/* Borland Pascal generic file open/close dispatcher. */

#include "tdkpin_borland_files.h"

enum {
    FILE_MODE_OFFSET = 2,
    FILE_BUFFER_POSITION_OFFSET = 8,
    FILE_BUFFER_END_OFFSET = 10,
    FILE_OPEN_PROCEDURE_OFFSET = 0x10,
    FILE_IN_OUT_PROCEDURE_OFFSET = 0x14,
    FILE_CLOSE_PROCEDURE_OFFSET = 0x1c,
    IO_ERROR_NOT_CLOSED = 0x66,
    IO_ERROR_NOT_OPEN = 0x67,
};

/* 1020:05c7 — invoke one far FileProc and publish nonzero AX to IOResult. */
uint16_t borland_call_file_procedure(
    Win16FarPtr record, uint16_t procedure_offset)
{
    Win16FarPtr procedure =
        win16_read_far_pointer(record, procedure_offset);
    uint16_t result = win16_call_file_procedure(procedure, record);
    if (result != 0) {
        atomic_store(&g_borland_io_result, result);
    }
    return result;
}

/* 1020:0586 — close input/output files; output files flush first. */
void borland_close_file(Win16FarPtr record)
{
    uint16_t mode = win16_read_u16(win16_far_add_offset(
        record, FILE_MODE_OFFSET));
    if (mode == BORLAND_FILE_OUTPUT) {
        (void)borland_call_file_procedure(
            record, FILE_IN_OUT_PROCEDURE_OFFSET);
    } else if (mode != BORLAND_FILE_INPUT) {
        atomic_store(&g_borland_io_result, IO_ERROR_NOT_OPEN);
        return;
    }
    (void)borland_call_file_procedure(record, FILE_CLOSE_PROCEDURE_OFFSET);
    win16_write_u16(record, FILE_MODE_OFFSET, BORLAND_FILE_CLOSED);
}

/* 1020:0534 — common Reset/Rewrite entry selected by DX. */
void borland_open_file(Win16FarPtr record, uint16_t mode)
{
    uint16_t current = win16_read_u16(win16_far_add_offset(
        record, FILE_MODE_OFFSET));
    if (current == BORLAND_FILE_INPUT || current == BORLAND_FILE_OUTPUT) {
        borland_close_file(record);
    } else if (current != BORLAND_FILE_CLOSED) {
        atomic_store(&g_borland_io_result, IO_ERROR_NOT_CLOSED);
        return;
    }

    win16_write_u16(record, FILE_MODE_OFFSET, mode);
    win16_write_u16(record, FILE_BUFFER_POSITION_OFFSET, 0);
    win16_write_u16(record, FILE_BUFFER_END_OFFSET, 0);
    if (borland_call_file_procedure(
            record, FILE_OPEN_PROCEDURE_OFFSET) != 0) {
        win16_write_u16(record, FILE_MODE_OFFSET, BORLAND_FILE_CLOSED);
    }
}

/* 1020:0527/052c — five-byte mode-selecting tail entries. */
void borland_reset_file(Win16FarPtr record)
{
    borland_open_file(record, BORLAND_FILE_INPUT);
}

void borland_rewrite_file(Win16FarPtr record)
{
    borland_open_file(record, BORLAND_FILE_OUTPUT);
}

/* 1020:05d8 — DOS AH=3f buffered read. */
uint16_t borland_file_read_buffer(Win16FarPtr record)
{
    uint16_t handle = win16_read_u16(record);
    uint16_t count = win16_read_u16(win16_far_add_offset(record, 4));
    Win16FarPtr buffer = win16_read_far_pointer(record, 12);
    Win16DosResult result = win16_dos_read(handle, buffer, count);
    win16_write_u16(record, 10, result.carry ? 0 : result.ax);
    win16_write_u16(record, 8, 0);
    return result.carry ? result.ax : 0;
}

static Win16DosResult write_pending_bytes(Win16FarPtr record)
{
    uint16_t count = win16_exchange_u16(
        win16_far_add_offset(record, 8), 0);
    uint16_t handle = win16_read_u16(record);
    Win16FarPtr buffer = win16_read_far_pointer(record, 12);
    Win16DosResult result = win16_dos_write(handle, buffer, count);
    if (!result.carry && result.ax != count) {
        result.ax = 0x65;
        result.carry = true;
    }
    return result;
}

