/*
 * Apple // emulator for Linux: C portion of Disk ][ emulation
 *
 * Copyright 1994 Alexander Jean-Claude Bottema
 * Copyright 1995 Stephen Lee
 * Copyright 1997, 1998 Aaron Culliney
 * Copyright 1998, 1999, 2000 Michael Deutschmann
 *
 * This software package is subject to the GNU General Public License
 * version 2 or later (your choice) as published by the Free Software
 * Foundation.
 *
 * THERE ARE NO WARRANTIES WHATSOEVER.
 *
 */

/*
 * (De-)nibblizing routines sourced from AppleWin project.
 */

#include "common.h"

#if DISK_TRACING
static FILE *test_read_fp = NULL;
static FILE *test_write_fp = NULL;
#endif

extern uint8_t slot6_rom[256];

drive_t disk6;

static int stepper_phases = 0; // state bits for stepper magnet phases 0-3
static int skew_table_6_po[16] = { 0x00,0x08,0x01,0x09,0x02,0x0A,0x03,0x0B, 0x04,0x0C,0x05,0x0D,0x06,0x0E,0x07,0x0F }; // ProDOS order
static int skew_table_6_do[16] = { 0x00,0x07,0x0E,0x06,0x0D,0x05,0x0C,0x04, 0x0B,0x03,0x0A,0x02,0x09,0x01,0x08,0x0F }; // DOS order

static uint8_t translate_table_6[0x40] = {
    0x96, 0x97, 0x9a, 0x9b, 0x9d, 0x9e, 0x9f, 0xa6,
    0xa7, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb2, 0xb3,
    0xb4, 0xb5, 0xb6, 0xb7, 0xb9, 0xba, 0xbb, 0xbc,
    0xbd, 0xbe, 0xbf, 0xcb, 0xcd, 0xce, 0xcf, 0xd3,
    0xd6, 0xd7, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde,
    0xdf, 0xe5, 0xe6, 0xe7, 0xe9, 0xea, 0xeb, 0xec,
    0xed, 0xee, 0xef, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6,
    0xf7, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
    /*
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x00, 0x01,
    0x80, 0x80, 0x02, 0x03, 0x80, 0x04, 0x05, 0x06,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x07, 0x08,
    0x80, 0x80, 0x80, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
    0x80, 0x80, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13,
    0x80, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
    0x80, 0x80, 0x80, 0x1b, 0x80, 0x1c, 0x1d, 0x1e,
    0x80, 0x80, 0x80, 0x1f, 0x80, 0x80, 0x20, 0x21,
    0x80, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x29, 0x2a, 0x2b,
    0x80, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32,
    0x80, 0x80, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38,
    0x80, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f
    */
};

static uint8_t rev_translate_table_6[0x80] = { 0x01 };

__attribute__((constructor(CTOR_PRIORITY_LATE)))
static void _initialize_reverse_translate(void) {
    for (unsigned int i=0; i<0x40; i++) {
        rev_translate_table_6[translate_table_6[i]-0x80] = i << 2;
    }
}

static inline void cut_gz(char *name) {
    size_t len = strlen(name);
    if (len <= _GZLEN) {
        return;
    }
    *(name+len-_GZLEN) = '\0';
}

static inline bool is_gz(const char * const name) {
    size_t len = strlen(name);
    if (len <= _GZLEN) {
        return false;
    }
    return strncmp(name+len-_GZLEN, DISK_EXT_GZ, _GZLEN) == 0;
}

static inline bool is_nib(const char * const name) {
    size_t len = strlen(name);
    if (len <= _NIBLEN) {
        return false;
    }
    if (is_gz(name)) {
        if (len <= _NIBLEN+_GZLEN) {
            return false;
        }
        len -= _GZLEN;
    }
    return strncmp(name+len-_NIBLEN, DISK_EXT_NIB, _NIBLEN) == 0;
}

static inline bool is_po(const char * const name) {
    size_t len = strlen( name );
    if (len <= _POLEN) {
        return false;
    }
    if (is_gz(name)) {
        if (len <= _POLEN+_GZLEN) {
            return false;
        }
        len -= _GZLEN;
    }
    return strncmp(name+len-_POLEN, DISK_EXT_PO, _POLEN) == 0;
}

