% @doc
% File ::= Block(TopDecl)
-record(ast_file,
        {top_decls = none :: none | [top_decl()]}).


-type ast() :: #ast_file{}
             | top_decl()
             | #ast_nyi{}
             .

%%   Decl ::= 'type'     Id ['(' TVar* ')'] '=' TypeAlias
%%          | 'record'   Id ['(' TVar* ')'] '=' RecordType
%%          | 'datatype' Id ['(' TVar* ')'] '=' DataType
%%          | 'let'      Id [':' Type]      '=' Expr
%%          | (EModifier* 'entrypoint' | FModifier* 'function') Block(FunDecl)
%%          | Using
%-record(ast_type_alias,
%        {name        = none :: none | string(),
%         tvars       = none :: none | [string()],
%         rewrites_to = none :: none | ast_type()}).


-type gulp_target()
    :: ast_file
     | top_decl
     | ast_ct
     | ast_nyi
     .

% gulp means it must consume all input
-spec gulp(AstTarget, SigTokens) -> Perhaps
    when AstTarget :: gulp_target(),
         SigTokens :: [sfc_token()],
         Perhaps   :: {gulp, ast()}
                    | {error, sfc_err()}.

gulp(ast_file, Tokens) ->
    gulp_file(Tokens);
gulp(top_decl, Tokens) ->
    Targets = [ast_ct,
               ast_nyi],
    gulp_oneof(Targets, Tokens);
gulp(ast_ct, Tokens) ->
    gulp_ct(#ast_ct{}, Tokens);
gulp(ast_nyi, Tokens) ->
    {gulp, #ast_nyi{tokens = Tokens}};
gulp({block_of, X}, Tokens) ->
    {barf, ItemChunks, []} = sfc_token_chunks:barf(block_as_items, Tokens),
    gulp_block_of(X, ItemChunks);
gulp(Nyi, Tokens) ->
    Msg = io_lib:format("sfc_ast:gulp/2: unknown target: ~p", [Nyi]),
    Err = #sfc_err{atom   = gulp_nyi,
                   string = Msg,
                   extra = [{target, Nyi}, {tokens, Tokens}]},
    {error, Err}.



% FIXME: payable and main need to be in that order i think
gulp_ct(Ast = #ast_ct{payable = none}, Tokens) ->
    case Tokens of
        [#sfc_token{string = "payable", type = kwd} | NewTokens] ->
            gulp_ct(Ast#ast_ct{payable = payable}, NewTokens);
        _ ->
            gulp_ct(Ast#ast_ct{payable = false}, Tokens)
    end;
gulp_ct(Ast = #ast_ct{main = none}, Tokens) ->
    case Tokens of
        [#sfc_token{string = "main", type = kwd} | NewTokens] ->
            gulp_ct(Ast#ast_ct{main = main}, NewTokens);
        _ ->
            gulp_ct(Ast#ast_ct{main = false}, Tokens)
    end;
gulp_ct(Ast = #ast_ct{contract = none}, Tokens) ->
    case Tokens of
        [#sfc_token{string = "contract", type = kwd} | NewTokens] ->
            gulp_ct(Ast#ast_ct{contract = contract}, NewTokens);
       % FIXME: reject logic applies to choice of branch, therefore
       % should be contained in branchpoint code
        _ ->
            reject
        %[#sfc_token{pos = P, string = S} | _] ->
        %   {error, #sfc_err{atom = no_kwd_contract,
        %                     extra = [{pos, P},
        %                              {expecting, "contract"},
        %                              {got, S},
        %                              {ast, Ast},
        %                              {tokens, Tokens}]}};
        %[] ->
        %   {error, #sfc_err{atom = no_kwd_contract,
        %                     extra = [{pos, none},
        %                              {expecting, "contract"},
        %                              {got, eof},
        %                              {ast, Ast},
        %                              {tokens, Tokens}]}}
    end;
gulp_ct(Ast = #ast_ct{name = none}, Tokens) ->
    case Tokens of
        [#sfc_token{string = Name, type = con} | NewTokens] ->
            gulp_ct(Ast#ast_ct{name = Name}, NewTokens);
        _ ->
            reject
    end;
gulp_ct(Ast = #ast_ct{implements = none}, Tokens) ->
    case slurp_ct_impls(Tokens) of
        {slurp, Names, NewTokens} ->
            gulp_ct(Ast#ast_ct{implements = {':', Names}}, NewTokens);
        reject ->
            gulp_ct(Ast#ast_ct{implements = {':', []}}, Tokens);
        Poison -> Poison
    end;
gulp_ct(Ast = #ast_ct{eq = none}, Tokens) ->
    case Tokens of
        [#sfc_token{string = "=", type = op} | NewTokens] ->
            gulp_ct(Ast#ast_ct{eq = '='}, NewTokens);
        _ ->
            {error, #sfc_err{atom = no_eq}}
    end;
gulp_ct(Ast = #ast_ct{decls = none}, Tokens) ->
    Decls = [gulp(decl, Item) || Item <- sfc_token_chunks:unsafe_block_to_items(Tokens)],
    {gulp, Ast#ast_ct{decls = Decls}};
gulp_ct(_, _) ->
    reject.


