/*
 * gcr.c - GCR handling.
 *
 * Written by
 *  Andreas Boose <viceteam@t-online.de>
 *  Daniel Sladic <sladic@eecg.toronto.edu>
 *  Kajtar Zsolt <soci@c64.rulez.org>
 *
 * This file is part of VICE, the Versatile Commodore Emulator.
 * See README for copyright notice.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
 *  02111-1307  USA.
 *
 */

/* #define DEBUG_GCR */

#ifdef DEBUG_GCR
#define DBG(_x_)  log_debug _x_
#else
#define DBG(_x_)
#endif

#include "vice.h"

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "gcr.h"
#include "lib.h"
#include "log.h"
#include "types.h"
#include "cbmdos.h"
#include "diskimage.h"

static const uint8_t GCR_conv_data[16] =
{
    0x0a, 0x0b, 0x12, 0x13,
    0x0e, 0x0f, 0x16, 0x17,
    0x09, 0x19, 0x1a, 0x1b,
    0x0d, 0x1d, 0x1e, 0x15
};

static const uint8_t From_GCR_conv_data[32] =
{
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 8, 0, 1, 0, 12, 4, 5,
    0, 0, 2, 3, 0, 15, 6, 7,
    0, 9, 10, 11, 0, 13, 14, 0
};


static void gcr_convert_4bytes_to_GCR(const uint8_t *source, uint8_t *dest)
{
    int i;
    register unsigned int tdest = 0;    /* at least 16 bits for overflow shifting */

    for (i = 2; i < 10; i += 2, source++, dest++)
    {
        tdest <<= 5;  /* make room for the upper nybble */
        tdest |= GCR_conv_data[(*source) >> 4];

        tdest <<= 5;  /* make room for the lower nybble */
        tdest |= GCR_conv_data[(*source) & 0x0f];

        *dest = (uint8_t)(tdest >> i);
    }

    *dest = (uint8_t)tdest;
}

static void gcr_convert_GCR_to_4bytes(const uint8_t *source, uint8_t *dest)
{
    int i;
    /* at least 24 bits for shifting into bits 16...20 */
    register uint32_t tdest = *source;

    tdest <<= 13;

    for (i = 5; i < 13; i += 2, dest++)
    {
        source++;
        tdest |= ((uint32_t)(*source)) << i;

        /*  "tdest >> 16" could be optimized to a word
         *  aligned access, hopefully the compiler does
         *  this for us (in a portable way)
         */
        *dest = From_GCR_conv_data[(tdest >> 16) & 0x1f] << 4;
        tdest <<= 5;

        *dest |= From_GCR_conv_data[(tdest >> 16) & 0x1f];
        tdest <<= 5;
    }
}

void gcr_convert_sector_to_GCR(const uint8_t *buffer, uint8_t *data, const gcr_header_t *header,
                               int gap, int sync, fdc_err_t error_code)
{
    int i;
    uint8_t buf[4], chksum, idm;

    idm = (error_code == CBMDOS_FDC_ERR_ID) ? 0xff : 0x00;

    memset(data, (error_code == CBMDOS_FDC_ERR_SYNC) ? 0x55 : 0xff, 5);       /* Sync */
    data += 5;

    chksum = (error_code == CBMDOS_FDC_ERR_HCHECK) ? 0xff : 0x00;
    chksum ^= header->sector ^ header->track ^ header->id2 ^ header->id1 ^ idm;
    buf[0] = (error_code == CBMDOS_FDC_ERR_HEADER) ? 0xff : 0x08;
    buf[1] = chksum;
    buf[2] = header->sector;
    buf[3] = header->track;
    gcr_convert_4bytes_to_GCR(buf, data);
    data += 5;

    buf[0] = header->id2;
    buf[1] = header->id1 ^ idm;
    buf[2] = buf[3] = 0x0f;
    gcr_convert_4bytes_to_GCR(buf, data);
    data += 5;

    data += gap;                   /* Gap */

    memset(data, (error_code == CBMDOS_FDC_ERR_SYNC) ? 0x55 : 0xff, sync);       /* Sync */
    data += sync;

    chksum = (error_code == CBMDOS_FDC_ERR_DCHECK) ? 0xff : 0x00;
    /* note: error 4 (CBMDOS_FDC_ERR_NOBLOCK) is considered a "soft error",
             meaning the data is still available. because of that, we must use
             a value (incase of error) here that in GCR will have its leftmost
             bit 0, or else it will be taken as part of the SYNC and the framing
             will break (and the data mess up).
     */
    buf[0] = (error_code == CBMDOS_FDC_ERR_NOBLOCK) ? 0x00 : 0x07;
    memcpy(buf + 1, buffer, 3);
    chksum ^= buffer[0] ^ buffer[1] ^ buffer[2];
    gcr_convert_4bytes_to_GCR(buf, data);
    buffer += 3;
    data += 5;

    for (i = 0; i < 63; i++) {
        chksum ^= buffer[0] ^ buffer[1] ^ buffer[2] ^ buffer[3];
        gcr_convert_4bytes_to_GCR(buffer, data);
        buffer += 4;
        data += 5;
    }

