Feat: Support ISO 8601 timestamp with offset (#124)

Fixes timezone offset support to date parsing from Gitlab as specified by the ISO 8601 format

lua/gitlab/spec/util_spec.lua

@@ -205,6 +205,10 @@ describe("utils/init.lua", function()
       { "2016-11-22T1:25:09.482Z", "-0500", "11/21/2016 at 20:25" },
       { "2016-11-22T1:25:09.482Z", "-0000", "11/22/2016 at 01:25" },
       { "2017-3-22T13:25:09.482Z", "+0700", "03/22/2017 at 20:25" },
+      { "2023-10-28T11:25:09.482-05:00", "-0500", "10/28/2023 at 11:25" },
+      { "2016-11-21T20:25:09.482-05:00", "-0500", "11/21/2016 at 20:25" },
+      { "2016-11-22T1:25:09.482-00:00", "-0000", "11/22/2016 at 01:25" },
+      { "2017-3-22T20:25:09.482+07:00", "+0700", "03/22/2017 at 20:25" },
     }
     for _, val in ipairs(tests) do
       local got = u.format_to_local(val[1], val[2])

lua/gitlab/utils/init.lua

@@ -168,7 +168,18 @@ end
 ---@param offset string The offset of the user's local time zone, e.g. -0500 for EST
 ---@return string
 M.format_to_local = function(date_string, offset)
+  -- ISO 8601 format
+  -- 2021-01-01T00:00:00.000Z
   local year, month, day, hour, min, sec, _, tzOffset = date_string:match("(%d+)-(%d+)-(%d+)T(%d+):(%d+):(%d+).(%d+)Z")
+  if year == nil then
+    -- ISO 8601 format with timezone offset
+    -- 2021-01-01T00:00:00.000-05:00
+    local tzOffsetSign, tzOffsetHour, tzOffsetMin
+    year, month, day, hour, min, sec, _, tzOffsetSign, tzOffsetHour, tzOffsetMin =
+      date_string:match("(%d+)-(%d+)-(%d+)T(%d+):(%d+):(%d+).(%d+)([%+%-])(%d%d):(%d%d)")
+    tzOffset = tzOffsetSign .. tzOffsetHour .. tzOffsetMin
+  end
+
   local localTime = os.time({
     year = year,
     month = month,
@@ -179,7 +190,9 @@ M.format_to_local = function(date_string, offset)
     tzOffset = tzOffset,
   })
 
-  local localTimestamp = localTime + M.offset_to_seconds(offset)
+  -- Subtract the tzOffset from the local time to get the UTC time
+  local localTimestamp = tzOffset ~= nil and localTime - M.offset_to_seconds(tzOffset) or localTime
+  localTimestamp = localTimestamp + M.offset_to_seconds(offset)
 
   return tostring(os.date("%m/%d/%Y at %H:%M", localTimestamp))
 end