#define SIXBIT_MASK 0x3F // 111111
#define SIXBIT_EXTRA_BYTES 0x56 // 86
#define SIXBIT_EXTRA_WRAP 0x53 // 86 + 86 + 83 == 255
#define SIXBIT_OFF_BEGIN (SIXBIT_EXTRA_BYTES<<1) // 0xAC
#define NUM_SIXBIT_NIBS (0x100 + SIXBIT_EXTRA_BYTES) // 256 + 86 == 342

#if DISK_TRACING
#define _DISK_TRACE_SIXBITNIBS() \
    if (test_write_fp) { \
        fprintf(test_write_fp, "SIXBITNIBS:\n"); \
        for (unsigned int i=0; i<NUM_SIXBIT_NIBS+1; i++) { \
            fprintf(test_write_fp, "%02X", work_buf[i]); \
        } \
        fprintf(test_write_fp, "\n"); \
    }
#define _DISK_TRACE_XORNIBS() \
    if (test_write_fp) { \
        fprintf(test_write_fp, "XORNIBS:\n"); \
        for (unsigned int i=0; i<NUM_SIXBIT_NIBS; i++) { \
            fprintf(test_write_fp, "%02X", work_buf[i]); \
        } \
        fprintf(test_write_fp, "\n"); \
    }
#define _DISK_TRACE_SECDATA() \
    if (test_write_fp) { \
        fprintf(test_write_fp, "SECTOR:\n"); \
        for (unsigned int i = 0; i < 256; i++) { \
            fprintf(test_write_fp, "%02X", out[i]); \
        } \
        fprintf(test_write_fp, "%s", "\n"); \
    }
#else
#define _DISK_TRACE_SIXBITNIBS()
#define _DISK_TRACE_XORNIBS()
#define _DISK_TRACE_SECDATA()
#endif

static void nibblize_sector(const uint8_t * const src, uint8_t * const out) {
    SCOPE_TRACE_DISK("nibblize_sector");

    uint8_t work_buf[NUM_SIXBIT_NIBS+1];

    // Convert 256 8-bit bytes into 342 6-bit bytes
    unsigned int counter = 0;
    uint8_t offset = SIXBIT_OFF_BEGIN;
    while (offset != 0x02) {
        uint8_t value =        ((src[offset] & 0x01) << 1) | ((src[offset] & 0x02) >> 1);
        offset -= SIXBIT_EXTRA_BYTES;
        value = (value << 2) | ((src[offset] & 0x01) << 1) | ((src[offset] & 0x02) >> 1);
        offset -= SIXBIT_EXTRA_BYTES;
        value = (value << 2) | ((src[offset] & 0x01) << 1) | ((src[offset] & 0x02) >> 1);
        offset -= SIXBIT_EXTRA_WRAP;
        work_buf[counter] = value << 2;
        ++counter;
    }
    assert(counter == SIXBIT_EXTRA_BYTES && "nibblizing counter about to overflow");
    work_buf[counter-2] &= SIXBIT_MASK;
    work_buf[counter-1] &= SIXBIT_MASK;
    memcpy(&work_buf[counter], src, 0x100);

    // XOR the entire data block with itself offset by one byte, creating a final checksum byte
    uint8_t savedval = 0;
    for (unsigned int i=0; i<NUM_SIXBIT_NIBS; i++) {
        uint8_t prevsaved = savedval ^ work_buf[i];
        savedval = work_buf[i];
        work_buf[i] = prevsaved;
    }
    work_buf[NUM_SIXBIT_NIBS] = savedval;

    // Convert the 6-bit bytes into disk bytes using a lookup table.  A valid disk byte is a byte that has the high bit
    // set, at least two adjacent bits set (excluding the high bit), and at most one pair of consecutive zero bits.
    for (unsigned int i=0; i<NUM_SIXBIT_NIBS+1; i++) {
        out[i] = translate_table_6[work_buf[i] >> 2];
    }
}

static void denibblize_sector(const uint8_t * const src, uint8_t * const out) {
    SCOPE_TRACE_DISK("denibblize_sector");

    uint8_t work_buf[NUM_SIXBIT_NIBS+1];

