parseIsoUtcOffset.lua

--[[
  Parses a ISO 8601 UTC offset string into a float.

  parseIsoUtcOffset("-0500") --> -5
  parseIsoUtcOffset("+02") --> 2
  parseIsoUtcOffset("-04:30") --> -4.5
  parseIsoUtcOffset("Z") --> 0

  local localTimezoneOffset = os.date("%z")
  parseIsoUtcOffset(localTimezoneOffset)
]]
local function parseIsoUtcOffset(isoOffset: string)
  local sign, hour, minute = isoOffset:match("([%+%-])(%d%d):?(%d?%d?)")

  if not hour then
    return 0
  end

  minute = if minute and minute ~= ""
    then (tonumber(minute, 10) :: number) / 60
    else "00"

  local offset = tonumber(`{sign}{hour + minute}`, 10)
  return offset or 0
end