-module(iso8601).

-export([add_time/4,
         add_days/2,
         add_months/2,
         add_years/2,
         subtract_time/4,
         format/1,
         parse/1,
         parse_exact/1,
         parse_duration/1,
         apply_duration/2]).

-define(MIDNIGHT, {0,0,0}).
-define(NOON, {12,0,0}).
-define(TEATIME, {16,0,0}).
-define(V, proplists:get_value).

%%----------------------------------------------------------------------
%% Types
%%----------------------------------------------------------------------

-export_type([timestamp/0, year/0, month/0, day/0, hour/0, minute/0, second/0]).

-type option(T) :: undefined | T.

%% This group of types is from calendar.erl; we need to use some of them
%% for this  lib, but thought it might be nice to provide the rest to users.
-type year()     :: non_neg_integer().
-type month()    :: 1..12.
-type day()      :: 1..31.
-type hour()     :: 0..23.
-type minute()   :: 0..59.
-type second()   :: 0..59.

-type datetime() :: {calendar:date(), {hour(),
                                       minute(),
                                       second() | float()}}.
-type datetime_plist() :: list({atom(), integer()}).
-type timestamp() :: {MegaSecs::integer(),
                      Secs::integer(),
                      MicroSecs::integer() | float()}.

%%----------------------------------------------------------------------
%% API
%%----------------------------------------------------------------------

-spec add_time (calendar:datetime(), integer(), integer(), integer())
                -> calendar:datetime().
%% @doc Add some time to the supplied `calendar:datetime()'.
add_time({_, _, _}=Timestamp, H, M, S) ->
    add_time(calendar:now_to_datetime(Timestamp), H, M, S);
add_time(Datetime, H, M, S) ->
    apply_offset(Datetime, H, M, S).

-spec add_days (datetime() | timestamp(), integer()) -> datetime().
%% @doc Add some days to the supplied `datetime()'.
add_days({_, _, _}=Timestamp, D) ->
    add_days(calendar:now_to_datetime(Timestamp), D);
add_days(Datetime,  D) ->
    apply_days_offset(Datetime, D).

-spec add_months (datetime() | timestamp(), integer()) -> datetime().
%% @doc Add some months to the supplied `datetime()'.
add_months({_, _, _}=Timestamp, M) ->
    add_months(calendar:now_to_datetime(Timestamp), M);
add_months(Datetime,  M) ->
    apply_months_offset(Datetime, M).

-spec add_years (datetime() | timestamp(), integer()) -> datetime().
%% @doc Add some years to the supplied `datetime()'.
add_years({_, _, _}=Timestamp, Y) ->
        add_years(calendar:now_to_datetime(Timestamp), Y);
add_years(Datetime,  Y) ->
    apply_years_offset(Datetime, Y).

-spec subtract_time (calendar:datetime(), integer(), integer(), integer())
                    -> calendar:datetime().
%% @doc Subtract some time from the supplied `calendar:datetime()'.
subtract_time(Datetime, H, M, S) ->
    apply_offset(Datetime, -H, -M, -S).

-spec format (datetime() | timestamp()) -> binary().
%% @doc Convert a `util:timestamp()' or a calendar-style `{date(), time()}'
%% tuple to an ISO 8601 formatted string. Note that this function always
%% returns a string with no offset (i.e., ending in "Z").
format({_,_,_}=Timestamp) ->
    format(calendar:now_to_datetime(Timestamp));
format({{Y,Mo,D}, {H,Mn,S}}) when is_float(S) ->
    FmtStr = "~4.10.0B-~2.10.0B-~2.10.0BT~2.10.0B:~2.10.0B:~9.6.0fZ",
    IsoStr = io_lib:format(FmtStr, [Y, Mo, D, H, Mn, S]),
    list_to_binary(IsoStr);
format({{Y,Mo,D}, {H,Mn,S}}) ->
    FmtStr = "~4.10.0B-~2.10.0B-~2.10.0BT~2.10.0B:~2.10.0B:~2.10.0BZ",
    IsoStr = io_lib:format(FmtStr, [Y, Mo, D, H, Mn, S]),
    list_to_binary(IsoStr).

