#![forbid(unsafe_code)]

use super::*;

pub(crate) fn encode_oracle_date(
    year: i32,
    month: u8,
    day: u8,
    hour: u8,
    minute: u8,
    second: u8,
) -> Result<[u8; ORA_TYPE_SIZE_DATE as usize]> {
    if !(1..=9999).contains(&year)
        || !(1..=12).contains(&month)
        || !(1..=31).contains(&day)
        || hour > 23
        || minute > 59
        || second > 59
    {
        return Err(ProtocolError::TtcDecode("invalid DATE bind"));
    }
    let century = year / 100 + 100;
    let year_in_century = year % 100 + 100;
    Ok([
        u8::try_from(century).map_err(|_| ProtocolError::TtcDecode("invalid DATE century"))?,
        u8::try_from(year_in_century).map_err(|_| ProtocolError::TtcDecode("invalid DATE year"))?,
        month,
        day,
        hour + 1,
        minute + 1,
        second + 1,
    ])
}

pub(crate) fn encode_oracle_timestamp(
    year: i32,
    month: u8,
    day: u8,
    hour: u8,
    minute: u8,
    second: u8,
    nanosecond: u32,
) -> Result<Vec<u8>> {
    if nanosecond > 999_999_999 {
        return Err(ProtocolError::TtcDecode("invalid TIMESTAMP fraction"));
    }
    let date = encode_oracle_date(year, month, day, hour, minute, second)?;
    if nanosecond == 0 {
        return Ok(date.to_vec());
    }
    let mut bytes = Vec::with_capacity(ORA_TYPE_SIZE_TIMESTAMP as usize);
    bytes.extend_from_slice(&date);
    bytes.extend_from_slice(&nanosecond.to_be_bytes());
    Ok(bytes)
}

pub(crate) fn encode_oracle_timestamp_tz(
    year: i32,
    month: u8,
    day: u8,
    hour: u8,
    minute: u8,
    second: u8,
    nanosecond: u32,
) -> Result<Vec<u8>> {
    if nanosecond > 999_999_999 {
        return Err(ProtocolError::TtcDecode(
            "invalid TIMESTAMP WITH TIME ZONE fraction",
        ));
    }
    let mut bytes = Vec::with_capacity(ORA_TYPE_SIZE_TIMESTAMP_TZ as usize);
    let date = encode_oracle_date(year, month, day, hour, minute, second)?;
    bytes.extend_from_slice(&date);
    bytes.extend_from_slice(&nanosecond.to_be_bytes());
    bytes.push(TZ_HOUR_OFFSET);
    bytes.push(TZ_MINUTE_OFFSET);
    Ok(bytes)
}

pub fn decode_datetime_value(bytes: &[u8]) -> Result<QueryValue> {
    if bytes.len() < ORA_TYPE_SIZE_DATE as usize {
        return Err(ProtocolError::TtcDecode("DATE value too short"));
    }
    let mut year = (i32::from(bytes[0]) - 100) * 100 + i32::from(bytes[1]) - 100;
    let mut month = bytes[2];
    let mut day = bytes[3];
    let mut hour = bytes[4].saturating_sub(1);
    let mut minute = bytes[5].saturating_sub(1);
    let mut second = bytes[6].saturating_sub(1);
    let nanosecond = if bytes.len() >= ORA_TYPE_SIZE_TIMESTAMP as usize {
        u32::from_be_bytes(
            bytes[7..11]
                .try_into()
                .map_err(|_| ProtocolError::TtcDecode("invalid TIMESTAMP fraction"))?,
        )
    } else {
        0
    };
    if bytes.len() >= ORA_TYPE_SIZE_TIMESTAMP_TZ as usize && bytes[11] != 0 && bytes[12] != 0 {
        if bytes[11] & TNS_HAS_REGION_ID != 0 {
            return Err(ProtocolError::UnsupportedFeature(
                "named TIMESTAMP WITH TIME ZONE region",
            ));
        }
        let offset_minutes = (i32::from(bytes[11]) - i32::from(TZ_HOUR_OFFSET)) * 60
            + i32::from(bytes[12])
            - i32::from(TZ_MINUTE_OFFSET);
        (year, month, day, hour, minute, second) =
            adjust_datetime_by_minutes(year, month, day, hour, minute, second, offset_minutes)?;
    }
    Ok(QueryValue::DateTime {
        year,
        month,
        day,
        hour,
        minute,
        second,
        nanosecond,
    })
}

