-- timestamp.lua
local timestamp = {}

-- Standard format presets using Lua format codes
local FORMATS = {
	iso = "%Y-%m-%dT%H:%M:%SZ",
	datetime = "%Y-%m-%d %H:%M:%S",
	us_date = "%m/%d/%Y",
	us_datetime = "%m/%d/%Y %I:%M:%S %p",
	date = "%Y-%m-%d",
	time = "%H:%M:%S",
	time12 = "%I:%M:%S %p",
	readable = "%B %d, %Y %I:%M:%S %p",
	compact = "%Y%m%d_%H%M%S"
}

-- Parse input to unix timestamp and microseconds
local function parse_input(input)
	local unix_time, micros = 0, 0

	if type(input) == "string" then
		local frac, secs = input:match("^(0%.%d+)%s+(%d+)$")
		if frac and secs then
			unix_time = tonumber(secs)
			micros = math.floor((tonumber(frac) * 1000000) + 0.5)
		else
			unix_time = tonumber(input) or 0
		end
	elseif type(input) == "number" then
		unix_time = math.floor(input)
		micros = math.floor(((input - unix_time) * 1000000) + 0.5)
	end

	return unix_time, micros
end

-- Remove leading zeros from number string
local function no_leading_zero(s)
	return s:gsub("^0+", "") or "0"
end

-- Main format function
function timestamp.format(input, fmt)
	fmt = fmt or "datetime"
	local format_str = FORMATS[fmt] or fmt
	local unix_time, micros = parse_input(input)
	local result = os.date(format_str, unix_time)

	-- Handle microseconds if format contains dot
	if format_str:find("%.") then
		result = result .. string.format(".%06d", micros)
	end

	return result
end

-- US date/time with no leading zeros
function timestamp.us_datetime_no_zero(input)
	local unix_time, micros = parse_input(input)
	local month = no_leading_zero(os.date("%m", unix_time))
	local day = no_leading_zero(os.date("%d", unix_time))
	local year = os.date("%Y", unix_time)
	local hour = no_leading_zero(os.date("%I", unix_time))
	local min = os.date("%M", unix_time)
	local sec = os.date("%S", unix_time)
	local ampm = os.date("%p", unix_time)

	return string.format("%s/%s/%s %s:%s:%s %s", month, day, year, hour, min, sec, ampm)
end

-- Quick preset functions
function timestamp.iso(input) return timestamp.format(input, "iso") end
function timestamp.datetime(input) return timestamp.format(input, "datetime") end
function timestamp.us_date(input) return timestamp.format(input, "us_date") end
function timestamp.us_datetime(input) return timestamp.us_datetime_no_zero(input) end
function timestamp.date(input) return timestamp.format(input, "date") end
function timestamp.time(input) return timestamp.format(input, "time") end
function timestamp.time12(input) return timestamp.format(input, "time12") end
function timestamp.readable(input) return timestamp.format(input, "readable") end

-- Microsecond precision variants
function timestamp.datetime_micro(input)
	return timestamp.format(input, "%Y-%m-%d %H:%M:%S.") .. string.format("%06d", select(2, parse_input(input)))
end

function timestamp.iso_micro(input)
	return timestamp.format(input, "%Y-%m-%dT%H:%M:%S.") .. string.format("%06dZ", select(2, parse_input(input)))
end

-- Register global convenience function
_G.format_time = timestamp.format

return timestamp