background.js

var disable = false;
var reverse = false;
var shuffle = false;
var folder = "playlist";

// todo use 'browser' everywhere
var browser = browser || chrome;

function loadSettings()
{
    chrome.storage.sync.get([
            "disable", 
            "shuffle", 
            "reverse",
            "folder",
        ], function(cfg) { 
            disable = cfg.disable;
            reverse = cfg.reverse;
            shuffle = cfg.shuffle;
            folder = cfg.folder || "playlist";
    });
}

loadSettings();

function updateTabUrl(tabId, newUrl)
{
    chrome.tabs.update(tabId, {url: newUrl});
}

function pickNext(tab)
{
    // disable can be true when the user clicks our action icon
    if (disable) {
        disable = false;
        chrome.storage.sync.set({disable: false});
    }

    function pickNonShuffle(items, begin, end) {
        var found = false;
        
        var n = items.length;
        var a = !reverse ? begin : end-1;
        var b = !reverse ? end-1 : begin;
        var d = !reverse ? 1 : -1;

        for (var i = a; i != b; i += d) {
            if (found && items[i].url && items[i].url.indexOf(".youtube.com/watch") != -1) {
                updateTabUrl(tab.id, items[i].url);
                return true;
            }

            found |= items[i].url == tab.url;
        }

        return false;
    }
    
    function pickShuffle(items, begin, end) {
        if (! (begin < end)) return;

        var cur;
        for (cur=begin; cur<end; cur++)
            if (items[cur].url == tab.url)
                break;
        
        if (cur == end)
            cur = begin;

        for (;;) {
            var n = end - begin;
            var r = Math.floor(Math.random() * (n - 1));
            var next = begin + (cur + 1 + r) % n;

            if (items[next].url && items[next].url.indexOf(".youtube.com/watch") != -1) {
                updateTabUrl(tab.id, items[next].url);
                return;
            }
        }
    }

    chrome.bookmarks.search({}, function(items) {
        var begin = 0;
        var end = items.length;

        for (var i=0; i<items.length; i++) {
            if (items[i].title == folder && !items[i].url) {
                begin = i;
            } else if (begin && items[i].parentId == items[begin].parentId) {
                end = i;
                break;
            }
        }
        
        if (shuffle || !pickNonShuffle(items, begin, end))
            pickShuffle(items, begin, end);
    });
}

chrome.browserAction.onClicked.addListener(function(tab__unused) {
    chrome.tabs.query({'active': true, 'lastFocusedWindow': true}, function (tabs) {
        if (!tabs[0]) return;
        
        if (tabs[0].url.indexOf(".youtube.com") != -1) {
            pickNext(tabs[0]);
            return;
        }
    
        chrome.tabs.query({'url': "https://*.youtube.com/*"}, function (tabs) {
            if (tabs[0]) {
                pickNext(tabs[0]);
                return;
            }

            alert("Open a youtube tab first.");
        });
    });
});

browser.runtime.onMessage.addListener(function(msg, sender) {
    if (msg.name == "settings-changed") {
        loadSettings();
    } else if (msg.name == "video-ended") {
        if (!disable)
            pickNext(sender.tab);
    }
});