pub(crate) fn adjust_datetime_by_minutes(
    year: i32,
    month: u8,
    day: u8,
    hour: u8,
    minute: u8,
    second: u8,
    offset_minutes: i32,
) -> Result<(i32, u8, u8, u8, u8, u8)> {
    let days = days_from_civil(year, month, day)?;
    let seconds_of_day = i64::from(hour) * 3_600 + i64::from(minute) * 60 + i64::from(second);
    let total_seconds = days
        .checked_mul(86_400)
        .and_then(|value| value.checked_add(seconds_of_day))
        .and_then(|value| value.checked_add(i64::from(offset_minutes) * 60))
        .ok_or(ProtocolError::TtcDecode(
            "TIMESTAMP WITH TIME ZONE offset overflow",
        ))?;
    let adjusted_days = total_seconds.div_euclid(86_400);
    let adjusted_seconds = total_seconds.rem_euclid(86_400);
    let (year, month, day) = civil_from_days(adjusted_days)?;
    let hour = u8::try_from(adjusted_seconds / 3_600)
        .map_err(|_| ProtocolError::TtcDecode("invalid adjusted TIMESTAMP hour"))?;
    let minute = u8::try_from((adjusted_seconds % 3_600) / 60)
        .map_err(|_| ProtocolError::TtcDecode("invalid adjusted TIMESTAMP minute"))?;
    let second = u8::try_from(adjusted_seconds % 60)
        .map_err(|_| ProtocolError::TtcDecode("invalid adjusted TIMESTAMP second"))?;
    Ok((year, month, day, hour, minute, second))
}

pub(crate) fn days_from_civil(year: i32, month: u8, day: u8) -> Result<i64> {
    if !(1..=12).contains(&month) || !(1..=31).contains(&day) {
        return Err(ProtocolError::TtcDecode("invalid TIMESTAMP date"));
    }
    let year = year - i32::from(month <= 2);
    let era = if year >= 0 { year } else { year - 399 } / 400;
    let year_of_era = year - era * 400;
    let month = i32::from(month);
    let day = i32::from(day);
    let month_prime = month + if month > 2 { -3 } else { 9 };
    let day_of_year = (153 * month_prime + 2) / 5 + day - 1;
    let day_of_era = year_of_era * 365 + year_of_era / 4 - year_of_era / 100 + day_of_year;
    Ok(i64::from(era) * 146_097 + i64::from(day_of_era) - 719_468)
}

pub(crate) fn civil_from_days(days: i64) -> Result<(i32, u8, u8)> {
    let days = days + 719_468;
    let era = if days >= 0 { days } else { days - 146_096 } / 146_097;
    let day_of_era = days - era * 146_097;
    let year_of_era =
        (day_of_era - day_of_era / 1_460 + day_of_era / 36_524 - day_of_era / 146_096) / 365;
    let year = year_of_era + era * 400;
    let day_of_year = day_of_era - (365 * year_of_era + year_of_era / 4 - year_of_era / 100);
    let month_prime = (5 * day_of_year + 2) / 153;
    let day = day_of_year - (153 * month_prime + 2) / 5 + 1;
    let month = month_prime + if month_prime < 10 { 3 } else { -9 };
    let year = year + i64::from(month <= 2);
    Ok((
        i32::try_from(year)
            .map_err(|_| ProtocolError::TtcDecode("invalid adjusted TIMESTAMP year"))?,
        u8::try_from(month)
            .map_err(|_| ProtocolError::TtcDecode("invalid adjusted TIMESTAMP month"))?,
        u8::try_from(day)
            .map_err(|_| ProtocolError::TtcDecode("invalid adjusted TIMESTAMP day"))?,
    ))
}

