// ==UserScript==
// @name           (Re)fork any gist, including your own
// @namespace      https://github.com/johan
// @description    Adds a "fork" button to gists missing one at gist.github.com, so you can create multiple forks
// @match          https://gist.github.com/*
// @include        https://gist.github.com/*
// ==/UserScript==

var resourceUri;

// Only create the button on initial load and reuse on pjax reloads
var reforkListItem = (function () {
    var li = document.createElement('li')
      , a = document.createElement('a')
      , sp = document.createElement('span');

    a.className = 'minibutton fork-button';        // Apply button look and feel
    a.title = 'Create another fork of this gist';  // Set hover text

    // When clicked, append an http form for the uri/fork post and submit it
    a.addEventListener('click', function () {
        var f = document.body.appendChild(document.createElement('form'));
        f.method = 'POST';
        f.action = resourceUri + '/fork';
        f.appendChild(document.querySelector('input[name=authenticity_token]'));
        f.submit();
        return false;
    });

    sp.className = 'mini-icon mini-icon-fork';;    // Apply the fork icon

    // Create the control tree
    li.appendChild(a);
    a.appendChild(sp);
    a.appendChild(document.createTextNode('(Re)Fork'));

    return li;
})();

// If missing and appropriate, add in the fork button
function injectForkButton() {
    var pageActions = document.querySelector('.pagehead-actions');
    var resourceLink = document.querySelector('input[name="link-field"]');

    // Only attempt to inject when on an actual gist url (https://gist.github.com/\d+) 
    //    and only when a '.pagehead-actions' element exists
    //    and only when the 'input[name="link-field"]' element exists 
    //    and only when an existing '.fork-button' element is missing 
    if (/*/^\/\d+/.test(location.pathname) &&*/ pageActions && resourceLink && !document.querySelector('.fork-button')) {
        resourceUri = resourceLink.getAttribute('value');

        pageActions.appendChild(reforkListItem);

        // Leave logging in for a while to confirm expected behavior
        console.log('(Re)fork button injected');
    }
}

// Initial page load injection 
injectForkButton();

// Dynamic injection after pjax load and subsequent dom update of '#js-pjax-container'
//
// Observe 'childList' changes to '#js-pjax-container' and rerun injectForkButton
var target = document.querySelector('#js-pjax-container');
var JsMutationObserver = window.MutationObserver || window.WebKitMutationObserver;
var observer = new JsMutationObserver(function (mutations) {
    console.log('pjax-container mutation - checking for fork button');
    injectForkButton();
});
observer.observe(target, { childList: true });

// TODO: Is it necessary to call observer.disconnect()