(*
    BSD 2-Clause License

    Copyright (c) 2018-2019, Anton Krotov
    All rights reserved.
*)

MODULE TEXTDRV;

IMPORT FILES, C := COLLECTIONS;


CONST

    CR = 0DX; LF = 0AX;

    CHUNK = 1024 * 256;


TYPE

    TEXT* = POINTER TO RECORD (C.ITEM)

        chunk:        ARRAY CHUNK OF CHAR;
        pos, size:    INTEGER;
        file:         FILES.FILE;
        utf8:         BOOLEAN;
        CR:           BOOLEAN;

        line*, col*:  INTEGER;
        eof*:         BOOLEAN;
        eol*:         BOOLEAN;
        peak*:        CHAR

    END;


VAR

    texts: C.COLLECTION;


PROCEDURE load (text: TEXT);
BEGIN
    IF ~text.eof THEN
        text.size := FILES.read(text.file, text.chunk, LEN(text.chunk));
        text.pos := 0;
        IF text.size = 0 THEN
            text.eof := TRUE;
            text.chunk[0] := 0X
        END;
        text.peak := text.chunk[0]
    END
END load;


PROCEDURE next* (text: TEXT);
VAR
    c: CHAR;

BEGIN
    IF text.pos < text.size - 1 THEN
        INC(text.pos);
        text.peak := text.chunk[text.pos]
    ELSE
        load(text)
    END;

    IF ~text.eof THEN

        c := text.peak;

        IF c = CR THEN
            INC(text.line);
            text.col := 0;
            text.eol := TRUE;
            text.CR  := TRUE
        ELSIF c = LF THEN
            IF ~text.CR THEN
                INC(text.line);
                text.col := 0;
                text.eol := TRUE
            ELSE
                text.eol := FALSE
            END;
            text.CR := FALSE
        ELSE
            text.eol  := FALSE;
            IF text.utf8 THEN
                IF ORD(c) DIV 64 # 2 THEN
                    INC(text.col)
                END
            ELSE
                INC(text.col)
            END;
            text.CR := FALSE
        END

    END

END next;


PROCEDURE init (text: TEXT);
BEGIN
    IF (text.pos = 0) & (text.size >= 3) THEN
        IF (text.chunk[0] = 0EFX) &
           (text.chunk[1] = 0BBX) &
           (text.chunk[2] = 0BFX) THEN
            text.pos := 3;
            text.utf8 := TRUE
        END
    END;

    IF text.size = 0 THEN
        text.chunk[0] := 0X;
        text.size := 1;
        text.eof := FALSE
    END;

    text.line := 1;
    text.col  := 1;

    text.peak := text.chunk[text.pos]
END init;


PROCEDURE close* (VAR text: TEXT);
BEGIN
    IF text # NIL THEN
        IF text.file # NIL THEN
            FILES.close(text.file)
        END;

        C.push(texts, text);
        text := NIL
    END
END close;


PROCEDURE open* (name: ARRAY OF CHAR): TEXT;
VAR
    text: TEXT;
    citem: C.ITEM;

BEGIN
    citem := C.pop(texts);
    IF citem = NIL THEN
        NEW(text)
    ELSE
        text := citem(TEXT)
    END;

    IF text # NIL THEN
        text.chunk[0] := 0X;
        text.pos  := 0;
        text.size := 0;
        text.utf8 := FALSE;
        text.CR   := FALSE;
        text.line := 1;
        text.col  := 1;
        text.eof  := FALSE;
        text.eol  := FALSE;
        text.peak := 0X;
        text.file := FILES.open(name);
        IF text.file # NIL THEN
            load(text);
            init(text)
        ELSE
            close(text)
        END
    END

    RETURN text
END open;


BEGIN
    texts := C.create()
END TEXTDRV.