pub(crate) fn encode_binary_double(value: f64) -> [u8; 8] {
    let mut bytes = value.to_bits().to_be_bytes();
    if bytes[0] & 0x80 == 0 {
        bytes[0] |= 0x80;
    } else {
        for byte in &mut bytes {
            *byte = !*byte;
        }
    }
    bytes
}

pub(crate) fn encode_binary_float(value: f32) -> [u8; 4] {
    let mut bytes = value.to_bits().to_be_bytes();
    if bytes[0] & 0x80 == 0 {
        bytes[0] |= 0x80;
    } else {
        for byte in &mut bytes {
            *byte = !*byte;
        }
    }
    bytes
}

pub(crate) fn decode_binary_float(bytes: &[u8]) -> Result<f32> {
    let bytes: [u8; 4] = bytes
        .try_into()
        .map_err(|_| ProtocolError::TtcDecode("invalid BINARY_FLOAT length"))?;
    let mut decoded = bytes;
    if decoded[0] & 0x80 != 0 {
        decoded[0] &= 0x7f;
    } else {
        for byte in &mut decoded {
            *byte = !*byte;
        }
    }
    Ok(f32::from_bits(u32::from_be_bytes(decoded)))
}

pub(crate) fn encode_interval_ds(days: i32, seconds: i32, nanoseconds: i32) -> Result<[u8; 11]> {
    let mut bytes = [0u8; 11];
    let wire_days = u32::try_from(i64::from(days) + TNS_DURATION_MID)
        .map_err(|_| ProtocolError::TtcDecode("INTERVAL DS days out of range"))?;
    bytes[..4].copy_from_slice(&wire_days.to_be_bytes());
    let to_offset_byte = |value: i32| -> Result<u8> {
        u8::try_from(value + TNS_DURATION_OFFSET)
            .map_err(|_| ProtocolError::TtcDecode("INTERVAL DS component out of range"))
    };
    bytes[4] = to_offset_byte(seconds / 3600)?;
    bytes[5] = to_offset_byte((seconds % 3600) / 60)?;
    bytes[6] = to_offset_byte(seconds % 60)?;
    let fseconds = i64::from(nanoseconds);
    let wire_fseconds = u32::try_from(fseconds + TNS_DURATION_MID)
        .map_err(|_| ProtocolError::TtcDecode("INTERVAL DS fractional seconds out of range"))?;
    bytes[7..].copy_from_slice(&wire_fseconds.to_be_bytes());
    Ok(bytes)
}

pub(crate) fn decode_interval_ds(bytes: &[u8]) -> Result<QueryValue> {
    if bytes.len() < 11 {
        return Err(ProtocolError::TtcDecode("invalid INTERVAL DS length"));
    }
    let days_wire = u32::from_be_bytes([bytes[0], bytes[1], bytes[2], bytes[3]]);
    let fseconds_wire = u32::from_be_bytes([bytes[7], bytes[8], bytes[9], bytes[10]]);
    let to_component = |value: i64| -> Result<i32> {
        i32::try_from(value).map_err(|_| ProtocolError::TtcDecode("INTERVAL DS out of range"))
    };
    Ok(QueryValue::IntervalDS {
        days: to_component(i64::from(days_wire) - TNS_DURATION_MID)?,
        hours: i32::from(bytes[4]) - TNS_DURATION_OFFSET,
        minutes: i32::from(bytes[5]) - TNS_DURATION_OFFSET,
        seconds: i32::from(bytes[6]) - TNS_DURATION_OFFSET,
        fseconds: to_component(i64::from(fseconds_wire) - TNS_DURATION_MID)?,
    })
}

/// Encodes an INTERVAL YEAR TO MONTH value (reference
/// impl/base/encoders.pyx:151-161): big-endian years offset by
/// TNS_DURATION_MID followed by months offset by TNS_DURATION_OFFSET.
pub(crate) fn encode_interval_ym(years: i32, months: i32) -> Result<[u8; 5]> {
    let mut bytes = [0u8; 5];
    let wire_years = u32::try_from(i64::from(years) + TNS_DURATION_MID)
        .map_err(|_| ProtocolError::TtcDecode("INTERVAL YM years out of range"))?;
    bytes[..4].copy_from_slice(&wire_years.to_be_bytes());
    bytes[4] = u8::try_from(months + TNS_DURATION_OFFSET)
        .map_err(|_| ProtocolError::TtcDecode("INTERVAL YM months out of range"))?;
    Ok(bytes)
}