-spec parse (iodata()) -> calendar:datetime().
%% @doc Convert an ISO 8601 formatted string to a `{date(), time()}'
parse(Bin) when is_binary(Bin) ->
    parse(binary_to_list(Bin));
parse(Str) ->
    {{Date, {H, M, S}}, Subsecond} = year(Str, []),
    {Date, {H, M, S + trunc(Subsecond)}}.

-spec parse_exact (iodata()) -> calendar:datetime().
%% @doc Convert an ISO 8601 formatted string to a `{date(), time()}'
%% tuple with seconds precision to 3 decimal places
parse_exact(Bin) when is_binary(Bin) ->
    parse_exact(binary_to_list(Bin));
parse_exact(Str) ->
    {{Date, {H, M, S}}, SecondsDecimal} = year(Str, []),
    {Date, {H, M, S + SecondsDecimal}}.

-spec gi(string()) ->integer().
%doc get string and return integer part or 0 on error
gi(DS)->
   {Int, _Rest} = string:to_integer(DS),
    case Int of
    error->0;
    _->Int
    end.

-spec parse_duration(string()) ->datetime_plist().
%% @doc Convert an ISO 8601 Durations string to a
parse_duration(Bin) when is_binary(Bin)-> %TODO extended format
    parse_duration(binary_to_list(Bin));
parse_duration(Str) ->
    case re:run(Str, "^(?<sign>-|\\+)?P"
    "(?:(?<years>[0-9]+)Y)?"
    "(?:(?<months>[0-9]+)M)?"
    "(?:(?<days>[0-9]+)D)?"
    "(T(?:(?<hours>[0-9]+)H)?"
    "(?:(?<minutes>[0-9]+)M)?"
    "(?:(?<seconds>[0-9]+(?:\\.[0-9]+)?)S)?)?$",
    [{capture, [sign, years, months, days, hours, minutes, seconds], list}]) of
    {match, [Sign, Years, Months, Days, Hours, Minutes, Seconds]} ->
    [{sign, Sign}, {years, gi(Years)}, {months, gi(Months)},
     {days, gi(Days)}, {hours, gi(Hours)}, {minutes, gi(Minutes)},
     {seconds, gi(Seconds)}];
    nomatch -> error(badarg)
    end.

-spec apply_duration(datetime(), string()) -> datetime().
%% @doc Return new datetime after apply duration.
apply_duration(Datetime, Duration) ->
    [{sign, _S}, {years, Y}, {months, M}, {days, D}, {hours, H},
     {minutes, MM}, {seconds, SS}] = parse_duration(Duration),
    D1 = apply_years_offset(Datetime, Y),
    D2 = apply_months_offset(D1, M),
    D3 = apply_days_offset(D2, D),
    apply_offset(D3, H, MM, SS).

%% Private functions

year([Y1,Y2,Y3,Y4|Rest], Acc) ->
    acc([Y1,Y2,Y3,Y4], Rest, year, Acc, fun month_or_week/2);
year(_, _) ->
    error(badarg).

month_or_week([], Acc) ->
    datetime(Acc);
month_or_week([$-,$W,W1,W2|Rest], Acc) ->
    acc([W1,W2], Rest, week, Acc, fun week_day/2);
month_or_week([$-,D1,D2,D3], Acc) ->
    %% ordinal date, no time
    io:format("Ordinal date, no time!~n"),
    acc_ordinal_date(D1, D2, D3, [], Acc, fun hour/2);
month_or_week([$-,D1,D2,D3,$T|Rest], Acc) ->
    %% ordinal date with time
    io:format("Ordinal date, time is ~p!~n", [Rest]),
    acc_ordinal_date(D1, D2, D3, [$T|Rest], Acc, fun hour/2);
month_or_week([$-,M1,M2|Rest], Acc) ->
    acc([M1,M2], Rest, month, Acc, fun month_day/2);
month_or_week([$W,W1,W2|Rest], Acc) ->
    acc([W1,W2], Rest, week, Acc, fun week_day_no_hyphen/2);
month_or_week([M1,M2|Rest], Acc) ->
    acc([M1,M2], Rest, month, Acc, fun month_day_no_hyphen/2);
month_or_week(_, _) ->
    error(badarg).