    // Convert disk bytes into 6-bit bytes
    for (unsigned int i=0; i<(NUM_SIXBIT_NIBS+1); i++) {
        work_buf[i] = rev_translate_table_6[src[i] & 0x7F];
        assert(work_buf[i] != 0x1);
    }
    _DISK_TRACE_SIXBITNIBS();

    // XOR the entire data block with itself offset by one byte to undo checksumming
    uint8_t savedval = 0;
    for (unsigned int i=0; i<NUM_SIXBIT_NIBS; i++) {
        work_buf[i] = savedval ^ work_buf[i];
        savedval = work_buf[i];
    }
    _DISK_TRACE_XORNIBS();

    // Convert 342 6-bit bytes into 256 8-bit bytes

    uint8_t *lowbitsptr = work_buf;
    uint8_t *sectorbase = work_buf+SIXBIT_EXTRA_BYTES;
    uint8_t offset = SIXBIT_OFF_BEGIN;
    unsigned int counter = 0;
    for (unsigned int i=0; i<SIXBIT_EXTRA_BYTES; i++) {
        if (offset >= SIXBIT_OFF_BEGIN) {
            out[offset] = (sectorbase[offset] & 0xFC) | ((lowbitsptr[i] & 0x80) >> 7) | ((lowbitsptr[i] & 0x40) >> 5);
            ++counter;
        }
        offset -= SIXBIT_EXTRA_BYTES;
        out[offset]     = (sectorbase[offset] & 0xFC) | ((lowbitsptr[i] & 0x20) >> 5) | ((lowbitsptr[i] & 0x10) >> 3);
        ++counter;
        offset -= SIXBIT_EXTRA_BYTES;
        out[offset]     = (sectorbase[offset] & 0xFC) | ((lowbitsptr[i] & 0x08) >> 3) | ((lowbitsptr[i] & 0x04) >> 1);
        ++counter;
        offset -= SIXBIT_EXTRA_WRAP;
    }
    assert(counter == 0x100 && "invalid bytes count");
    assert(offset == 2 && "invalid bytes count");
    _DISK_TRACE_SECDATA();
}

#define CODE44A(a) ((((a)>> 1) & 0x55) | 0xAA)
#define CODE44B(b) (((b) & 0x55) | 0xAA)

static unsigned long nibblize_track(const uint8_t * const buf, int drive, uint8_t *output) {
    SCOPE_TRACE_DISK("nibblize_track");

    uint8_t * const begin_track = output;

#if CONFORMANT_TRACKS
    // Write track-beginning gap containing 48 self-sync bytes
    for (unsigned int i=0; i<48; i++) {
        *(output++) = 0xFF;
    }
#else
    // NOTE : original apple2emul used X sync bytes here and disk loading becomes much faster at a cost of conformance
    // for certain disk images.  For resource-constrained mobile/wearable devices, this is prolly the right path.
    for (unsigned int i=0; i<8; i++) {
        *(output++) = 0xFF;
    }
#endif

    unsigned int sector = 0;
    while (sector < 16) {
        // --- Address field

        // Prologue
        *(output)++ = 0xD5;
        *(output)++ = 0xAA;
        *(output)++ = 0x96;

        // Volume   (4-and-4 encoded)
        *(output)++ = CODE44A(DSK_VOLUME);
        *(output)++ = CODE44B(DSK_VOLUME);

        // Track    (4-and-4 encoded)
        int track = (disk6.disk[drive].phase>>1);
        *(output)++ = CODE44A(track);
        *(output)++ = CODE44B(track);

        // Sector   (4-and-4 encoded)
        *(output)++ = CODE44A(sector);
        *(output)++ = CODE44B(sector);

        // Checksum (4-and-4 encoded)
        uint8_t checksum = (DSK_VOLUME ^ track ^ sector);
        *(output)++ = CODE44A(checksum);
        *(output)++ = CODE44B(checksum);

        // Epilogue
        *(output)++ = 0xDE;
        *(output)++ = 0xAA;
        *(output)++ = 0xEB;

