Assembling pages

This is the thirteenth post in the Mostly Oberon series. Mostly Oberon documents my exploration of the Oberon Language, Oberon System and the various rabbit holes I will inevitably fall into.

Pandoc and JSON

I use Pandoc to process Markdown documents. I like to keep my front matter in JSON rather than Pandoc's YAML. Fortunately Pandoc does support working with JSON as a metadata file include. Normally I would manually split the JSON front matter and the rest of the markup into two separate files, then process with Pandoc and other tooling likeLunrJS. AssemblePage automates this process.

Example shell usage:


         AssemblePage MyText.txt \
            metadata=document.json \
            document=document.md
         pandoc --from markdown --to html \
            --metadata-file document.json \
            --standalone \
            document.md >MyText.html

Source code for AssemblePage.Mod


      MODULE AssemblePage;
        IMPORT Out, Strings, Files, Args := extArgs;
      
      VAR
        srcName, metaName, docName : ARRAY 1024 OF CHAR;
      
      (* FrontMatter takes a "read" Rider, r, and a "write" Rider "w".
      If the first character read by r is an opening curly bracket
      (the start of the front matter) it writes it out with w, until
      it finds a matching closing curly bracket or the file ends. *)
      PROCEDURE FrontMatter*(VAR r : Files.Rider; VAR w : Files.Rider);
        VAR c : BYTE; cCnt : INTEGER;
      BEGIN
        (* Scan for opening JSON front matter *)
        cCnt := 0;
        REPEAT
          Files.Read(r, c);
          IF r.eof = FALSE THEN
            IF c = ORD("{") THEN
              cCnt := cCnt + 1;
            ELSIF c = ORD("}") THEN
              cCnt := cCnt - 1;
            END;
            Files.Write(w, c);
          END;
        UNTIL (r.eof = TRUE) OR (cCnt = 0);
        IF cCnt # 0 THEN
          Out.String("ERROR: mis matched '{' and '}' in front matter");
          ASSERT(FALSE);
        END;
      END FrontMatter;
      
      (* CopyIO copies the characters from a "read" Rider to a "write" Rider *)
      PROCEDURE CopyIO*(VAR r : Files.Rider; VAR w: Files.Rider);
        VAR c : BYTE;
      BEGIN
        REPEAT
          Files.Read(r, c);
          IF r.eof = FALSE THEN
            Files.Write(w, c);
          END;
        UNTIL r.eof = TRUE;
      END CopyIO;
      
      PROCEDURE ProcessParameters(VAR sName, mName, dName : ARRAY OF CHAR);
        VAR
          arg : ARRAY 1024 OF CHAR;
          i, res : INTEGER;
      BEGIN
        mName := "document.json";
        dName := "document.txt";
        arg := "";
        FOR i := 0 TO (Args.count - 1) DO
          Args.Get(i, arg, res);
          IF Strings.Pos("metadata=", arg, 0) = 0 THEN
            Strings.Extract(arg, 9, Strings.Length(arg), mName);
          ELSIF Strings.Pos("document=", arg, 0) = 0 THEN
            Strings.Extract(arg, 9, Strings.Length(arg), dName);
          ELSE
            Strings.Extract(arg, 0, Strings.Length(arg), sName);
          END;
        END;
      END ProcessParameters;
      
      PROCEDURE AssemblePage(srcName, metaName, docName : ARRAY OF CHAR);
      VAR
        src, meta, doc : Files.File;
        reader, writer : Files.Rider;
      BEGIN
        src := Files.Old(srcName);
        IF src # NIL THEN
          Files.Set(reader, src, 0);
          IF metaName # "" THEN
            meta := Files.New(metaName);
            Files.Register(meta);
            Files.Set(writer, meta, 0);
            FrontMatter(reader, writer);
            Files.Close(meta);
          END;
          IF docName # "" THEN
            doc := Files.New(docName);
            Files.Register(doc);
            Files.Set(writer, doc, 0);
            CopyIO(reader, writer);
            Files.Close(doc);
          END;
        ELSE
          Out.String("ERROR: Could not read ");Out.String(srcName);Out.Ln();
          ASSERT(FALSE);
        END;
        Files.Close(src);
      END AssemblePage;
      
      BEGIN
        ProcessParameters(srcName, metaName, docName);
        AssemblePage(srcName, metaName, docName);
      END AssemblePage.

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