle + '"><strong>'
                     + pluralizeText("new post",     newPosts)     + '. '
                     + pluralizeText("updated post", updatedPosts) + '.'
                     + '</strong></p></td>'
                     ;
        nspot.append(ntext);
    }

    /* Route page to proper processing logic */
    switch (window.location.pathname) {
        // Posts
        case "/":
        case "/x":
        case "/active":
        case "/ask":
        case "/best":
        case "/newest":
        case "/news":
        case "/news2":
        case "/noobstories":
            processPosts();
            break;
        // Comments
        case "/item":
            processComments();
            break;
        // Other pages are irrelevant
        default:
            break;
    }
}

/* Injects jQuery into the page and makes useable from the below Greasemonkey
   script.

   Snippet via
   http://erikvold.com/blog/index.cfm/2010/6/14/using-jquery-with-a-user-script
 */
function addJQuery(callback) {
    var script = document.createElement("script");
    script.setAttribute("src", jqURL);
    script.addEventListener('load', function() {
            var script = document.createElement("script");
            script.textContent = "(" + callback.toString() + ")();";
            document.body.appendChild(script);
            }, false);
    document.body.appendChild(script);
}

addJQuery(main);