/// Decodes an INTERVAL YEAR TO MONTH value (reference
/// impl/base/decoders.pyx:147-155). Components are signed: negative
/// intervals subtract below the offsets.
pub(crate) fn decode_interval_ym(bytes: &[u8]) -> Result<QueryValue> {
    if bytes.len() < 5 {
        return Err(ProtocolError::TtcDecode("invalid INTERVAL YM length"));
    }
    let years_wire = u32::from_be_bytes([bytes[0], bytes[1], bytes[2], bytes[3]]);
    let years = i32::try_from(i64::from(years_wire) - TNS_DURATION_MID)
        .map_err(|_| ProtocolError::TtcDecode("INTERVAL YM out of range"))?;
    Ok(QueryValue::IntervalYM {
        years,
        months: i32::from(bytes[4]) - TNS_DURATION_OFFSET,
    })
}

pub(crate) fn decode_binary_double(bytes: &[u8]) -> Result<f64> {
    let bytes: [u8; 8] = bytes
        .try_into()
        .map_err(|_| ProtocolError::TtcDecode("invalid BINARY_DOUBLE length"))?;
    let mut decoded = bytes;
    if decoded[0] & 0x80 != 0 {
        decoded[0] &= 0x7f;
    } else {
        for byte in &mut decoded {
            *byte = !*byte;
        }
    }
    Ok(f64::from_bits(u64::from_be_bytes(decoded)))
}

/// Encode a canonical decimal `value` into the Oracle `NUMBER` wire form
/// (the inverse of [`decode_number_value`]). Public so benches / parity
/// harnesses can synthesize fetch payloads. Reference
/// impl/base/encoders.pyx.
pub fn encode_number_text(value: &str) -> Result<Vec<u8>> {
    let value = value.as_bytes();
    if value.is_empty() {
        return Err(ProtocolError::TtcDecode("empty NUMBER bind"));
    }
    if value.len() > NUMBER_AS_TEXT_CHARS {
        return Err(ProtocolError::TtcDecode("NUMBER bind text too long"));
    }

    let mut pos = 0;
    let mut is_negative = false;
    if matches!(value.first(), Some(&b'-')) {
        is_negative = true;
        pos += 1;
    }

    let mut digits = Vec::with_capacity(NUMBER_AS_TEXT_CHARS);
    while let Some(byte) = value.get(pos).copied() {
        if matches!(byte, b'.' | b'e' | b'E') {
            break;
        }
        if !byte.is_ascii_digit() {
            return Err(ProtocolError::TtcDecode("invalid NUMBER bind"));
        }
        let digit = byte - b'0';
        pos += 1;
        if digit == 0 && digits.is_empty() {
            continue;
        }
        digits.push(digit);
    }
    let mut decimal_point_index = i32::try_from(digits.len()).unwrap_or(i32::MAX);

    if matches!(value.get(pos), Some(&b'.')) {
        pos += 1;
        while let Some(byte) = value.get(pos).copied() {
            if matches!(byte, b'e' | b'E') {
                break;
            }
            if !byte.is_ascii_digit() {
                return Err(ProtocolError::TtcDecode("invalid NUMBER bind"));
            }
            let digit = byte - b'0';
            pos += 1;
            if digit == 0 && digits.is_empty() {
                decimal_point_index -= 1;
                continue;
            }
            digits.push(digit);
        }
    }