        // Gap of 6 self-sync bytes
        for (unsigned int i=0; i<6; i++) {
            *(output++) = 0xFF;
        }

        // --- Data field

        // Prologue
        *(output)++ = 0xD5;
        *(output)++ = 0xAA;
        *(output)++ = 0xAD;

        // 343 6-bit bytes of nibblized data + 6-bit checksum
        int sec_off = 256 * disk6.disk[drive].skew_table[ sector ];
        nibblize_sector(buf+sec_off, output);
        output += NUM_SIXBIT_NIBS+1;

        // Epilogue
        *(output)++ = 0xDE;
        *(output)++ = 0xAA;
        *(output)++ = 0xEB;

#if CONFORMANT_TRACKS
        // Sector gap of 27 self-sync bytes
        for (unsigned int i=0; i<27; i++) {
            *(output++) = 0xFF;
        }
#else
        // NOTE : original apple2emul used X self-sync bytes here
        for (unsigned int i=0; i<8; i++) {
            *(output++) = 0xFF;
        }
#endif

        ++sector;
    }

    return output - begin_track;
}

static void denibblize_track(const uint8_t * const src, int drive, uint8_t * const dst) {
    SCOPE_TRACE_DISK("denibblize_track");

    // Searches through the track data for each sector and decodes it

    const uint8_t * const trackimage = src;
#if DISK_TRACING
    if (test_write_fp) {
        fprintf(test_write_fp, "DSK OUT:\n");
    }
#endif

    unsigned int offset = 0;
    int sector = -1;

    // iterate over 2x sectors (accounting for header and data sections)
    for (unsigned int sct2=0; sct2<(NUM_SECTORS<<1)+1; sct2++) {
        uint8_t prologue[3] = {0,0,0}; // D5AA..

        // Find the beginning of a header or data prologue
        for (unsigned int i=0, idx=0; i<NIB_TRACK_SIZE; i++) { // FIXME: probably can change this to NIB_SEC_SIZE*2 ...
            uint8_t byte = trackimage[offset];
            if (idx || (byte == 0xD5)) {
                prologue[idx] = byte;
                ++idx;
            }
            ++offset;
            if (offset >= disk6.disk[drive].track_width) {
                offset = 0;
            }
            if (idx >= 3) {
                break;
            }
        }

        if (prologue[1] != 0xAA) {
            continue;
        }

#define SCTOFF 0x4
        if (prologue[2] == 0x96) {
            // found header prologue : extract sector
            offset += SCTOFF;
            if (offset >= disk6.disk[drive].track_width) {
                RELEASE_LOG("WRAPPING PROLOGUE ...");
                offset -= disk6.disk[drive].track_width;
            }
            sector = ((trackimage[offset++] & 0x55) << 1);
            sector |= (trackimage[offset++] & 0x55);
            continue;
        }
        if (UNLIKELY(prologue[2] != 0xAD)) {
            RELEASE_LOG("OMG, found mid-track 0xD5 byte...");
            continue;
        }

        // found data prologue : copy and write data to sector

        uint8_t work_buf[NUM_SIXBIT_NIBS+1];
        for (unsigned int idx=0; idx<(NUM_SIXBIT_NIBS+1); idx++) {
            work_buf[idx] = trackimage[offset];
            ++offset;
            if (offset >= disk6.disk[drive].track_width) {
                offset = 0;
            }
        }
        assert(sector >= 0 && sector < 16 && "invalid previous nibblization");
        int sec_off = 256 * disk6.disk[drive].skew_table[ sector ];
        denibblize_sector(work_buf, dst+sec_off);
        sector = -1;
    }
}

static size_t load_track_data(int drive, uint8_t * const out) {
    SCOPE_TRACE_DISK("load_track_data");

    size_t expected = 0;
    uint8_t *buf = NULL;
    if (disk6.disk[drive].nibblized) {
        // .nib image
        expected = NIB_TRACK_SIZE;
        buf = out;
        disk6.disk[disk6.drive].track_width = expected;
    } else {
        // .dsk, .do, .po images
        expected = DSK_TRACK_SIZE;
        uint8_t _buf[DSK_TRACK_SIZE] = { 0 };
        buf = _buf; // !!!
    }

