-module(glisp@parser).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([parse/1]).

-if(?OTP_RELEASE >= 27).
-define(MODULEDOC(Str), -moduledoc(Str)).
-define(DOC(Str), -doc(Str)).
-else.
-define(MODULEDOC(Str), -compile([])).
-define(DOC(Str), -compile([])).
-endif.

?MODULEDOC("// Parses a list of tokens into an abstract syntax tree expression.\n").

-file("src/glisp/parser.gleam", 32).
-spec is_digit(binary()) -> boolean().
is_digit(Token) ->
    gleam@result:is_ok(gleam_stdlib:parse_int(Token)).

-file("src/glisp/parser.gleam", 36).
-spec as_int_or(binary(), integer()) -> integer().
as_int_or(Token, Ex) ->
    gleam@result:unwrap(gleam_stdlib:parse_int(Token), Ex).

-file("src/glisp/parser.gleam", 56).
-spec flip(list(glisp@ast:expr())) -> list(glisp@ast:expr()).
flip(Arr) ->
    lists:reverse(Arr).

-file("src/glisp/parser.gleam", 60).
-spec parse_list(list(glisp@ast:expr()), list(binary())) -> {ok,
        {glisp@ast:expr(), list(binary())}} |
    {error, binary()}.
parse_list(Acc, Tokens) ->
    case Tokens of
        [] ->
            {error, <<"Unclosed list"/utf8>>};

        [Head | Rest] ->
            case Head of
                <<")"/utf8>> ->
                    {ok, {{list, flip(Acc)}, Rest}};

                <<"("/utf8>> ->
                    case parse_list([], Rest) of
                        {ok, {Inner_expr, Remaining}} ->
                            parse_list([Inner_expr | Acc], Remaining);

                        {error, Msg} ->
                            {error, Msg}
                    end;

                _ ->
                    case parse_tokens([Head]) of
                        {ok, {Item, _}} ->
                            parse_list([Item | Acc], Rest);

                        {error, Msg@1} ->
                            {error, Msg@1}
                    end
            end
    end.

-file("src/glisp/parser.gleam", 40).
-spec parse_tokens(list(binary())) -> {ok, {glisp@ast:expr(), list(binary())}} |
    {error, binary()}.
parse_tokens(Tokens) ->
    case Tokens of
        [] ->
            {error, <<"Unexpected EOF"/utf8>>};

        [Head | Rest] ->
            case Head of
                <<"("/utf8>> ->
                    parse_list([], Rest);

                <<")"/utf8>> ->
                    {error, <<"Unexpected ')'"/utf8>>};

                _ ->
                    case is_digit(Head) of
                        true ->
                            {ok, {{number, as_int_or(Head, 0)}, Rest}};

                        false ->
                            {ok, {{atom, Head}, Rest}}
                    end
            end
    end.

-file("src/glisp/parser.gleam", 24).
?DOC(
    " This function takes a list of string tokens and attempts to parse them\n"
    " into a structured expression according to a simple Lisp-like syntax.\n"
    " It can recognize atoms, numbers, and nested lists.\n"
    "\n"
    " ## Examples\n"
    "\n"
    " ```\n"
    " parse([\"(\", \"hello\", \"world\", \")\"])\n"
    " // -> Ok(List([Atom(\"hello\"), Atom(\"world\")]))\n"
    "\n"
    " parse([\"42\"])\n"
    " // -> Ok(Number(42))\n"
    "\n"
    " parse([\"missing_paren\", \"(\"])\n"
    " // -> Error(\"Unclosed list\")\n"
    " ```\n"
).
-spec parse(list(binary())) -> {ok, glisp@ast:expr()} | {error, binary()}.
parse(Tokens) ->
    case parse_tokens(Tokens) of
        {ok, {Expr, []}} ->
            {ok, Expr};

        {ok, {_, _}} ->
            {error, <<"Unexpected tokens after valid expression"/utf8>>};

        {error, Msg} ->
            {error, Msg}
    end.