week_day([], Acc) ->
    datetime(Acc);
week_day([$-,D|Rest], Acc) ->
    acc([D], Rest, week_day, Acc, fun hour/2);
week_day(_, _) ->
    error(badarg).

week_day_no_hyphen([], Acc) ->
    datetime(Acc);
week_day_no_hyphen([D|Rest], Acc) ->
    acc([D], Rest, week_day, Acc, fun hour/2);
week_day_no_hyphen(_, _) ->
    error(badarg).

month_day([], Acc) ->
    datetime(Acc);
month_day([$-,D1,D2|Rest], Acc) ->
    acc([D1,D2], Rest, month_day, Acc, fun hour/2);
month_day(_, _) ->
    error(badarg).

month_day_no_hyphen([], _) ->
    error(badarg); % omission of day disallowed by spec in this case
month_day_no_hyphen([D1,D2|Rest], Acc) ->
    acc([D1,D2], Rest, month_day, Acc, fun hour/2);
month_day_no_hyphen(_, _) ->
    error(badarg).

hour([], Acc) ->
    datetime(Acc);
hour([$T,H1,H2,$.|Rest], Acc) ->
    acc([H1,H2], Rest, hour, Acc, fun hour_decimal/2);
hour([$T,H1,H2,$,|Rest], Acc) ->
    acc([H1,H2], Rest, hour, Acc, fun hour_decimal/2);
hour([$T,H1,H2|Rest], Acc) ->
    acc([H1,H2], Rest, hour, Acc, fun minute/2);
hour(_, _) ->
    error(badarg).

hour_decimal(Str, Acc) ->
    decimal(Str, Acc, hour_decimal).

minute([], Acc) ->
    datetime(Acc);
minute([$:,M1,M2,$.|Rest], Acc) ->
    acc([M1,M2], Rest, minute, Acc, fun minute_decimal/2);
minute([$:,M1,M2,$,|Rest], Acc) ->
    acc([M1,M2], Rest, minute, Acc, fun minute_decimal/2);
minute([$:,M1,M2|Rest], Acc) ->
    acc([M1,M2], Rest, minute, Acc, fun second/2);
minute([M1,M2,$.|Rest], Acc) ->
    acc([M1,M2], Rest, minute, Acc, fun minute_decimal/2);
minute([M1,M2,$,|Rest], Acc) ->
    acc([M1,M2], Rest, minute, Acc, fun minute_decimal/2);
minute([M1,M2|Rest], Acc) ->
    acc([M1,M2], Rest, minute, Acc, fun second_no_colon/2);
minute(_, _) ->
    error(badarg).

minute_decimal(Str, Acc) ->
    decimal(Str, Acc, minute_decimal).

second([], Acc) ->
    datetime(Acc);
second([$:,S1,S2,$.|Rest], Acc) ->
    acc([S1,S2], Rest, second, Acc, fun second_decimal/2);
second([$:,S1,S2,$,|Rest], Acc) ->
    acc([S1,S2], Rest, second, Acc, fun second_decimal/2);
second([$:,S1,S2|Rest], Acc) ->
    acc([S1,S2], Rest, second, Acc, fun offset_hour/2);
second(_, _) ->
    error(badarg).

second_no_colon([], Acc) ->
    datetime(Acc);
second_no_colon([S1,S2,$.|Rest], Acc) ->
    acc([S1,S2], Rest, second, Acc, fun second_decimal/2);
second_no_colon([S1,S2,$,|Rest], Acc) ->
    acc([S1,S2], Rest, second, Acc, fun second_decimal/2);
second_no_colon([S1,S2|Rest], Acc) ->
    acc([S1,S2], Rest, second, Acc, fun offset_hour/2);
second_no_colon(_, _) ->
    error(badarg).

second_decimal(Str, Acc) ->
    decimal(Str, Acc, second_decimal).

