EXTERNAL CLASS Util;

EXTERNAL C PROCEDURE getenv IS
   TEXT PROCEDURE GetEnv(key); TEXT key;;

EXTERNAL C PROCEDURE add_history IS
   PROCEDURE add_history(line); TEXT line;;

BEGIN
   TEXT historyfile;

   BOOLEAN PROCEDURE IsWhitespace(c); CHARACTER c;
   IsWhitespace := c = ' ' OR c = '!10!' OR c = '!9!';

   BOOLEAN PROCEDURE IsBlank(line); TEXT Line;
   BEGIN INTEGER i; BOOLEAN result;
      i := 1;
      result := TRUE;
      WHILE i <= line.Length AND THEN result DO BEGIN
            IF NOT IsWhitespace(CharAt(line, i)) THEN result := FALSE;
            i := i + 1;
         END;
      IsBlank := result;
   END;

   PROCEDURE AddHistory(line); TEXT line;
   COMMENT HACK: foreign function doesn't see the substring, but the
      main string unless it's copied...;
   add_history(Copy(line));

   TEXT PROCEDURE FileContent(path); TEXT path;
   BEGIN TEXT buffer; REF(InByteFile) f;
      f :- NEW InByteFile(path);
      f.Open;
      buffer :- Blanks(FileSize(path));
      f.InText(buffer);
      f.Close;
      FileContent :- buffer;
   END;

   BOOLEAN PROCEDURE FileExists(path); TEXT path;
   BEGIN REF(InByteFile) f; BOOLEAN result;
      f :- NEW InByteFile(path);
      f.Open;
      COMMENT HACK: this shouldn't even work, but it does;
      result := NOT f.Endfile;
      f.Close;
      FileExists := result;
   END;

   INTEGER PROCEDURE FindChar(buffer, c, i); TEXT buffer; CHARACTER c; INTEGER i;
   BEGIN
      buffer.SetPos(i);
      WHILE buffer.More AND THEN buffer.GetChar <> c DO i := i + 1;
      FindChar := IF i > buffer.Length THEN -1 ELSE i;
   END;

   PROCEDURE LoadHistory;
   BEGIN TEXT buffer, line; INTEGER beg, i; BOOLEAN done;
      IF FileExists(historyfile) THEN BEGIN
            buffer :- FileContent(historyfile);
            done := FALSE;
            beg := 1;
            WHILE NOT done DO BEGIN
                  i := FindChar(buffer, '!10!', beg);
                  IF i > 0 THEN BEGIN
                        line :- buffer.Sub(beg, i - beg);
                        IF NOT IsBlank(line) THEN
                           AddHistory(buffer.Sub(beg, i - beg));
                        beg := i + 1;
                     END
                  ELSE done := TRUE
               END;
         END;
   END;

   PROCEDURE AppendLine(path, line); TEXT path, line;
   BEGIN REF(DirectByteFile) f;
      f :- NEW DirectByteFile(path);
      f.Open;
      COMMENT HACK: setting mode to append isn't honored, so seek to END;
      WHILE NOT f.Endfile DO f.InByte;
      f.OutText(Line);
      f.OutByte(10);
      f.Close;
   END;

   PROCEDURE AddToHistory(line); TEXT line;
   BEGIN
      AddHistory(line);
      AppendLine(historyfile, line);
   END;

   PROCEDURE Repl(prompt); TEXT prompt;
   BEGIN TEXT line; BOOLEAN done;
      LoadHistory;
      WHILE NOT done DO BEGIN
            line :- Readline(prompt);
            IF Eofp(line) THEN
               done := TRUE
            ELSE IF NOT IsBlank(line) THEN BEGIN
                  line :- Chomp(Line);
                  OutText(line);
                  OutImage;
                  AddToHistory(line);
               END;
         END;
      OutImage;
   END;

   historyfile :- GetEnv("HOME") & "/.mal_history";
   Repl("> ");
END;