    const long track_pos = expected * (disk6.disk[drive].phase >> 1);
    TEMP_FAILURE_RETRY(fseek(disk6.disk[drive].fp, track_pos, SEEK_SET));

    size_t idx = 0;
    do {
        size_t ct = fread(buf+idx, 1, expected-idx, disk6.disk[drive].fp);
        if (UNLIKELY(ct == 0)) {
            if (ferror(disk6.disk[drive].fp)) {
                // hopefully a transient error ...
                if (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK) {
                    usleep(10);
                    continue;
                } else {
                    ERRLOG("OOPS, fatal error reading disk image %s at phase %d", disk6.disk[drive].file_name,  disk6.disk[drive].phase);
                    break;
                }
            } else {
                ERRLOG("OOPS, EOF attemping to read disk image %s at phase %d", disk6.disk[drive].file_name,  disk6.disk[drive].phase);
                break;
            }
        }
        idx += ct;

        if (LIKELY(idx == expected)) {
            break;
        }
        assert(idx < expected && "the world is not sane");
    } while (1);

    if (!disk6.disk[drive].nibblized) {
        disk6.disk[disk6.drive].track_width = nibblize_track(buf, drive, out);
        expected = disk6.disk[disk6.drive].track_width;
#if CONFORMANT_TRACKS
        if (disk6.disk[drive].track_width != NI2_TRACK_SIZE) {
            ERRLOG("Invalid dsk image creation...");
            expected = 0;
        }
#endif
    }

    return expected;
}

static bool save_track_data(const uint8_t * const src, int drive) {
    SCOPE_TRACE_DISK("save_track_data");

    size_t expected = 0;
    const uint8_t *buf = NULL;
    if (disk6.disk[drive].nibblized) {
        // .nib image
        expected = NIB_TRACK_SIZE;
        buf = src;
    } else {
        // .dsk, .do, .po images
        expected = DSK_TRACK_SIZE;
        uint8_t _buf[DSK_TRACK_SIZE] = { 0 };
        denibblize_track(src, drive, _buf);
        buf = _buf; // !!!
    }

    const long track_pos = expected * (disk6.disk[disk6.drive].phase >> 1);
    TEMP_FAILURE_RETRY(fseek(disk6.disk[drive].fp, track_pos, SEEK_SET));

    size_t idx = 0;
    do {
        size_t ct = fwrite(buf+idx, 1, expected-idx, disk6.disk[drive].fp);
        if (UNLIKELY(ct == 0)) {
            if (ferror(disk6.disk[drive].fp)) {
                // hopefully a transient error ...
                if (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK) {
                    usleep(10);
                    continue;
                } else {
                    ERRLOG("OOPS, fatal error reading disk image %s at phase %d", disk6.disk[drive].file_name,  disk6.disk[drive].phase);
                    break;
                }
            } else {
                ERRLOG("OOPS, EOF attemping to read disk image %s at phase %d", disk6.disk[drive].file_name,  disk6.disk[drive].phase);
                break;
            }
        }
        idx += ct;

        if (LIKELY(idx == expected)) {
            break;
        }
        assert(idx < expected && "the world is not sane");
    } while (1);

    TEMP_FAILURE_RETRY(fflush(disk6.disk[drive].fp));

    disk6.disk[drive].track_dirty = false;
    return true;
}

// ----------------------------------------------------------------------------
// Emulator hooks

GLUE_C_READ(disk_read_write_byte)
{
    uint8_t value = 0x00;
    do {
        if (disk6.disk[disk6.drive].fp == NULL) {
            ////ERRLOG_THROTTLE("OOPS, attempt to read byte from NULL image in drive (%d)", disk6.drive+1);
            break;
        }

        if (!disk6.disk[disk6.drive].track_valid) {
            assert(!disk6.disk[disk6.drive].track_dirty);
            if (!load_track_data(disk6.drive, disk6.disk[disk6.drive].track_image)) {
                ERRLOG("OOPS, problem loading track data");
                break;
            }
            disk6.disk[disk6.drive].track_valid = true;
            disk6.disk[disk6.drive].run_byte = 0;
        }

        if (disk6.ddrw) {
            if (disk6.disk[disk6.drive].is_protected) {
                value = 0x00;
                break; // Do not write if diskette is write protected
            }

            if (disk6.disk_byte < 0x96) {
                ERRLOG("OOPS, attempting to write a non-nibblized byte");
                value = 0x00;
                break;
            }

