// ==UserScript==
// @name          GitHub Diff Files Filter
// @version       0.1.1
// @description   A userscript that adds filters that toggle diff & PR files by extension
// @license       https://creativecommons.org/licenses/by-sa/4.0/
// @namespace     http://github.com/Mottie
// @include       https://github.com/*
// @grant         none
// @run-at        document-idle
// @author        Rob Garrison
// @downloadURL none
// ==/UserScript==
/* jshint unused:true, esnext:true */
(function() {
	"use strict";

	const allExtLabel = "\u00ABall\u00BB",
		noExtLabel = "\u00ABno-ext\u00BB",
		dotExtLabel = "\u00ABdot-files\u00BB";

	let list = {},
		busy = false;

	function toggleBlocks(extension, type) {
		busy = true;
		const files = $("#files"),
			view = type === "show" ? "" : "none";
		if (extension === allExtLabel) {
			// Toggle "all" blocks
			$$("#files div[id*='diff']").forEach(el => {
				el.style.display = view;
			});
			// update filter buttons
			$$("#files .gdf-filter a").forEach(el => {
				el.classList.toggle("selected", type === "show");
			});
		} else if (list[extension]) {
			/* list[extension] contains an array of anchor names used to target the
			 * hidden link added immediately above each file div container
			 * <a name="diff-xxxxx"></a>
			 * <div id="diff-#" class="file js-file js-details container">
			 */
			list[extension].forEach(anchor => {
				const file = $(`a[name="${anchor}"]`, files);
				if (file && file.nextElementSibling) {
					file.nextElementSibling.style.display = view;
				}
			});
		}
		updateAllButton();
		busy = false;
	}

	function updateAllButton() {
		const buttons = $("#files .gdf-filter"),
			filters = $$("a:not(.gdf-all)", buttons),
			selected = $$("a:not(.gdf-all).selected", buttons);
		// set "all" button
		$(".gdf-all", buttons).classList.toggle(
			"selected",
			filters.length === selected.length
		);
	}

	function buildList() {
		list = {};
		// make noExtLabel the first element in the object
		list[noExtLabel] = [];
		list[dotExtLabel] = [];
		// TOC in file diffs and pr-toolbar in Pull requests
		$$("#toc > ol > li > a, .pr-toolbar .filename").forEach(file => {
			let ext,
				txt = (file.textContent || "").trim(),
				filename = txt.split("/").slice(-1)[0];
			// test for no extension, then get extension name
			// regexp from https://github.com/silverwind/file-extension
			ext = /\./.test(filename) ? /[^./\\]*$/.exec(filename)[0] : noExtLabel;
			if (ext === filename.slice(1)) {
				ext = dotExtLabel;
			}
			if (ext) {
				if (!list[ext]) {
					list[ext] = [];
				}
				list[ext].push(
					file.hash ?
						// #toc points to "a"
						file.hash.slice(1) :
						// .pr-toolbar points to "a > div > div.filename"
						closest("a", file).hash.slice(1)
				);
			}
		});
	}

	function makeFilter() {
		buildList();
		const files = $("#files");
		let filters = 0,
			keys = Object.keys(list),
			html = "Filter file extension: <div class='BtnGroup gdf-filter'>",
			btnClass = "btn btn-sm selected BtnGroup-item";
		// get length, but don't count empty arrays
		keys.forEach(ext => {
			filters += list[ext].length > 0 ? 1 : 0;
		});
		// Don't bother if only one extension is found
		if (files && filters > 1) {
			filters = document.createElement("p");
			// add a filter "all" button to the beginning
			html += `<a class="${btnClass} gdf-all" href="#">${allExtLabel}</a>`;
			keys.forEach(ext => {
				if (list[ext].length) {
					html += `<a class="${btnClass}" href="#">${ext}</a>`;
				}
			});
			// prepend filter buttons
			filters.innerHTML = html + "</div>";
			files.insertBefore(filters, files.firstChild);
			filters.addEventListener("click", event => {
				event.preventDefault();
				event.stopPropagation();
				const el = event.target;
				el.classList.toggle("selected");
				toggleBlocks(
					el.textContent.trim(),
					el.classList.contains("selected") ? "show" : "hide"
				);
			});
		}
	}

	function init() {
		if (($("#files.diff-view") || $(".pr-toolbar")) && !$(".gdf-filter")) {
			makeFilter();
		}
	}

	function $(str, el) {
		return (el || document).querySelector(str);
	}
	function $$(str, el) {
		return Array.from((el || document).querySelectorAll(str));
	}
	function closest(selector, el) {
		while (el && el.nodeName !== "BODY" && !el.matches(selector)) {
			el = el.parentNode;
		}
		return el && el.matches(selector) ? el : null;
	}

	// DOM targets - to detect GitHub dynamic ajax page loading
	$$("#js-repo-pjax-container, #js-pjax-container").forEach(target => {
		new MutationObserver(mutations => {
			mutations.forEach(mutation => {
				// preform checks before adding code wrap to minimize function calls
				if (!busy && mutation.target === target) {
					init();
				}
			});
		}).observe(target, {
			childList: true,
			subtree: true
		});
	});

	init();

})();