-module(gleam@iterator).
-compile(no_auto_import).

-export([unfold/2, repeatedly/1, repeat/1, from_list/1, fold/3, run/1, to_list/1, step/1, take/2, drop/2, map/2, append/2, flatten/1, flat_map/2, filter/2, cycle/1, range/2, find/2, index/1, iterate/2, take_while/2, drop_while/2, scan/3, zip/2]).
-export_type([action/1, iterator/1, step/2]).

-type action(AYJ) :: stop | {continue, AYJ, fun(() -> action(AYJ))}.

-opaque iterator(AYK) :: {iterator, fun(() -> action(AYK))}.

-type step(AYL, AYM) :: {next, AYL, AYM} | done.

-spec do_unfold(AYP, fun((AYP) -> step(AYQ, AYP))) -> fun(() -> action(AYQ)).
do_unfold(Initial, F) ->
    fun() -> case F(Initial) of
            {next, X, Acc} ->
                {continue, X, do_unfold(Acc, F)};

            done ->
                stop
        end end.

-spec unfold(AYU, fun((AYU) -> step(AYV, AYU))) -> iterator(AYV).
unfold(Initial, F) ->
    {iterator, do_unfold(Initial, F)}.

-spec repeatedly(fun(() -> AYZ)) -> iterator(AYZ).
repeatedly(F) ->
    unfold(nil, fun(_) -> {next, F(), nil} end).

-spec repeat(AZB) -> iterator(AZB).
repeat(X) ->
    repeatedly(fun() -> X end).

-spec from_list(list(AZD)) -> iterator(AZD).
from_list(List) ->
    Yield = fun(Acc) -> case Acc of
            [] ->
                done;

            [Head | Tail] ->
                {next, Head, Tail}
        end end,
    unfold(List, Yield).

-spec do_fold(fun(() -> action(AZG)), AZI, fun((AZG, AZI) -> AZI)) -> AZI.
do_fold(Continuation, Initial, F) ->
    case Continuation() of
        {continue, Element, Iterator} ->
            do_fold(Iterator, F(Element, Initial), F);

        stop ->
            Initial
    end.

-spec fold(iterator(AZJ), AZL, fun((AZJ, AZL) -> AZL)) -> AZL.
fold(Iterator, Initial, F) ->
    do_fold(erlang:element(2, Iterator), Initial, F).

-spec run(iterator(any())) -> nil.
run(Iterator) ->
    fold(Iterator, nil, fun(_, _) -> nil end).

-spec to_list(iterator(AZO)) -> list(AZO).
to_list(Iterator) ->
    gleam@list:reverse(fold(Iterator, [], fun(E, Acc) -> [E | Acc] end)).

-spec step(iterator(AZR)) -> step(AZR, iterator(AZR)).
step(Iterator) ->
    case (erlang:element(2, Iterator))() of
        stop ->
            done;

        {continue, E, A} ->
            {next, E, {iterator, A}}
    end.

-spec do_take(fun(() -> action(AZW)), integer(), list(AZW)) -> list(AZW).
do_take(Continuation, Desired, Acc) ->
    case Desired > 0 of
        true ->
            case Continuation() of
                {continue, Element, Iterator} ->
                    do_take(Iterator, Desired - 1, [Element | Acc]);

                stop ->
                    gleam@list:reverse(Acc)
            end;

        false ->
            gleam@list:reverse(Acc)
    end.

-spec take(iterator(BAA), integer()) -> list(BAA).
take(Iterator, Desired) ->
    do_take(erlang:element(2, Iterator), Desired, []).

-spec do_drop(fun(() -> action(BAD)), integer()) -> fun(() -> action(BAD)).
do_drop(Continuation, Desired) ->
    case Desired > 0 of
        true ->
            case Continuation() of
                {continue, _, Iterator} ->
                    do_drop(Iterator, Desired - 1);

                stop ->
                    fun() -> stop end
            end;

        false ->
            Continuation
    end.

-spec drop(iterator(BAG), integer()) -> iterator(BAG).
drop(Iterator, Desired) ->
    {iterator, do_drop(erlang:element(2, Iterator), Desired)}.

-spec do_map(fun(() -> action(BAJ)), fun((BAJ) -> BAL)) -> fun(() -> action(BAL)).
do_map(Continuation, F) ->
    fun() -> case Continuation() of
            {continue, E, Continuation@1} ->
                {continue, F(E), do_map(Continuation@1, F)};

            stop ->
                stop
        end end.

-spec map(iterator(BAN), fun((BAN) -> BAP)) -> iterator(BAP).
map(Iterator, F) ->
    {iterator, do_map(erlang:element(2, Iterator), F)}.

-spec do_append(fun(() -> action(BAR)), fun(() -> action(BAR))) -> fun(() -> action(BAR)).
do_append(First, Second) ->
    fun() -> case First() of
            {continue, E, First@1} ->
                {continue, E, do_append(First@1, Second)};

            stop ->
                Second()
        end end.

-spec append(iterator(BAV), iterator(BAV)) -> iterator(BAV).
append(First, Second) ->
    {iterator, do_append(erlang:element(2, First), erlang:element(2, Second))}.

-spec do_flatten(fun(() -> action(iterator(BAZ)))) -> fun(() -> action(BAZ)).
do_flatten(Continuation) ->
    fun() -> case Continuation() of
            {continue, E, Continuation@1} ->
                (do_append(erlang:element(2, E), do_flatten(Continuation@1)))();

            stop ->
                stop
        end end.

-spec flatten(iterator(iterator(BBD))) -> iterator(BBD).
flatten(Iterator) ->
    {iterator, do_flatten(erlang:element(2, Iterator))}.