#if DISK_TRACING
            if (test_write_fp) {
                fprintf(test_write_fp, "%02X", disk6.disk_byte);
            }
#endif
            disk6.disk[disk6.drive].track_image[disk6.disk[disk6.drive].run_byte] = disk6.disk_byte;
            disk6.disk[disk6.drive].track_dirty = true;
        } else {

            if (disk6.motor_off) { // ???
                if (disk6.motor_off > 99) {
                    ERRLOG("OOPS, potential disk motor issue");
                    value = 0x00;
                    break;
                } else {
                    disk6.motor_off++;
                }
            }

            value = disk6.disk[disk6.drive].track_image[disk6.disk[disk6.drive].run_byte];
#if DISK_TRACING
            if (test_read_fp) {
                fprintf(test_read_fp, "%02X", value);
            }
#endif
        }
    } while (0);

    ++disk6.disk[disk6.drive].run_byte;
    if (disk6.disk[disk6.drive].run_byte >= disk6.disk[disk6.drive].track_width) {
        disk6.disk[disk6.drive].run_byte = 0;
    }
#if DISK_TRACING
    if ((disk6.disk[disk6.drive].run_byte % NIB_SEC_SIZE) == 0) {
        if (disk6.ddrw) {
            if (test_write_fp) {
                fprintf(test_write_fp, "%s", "\n");
            }
        } else {
            if (test_read_fp) {
                fprintf(test_read_fp, "%s", "\n");
            }
        }
    }
#endif

    return value;
}

GLUE_C_READ(disk_read_phase)
{
    ea &= 0xFF;
    int phase = (ea>>1)&3;
    int phase_bit = (1 << phase);

    char *phase_str = NULL;
    if (ea & 1) {
        phase_str = "on ";
        stepper_phases |= phase_bit;
    } else {
        phase_str = "off";
        stepper_phases &= ~phase_bit;
    }
#if DISK_TRACING
    if (test_read_fp) {
        fprintf(test_read_fp,  "\ntrack %02X phases %X phase %d %s address $C0E%X\n", disk6.disk[disk6.drive].phase, stepper_phases, phase, phase_str, ea&0xF);
    }
    if (test_write_fp) {
        fprintf(test_write_fp, "\ntrack %02X phases %X phase %d %s address $C0E%X\n", disk6.disk[disk6.drive].phase, stepper_phases, phase, phase_str, ea&0xF);
    }
#endif

    // Disk ][ Magnet causes stepping effect:
    //  - move only when the magnet opposite the cog is off
    //  - move in the direction of an adjacent magnet if one is on
    //  - do not move if both adjacent magnets are on
    int direction = 0;
    int cur_phase = disk6.disk[disk6.drive].phase;
    if (stepper_phases & (1 << ((cur_phase + 1) & 3))) {
        direction += 1;
    }
    if (stepper_phases & (1 << ((cur_phase + 3) & 3))) {
        direction -= 1;
    }

    if (direction) {
        if (disk6.disk[disk6.drive].track_dirty) {
            save_track_data(disk6.disk[disk6.drive].track_image, disk6.drive);
        }
        disk6.disk[disk6.drive].track_valid = false;
        disk6.disk[disk6.drive].phase += direction;

        if (disk6.disk[disk6.drive].phase<0) {
            disk6.disk[disk6.drive].phase=0;
        }

        if (disk6.disk[disk6.drive].phase>69) { // AppleWin uses 79 (extra tracks/phases)?
            disk6.disk[disk6.drive].phase=69;
        }

