DEFINITION MODULE RndFile;

  (* Random access files *)

IMPORT IOChan, ChanConsts, SYSTEM;

TYPE
  ChanId = IOChan.ChanId;
  FlagSet = ChanConsts.FlagSet;
  OpenResults = ChanConsts.OpenResults;

  (* Accepted singleton values of FlagSet *)

CONST
  read = FlagSet{ChanConsts.readFlag};   (* input operations are requested/available *)
  write = FlagSet{ChanConsts.writeFlag}; (* output operations are requested/available *)
  old = FlagSet{ChanConsts.oldFlag};     (* a file may/must/did exist before the channel is
                                            opened *)
  text = FlagSet{ChanConsts.textFlag};   (* text operations are requested/available *)
  raw = FlagSet{ChanConsts.rawFlag};     (* raw operations are requested/available *)

PROCEDURE OpenOld (VAR cid: ChanId; name: ARRAY OF CHAR; flags: FlagSet;
                   VAR res: OpenResults);
  (* Attempts to obtain and open a channel connected to a stored random access file of the
     given name.
     The old flag is implied; without the write flag, read is implied; without the text
     flag, raw is implied.
     If successful, assigns to cid the identity of the opened channel, assigns the value
     opened to res, and sets the read/write position to the start of the file.
     If a channel cannot be opened as required, the value of res indicates the reason, and
     cid identifies the invalid channel.
  *)

PROCEDURE OpenClean (VAR cid: ChanId; name: ARRAY OF CHAR; flags: FlagSet;
                     VAR res: OpenResults);
  (* Attempts to obtain and open a channel connected to a stored random access file of the
     given name.
     The write flag is implied; without the text flag, raw is implied.
     If successful, assigns to cid the identity of the opened channel, assigns the value
     opened to res, and truncates the file to zero length.
     If a channel cannot be opened as required, the value of res indicates the reason, and
     cid identifies the invalid channel.
  *)

PROCEDURE IsRndFile (cid: ChanId): BOOLEAN;
  (* Tests if the channel identified by cid is open to a random access file. *)

PROCEDURE IsRndFileException (): BOOLEAN;
  (* Returns TRUE if the current coroutine is in the exceptional execution state because
     of the raising of a RndFile exception; otherwise returns FALSE.
  *)

CONST
  FilePosSize = 8;
  (*<implementation-defined whole number greater than zero>;*)

TYPE
  FilePos = ARRAY [1 .. FilePosSize] OF SYSTEM.LOC;

PROCEDURE StartPos (cid: ChanId): FilePos;
  (* If the channel identified by cid is not open to a random access file, the exception
     wrongDevice is raised; otherwise returns the position of the start of the file.
  *)

PROCEDURE CurrentPos (cid: ChanId): FilePos;
  (* If the channel identified by cid is not open to a random access file, the exception
     wrongDevice is raised; otherwise returns the position of the current read/write
     position.
  *)

PROCEDURE EndPos (cid: ChanId): FilePos;
  (* If the channel identified by cid is not open to a random access file, the exception
     wrongDevice is raised; otherwise returns the first position after which there have been
     no writes.
  *)

PROCEDURE NewPos (cid: ChanId; chunks: INTEGER; chunkSize: CARDINAL; from: FilePos): FilePos;
  (* If the channel identified by cid is not open to a random access file, the exception
     wrongDevice is raised; otherwise returns the position (chunks * chunkSize) relative to
     the position given by from, or raises the exception posRange if the required position
     cannot be represented as a value of type FilePos.
  *)

PROCEDURE SetPos (cid: ChanId; pos: FilePos);
  (* If the channel identified by cid is not open to a random access file, the exception
     wrongDevice is raised; otherwise sets the read/write position to the value given by
     pos.
  *)

PROCEDURE Close (VAR cid: ChanId);
  (* If the channel identified by cid is not open to a random access file, the exception
     wrongDevice is raised; otherwise closes the channel, and assigns the value identifying
     the invalid channel to cid.
  *)

END RndFile.