/* 1020:0608 — buffered flush with short-write detection. */
uint16_t borland_file_flush_buffer(Win16FarPtr record)
{
    Win16DosResult result = write_pending_bytes(record);
    return result.carry ? result.ax : 0;
}

/* 1020:062d — same DOS write, but only carry is an error. */
uint16_t borland_file_write_buffer(Win16FarPtr record)
{
    uint16_t count = win16_exchange_u16(
        win16_far_add_offset(record, 8), 0);
    Win16DosResult result = win16_dos_write(
        win16_read_u16(record), win16_read_far_pointer(record, 12), count);
    return result.carry ? result.ax : 0;
}

/* 1020:064d — preserve DOS standard handles 0..4; close larger handles. */
uint16_t borland_file_close_handle(Win16FarPtr record)
{
    uint16_t handle = win16_read_u16(record);
    if (handle <= 4) {
        return 0;
    }
    Win16DosResult result = win16_dos_close(handle);
    return result.carry ? result.ax : 0;
}

/* 1020:0751 — generic files must be in open sentinel mode 0xd7b3. */
bool borland_validate_open_file(Win16FarPtr record)
{
    if (win16_read_u16(win16_far_add_offset(record, 2)) == 0xd7b3) {
        return true;
    }
    atomic_store(&g_borland_io_result, 0x67);
    return false;
}

/* 1020:0710 — DOS zero-byte write truncates at the current file position. */
void borland_truncate_file(Win16FarPtr record)
{
    if (!borland_validate_open_file(record)) {
        return;
    }
    uint16_t indeterminate = win16_indeterminate_u16();
    Win16DosResult result = win16_dos_write(
        win16_read_u16(record),
        win16_make_far_pointer(indeterminate, indeterminate),
        0);
    if (result.carry) {
        atomic_store(&g_borland_io_result, result.ax);
    }
}

/* 1020:072c — close a valid generic file and always mark it closed. */
void borland_close_generic_file(Win16FarPtr record)
{
    if (!borland_validate_open_file(record)) {
        return;
    }
    uint16_t handle = win16_read_u16(record);
    if (handle > 4) {
        Win16DosResult result = win16_dos_close(handle);
        if (result.carry) {
            atomic_store(&g_borland_io_result, result.ax);
        }
    }
    win16_write_u16(record, 2, BORLAND_FILE_CLOSED);
}

static void transfer_one_record(
    Win16FarPtr buffer, Win16FarPtr record, bool write)
{
    if (!borland_validate_open_file(record)) {
        return;
    }
    uint16_t bytes = win16_read_u16(win16_far_add_offset(record, 4));
    Win16DosResult result = write
        ? win16_dos_write(win16_read_u16(record), buffer, bytes)
        : win16_dos_read(win16_read_u16(record), buffer, bytes);
    if (result.carry) {
        atomic_store(&g_borland_io_result, result.ax);
    } else if (result.ax != bytes) {
        atomic_store(&g_borland_io_result, write ? 0x65 : 0x64);
    }
}

void borland_file_read_record(Win16FarPtr buffer, Win16FarPtr record)
{
    transfer_one_record(buffer, record, false);
}

void borland_file_write_record(Win16FarPtr buffer, Win16FarPtr record)
{
    transfer_one_record(buffer, record, true);
}

static void transfer_record_block(
    Win16FarPtr result_count,
    uint16_t requested_records,
    Win16FarPtr buffer,
    Win16FarPtr record,
    bool write)
{
    uint16_t records_transferred = 0;
    if (borland_validate_open_file(record)) {
        uint16_t record_size =
            win16_read_u16(win16_far_add_offset(record, 4));
        if (requested_records != 0) {
            uint16_t byte_count =
                (uint16_t)((uint32_t)requested_records * record_size);
            Win16DosResult result = write
                ? win16_dos_write(
                      win16_read_u16(record), buffer, byte_count)
                : win16_dos_read(
                      win16_read_u16(record), buffer, byte_count);
            if (result.carry) {
                atomic_store(&g_borland_io_result, result.ax);
                goto publish;
            }
            if (record_size == 0) {
                win16_integer_divide_fault();
            }
            records_transferred = (uint16_t)(result.ax / record_size);
        }
        if (result_count == 0 && records_transferred != requested_records) {
            atomic_store(&g_borland_io_result, write ? 0x65 : 0x64);
        }
    }

