#include "tdkpin_numeric.h"

static uint8_t digit_character(uint8_t digit)
{
    return (uint8_t)(digit + (digit < 10 ? '0' : 'A' - 10));
}

BorlandFormattedSlice borland_format_u32_backward(
    Win16FarPtr end, uint32_t value, uint16_t base)
{
    Win16FarPtr cursor = end;
    do {
        uint8_t digit = (uint8_t)(value % base);
        value /= base;
        cursor = win16_far_add_offset(cursor, 0xffff);
        win16_write_u8(cursor, digit_character(digit));
    } while (value != 0);
    return (BorlandFormattedSlice){
        cursor,
        (uint16_t)(win16_far_offset(end) - win16_far_offset(cursor)),
    };
}

BorlandFormattedSlice borland_format_i32_decimal_backward(
    Win16FarPtr end, int32_t value)
{
    bool negative = value < 0;
    uint32_t magnitude = negative
        ? (uint32_t)(0u - (uint32_t)value)
        : (uint32_t)value;
    BorlandFormattedSlice result =
        borland_format_u32_backward(end, magnitude, 10);
    if (negative) {
        result.start = win16_far_add_offset(result.start, 0xffff);
        win16_write_u8(result.start, '-');
        result.length++;
    }
    return result;
}

/*
 * 1020:1629 — format an int32_t into a Pascal ShortString with a signed field
 * width, left space padding, and a caller-supplied maximum length. If the
 * decimal representation is truncated, the target copies its leading bytes.
 */
void borland_format_i32_short_string(
    int16_t maximum_length,
    Win16FarPtr destination,
    int16_t field_width,
    int32_t value)
{
    uint8_t workspace[32];
    Win16FarPtr end = win16_stack_pointer(workspace + sizeof(workspace));
    BorlandFormattedSlice formatted =
        borland_format_i32_decimal_backward(end, value);
    int16_t copy_length = (int16_t)formatted.length;
    if (field_width > maximum_length) {
        field_width = maximum_length;
    }
    if (copy_length > maximum_length) {
        copy_length = maximum_length;
    }
    if (field_width < copy_length) {
        field_width = copy_length;
    }

    win16_write_u8(destination, (uint8_t)field_width);
    Win16FarPtr output = win16_far_add_offset(destination, 1);
    uint16_t padding = (uint16_t)(field_width - copy_length);
    for (uint16_t index = 0; index < padding; index++) {
        win16_write_u8(win16_far_add_offset(output, index), ' ');
    }
    output = win16_far_add_offset(output, padding);
    for (uint16_t index = 0; index < (uint16_t)copy_length; index++) {
        win16_write_u8(
            win16_far_add_offset(output, index),
            win16_read_u8(win16_far_add_offset(formatted.start, index)));
    }
}

static BorlandParseI32Result parse_finish(
    uint32_t magnitude,
    bool negative,
    Win16FarPtr cursor,
    uint16_t remaining,
    bool validate_signed_range)
{
    uint32_t result = negative ? 0u - magnitude : magnitude;
    if (validate_signed_range && magnitude != 0 &&
        negative != ((result & 0x80000000u) != 0)) {
        return (BorlandParseI32Result){0, cursor, remaining, true};
    }
    return (BorlandParseI32Result){(int32_t)result, cursor, remaining, false};
}

BorlandParseI32Result borland_parse_i32_span(
    Win16FarPtr text, uint16_t length)
{
    Win16FarPtr cursor = text;
    uint16_t remaining = length;
    bool negative = false;
    if (remaining == 0) {
        return (BorlandParseI32Result){0, cursor, 0, true};
    }

    uint8_t current = win16_read_u8(cursor);
    if (current == '+' || current == '-') {
        negative = current == '-';
        cursor = win16_far_add_offset(cursor, 1);
        remaining--;
        if (remaining == 0) {
            return (BorlandParseI32Result){0, cursor, 0, true};
        }
        current = win16_read_u8(cursor);
    }

    uint32_t magnitude = 0;
    if (current == '$') {
        cursor = win16_far_add_offset(cursor, 1);
        remaining--;
        if (remaining == 0) {
            return (BorlandParseI32Result){0, cursor, 0, true};
        }
        while (remaining != 0) {
            uint8_t value = win16_read_u8(cursor);
            if (value > 0x60) {
                value = (uint8_t)(value - 0x20);
            }
            uint8_t digit;
            if (value >= '0' && value <= '9') {
                digit = (uint8_t)(value - '0');
            } else if (value >= 'A' && value <= 'F') {
                digit = (uint8_t)(value - 'A' + 10);
            } else {
                return parse_finish(
                    magnitude, negative, cursor, remaining, true);
            }
            if ((magnitude & 0xf0000000u) != 0) {
                return (BorlandParseI32Result){0, cursor, remaining, true};
            }
            magnitude = (magnitude << 4) | digit;
            cursor = win16_far_add_offset(cursor, 1);
            remaining--;
        }
        return parse_finish(magnitude, negative, cursor, 0, false);
    }

    while (remaining != 0) {
        uint8_t value = win16_read_u8(cursor);
        if (value < '0' || value > '9') {
            break;
        }
        if ((magnitude & 0xf0000000u) != 0) {
            return (BorlandParseI32Result){0, cursor, remaining, true};
        }
        magnitude = magnitude * 10u + (uint8_t)(value - '0');
        cursor = win16_far_add_offset(cursor, 1);
        remaining--;
    }
    return parse_finish(magnitude, negative, cursor, remaining, true);
}

BorlandValI32Result borland_val_i32_short_string(Win16FarPtr string)
{
    uint16_t remaining = win16_read_u8(string);
    Win16FarPtr cursor = win16_far_add_offset(string, 1);
    while (remaining != 0 && win16_read_u8(cursor) == ' ') {
        cursor = win16_far_add_offset(cursor, 1);
        remaining--;
    }

    BorlandParseI32Result parsed =
        borland_parse_i32_span(cursor, remaining);
    if (parsed.failed || parsed.remaining != 0) {
        return (BorlandValI32Result){
            0,
            (uint16_t)(
                win16_far_offset(parsed.cursor) - win16_far_offset(string)),
        };
    }
    return (BorlandValI32Result){parsed.value, 0};
}