#if DISK_TRACING
        if (test_read_fp) {
            fprintf(test_read_fp, "NEW TRK:%d\n", (disk6.disk[disk6.drive].phase>>1));
        }
        if (test_write_fp) {
            fprintf(test_write_fp, "NEW TRK:%d\n", (disk6.disk[disk6.drive].phase>>1));
        }
#endif
    }

    return ea == 0xE0 ? 0xFF : floating_bus_hibit(1);
}

GLUE_C_READ(disk_read_motor_off)
{
    clock_gettime(CLOCK_MONOTONIC, &disk6.motor_time);
    disk6.motor_off = 1;
    return floating_bus_hibit(1);
}

GLUE_C_READ(disk_read_motor_on)
{
    clock_gettime(CLOCK_MONOTONIC, &disk6.motor_time);
    disk6.motor_off = 0;
    return floating_bus_hibit(1);
}

GLUE_C_READ(disk_read_select_a)
{
    disk6.drive = 0;
    return floating_bus();
}

GLUE_C_READ(disk_read_select_b)
{
    disk6.drive = 1;
    return floating_bus();
}

GLUE_C_READ(disk_read_latch)
{
    return disk6.drive;
}

GLUE_C_READ(disk_read_prepare_in)
{
    disk6.ddrw = 0;
    return floating_bus_hibit(disk6.disk[disk6.drive].is_protected);
}

GLUE_C_READ(disk_read_prepare_out)
{
    disk6.ddrw = 1;
    return floating_bus_hibit(1);
}

GLUE_C_WRITE(disk_write_latch)
{
    disk6.disk_byte = b;
    //return b;
}

// ----------------------------------------------------------------------------

void disk6_init(void) {

    disk6_flush(0);
    disk6_flush(1);

    // load Disk II ROM
    memcpy(apple_ii_64k[0] + 0xC600, slot6_rom, 0x100);

    // disk softswitches
    // 0xC0Xi : X = slot 0x6 + 0x8 == 0xE
    cpu65_vmem_r[0xC0E0] = cpu65_vmem_r[0xC0E2] = cpu65_vmem_r[0xC0E4] = cpu65_vmem_r[0xC0E6] = disk_read_phase;
    cpu65_vmem_r[0xC0E1] = cpu65_vmem_r[0xC0E3] = cpu65_vmem_r[0xC0E5] = cpu65_vmem_r[0xC0E7] = disk_read_phase;

    cpu65_vmem_r[0xC0E8] = disk_read_motor_off;
    cpu65_vmem_r[0xC0E9] = disk_read_motor_on;
    cpu65_vmem_r[0xC0EA] = disk_read_select_a;
    cpu65_vmem_r[0xC0EB] = disk_read_select_b;
    cpu65_vmem_r[0xC0EC] = disk_read_write_byte;
    cpu65_vmem_r[0xC0ED] = disk_read_latch;
    cpu65_vmem_r[0xC0EE] = disk_read_prepare_in;
    cpu65_vmem_r[0xC0EF] = disk_read_prepare_out;

    for (unsigned int i = 0xC0E0; i < 0xC0F0; i++) {
        cpu65_vmem_w[i] = cpu65_vmem_r[i];
    }

    cpu65_vmem_w[0xC0ED] = disk_write_latch;

    disk6.disk[0].phase = disk6.disk[1].phase = 0;
    disk6.disk[0].track_valid = disk6.disk[1].track_valid = 0;
    disk6.motor_time = (struct timespec){ 0 };
    disk6.motor_off = 1;
    disk6.drive = 0;
    disk6.ddrw = 0;
}

const char *disk6_eject(int drive) {

    const char *err = NULL;

    if (disk6.disk[drive].fp) {
        disk6_flush(drive);
        TEMP_FAILURE_RETRY(fclose(disk6.disk[drive].fp));

        // foo.dsk -> foo.dsk.gz
        err = zlib_deflate(disk6.disk[drive].file_name, is_nib(disk6.disk[drive].file_name) ? NIB_SIZE : DSK_SIZE);
        if (err) {
            ERRLOG("OOPS: An error occurred when attempting to compress a disk image : %s", err);
        } else {
            unlink(disk6.disk[drive].file_name);
        }
    }

