local _M = {}

_M.source, _M.resolution, _M.gettime = (function()
	local has_syscall, syscall = pcall(require, "syscall")
	if has_syscall and syscall.clock_gettime and syscall.c.CLOCK then
		local clock_id = syscall.c.CLOCK.REALTIME
		local function timespec_to_number(timespec)
			return tonumber(timespec.tv_sec) + tonumber(timespec.tv_nsec) * 1e-9
		end
		return "syscall.clock_gettime(CLOCK_REALTIME)",
			syscall.clock_getres and timespec_to_number(syscall.clock_getres(clock_id)) or 1e-9,
			function()
				return timespec_to_number(syscall.clock_gettime(clock_id))
			end
	end

	local has_unix, unix = pcall(require, "unix")
	-- On Apple devices lunix only uses gettimeofday()
	if has_unix and unix.clock_gettime and unix.uname and unix.uname().sysname ~= "Darwin" then
		return "unix.clock_gettime(CLOCK_REALTIME)", 1e-9, function()
			return unix.clock_gettime()
		end
	end

	if has_syscall and syscall.gettimeofday then
		local function timeval_to_number(timeval)
			return tonumber(timeval.tv_sec) + tonumber(timeval.tv_nsec) * 1e-6
		end
		return "syscall.gettimeofday()", 1e-6,
			function()
				return timeval_to_number(syscall.gettimeofday())
			end
	end

	if has_unix and unix.gettimeofday then
		return "unix.gettimeofday()", 1e-6, unix.gettimeofday
	end

	local has_socket, socket = pcall(require, "socket")
	if has_socket and socket.gettime then
		-- on windows, this uses GetSystemTimeAsFileTime, which has resolution of 1e-7
		-- on linux, this uses gettimeofday, which has resolution of 1e-6
		return "socket.gettime()", 1e-6, socket.gettime
	end

	if ngx and ngx.now then -- luacheck: ignore 113
		return "ngx.now()", 1e-3, ngx.now -- luacheck: ignore 113
	end

	return "os.time()", 1, os.time
end)()

return _M