publish:
    if (result_count != 0) {
        win16_write_u16(result_count, 0, records_transferred);
    }
}

void borland_file_block_read(
    Win16FarPtr result_count,
    uint16_t requested_records,
    Win16FarPtr buffer,
    Win16FarPtr record)
{
    transfer_record_block(
        result_count, requested_records, buffer, record, false);
}

void borland_file_block_write(
    Win16FarPtr result_count,
    uint16_t requested_records,
    Win16FarPtr buffer,
    Win16FarPtr record)
{
    transfer_record_block(
        result_count, requested_records, buffer, record, true);
}

void borland_file_seek_record(uint32_t record_index, Win16FarPtr record)
{
    if (!borland_validate_open_file(record)) {
        return;
    }
    uint16_t record_size =
        win16_read_u16(win16_far_add_offset(record, 4));
    uint32_t byte_offset = record_index * record_size;
    Win16DosResult result =
        win16_dos_seek(win16_read_u16(record), byte_offset, 0);
    if (result.carry) {
        atomic_store(&g_borland_io_result, result.ax);
    }
}

static void open_or_create_generic_file(
    uint16_t record_size, Win16FarPtr record, bool create)
{
    uint16_t mode = win16_read_u16(win16_far_add_offset(record, 2));
    if (mode == 0xd7b3) {
        borland_close_generic_file(record);
    } else if (mode != BORLAND_FILE_CLOSED) {
        atomic_store(&g_borland_io_result, 0x66);
        return;
    }

    Win16FarPtr name = win16_far_add_offset(record, 48);
    Win16DosResult result;
    if (win16_read_u8(name) == 0) {
        result = (Win16DosResult){create ? 1 : 0, false};
    } else {
        result = create
            ? win16_dos_create(name, 0)
            : win16_dos_open(name, g_borland_file_mode);
        if (result.carry) {
            atomic_store(&g_borland_io_result, result.ax);
            return;
        }
    }
    win16_write_u16(record, 2, 0xd7b3);
    win16_write_u16(record, 0, result.ax);
    win16_write_u16(record, 4, record_size);
}

void borland_open_generic_file(uint16_t record_size, Win16FarPtr record)
{
    open_or_create_generic_file(record_size, record, false);
}

void borland_create_generic_file(uint16_t record_size, Win16FarPtr record)
{
    open_or_create_generic_file(record_size, record, true);
}

/*
 * 1020:0c76 -- when Append opens an ordinary DOS file, inspect only its last
 * 128 bytes and remove the first DOS text EOF marker (Ctrl-Z) found there.
 * Every INT 21h error is deliberately ignored by the original helper.
 */
void borland_text_truncate_at_ctrl_z(Win16FarPtr record)
{
    uint16_t handle = win16_read_u16(record);
    Win16DosExtendedResult end =
        win16_dos_seek_extended(handle, 0, 2);
    uint32_t file_size = ((uint32_t)end.dx << 16) | end.ax;
    uint32_t scan_start = file_size >= 128 ? file_size - 128 : 0;

    (void)win16_dos_seek_extended(handle, scan_start, 0);
    Win16FarPtr buffer = win16_far_add_offset(record, 0x80);
    Win16DosResult read = win16_dos_read(handle, buffer, 128);
    uint16_t bytes_read = read.carry ? 0 : read.ax;

    for (uint16_t index = 0; index != bytes_read; index++) {
        if (win16_read_u8(win16_far_add_offset(buffer, index)) != 0x1a) {
            continue;
        }