decimal([], _, _) ->
    error(badarg);
decimal(Str, Acc, Key) ->
    F = fun(X) when is_integer(X), X >= $0, X =< $9 ->
                true;
           (_) ->
                false
        end,
    {Parts, Rest} = lists:splitwith(F, Str),
    acc_float([$0,$.|Parts], Rest, Key, Acc, fun offset_hour/2).

offset_hour([], Acc) ->
    datetime(Acc);
offset_hour([$Z], Acc) ->
    datetime(Acc);
offset_hour([$+,H1,H2|Rest], Acc) ->
    acc([H1,H2], Rest, offset_hour, Acc, fun offset_minute/2);
offset_hour([$-,H1,H2|Rest], Acc) ->
    acc([H1,H2], Rest, offset_hour, [{offset_sign, -1}|Acc], fun offset_minute/2);
offset_hour(_, _) ->
    error(badarg).

offset_minute([], Acc) ->
    datetime(Acc);
offset_minute([$:,M1,M2], Acc) ->
    acc([M1,M2], [], offset_minute, Acc, fun datetime/2);
offset_minute([M1,M2], Acc) ->
    acc([M1,M2], [], offset_minute, Acc, fun datetime/2);
offset_minute(_, _) ->
    error(badarg).

acc(IntStr, Rest, Key, Acc, NextF) ->
    Acc1 = [{Key, list_to_integer(IntStr)}|Acc],
    NextF(Rest, Acc1).

acc_float(FloatStr, Rest, Key, Acc, NextF) ->
    Acc1 = [{Key, list_to_float(FloatStr)}|Acc],
    NextF(Rest, Acc1).

acc_ordinal_date(D1, D2, D3, Rest, Acc, NextF) ->
    Days = list_to_integer([D1, D2, D3]),
    Days > 0 orelse error(badarg),
    Year = ?V(year, Acc),
    Year =/= undefined orelse error(badarg),
    DaysInMonths = days_in_months_for_year(Year),
    { Month, Day } = unpack_ordinal_date(Days, DaysInMonths),
    Acc1 = [{ month, Month }, { month_day, Day }|Acc],
    NextF(Rest, Acc1).

unpack_ordinal_date(Days, DaysInMonths) -> unpack_ordinal_date(1, Days, DaysInMonths).
unpack_ordinal_date(_Month, _Days, []) -> error(badarg), { 0, 0 };
unpack_ordinal_date(_Month, Days, _DaysInMonths) when Days < 0 -> error(badarg), { 0, 0 };
unpack_ordinal_date(Month, Days, [DaysThisMonth|DaysInMonths]) ->
    case Days > DaysThisMonth of
        true -> unpack_ordinal_date(Month + 1, Days - DaysThisMonth, DaysInMonths);
        _ -> { Month, Days }
    end.

days_in_months_for_year(Year) ->
    case is_leap_year(Year) of
        true -> [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
        false -> [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
    end.

is_leap_year(Year) ->
    case Year rem 100 of
         0 -> Year rem 400 =:= 0;
         _ ->  Year rem 4 =:= 0
    end.

add_decimal(Datetime, Plist) ->
    HDecimal = ?V(hour_decimal, Plist, 0.0),
    MDecimal = ?V(minute_decimal, Plist, 0.0),
    apply_offset(Datetime, HDecimal, MDecimal, 0.0).

datetime(Plist) ->
    {Date, WeekOffsetH} = make_date(Plist),
    Time = {?V(hour, Plist, 0), ?V(minute, Plist, 0), ?V(second, Plist, 0)},
    Datetime = add_decimal({Date, Time}, Plist),
    OffsetSign = ?V(offset_sign, Plist, 1),
    OffsetH = -1 * OffsetSign * ?V(offset_hour, Plist, 0),
    OffsetM = -1 * OffsetSign * ?V(offset_minute, Plist, 0),
    { apply_offset(Datetime, WeekOffsetH+OffsetH, OffsetM, 0), ?V(second_decimal, Plist, 0.0) }.


datetime(_, Plist) ->
    datetime(Plist).