    if matches!(value.get(pos).copied(), Some(b'e' | b'E')) {
        pos += 1;
        let mut exponent_is_negative = false;
        if let Some(byte) = value.get(pos).copied() {
            if byte == b'-' {
                exponent_is_negative = true;
                pos += 1;
            } else if byte == b'+' {
                pos += 1;
            }
        }
        let exponent_start = pos;
        while let Some(byte) = value.get(pos).copied() {
            if !byte.is_ascii_digit() {
                return Err(ProtocolError::TtcDecode("invalid NUMBER exponent"));
            }
            pos += 1;
        }
        if exponent_start == pos {
            return Err(ProtocolError::TtcDecode("empty NUMBER exponent"));
        }
        let exponent_text = std::str::from_utf8(&value[exponent_start..pos])
            .map_err(|_| ProtocolError::TtcDecode("invalid NUMBER exponent"))?;
        let mut exponent = exponent_text
            .parse::<i32>()
            .map_err(|_| ProtocolError::TtcDecode("invalid NUMBER exponent"))?;
        if exponent_is_negative {
            exponent = -exponent;
        }
        // `exponent` is parsed as a full i32 (the sign is stripped before
        // parsing, so it is in [0, i32::MAX] before negation) while the
        // reference treats it as int16_t. A crafted bind such as
        // "1"*160 + "e+2147483647" (within NUMBER_AS_TEXT_CHARS) would overflow
        // this add — panicking in debug builds — so add checked and reject
        // out-of-range like the reference's range check does (encoders.pyx).
        decimal_point_index = decimal_point_index
            .checked_add(exponent)
            .ok_or(ProtocolError::TtcDecode("NUMBER bind out of range"))?;
    }

    if pos < value.len() {
        return Err(ProtocolError::TtcDecode("invalid NUMBER bind suffix"));
    }

    while digits.last().is_some_and(|digit| *digit == 0) {
        digits.pop();
    }
    if digits.len() > NUMBER_MAX_DIGITS || !(-129..=126).contains(&decimal_point_index) {
        return Err(ProtocolError::TtcDecode("NUMBER bind out of range"));
    }

    let mut prepend_zero = false;
    if decimal_point_index % 2 != 0 {
        prepend_zero = true;
        if !digits.is_empty() {
            digits.push(0);
            decimal_point_index += 1;
        }
    }
    if digits.len() % 2 == 1 {
        digits.push(0);
    }

    if digits.is_empty() {
        return Ok(vec![128]);
    }

    let mut encoded = Vec::with_capacity(digits.len() / 2 + 2);
    let exponent_on_wire = decimal_point_index / 2 + 192;
    if !(0..=255).contains(&exponent_on_wire) {
        return Err(ProtocolError::TtcDecode(
            "NUMBER bind exponent out of range",
        ));
    }
    let exponent_byte = exponent_on_wire as u8;
    encoded.push(if is_negative {
        !exponent_byte
    } else {
        exponent_byte
    });

    let mut digit_pos = 0;
    for pair_num in 0..(digits.len() / 2) {
        let mut digit = if pair_num == 0 && prepend_zero {
            let digit = digits[digit_pos];
            digit_pos += 1;
            digit
        } else {
            let digit = digits[digit_pos] * 10 + digits[digit_pos + 1];
            digit_pos += 2;
            digit
        };
        if is_negative {
            digit = 101 - digit;
        } else {
            digit += 1;
        }
        encoded.push(digit);
    }

    if is_negative && digits.len() < NUMBER_MAX_DIGITS {
        encoded.push(102);
    }

    Ok(encoded)
}

pub fn decode_number_value(bytes: &[u8]) -> Result<QueryValue> {
    Ok(QueryValue::Number(super::number::OracleNumber::from_wire(
        bytes,
    )?))
}

/// Decode the Oracle `NUMBER` wire form into canonical decimal text, **appending
/// to `text`** and returning whether the value is integral. `digits` is a
/// caller-owned scratch buffer (cleared on entry) so a tight decode loop can
/// reuse one allocation across many values — this is the allocation-free core
/// the borrowed fetch path drives, writing straight into its per-row arena.
/// [`decode_number_value`] is the owning convenience wrapper.
///
/// Implemented in terms of [`decode_number_parts`] + the shared formatter
/// fragment below, so the borrowed-arena text and the owned inline
/// [`super::number::OracleNumber`] are byte-identical by construction (they walk
/// the same digits and format with the same code).
pub fn decode_number_text_into(
    bytes: &[u8],
    digits: &mut Vec<u8>,
    text: &mut String,
) -> Result<bool> {
    match decode_number_parts(bytes, digits, text)? {
        // The single-byte sentinels already wrote their canonical text.
        super::number::DecodedNumber::Text { is_integer } => Ok(is_integer),
        super::number::DecodedNumber::Parts {
            is_negative,
            decimal_point_index,
            is_integer,
        } => {
            format_number_digits(digits, is_negative, decimal_point_index, text);
            Ok(is_integer)
        }
    }
}

