-module(gleam@option).
-compile([no_auto_import, nowarn_unused_vars]).

-export([is_some/1, is_none/1, to_result/2, from_result/1, unwrap/2, lazy_unwrap/2, map/2, flatten/1, then/2, 'or'/2, lazy_or/2, all/1, values/1]).
-export_type([option/1]).

-type option(FG) :: {some, FG} | none.

-spec is_some(option(any())) -> boolean().
is_some(Option) ->
    Option /= none.

-spec is_none(option(any())) -> boolean().
is_none(Option) ->
    Option =:= none.

-spec to_result(option(FW), FZ) -> {ok, FW} | {error, FZ}.
to_result(Option, E) ->
    case Option of
        {some, A} ->
            {ok, A};

        _ ->
            {error, E}
    end.

-spec from_result({ok, GC} | {error, any()}) -> option(GC).
from_result(Result) ->
    case Result of
        {ok, A} ->
            {some, A};

        _ ->
            none
    end.

-spec unwrap(option(GH), GH) -> GH.
unwrap(Option, Default) ->
    case Option of
        {some, X} ->
            X;

        none ->
            Default
    end.

-spec lazy_unwrap(option(GJ), fun(() -> GJ)) -> GJ.
lazy_unwrap(Option, Default) ->
    case Option of
        {some, X} ->
            X;

        none ->
            Default()
    end.

-spec map(option(GL), fun((GL) -> GN)) -> option(GN).
map(Option, Fun) ->
    case Option of
        {some, X} ->
            {some, Fun(X)};

        none ->
            none
    end.

-spec flatten(option(option(GP))) -> option(GP).
flatten(Option) ->
    case Option of
        {some, X} ->
            X;

        none ->
            none
    end.

-spec then(option(GT), fun((GT) -> option(GV))) -> option(GV).
then(Option, Fun) ->
    case Option of
        {some, X} ->
            Fun(X);

        none ->
            none
    end.

-spec 'or'(option(GY), option(GY)) -> option(GY).
'or'(First, Second) ->
    case First of
        {some, _} ->
            First;

        none ->
            Second
    end.

-spec lazy_or(option(HC), fun(() -> option(HC))) -> option(HC).
lazy_or(First, Second) ->
    case First of
        {some, _} ->
            First;

        none ->
            Second()
    end.

-spec do_all(list(option(FH)), list(FH)) -> option(list(FH)).
do_all(List, Acc) ->
    case List of
        [] ->
            {some, Acc};

        [X | Rest] ->
            Accumulate = fun(Acc@1, Item) -> case {Acc@1, Item} of
                    {{some, Values}, {some, Value}} ->
                        {some, [Value | Values]};

                    {_, _} ->
                        none
                end end,
            Accumulate(do_all(Rest, Acc), X)
    end.

-spec all(list(option(FN))) -> option(list(FN)).
all(List) ->
    do_all(List, []).

-spec do_values(list(option(HG)), list(HG)) -> list(HG).
do_values(List, Acc) ->
    case List of
        [] ->
            Acc;

        [X | Xs] ->
            Accumulate = fun(Acc@1, Item) -> case Item of
                    {some, Value} ->
                        [Value | Acc@1];

                    none ->
                        Acc@1
                end end,
            Accumulate(do_values(Xs, Acc), X)
    end.

-spec values(list(option(HL))) -> list(HL).
values(Options) ->
    do_values(Options, []).