-module(dd).
-compile([export_all, nowarn_export_all]).

% do(1571882864) % timestamp
% do({ {2018, 3, 1}, {5, 21, 51} }) % { {Year, Month, Day}, {Hour, Minute, Second} }
do(T0) when is_integer(T0) ->
  T1 = erlang:system_time(second), % second | millisecond | microsecond | nanosecond ...
  do2(T1 - T0);
do({{_Year, _Month, _Day},{_Hour, _Minute, _Second}} = T0) ->
  T1 = calendar:now_to_datetime(erlang:timestamp()), % { {Year, Month, Day}, {Hour, Minute, Second} }
  Z = calendar:time_difference(T0, T1),
  do3(Z);
do(_) -> io:format("~ts~n",[<<"Ви щось переплутали!"/utf8>>]).


do2(T) when is_integer(T) andalso T < 0 ->
  io:format("~ts~n",[<<"Назад у майбутнє!"/utf8>>]);
do2(T) when T =:= 0 ->
  io:format("~ts~n",[<<"Вітання Вам у моменті \"зараз\"!"/utf8>>]);
do2(T) ->
  Z = calendar:seconds_to_daystime(T), % {Days, {Hour, Minute, Second}}
  do3(Z). % helper function
  % here we also can use next functions:
  % calendar:gregorian_seconds_to_datetime(Seconds)
  % calendar:datetime_to_gregorian_seconds({ {Year, Month, Day}, {Hour, Minute, Second} })
  % calendar:time_difference(T1, T2)


do3({Days, {_, _, _}}) when Days < 0 ->
  io:format("~ts~n",[<<"Назад у майбутнє!"/utf8>>]);
do3({0, {0, 0, 0}}) ->
  io:format("~ts~n",[<<"Вітання Вам у моменті \"зараз\"!"/utf8>>]);
do3({0, {0, 0, Second}}) ->
  V = num2word(Second, [<<"секунду"/utf8>>, <<"секунди"/utf8>>, <<"секунд"/utf8>>]),
  io:format("~p ~ts ~ts~n",[Second, V, <<"назад"/utf8>>]);
do3({0, {0, Minute, _}}) ->
  V = num2word(Minute, [<<"хвилину"/utf8>>, <<"хвилини"/utf8>>, <<"хвилин"/utf8>>]),
  io:format("~p ~ts ~ts~n",[Minute, V, <<"назад"/utf8>>]);
do3({0, {Hour, _, _}}) ->
  V = num2word(Hour, [<<"годину"/utf8>>, <<"години"/utf8>>, <<"годин"/utf8>>]),
  io:format("~p ~ts ~ts~n",[Hour, V, <<"назад"/utf8>>]);
do3({Days, {_Hour, _Minute, _Second}}) when Days < 30 ->
  V = num2word(Days, [<<"день"/utf8>>, <<"дні"/utf8>>, <<"днів"/utf8>>]),
  io:format("~p ~ts ~ts~n",[Days, V, <<"назад"/utf8>>]);
do3({Days, {_Hour, _Minute, _Second}}) when Days >= 30 andalso Days < 365 ->
  M = Days div 30,
  V = num2word(M, [<<"місяць"/utf8>>, <<"місяці"/utf8>>, <<"місяців"/utf8>>]),
  io:format("~p ~ts ~ts~n",[M, V, <<"назад"/utf8>>]);
%do3({Days, {_Hour, _Minute, _Second}}) when Days >= 365 ->
do3({Days, {_Hour, _Minute, _Second}}) ->
  Y = Days div 365,
  V = num2word(Y, [<<"рік"/utf8>>, <<"роки"/utf8>>, <<"років"/utf8>>]),
  io:format("~p ~ts ~ts~n",[Y, V, <<"назад"/utf8>>]).


% num2word(50, ["рік", "роки", "років"]) % ["хвилину", "хвилини", "хвилин"]
num2word(Num, Words) ->
  N0 = Num rem 100,
  N = if N0 > 19 -> N0 rem 10; true -> N0 end,
  case N of
    1 -> lists:nth(1, Words);
    2 -> lists:nth(2, Words);
    3 -> lists:nth(2, Words);
    4 -> lists:nth(2, Words);
    _ -> lists:nth(3, Words)
  end.

$ erl
Erlang/OTP 22 [erts-10.4] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]

Eshell V10.4  (abort with ^G)
1> c(dd).
{ok,dd}
2> dd:do(1572078000).
49 хвилин назад
ok
3> dd:do(1572078000 - 60*60).
1 годину назад
ok
4> dd:do(1572078000 - 60 * 60 * 24).
1 день назад
ok


5> dd:do(1572078000 - 60 * 60 * 24 * 365).
1 рік назад
ok
6> dd:do(1572078000 + 777777).
Назад у майбутнє!
ok
7> dd:do({{2018,12,23},{12,45,32}}).
10 місяців назад
ok
8> dd:do({{2015,12,23},{12,45,32}}).
3 роки назад
ok
9> dd:do({{2019,10,23},{12,45,32}}).
2 дні назад
ok

10> dd:do({{2019,10,26},{12,45,32}}).
Назад у майбутнє!
ok
11> dd:do("test99").
Ви щось переплутали!
ok

extern crate chrono; //for UNIX timestamp
use chrono::{Local, TimeZone, Duration, NaiveDateTime};

fn ago(timestamp: i64) -> String {
    let now = Local::now();
    let datetime = now.timezone().from_local_datetime(
      &NaiveDateTime::from_timestamp(timestamp, 0))
      .unwrap();
    
    match now - datetime {
        duration if duration>Duration::days(365) =>
            format!("{} р.",duration.num_days()%365),
        duration if duration>Duration::days(30) =>
            format!("{} м.",duration.num_days()%30),
        duration if duration>Duration::days(1) =>
            format!("{} д.",duration.num_days()),
        duration if duration>Duration::hours(1) =>
            format!("{} г.",duration.num_hours()),
        duration if duration>Duration::minutes(1) =>
            format!("{} хв.",duration.num_minutes()),
        _ => String::from("Щойно!"),
    }
}


fn main() {
    let now = Local::now();
    //taking slightly more
    let five_minutes = (now - Duration::minutes(5) ).timestamp();
    let two_hours    = (now - Duration::hours(2)   ).timestamp();
    let ten_days     = (now - Duration::days(10)   ).timestamp();
    let three_months = (now - Duration::days(3*31) ).timestamp();
    let four_years   = (now - Duration::days(4*366)).timestamp();
    
    for &span in &[five_minutes, two_hours, ten_days, three_months, four_years] {
        println!("Timestamp: {} Ago: {}", span, ago(span));
    }
}

Timestamp: 1572104887 Ago: 5 хв.
Timestamp: 1572097987 Ago: 2 г.
Timestamp: 1571241187 Ago: 10 д.
Timestamp: 1564069987 Ago: 3 м.
Timestamp: 1445615587 Ago: 4 р.