    buf[0] = buffer[0];
    buf[1] = chksum ^ buffer[0];
    buf[2] = buf[3] = 0;
    gcr_convert_4bytes_to_GCR(buf, data);
}

static int gcr_find_sync(const disk_track_t *raw, int p, int s)
{
    unsigned int w;
    int b;

    if (!raw->data || !raw->size) {
        return -CBMDOS_FDC_ERR_SYNC;
    }

    w = 0;
    b = raw->data[p >> 3] << (p & 7);
    while (s--) {
        if (b & 0x80) {
            w = (w << 1) | 1;
        } else {
            if (~w & 0x3ff) {
                w <<= 1;
            } else {
                return p;
            }
        }
        if (~p & 7) {
            p++;
            b <<= 1;
        } else {
            p++;
            if (p >= raw->size * 8) {
                p = 0;
            }
            b = raw->data[p >> 3];
        }
    }
    return -CBMDOS_FDC_ERR_SYNC;
}

static void gcr_decode_block(const disk_track_t *raw, int p, uint8_t *buf, int num)
{
    int shift, i, j;
    uint8_t gcr[5], b;
    uint8_t *offset, *end = raw->data + raw->size;

    shift = p & 7;
    offset = raw->data + (p >> 3);

    b = offset[0] << shift;
    for (i = 0; i < num; i++, buf += 4) {
        /* get 5 bytes of gcr data */
        for (j = 0; j < 5; j++) {
            offset++;
            if (offset >= end) {
                offset = raw->data;
            }
            if (shift) {
                gcr[j] = b | ((offset[0] << shift) >> 8);
                b = offset[0] << shift;
            } else {
                gcr[j] = b;
                b = offset[0];
            }
        }
        gcr_convert_GCR_to_4bytes(gcr, buf);
    }
}

static int gcr_find_sector_header(const disk_track_t *raw, uint8_t sector)
{
    uint8_t header[4];
    int p, p2;

    p = 0;
    p2 = -CBMDOS_FDC_ERR_SYNC;
    for (;; ) {
        p = gcr_find_sync(raw, p, raw->size * 8);
        if (p2 == p) {
            break;
        }
        if (p2 < 0) {
            p2 = p;
        }
        gcr_decode_block(raw, p, header, 1);

        if (header[0] == 0x08 && header[2] == sector) {
            /* Track, checksum or ID's are not checked here */
            DBG(("GCR: shift: %d hdr: %02x %02x sec:%02d trk:%02d", shift, header[0], header[1], header[2], header[3]));
            return p;
        }
    }
    if (p2 < 0) {
        return p2;
    }
    return -CBMDOS_FDC_ERR_HEADER;
}

fdc_err_t gcr_read_sector(const disk_track_t *raw, uint8_t *data, uint8_t sector)
{
    uint8_t buffer[260];
    uint8_t b;
    int i, p;

    p = gcr_find_sector_header(raw, sector);
    if (p < 0) {
        return -p;
    }

    p = gcr_find_sync(raw, p, 500 * 8);
    if (p < 0) {
        return -p;
    }

    gcr_decode_block(raw, p, buffer, 65);

    b = buffer[257];
    for (i = 0; i < 256; i++) {
        data[i] = buffer[i + 1];
        b ^= data[i];
    }

    if (buffer[0] != 0x07) {
        return CBMDOS_FDC_ERR_NOBLOCK;
    }

    return b ? CBMDOS_FDC_ERR_DCHECK : CBMDOS_FDC_ERR_OK;
}

fdc_err_t gcr_write_sector(disk_track_t *raw, const uint8_t *data, uint8_t sector)
{
    uint8_t buffer[260], *offset, *buf;
    uint8_t *end = raw->data + raw->size;
    uint8_t gcr[5], chksum, b;
    int i, j, shift, p;

    p = gcr_find_sector_header(raw, sector);
    if (p < 0) {
        return -p;
    }

    p = gcr_find_sync(raw, p, 500 * 8);
    if (p < 0) {
        return -p;
    }

    shift = p & 7;
    offset = raw->data + (p >> 3);

    b = offset[0] & (0xff00 >> shift);

    buffer[0] = 0x07;
    memcpy(buffer + 1, data, 256);
    chksum = buffer[1];
    for (i = 2; i < 257; i++) {
        chksum ^= buffer[i];
    }
    buffer[257] = chksum;
    buffer[258] = buffer[259] = 0;

    buf = buffer;

    for (i = 0; i < 65; i++) {
        gcr_convert_4bytes_to_GCR(buf, gcr);
        buf += 4;
        for (j = 0; j < 5; j++) {
            if (shift) {
                offset[0] = b | (gcr[j] >> shift);
                b = (gcr[j] << 8) >> shift;
            } else {
                offset[0] = gcr[j];
            }
            offset++;
            if (offset >= end) {
                offset = raw->data;
            }
        }
    }
    offset[0] = b | (offset[0] & (0xff >> shift));

    return CBMDOS_FDC_ERR_OK;
}

gcr_t *gcr_create_image(void)
{
    return (gcr_t *)lib_calloc(1, sizeof(gcr_t));
}

void gcr_destroy_image(gcr_t *gcr)
{
    lib_free(gcr);
    return;
}