        /* CX:DX = FFFF:(index-bytes_read), exactly as the 16-bit SUB forms it. */
        uint32_t relative_offset =
            0xffff0000u | (uint16_t)(index - bytes_read);
        Win16DosExtendedResult position =
            win16_dos_seek_extended(handle, relative_offset, 2);
        Win16FarPtr ignored_buffer = win16_make_far_pointer(
            win16_far_selector(record), position.dx);
        (void)win16_dos_write(handle, ignored_buffer, 0);
        return;
    }
}

static void write_text_procedure(
    Win16FarPtr record, uint16_t offset, Win16FarPtr procedure)
{
    win16_write_u16(record, offset, win16_far_offset(procedure));
    win16_write_u16(
        record,
        (uint16_t)(offset + 2),
        win16_far_selector(procedure));
}

/*
 * 1020:0be9 -- TextRec OpenFunc.  The incoming mode selects Reset (input),
 * Rewrite (create output), or Append (read/write output).  On success it
 * installs the relocated Borland buffer callbacks used by the generic text
 * dispatcher.  DOS character devices use the unbuffered write callback in
 * both InOutFunc and FlushFunc; ordinary files use the buffered flush callback
 * in InOutFunc and a null FlushFunc.
 */
uint16_t borland_open_text_record(Win16FarPtr record)
{
    enum {
        TEXTREC_MODE_OFFSET = 2,
        TEXTREC_NAME_OFFSET = 0x30,
        TEXTREC_IN_OUT_PROCEDURE_OFFSET = 0x14,
        TEXTREC_FLUSH_PROCEDURE_OFFSET = 0x18,
        TEXTREC_CLOSE_PROCEDURE_OFFSET = 0x1c,
        BORLAND_READ_BUFFER_OFFSET = 0x05d8,
        BORLAND_FLUSH_BUFFER_OFFSET = 0x0608,
        BORLAND_WRITE_BUFFER_OFFSET = 0x062d,
        BORLAND_CLOSE_HANDLE_OFFSET = 0x064d,
    };

    uint16_t mode = win16_read_u16(
        win16_far_add_offset(record, TEXTREC_MODE_OFFSET));
    uint16_t default_handle = mode == BORLAND_FILE_INPUT ? 0 : 1;
    win16_write_u16(record, 0, default_handle);

    Win16FarPtr name = win16_far_add_offset(record, TEXTREC_NAME_OFFSET);
    if (win16_read_u8(name) != 0) {
        Win16DosResult opened;
        if (mode == BORLAND_FILE_INPUT) {
            opened = win16_dos_open(name, 0);
        } else if (mode == BORLAND_TEXT_APPEND) {
            opened = win16_dos_open(name, 2);
        } else {
            opened = win16_dos_create(name, 0);
        }
        if (opened.carry) {
            return opened.ax;
        }
        win16_write_u16(record, 0, opened.ax);
    }

    Win16FarPtr in_out_procedure = win16_relocated_code_pointer(
        5, BORLAND_READ_BUFFER_OFFSET);
    Win16FarPtr flush_procedure = 0;

    if (mode != BORLAND_FILE_INPUT) {
        Win16DosExtendedResult device = win16_dos_get_device_info(
            win16_read_u16(record));
        if ((device.dx & 0x0080u) != 0) {
            in_out_procedure = win16_relocated_code_pointer(
                5, BORLAND_WRITE_BUFFER_OFFSET);
            flush_procedure = in_out_procedure;
        } else {
            if (mode == BORLAND_TEXT_APPEND) {
                borland_text_truncate_at_ctrl_z(record);
            }
            in_out_procedure = win16_relocated_code_pointer(
                5, BORLAND_FLUSH_BUFFER_OFFSET);
        }
        win16_write_u16(record, TEXTREC_MODE_OFFSET, BORLAND_FILE_OUTPUT);
    }

    write_text_procedure(
        record, TEXTREC_IN_OUT_PROCEDURE_OFFSET, in_out_procedure);
    write_text_procedure(
        record, TEXTREC_FLUSH_PROCEDURE_OFFSET, flush_procedure);
    write_text_procedure(
        record,
        TEXTREC_CLOSE_PROCEDURE_OFFSET,
        win16_relocated_code_pointer(5, BORLAND_CLOSE_HANDLE_OFFSET));
    return 0;
}

/* 1008:2374 — stored FileProc callback; receiver ignored, AX=0. */
uint16_t tdkpin_file_close_noop(Win16FarPtr record)
{
    (void)record;
    return 0;
}