with

    Ada.Strings.Unbounded,
    Ada.Finalization;


package Packrat is


    type Result_Status is (Failure, Needs_More, Optional_More, Success);


    Parser_Error : exception;
    Lexer_Error  : exception;




    package Errors is


        subtype Error_Message is String
            with Dynamic_Predicate => Valid_Message (Error_Message);

        type Error_Info is record
            Symbol   : Ada.Strings.Unbounded.Unbounded_String;
            Position : Natural;
        end record;

        type Error_Info_Array is array (Positive range <>) of Error_Info;


        --  Note: No consideration is given to ordering of Error_Info items
        --        encoded into an Error_Message string.

        --  Note: Using "&" to join two Valid Error_Messages together
        --        will result in an Error_Message that is also Valid,
        --        but for best results Join should be used instead to
        --        prevent duplication of Error_Info in the message.


        function Valid_Identifier
               (Check : in String)
            return Boolean;

        function Valid_Identifier
               (Check : in Ada.Strings.Unbounded.Unbounded_String)
            return Boolean;

        function Valid_Identifier_Array
               (Check : in Error_Info_Array)
            return Boolean;

        function Valid_Message
               (Check : in String)
            return Boolean;

        function Debug_String
               (This : in Error_Message)
            return String;


        function Join
               (Left, Right : in Error_Message)
            return Error_Message;


        function Encode
               (Name : in String;
                Pos  : in Natural)
            return Error_Message
            with Pre => Valid_Identifier (Name);

        function Encode
               (Name : in Ada.Strings.Unbounded.Unbounded_String;
                Pos  : in Natural)
            return Error_Message
            with Pre => Valid_Identifier (Name);

        function Encode
               (Info : in Error_Info)
            return Error_Message
            with Pre => Valid_Identifier (Info.Symbol);

        function Encode_Array
               (Info : in Error_Info_Array)
            return Error_Message
            with Pre => Valid_Identifier_Array (Info);

        function Decode
               (Msg : in Error_Message)
            return Error_Info_Array;


    end Errors;




    generic
        type Label_Enum is (<>);
        type Element is private;
        type Element_Array is array (Positive range <>) of Element;
    package Tokens is


        type Token is new Ada.Finalization.Controlled with private;
        type Token_Array is array (Positive range <>) of Token;


        function Create
               (Ident  : in Label_Enum;
                Start  : in Positive;
                Finish : in Natural;
                Value  : in Element_Array)
            return Token;

        function "="
               (Left, Right : in Token)
            return Boolean;


        --  Note: The Start and Finish indices indicate where the token was found
        --        in whatever array it was lexed from. The Value does *not* have
        --        to correspond with whatever is found in the Start .. Finish range.


        function Initialized
               (This : in Token)
            return Boolean;

        function Debug_String
               (This : in Token)
            return String;


        function Label
               (This : in Token)
            return Label_Enum
            with Pre => Initialized (This);

        function Start
               (This : in Token)
            return Positive;

        function Finish
               (This : in Token)
            return Natural;

        function Value
               (This : in Token)
            return Element_Array
            with Pre => Initialized (This);


    private


        type Element_Array_Access is access Element_Array;


        type Token is new Ada.Finalization.Controlled with record
            Identifier  : Label_Enum;
            Start_At    : Positive;
            Finish_At   : Natural;
            Token_Value : Element_Array_Access;
        end record;


        overriding procedure Initialize
               (This : in out Token);

        overriding procedure Adjust
               (This : in out Token);

        overriding procedure Finalize
               (This : in out Token);


    end Tokens;




private


    function "+"
           (S : in String)
        return Ada.Strings.Unbounded.Unbounded_String
        renames Ada.Strings.Unbounded.To_Unbounded_String;

    function "-"
           (US : in Ada.Strings.Unbounded.Unbounded_String)
        return String
        renames Ada.Strings.Unbounded.To_String;


end Packrat;