package body Packrat.Lexer.Combinators is


    function Sequence
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result
    is
        Result : Combinator_Result := Create_Result (0, Success, Empty_Array);
        Position : Positive := Start;
    begin
        if Start > Input'Last then
            return Empty_Fail;
        end if;
        for C of Params loop
            if Position > Input'Last then
                Result.Status := Needs_More;
                exit;
            end if;
            Result := Result.Join (C (Input, Position));
            exit when Result.Status = Failure;
            Position := Start + Result.Length;
        end loop;
        return Result;
    end Sequence;


    function Count
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result
    is
        Result : Combinator_Result := Create_Result (0, Success, Empty_Array);
        Position : Positive := Start;
    begin
        if Start > Input'Last then
            return Empty_Fail;
        end if;
        for I in Integer range 1 .. Number loop
            if Position > Input'Last then
                Result.Status := Needs_More;
                exit;
            end if;
            Result := Result.Join (Param (Input, Position));
            exit when Result.Status = Failure;
            Position := Start + Result.Length;
        end loop;
        return Result;
    end Count;


    function Many
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result
    is
        Result : Combinator_Result := Create_Result (0, Success, Empty_Array);
        Temp   : Combinator_Result;
        Position : Positive := Start;
        Counter  : Natural := 0;
    begin
        if Start > Input'Last then
            return Empty_Fail;
        end if;
        loop
            Temp := Param (Input, Position);
            exit when Temp.Status = Failure;
            if Temp.Status = Needs_More then
                Result.Status := Optional_More;
                exit;
            end if;
            Result := Result.Join (Temp);
            Counter := Counter + 1;
            Position := Start + Result.Length;
            if Position > Input'Last then
                Result.Status := Optional_More;
                exit;
            end if;
        end loop;
        if Counter < Minimum then
            if Result.Status = Optional_More then
                Result.Status := Needs_More;
            else
                Result.Status := Failure;
            end if;
        end if;
        return Result;
    end Many;


    function Many_Until
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result is
    begin
        return Empty_Fail;
    end Many_Until;





    function Satisfy
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result is
    begin
        if Start > Input'Last then
            return Empty_Fail;
        elsif Test (Input (Start)) then
            return Create_Result (1, Success, (1 => Input (Start)));
        else
            return Empty_Fail;
        end if;
    end Satisfy;


    function Satisfy_With
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result is
    begin
        if Start > Input'Last then
            return Empty_Fail;
        elsif Test (Change (Input (Start))) then
            return Create_Result (1, Success, (1 => Input (Start)));
        else
            return Empty_Fail;
        end if;
    end Satisfy_With;


    function Match
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result is
    begin
        if Start > Input'Last then
            return Empty_Fail;
        elsif Input (Start) = Item then
            return Create_Result (1, Success, (1 => Item));
        else
            return Empty_Fail;
        end if;
    end Match;


    function Match_With
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result is
    begin
        if Start > Input'Last then
            return Empty_Fail;
        elsif Change (Input (Start)) = Item then
            return Create_Result (1, Success, (1 => Input (Start)));
        else
            return Empty_Fail;
        end if;
    end Match_With;


    function Multimatch
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result
    is
        Current_Offset : Natural := 0;
    begin
        if Items'Length = 0 then
            return Create_Result (0, Success, Empty_Array);
        end if;

        if Input'Last - Start + 1 <= 0 then
            return Empty_Fail;
        end if;

        while Input (Start + Current_Offset) = Items (Items'First + Current_Offset) loop
            if Items'First + Current_Offset = Items'Last then
                return Create_Result (Current_Offset + 1, Success, Items);
            elsif Start + Current_Offset = Input'Last then
                return Create_Result (Current_Offset + 1, Needs_More, Input (Start .. Input'Last));
            end if;
            Current_Offset := Current_Offset + 1;
        end loop;
        return Create_Result (Current_Offset, Failure, Input (Start .. Start + Current_Offset - 1));
    end Multimatch;


    function Take
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result is
    begin
        if Start > Input'Last then
            return Empty_Fail;
        elsif Start + Number - 1 > Input'Last then
            return Create_Result (Input'Last - Start + 1, Needs_More, Input (Start .. Input'Last));
        else
            return Create_Result (Number, Success, Input (Start .. Start + Number - 1));
        end if;
    end Take;


    function Take_While
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result
    is
        Finish : Positive := Start;
        Status : Result_Status;
    begin
        if Start > Input'Last or else not Test (Input (Start)) then
            return Empty_Fail;
        end if;
        while Finish <= Input'Last and then Test (Input (Finish)) loop
            Finish := Finish + 1;
        end loop;
        if Finish > Input'Last then
            Status := Optional_More;
        else
            Status := Success;
        end if;
        return Create_Result (Finish - Start, Status, Input (Start .. Finish - 1));
    end Take_While;


    function Take_Until
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result
    is
        Finish : Positive := Start;
        Status : Result_Status;
    begin
        if Start > Input'Last or else Test (Input (Start)) then
            return Empty_Fail;
        end if;
        while Finish <= Input'Last and then not Test (Input (Finish)) loop
            Finish := Finish + 1;
        end loop;
        if Finish > Input'Last then
            Status := Optional_More;
        else
            Status := Success;
        end if;
        return Create_Result (Finish - Start, Status, Input (Start .. Finish - 1));
    end Take_Until;





    function Line_End
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result is
    begin
        if Start > Input'Last then
            return Empty_Fail;
        elsif Input (Start) = EOL_Item then
            return Create_Result (1, Success, (1 => EOL_Item));
        else
            return Empty_Fail;
        end if;
    end Line_End;


    function Input_End
           (Input : in Element_Array;
            Start : in Positive)
        return Combinator_Result is
    begin
        if Start > Input'Last then
            return Empty_Fail;
        elsif Input (Start) = EOF_Item then
            return Create_Result (1, Success, (1 => EOF_Item));
        else
            return Empty_Fail;
        end if;
    end Input_End;


end Packrat.Lexer.Combinators;