-spec make_date (datetime_plist())
                -> {Date::calendar:date(), WeekOffsetH::non_neg_integer()}.
%% @doc Return a `tuple' containing a date and, if the date is in week format,
%% an offset in hours that can be applied to the date to adjust it to midnight
%% of the day specified. If month format is used, the offset will be zero.
make_date(Plist) ->
    Year = ?V(year, Plist),
    Year =/= undefined orelse error(badarg),
    make_date(Year, ?V(month, Plist, 1), ?V(week, Plist), Plist).

-spec make_date (non_neg_integer(),
                 option(pos_integer()),
                 option(pos_integer()),
                 datetime_plist())
                -> {calendar:date(), non_neg_integer()}.
%% @doc Return a `tuple' containing a date and - if the date is in week format
%% (i.e., `Month' is undefined, `Week' is not) - an offset in hours that can be
%% applied to the date to adjust it to midnight of the day specified. If month
%% format is used (i.e., `Week' is undefined, `Month' is not), the offset will
%% be zero.
make_date(Year, Month, undefined, Plist) ->
    Date = {Year, Month, ?V(month_day, Plist, 1)},
    {Date, 0};
make_date(Year, _, Week, Plist) ->
    Weekday = ?V(week_day, Plist, 1),
    OffsetH = ((Week-1)*7 + (Weekday-1))*24, % week/weekday offset in hours
    {date_at_w01_1(Year), OffsetH}.

-spec date_at_w01_1(pos_integer()) -> calendar:date().
%% @doc Calculate the `calendar:date()' at ISO week 1, day 1 in the supplied
%% year.
date_at_w01_1(Year) ->
    case calendar:day_of_the_week({Year,1,1}) of
        1 -> {Year, 1, 1};
        2 -> {Year-1, 12, 31};
        3 -> {Year-1, 12, 30};
        4 -> {Year-1, 12, 29};
        5 -> {Year, 1, 4};
        6 -> {Year, 1, 3};
        7 -> {Year, 1, 2}
    end.

-spec apply_offset (calendar:datetime(), number(), number(), number())
            -> calendar:datetime().
%% @doc Add the specified number of hours, minutes and seconds to `Datetime'.
apply_offset(Datetime, H, M, S) ->
    OffsetS = S + (60 * (M + (60 * H))),
    Gs = round(OffsetS) + calendar:datetime_to_gregorian_seconds(Datetime),
    calendar:gregorian_seconds_to_datetime(Gs).

-spec apply_months_offset (datetime(), number()) -> datetime().
%% @doc Add the specified number of months to `Datetime'.
apply_months_offset(Datetime, 0) ->
    Datetime;
apply_months_offset(Datetime, AM) ->
    {{Y, M, D}, {H, MM, S}} = Datetime,
    AY = (Y*12)+M+AM,
    Year = ((AY-1) div 12),
    Month =
        case (AY rem 12) of
            0 -> 12;
            Result -> Result
        end,
    find_last_valid_date({{Year, Month, D}, {H, MM, S}}).

-spec apply_days_offset (datetime(), number()) -> datetime().
%% @doc Add the specified days to `Datetime'.
apply_days_offset(Datetime, AD) ->
    {{Y, M, D}, {H, MM, S}} = Datetime,
    DaysTotal=calendar:date_to_gregorian_days({Y, M, D})+AD,
    {calendar:gregorian_days_to_date(DaysTotal), {H, MM, S}}.

-spec apply_years_offset (datetime(), number()) -> datetime().
%% @doc Add the specified years to `Datetime'.
apply_years_offset(Datetime, AY) ->
    {{Y, M, D}, {H, MM, S}} = Datetime,
    {{Y+AY, M, D}, {H, MM, S}}.

-spec find_last_valid_date(datetime()) -> datetime().
%% @doc Decrease days until found valid date'.
find_last_valid_date(Datetime)->
    {{Y, M, D}, {H, MM, S}} = Datetime,
    case calendar:valid_date({Y, M, D}) of
       true -> Datetime;
       false -> find_last_valid_date({{Y, M, D-1}, {H, MM, S}})
    end.