From 99bc635cd981e2564e154bd0ee6cb6d3614c11c2 Mon Sep 17 00:00:00 2001
From: Gerben <gerben@treora.com>
Date: Sun, 20 Oct 2019 21:47:43 +0530
Subject: [PATCH] Factor out and improve media fragment parser

---
 app/audio-player/contentscript.js           | 16 ++++-----
 app/util/parse-media-fragment-identifier.js | 38 +++++++++++++++++++++
 2 files changed, 45 insertions(+), 9 deletions(-)
 create mode 100644 app/util/parse-media-fragment-identifier.js

diff --git a/app/audio-player/contentscript.js b/app/audio-player/contentscript.js
index ab4e90a..510b9ef 100644
--- a/app/audio-player/contentscript.js
+++ b/app/audio-player/contentscript.js
@@ -1,6 +1,8 @@
 import * as WaveformPlaylist from 'waveform-playlist';
 import delay from 'delay';
 
+import parseMediaFragmentIdentifier from '../util/parse-media-fragment-identifier.js';
+
 async function init() {
 	document.body.innerHTML = `
 		<main>
@@ -46,15 +48,11 @@ async function init() {
 
 		const fragmentIdentifier = window.location.hash;
 		if (fragmentIdentifier) {
-			const match = fragmentIdentifier.match(/#t=(\d+(?:\.\d+)?)?(?:,(\d+(?:\.\d+)?))?/);
-			if (match) {
-				if (match[1] !== undefined) {
-					start = Number.parseFloat(match[1]);
-				}
-				if (match[2] !== undefined) {
-					end = Number.parseFloat(match[2]);
-				}
-			}
+			try {
+				const parsed = parseMediaFragmentIdentifier(fragmentIdentifier);
+				start = parsed.start;
+				end = parsed.end;
+			} catch (err) {}
 		}
 
 		// Emit event to update selection in player
diff --git a/app/util/parse-media-fragment-identifier.js b/app/util/parse-media-fragment-identifier.js
new file mode 100644
index 0000000..171f99e
--- /dev/null
+++ b/app/util/parse-media-fragment-identifier.js
@@ -0,0 +1,38 @@
+// Parses the time range from a media fragment identifier such as '#t=12.5,1:59:45.12'.
+// See https://www.w3.org/TR/media-frags/
+// Note this only supports npt (normal playing time) format, not smpte or wall clock time.
+// Returns an object { start, end }; both numbers are given in seconds (possibly non-integer).
+export default function parseMediaFragmentIdentifier(fragmentIdentifier) {
+	// Strip possible leading hash character '#'.
+	if (fragmentIdentifier.startsWith('#')) {
+		fragmentIdentifier = fragmentIdentifier.substring(1);
+	}
+
+	const temporalDimensionRegex = /(?:^|&)(?:t|%74)=([^&]+)(?=&|$)/g;
+	const temporalDimensionMatches = [...fragmentIdentifier.matchAll(temporalDimensionRegex)];
+	if (temporalDimensionMatches.length === 0) {
+		throw new Error('No time dimension defined');
+	}
+	// If there are multiple occurrences (e.g. t=1&t=2), take the last one.
+	const temporalDimensionMatch = temporalDimensionMatches[temporalDimensionMatches.length - 1];
+	const temporalDimensionValue = decodeURIComponent(temporalDimensionMatch[1]);
+
+	const nptRegex = /^(?:npt:)?(?:(?:(\d+):)??(?:(\d+):)?(\d+(?:\.\d*)?))?(?:,(?:(\d+):)??(?:(\d+):)?(\d+(?:\.\d*)?))?$/;
+	const nptMatch = temporalDimensionValue.match(nptRegex);
+	if (!nptMatch) {
+		throw new Error('Unable to parse fragment identifier.');
+	}
+
+	const start = (nptMatch[3] ? Number.parseFloat(nptMatch[3]) : 0)
+			+ (nptMatch[2] ? Number.parseInt(nptMatch[2]) * 60 : 0)
+			+ (nptMatch[1] ? Number.parseInt(nptMatch[1]) * 60 * 60 : 0);
+
+	let end;
+	if (nptMatch[6]) {
+		end = Number.parseFloat(nptMatch[6])
+			+ (nptMatch[5] ? Number.parseInt(nptMatch[5]) * 60 : 0)
+			+ (nptMatch[4] ? Number.parseInt(nptMatch[4]) * 60 * 60 : 0);
+	}
+
+	return { start, end };
+}