From 53fe8e9a125021e64ad9e65eb5afccb527c96138 Mon Sep 17 00:00:00 2001
From: Marius Gavrilescu <marius@ieval.ro>
Date: Sun, 28 May 2017 00:10:13 +0300
Subject: [PATCH] Add a "Previous" button to the player

---
 player.js | 37 +++++++++++++++++++++++++++++++------
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/player.js b/player.js
index 0941012..7adcdd8 100644
--- a/player.js
+++ b/player.js
@@ -6,8 +6,9 @@ var TYPES = {
 	"MP3": "audio/mpeg"
 };
 
-var audio, details, start, data;
+var audio, details, start, prev, data;
 var hash_to_id = {}, inhibit_handle_hash = false;
+var hist = []
 
 function load_song (id) {
 	audio.style.display = "inline";
@@ -34,24 +35,47 @@ function load_song (id) {
 function play_random () {
 	start.innerHTML = "Next";
 	var id = Math.floor(Math.random() * data.length);
+	hist.push(id);
+	if(hist.length > 1)
+		prev.disabled = false;
 	load_song(id);
 	audio.play();
 }
 
-function handle_hash(){
+function play_random_after_error () {
+	hist.pop(); /* Purge offending song from history */
+	play_random();
+}
+
+function play_prev () {
+	hist.pop();
+	var song = hist[hist.length - 1];
+	console.log("Will now play: " + song)
+	if(hist.length <= 1)
+		prev.disabled = true;
+	load_song(song);
+	audio.play();
+}
+
+function handle_hash(first_run){
 	if(!hash_to_id.hasOwnProperty(location.hash) || inhibit_handle_hash)
 		return;
-	load_song(hash_to_id[location.hash]);
+	var id = hash_to_id[location.hash]
+	if(first_run === true)
+		hist.push(id)
+	load_song(id);
 	start.innerHTML = "Next";
 	audio.play();
 }
 
 window.onload = function () {
 	var container = document.getElementById("player");
-	container.innerHTML = '<div id="details"></div> <button id="start_player">Play a random song</button> (or click a song title)<br><audio id="audio" controls></audio>';
+	container.innerHTML = '<div id="details"></div> <button id="prev_player">Previous</button><button id="start_player">Play a random song</button> (or click a song title)<br><audio id="audio" controls></audio>';
 	audio = document.getElementById("audio");
 	details = document.getElementById("details");
 	start = document.getElementById("start_player");
+	prev  = document.getElementById("prev_player")
+	prev.disabled = true;
 
 	data = [];
 	var trs = document.querySelectorAll("tbody tr");
@@ -77,8 +101,9 @@ window.onload = function () {
 
 	audio.style.display = "none";
 	audio.addEventListener('ended', play_random);
-	audio.addEventListener('error', play_random);
+	audio.addEventListener('error', play_random_after_error);
 	start.addEventListener('click', play_random);
+	prev.addEventListener('click', play_prev);
 	window.onhashchange = handle_hash;
-	handle_hash();
+	handle_hash(true);
 };
-- 
2.30.2