    FREE(disk6.disk[drive].file_name);
    memset(&disk6.disk[drive], 0x0, sizeof(disk6.disk[drive]));

    return err;
}

const char *disk6_insert(int drive, const char * const raw_file_name, int readonly) {

    disk6_eject(drive);

    disk6.disk[drive].file_name = strdup(raw_file_name);
    stepper_phases = 0;

    int expected = NIB_SIZE;
    disk6.disk[drive].nibblized = true;
    if (!is_nib(disk6.disk[drive].file_name)) {
        expected = DSK_SIZE;
        disk6.disk[drive].nibblized = false;
        disk6.disk[drive].skew_table = skew_table_6_do;
        if (is_po(disk6.disk[drive].file_name)) {
            disk6.disk[drive].skew_table = skew_table_6_po;
        }
    }

    char *err = NULL;
    do {
        if (is_gz(disk6.disk[drive].file_name)) {
            err = (char *)zlib_inflate(disk6.disk[drive].file_name, expected); // foo.dsk.gz -> foo.dsk
            if (err) {
                ERRLOG("OOPS: An error occurred when attempting to inflate/load a disk image : %s", err);
                break;
            }
            if (unlink(disk6.disk[drive].file_name)) { // temporarily remove .gz file
                ERRLOG("OOPS, cannot unlink %s", disk6.disk[drive].file_name);
            }
            cut_gz(disk6.disk[drive].file_name);
        }

        struct stat stat_buf;
        if (stat(disk6.disk[drive].file_name, &stat_buf) < 0) {
            ERRLOG("OOPS, could not stat %s", disk6.disk[drive].file_name);
            err = ERR_STAT_FAILED;
            break;
        }

        if (stat_buf.st_size != expected) {
            ERRLOG("OOPS, disk image %s does not have expected byte count!", disk6.disk[drive].file_name);
            err = ERR_IMAGE_NOT_EXPECTED_SIZE;
            break;
        }

        // open image file
        TEMP_FAILURE_RETRY_FOPEN(disk6.disk[drive].fp = fopen(disk6.disk[drive].file_name, readonly ? "r" : "r+"));
        if (!disk6.disk[drive].fp && !readonly) {
            ERRLOG("OOPS, could not open %s read/write, will attempt to open readonly ...", disk6.disk[drive].file_name);
            readonly = true;
            TEMP_FAILURE_RETRY_FOPEN(disk6.disk[drive].fp = fopen(disk6.disk[drive].file_name, "r"));
        }
        disk6.disk[drive].is_protected = readonly;
        if (!disk6.disk[drive].fp) {
            ERRLOG("OOPS, could not open %s", disk6.disk[drive].file_name);
            err = ERR_CANNOT_OPEN;
            break;
        }

        disk6.disk[drive].phase = 0;
    } while (0);

    if (err) {
        disk6_eject(drive);
    }

    return err;
}

void disk6_flush(int drive) {

    if (disk6.disk[drive].track_dirty) {
        LOG("WARNING : flushing previous session for drive (%d)...", drive+1);
        save_track_data(disk6.disk[drive].track_image, drive);
    }

    TEMP_FAILURE_RETRY(fflush(disk6.disk[drive].fp));
}

#if DISK_TRACING
void c_begin_disk_trace_6(const char *read_file, const char *write_file) {
    if (read_file) {
        TEMP_FAILURE_RETRY_FOPEN(test_read_fp = fopen(read_file, "w"));
    }
    if (write_file) {
        TEMP_FAILURE_RETRY_FOPEN(test_write_fp = fopen(write_file, "w"));
    }
}

void c_end_disk_trace_6(void) {
    if (test_read_fp) {
        TEMP_FAILURE_RETRY(fflush(test_read_fp));
        TEMP_FAILURE_RETRY(fclose(test_read_fp));
        test_read_fp = NULL;
    }
    if (test_write_fp) {
        TEMP_FAILURE_RETRY(fflush(test_write_fp));
        TEMP_FAILURE_RETRY(fclose(test_write_fp));
        test_write_fp = NULL;
    }
}

void c_toggle_disk_trace_6(const char *read_file, const char *write_file) {
    if (test_read_fp) {
        c_end_disk_trace_6();
    } else {
        c_begin_disk_trace_6(read_file, write_file);
    }
}
#endif