gitweb: JavaScript ability to adjust time based on timezone

This patch is based on Kevin Cernekee's <cernekee@gmail.com>
patch series entitled "gitweb: introduce localtime feature".  While
Kevin's patch changed the server side output so that the timezone
was output from gitweb itself, this has a number of drawbacks, in
particular with respect to gitweb-caching.

This patch takes the same basic goal, display the appropriate times in
a given common timezone, and implements it in JavaScript.  This
requires adding / using a new class, "datetime", to be able to find
elements to be adjusted from JavaScript.  Appropriate dates are
wrapped in a span with this class.

Timezone to be used can be retrieved from "gitweb_tz" cookie, though
currently there is no way to set / manipulate this cookie from gitweb;
this is left for later commit.

Valid timezones, currently, are: "utc", "local" (which means that
timezone is taken from browser), and "+/-ZZZZ" numeric timezone as in
RFC-2822.  Default timezone is "local" (currently not configurable,
left for later commit).

Fallback (should JavaScript not be enabled) is to treat dates as they
have been and display them, only, in UTC.

Pages affected:
* 'summary' view, "last change" field (commit time from latest change)
* 'log' view, author time
* 'commit' and 'commitdiff' views, author/committer time
* 'tag' view, tagger time

Based-on-code-from: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: John 'Warthog9' Hawley <warthog9@eaglescrag.net>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 75 insertions, 0 deletions

diff --git a/gitweb/static/js/adjust-timezone.js b/gitweb/static/js/adjust-timezone.js
new file mode 100644
index 0000000000..1577d780f0
--- /dev/null
+++ b/gitweb/static/js/adjust-timezone.js
@@ -0,0 +1,60 @@
+// Copyright (C) 2011, John 'Warthog9' Hawley <warthog9@eaglescrag.net>
+//               2011, Jakub Narebski <jnareb@gmail.com>
+
+/**
+ * @fileOverview Manipulate dates in gitweb output, adjusting timezone
+ * @license GPLv2 or later
+ */
+
+/**
+ * Get common timezone and adjust dates to use this common timezone.
+ *
+ * This function is called during onload event (added to window.onload).
+ *
+ * @param {String} tzDefault: default timezone, if there is no cookie
+ * @param {String} tzCookieName: name of cookie to store timezone
+ * @param {String} tzClassName: denotes elements with date to be adjusted
+ */
+function onloadTZSetup(tzDefault, tzCookieName, tzClassName) {
+	var tzCookie = getCookie(tzCookieName);
+	var tz = tzCookie ? tzCookie : tzDefault;
+
+	// server-side of gitweb produces datetime in UTC,
+	// so if tz is 'utc' there is no need for changes
+	if (tz !== 'utc') {
+		fixDatetimeTZ(tz, tzClassName);
+	}
+}
+
+
+/**
+ * Replace RFC-2822 dates contained in SPAN elements with tzClassName
+ * CSS class with equivalent dates in given timezone.
+ *
+ * @param {String} tz: numeric timezone in '(-|+)HHMM' format, or 'utc', or 'local'
+ * @param {String} tzClassName: specifies elements to be changed
+ */
+function fixDatetimeTZ(tz, tzClassName) {
+	// sanity check, method should be ensured by common-lib.js
+	if (!document.getElementsByClassName) {
+		return;
+	}
+
+	// translate to timezone in '(-|+)HHMM' format
+	tz = normalizeTimezoneInfo(tz);
+
+	// NOTE: result of getElementsByClassName should probably be cached
+	var classesFound = document.getElementsByClassName(tzClassName, "span");
+	for (var i = 0, len = classesFound.length; i < len; i++) {
+		var curElement = classesFound[i];
+
+		// we use *.firstChild.data (W3C DOM) instead of *.innerHTML
+		// as the latter doesn't always work everywhere in every browser
+		var epoch = parseRFC2822Date(curElement.firstChild.data);
+		var adjusted = formatDateRFC2882(epoch, tz);
+
+		curElement.firstChild.data = adjusted;
+	}
+}
+
+/* end of adjust-timezone.js */
diff --git a/gitweb/static/js/lib/datetime.js b/gitweb/static/js/lib/datetime.js
index b3dcedb141..f78c60a912 100644
--- a/gitweb/static/js/lib/datetime.js
+++ b/gitweb/static/js/lib/datetime.js
@@ -105,6 +105,21 @@ function formatTimezoneInfo(hours, minutes, sep) {
 }
 
 /**
+ * translate 'utc' and 'local' to numerical timezone
+ * @param {String} timezoneInfo: might be 'utc' or 'local' (browser)
+ */
+function normalizeTimezoneInfo(timezoneInfo) {
+	switch (timezoneInfo) {
+	case 'utc':
+		return '+0000';
+	case 'local': // 'local' is browser timezone
+		return localTimezoneInfo();
+	}
+	return timezoneInfo;
+}
+
+
+/**
  * return date in local time formatted in iso-8601 like format
  * 'yyyy-mm-dd HH:MM:SS +/-ZZZZ' e.g. '2005-08-07 21:49:46 +0200'
  *