slurp_ct_impls([#sfc_token{string = ":", type = op},
                #sfc_token{string = Con1, type = con}
                | Rest]) ->
    slurp_ct_impls2(Rest, [Con1]);
slurp_ct_impls(_) ->
    reject.

slurp_ct_impls2([#sfc_token{string = ",", type = punct},
                 #sfc_token{string = Con1, type = con}
                | Rest],
                Acc) ->
    slurp_ct_impls2(Rest, [Con1 | Acc]);
slurp_ct_impls2(Rest, Names) ->
    {slurp, lists:reverse(Names), Rest}.





-spec gulp_file(SigTokens) -> Perhaps
    when SigTokens :: [sfc_token()],
         Perhaps   :: {gulp, #ast_file{}}
                    | {error, sfc_err()}.
% @private
% `file` enforces that the entire SigTokens is one
% block, chokes otherwise

gulp_file([]) ->
    {error, #sfc_err{atom = empty_file}};
gulp_file(FileTokens = [#sfc_token{pos = FilePos} | _]) ->
    case sfc_token_chunks:barf(block, FileTokens) of
        % happy path: got the whole file back
        {barf, FileTokens, []} ->
            gulp_full_file(FileTokens);
        % sad path: block terminated
        {barf, _, [#sfc_token{pos = EndPos}]} ->
            Msg = io_lib:format("block starting at ~p ends at ~p instead of EOF",
                                [FilePos, EndPos]),
            {error, #sfc_err{atom   = bad_file,
                             string = Msg}};
        Nyi ->
            {error, #sfc_err{atom = bad_file_nyi, extra = Nyi}}
    end.


% FIXME: need to rethink types here in order to handle syntax errors
% from different blocks independently.

% file = block(top_decl)
gulp_full_file(BlockTokens) ->
    ItemChunks = sfc_token_chunks:unsafe_block_to_items(BlockTokens),
    gulp_file_decls([], [], ItemChunks).


gulp_file_decls(Decls, Errs, [DeclTokens | Rest]) ->
    case gulp(top_decl, DeclTokens) of
        {gulp, NewDecl} ->
            gulp_file_decls([NewDecl | Decls], Errs, Rest);
        reject ->
            ErrPos = sfc_token_chunks:start_pos(DeclTokens),
            NewErr = #sfc_err{atom = bad_top_decl,
                              extra = [{tokens, DeclTokens},
                                       {pos, ErrPos}]},
            gulp_file_decls(Decls, [NewErr | Errs], Rest);
        Poison ->
            gulp_file_decls(Decls, [Poison | Errs], Rest)
    end;
% end of block
gulp_file_decls(Decls, _Errs = [], _Input = []) ->
    {gulp, #ast_file{top_decls = lists:reverse(Decls)}};
gulp_file_decls(_Decls, Errs, _Input = []) ->
    {error, #sfc_err{atom = many,
                      extra = Errs}}.