edate

%%#!/usr/bin/env escript

-module(edate).
-export([main/1]).

-define(BUFSIZ, 1024).

usage() ->
	io:format("usage: edate [-u][-d date | -r seconds] [+format]~n"),
	io:format("-d date\t\tparse date and/or time string~n"),
	io:format("-r seconds\tUTC seconds from the Epoch~n"),
	io:format("-u\t\tdisplay UTC~n"),
	io:format("+format\t\tstr:ftime/2 format string~n"),
	halt(2).

main(Args) ->
	case egetopt:parse(Args, [
		{ $d, param, parse_date },
		{ $r, param, epoch_seconds },
		{ $u, flag, utc_time }
	]) of
	{ok, Options, ArgsN} ->
		ShiftTime = case proplists:get_value(utc_time, Options, false) of
		false ->
			fun (DTZ) -> DTZ end;
		true ->
			fun (DTZ) -> dtz:to_utc(DTZ) end
		end,

		{DateTimeTz, _Rest} = case proplists:get_value(parse_date, Options) of
		undefined ->
			case proplists:get_value(epoch_seconds, Options) of
			undefined ->
				{Date, Time} = calendar:local_time(),
				{{Date, Time, dtz:time_zone_seconds()}, undefined};
			UTC ->
				str:ptime(list_to_binary(UTC), <<"%s">>)
			end;
		ParseDate ->
			case str:to_date_time(str:trim(list_to_binary(ParseDate))) of
			{DTZ, <<>>} ->
				{DTZ, undefined};
			badarg ->
				io:format("edate: cannot parse ~s~n", [ParseDate]),
				halt(1);
			{_DTZ, Rest} ->
				io:format("edate: cannot parse ~s~n", [Rest]),
				halt(1)
			end
		end,

		Format = case ArgsN of
		[] ->
			% This is not historical nor POSIX, but practical.
			<<"%a, %c %z">>;
		[[$+ | Fmt] | _] ->
			list_to_binary(Fmt)
		end,

		io:format("~s~n", [str:ftime(Format, ShiftTime(DateTimeTz))]);
	{error, Reason, Opt} ->
		io:format("~s -~c~n", [Reason, Opt]),
		usage()
	end.