-spec flat_map(iterator(BBH), fun((BBH) -> iterator(BBJ))) -> iterator(BBJ).
flat_map(Iterator, F) ->
    flatten(map(Iterator, F)).

-spec do_filter(fun(() -> action(BBM)), fun((BBM) -> boolean())) -> fun(() -> action(BBM)).
do_filter(Continuation, Predicate) ->
    fun() -> case Continuation() of
            {continue, E, Iterator} ->
                case Predicate(E) of
                    true ->
                        {continue, E, do_filter(Iterator, Predicate)};

                    false ->
                        (do_filter(Iterator, Predicate))()
                end;

            stop ->
                stop
        end end.

-spec filter(iterator(BBP), fun((BBP) -> boolean())) -> iterator(BBP).
filter(Iterator, Predicate) ->
    {iterator, do_filter(erlang:element(2, Iterator), Predicate)}.

-spec do_cycle(fun(() -> action(BBS)), fun(() -> action(BBS))) -> fun(() -> action(BBS)).
do_cycle(Next, Reset) ->
    fun() -> case Next() of
            {continue, E, Iterator} ->
                {continue, E, do_cycle(Iterator, Reset)};

            stop ->
                (do_cycle(Reset, Reset))()
        end end.

-spec cycle(iterator(BBW)) -> iterator(BBW).
cycle(Iterator) ->
    {iterator,
     do_cycle(erlang:element(2, Iterator), erlang:element(2, Iterator))}.

-spec do_range(integer(), integer(), integer()) -> fun(() -> action(integer())).
do_range(Current, Limit, Inc) ->
    case Current =:= Limit of
        true ->
            fun() -> stop end;

        false ->
            fun() ->
                {continue, Current, do_range(Current + Inc, Limit, Inc)}
            end
    end.

-spec range(integer(), integer()) -> iterator(integer()).
range(Start, Stop) ->
    {iterator, do_range(Start, Stop, case Start < Stop of
             true ->
                 1;

             false ->
                 -1
         end)}.

-spec find(iterator(BCE), fun((BCE) -> boolean())) -> {ok, BCE} | {error, nil}.
find(Haystack, Is_desired) ->
    case (erlang:element(2, Haystack))() of
        {continue, Element, Continuation} ->
            case Is_desired(Element) of
                true ->
                    {ok, Element};

                false ->
                    find({iterator, Continuation}, Is_desired)
            end;

        stop ->
            {error, nil}
    end.

-spec do_index(fun(() -> action(BCI)), integer()) -> fun(() -> action({integer(),
                                                                       BCI})).
do_index(Continuation, Next) ->
    fun() -> case Continuation() of
            {continue, E, Continuation@1} ->
                {continue, {Next, E}, do_index(Continuation@1, Next + 1)};

            stop ->
                stop
        end end.

-spec index(iterator(BCL)) -> iterator({integer(), BCL}).
index(Iterator) ->
    {iterator, do_index(erlang:element(2, Iterator), 0)}.

-spec iterate(BCO, fun((BCO) -> BCO)) -> iterator(BCO).
iterate(Initial, F) ->
    unfold(Initial, fun(Element) -> {next, Element, F(Element)} end).

-spec do_take_while(fun(() -> action(BCQ)), fun((BCQ) -> boolean())) -> fun(() -> action(BCQ)).
do_take_while(Continuation, Predicate) ->
    fun() -> case Continuation() of
            stop ->
                stop;

            {continue, E, Next} ->
                case Predicate(E) of
                    false ->
                        stop;

                    true ->
                        {continue, E, do_take_while(Next, Predicate)}
                end
        end end.

-spec do_scan(fun(() -> action(BCT)), BCV, fun((BCT, BCV) -> BCV)) -> fun(() -> action(BCV)).
do_scan(Continuation, Accumulator, F) ->
    fun() -> case Continuation() of
            {continue, El, Next} ->
                Accumulated = F(El, Accumulator),
                {continue, Accumulated, do_scan(Next, Accumulated, F)};

            stop ->
                stop
        end end.

-spec do_zip(fun(() -> action(BCX)), fun(() -> action(BCZ))) -> fun(() -> action({BCX,
                                                                                  BCZ})).
do_zip(Left, Right) ->
    fun() -> case Left() of
            stop ->
                stop;

            {continue, El_left, Next_left} ->
                case Right() of
                    stop ->
                        stop;

                    {continue, El_right, Next_right} ->
                        {continue,
                         {El_left, El_right},
                         do_zip(Next_left, Next_right)}
                end
        end end.

-spec take_while(iterator(BDC), fun((BDC) -> boolean())) -> iterator(BDC).
take_while(Iterator, Predicate) ->
    {iterator, do_take_while(erlang:element(2, Iterator), Predicate)}.

-spec do_drop_while(fun(() -> action(BDF)), fun((BDF) -> boolean())) -> action(BDF).
do_drop_while(Continuation, Predicate) ->
    case Continuation() of
        stop ->
            stop;

        {continue, E, Next} ->
            case Predicate(E) of
                false ->
                    {continue, E, Next};

                true ->
                    do_drop_while(Next, Predicate)
            end
    end.

-spec drop_while(iterator(BDI), fun((BDI) -> boolean())) -> iterator(BDI).
drop_while(Iterator, Predicate) ->
    {iterator,
     fun() -> do_drop_while(erlang:element(2, Iterator), Predicate) end}.

-spec scan(iterator(BDL), BDN, fun((BDL, BDN) -> BDN)) -> iterator(BDN).
scan(Iterator, Initial, F) ->
    {iterator, do_scan(erlang:element(2, Iterator), Initial, F)}.

-spec zip(iterator(BDP), iterator(BDR)) -> iterator({BDP, BDR}).
zip(Left, Right) ->
    {iterator, do_zip(erlang:element(2, Left), erlang:element(2, Right))}.