IMPLEMENTATION MODULE TextBuf ;

VAR
   buf : ARRAY [0..TextLimit] OF CHAR ;   (* we use Indx as the stored length,
                                            no CR terminator needed *)
   used : CARDINAL ;

   (* The characters live in buf[0 .. used-1].  Lines end with CR. *)

PROCEDURE Clear ;
BEGIN
   used := 0
END Clear ;

PROCEDURE Length () : CARDINAL ;
BEGIN
   RETURN used
END Length ;

PROCEDURE CharAt (i : CARDINAL) : CHAR ;
BEGIN
   RETURN buf [i]
END CharAt ;

PROCEDURE InsertCh (i : CARDINAL ; ch : CHAR) ;
VAR j : CARDINAL ;
BEGIN
   IF used >= TextLimit THEN
      RETURN
   END ;
   IF i > used THEN
      i := used
   END ;
   j := used ;
   WHILE j > i DO
      buf [j] := buf [j - 1] ;
      DEC (j)
   END ;
   buf [i] := ch ;
   INC (used)
END InsertCh ;

PROCEDURE OverwriteCh (i : CARDINAL ; ch : CHAR) ;
BEGIN
   IF i < used THEN
      buf [i] := ch
   ELSE
      InsertCh (i, ch)
   END
END OverwriteCh ;

PROCEDURE DeleteAt (i : CARDINAL) ;
VAR j : CARDINAL ;
BEGIN
   IF i >= used THEN
      RETURN
   END ;
   j := i ;
   WHILE j < used - 1 DO
      buf [j] := buf [j + 1] ;
      INC (j)
   END ;
   DEC (used)
END DeleteAt ;

PROCEDURE DeleteFromTo (i, n : CARDINAL) ;
VAR j : CARDINAL ;
BEGIN
   IF i >= used THEN
      RETURN
   END ;
   IF i + n > used THEN
      n := used - i
   END ;
   j := i ;
   WHILE j + n < used DO
      buf [j] := buf [j + n] ;
      INC (j)
   END ;
   DEC (used, n)
END DeleteFromTo ;

BEGIN
   used := 0
END TextBuf.