-module(facet).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([parse/1]).
-export_type([error/0, format/0, frontmatter/0, document/0]).

-type error() :: empty | {parse_error, binary()}.

-type format() :: toml | json | yaml.

-type frontmatter() :: {frontmatter, binary(), format()}.

-type document() :: {document, gleam@option:option(frontmatter()), binary()}.

-spec grab_frontmatter(list(binary()), list(binary())) -> {ok, document()} |
    {error, error()}.
grab_frontmatter(Input, Frontmatter) ->
    case Input of
        [] ->
            {error, {parse_error, <<"expected ending delimitor"/utf8>>}};

        [<<"+++"/utf8>> | Rest] ->
            {ok,
                {document,
                    {some,
                        {frontmatter,
                            gleam@string:join(Frontmatter, <<"\n"/utf8>>),
                            toml}},
                    gleam@string:join(Rest, <<"\n"/utf8>>)}};

        [<<"}"/utf8>> | Rest@1] ->
            {ok,
                {document,
                    {some,
                        {frontmatter,
                            gleam@string:join(
                                lists:append(Frontmatter, [<<"}"/utf8>>]),
                                <<"\n"/utf8>>
                            ),
                            json}},
                    gleam@string:join(Rest@1, <<"\n"/utf8>>)}};

        [<<"---"/utf8>> | Rest@2] ->
            {ok,
                {document,
                    {some,
                        {frontmatter,
                            gleam@string:join(Frontmatter, <<"\n"/utf8>>),
                            yaml}},
                    gleam@string:join(Rest@2, <<"\n"/utf8>>)}};

        [Line | Rest@3] ->
            grab_frontmatter(Rest@3, lists:append(Frontmatter, [Line]))
    end.

-spec parse(binary()) -> {ok, document()} | {error, error()}.
parse(In) ->
    Lines = begin
        _pipe = In,
        gleam@string:split(_pipe, <<"\n"/utf8>>)
    end,
    case Lines of
        [] ->
            {error, empty};

        [<<"+++"/utf8>> | Rest] ->
            grab_frontmatter(Rest, []);

        [<<"{"/utf8>> | Rest@1] ->
            grab_frontmatter(Rest@1, [<<"{"/utf8>>]);

        [<<"---"/utf8>> | Rest@2] ->
            grab_frontmatter(Rest@2, []);

        Rest@3 ->
            {ok, {document, none, gleam@string:join(Rest@3, <<"\n"/utf8>>)}}
    end.