/// Walk the Oracle `NUMBER` wire form into `digits` (significant decimal digits,
/// each 0..=9) and report the parts needed to format the canonical text and to
/// build the inline [`super::number::OracleNumber`]. The single-byte sentinels
/// (positive zero, the `-1e126` negative sentinel) write their canonical text
/// directly into `text` and return [`super::number::DecodedNumber::Text`].
///
/// This is the SINGLE digit-decoding source of truth: both the owned inline
/// representation and the borrowed-arena text path drive it.
pub(crate) fn decode_number_parts(
    bytes: &[u8],
    digits: &mut Vec<u8>,
    text: &mut String,
) -> Result<super::number::DecodedNumber> {
    use super::number::DecodedNumber;

    if bytes.len() > 21 {
        return Err(ProtocolError::TtcDecode("encoded NUMBER too long"));
    }
    let Some(&first) = bytes.first() else {
        return Err(ProtocolError::TtcDecode("empty NUMBER"));
    };
    let is_positive = first & 0x80 != 0;
    digits.clear();
    if bytes.len() == 1 {
        if is_positive {
            text.push('0');
        } else {
            text.push_str("-1e126");
        }
        return Ok(DecodedNumber::Text { is_integer: true });
    }

    let exponent_byte = if is_positive { first } else { !first };
    let exponent = i16::from(exponent_byte) - 193;
    let mut decimal_point_index = exponent * 2 + 2;
    let mut end = bytes.len();
    if !is_positive && bytes[end - 1] == 102 {
        end -= 1;
    }

    for (index, encoded) in bytes.iter().enumerate().take(end).skip(1) {
        let value = if is_positive {
            encoded.saturating_sub(1)
        } else {
            101u8.saturating_sub(*encoded)
        };

        let first_digit = value / 10;
        if first_digit == 0 && digits.is_empty() {
            decimal_point_index -= 1;
        } else if first_digit == 10 {
            digits.push(1);
            digits.push(0);
            decimal_point_index += 1;
        } else if first_digit != 0 || index > 0 {
            digits.push(first_digit);
        }

        let second_digit = value % 10;
        if second_digit != 0 || index < end - 1 {
            digits.push(second_digit);
        }
    }

    // `is_integer` is true unless the canonical text gets a decimal point: that
    // happens when `decimal_point_index <= 0` (leading "0.") or the point falls
    // strictly inside the significant digits (`0 < dpi < len`).
    let len = i16::try_from(digits.len()).unwrap_or(i16::MAX);
    let is_integer = decimal_point_index > 0 && decimal_point_index >= len;

    Ok(DecodedNumber::Parts {
        is_negative: !is_positive,
        decimal_point_index,
        is_integer,
    })
}

/// Stack-buffer twin of [`decode_number_parts`]: walks the wire NUMBER digits
/// into `digit_buf` (no heap allocation) and reports the parts needed to build
/// the inline [`super::number::OracleNumber`]. The single-byte sentinels return
/// their fixed canonical text. The owned per-cell NUMBER decode drives this so a
/// NUMBER-heavy row allocates nothing per cell.
///
/// `digit_buf` MUST be at least [`super::number::MAX_DIGITS`] long. This shares
/// the exact digit-walk logic with [`decode_number_parts`]; keep them aligned.
pub(crate) fn decode_number_parts_stack(
    bytes: &[u8],
    digit_buf: &mut [u8],
) -> Result<super::number::DecodedNumberStack> {
    use super::number::DecodedNumberStack;

    if bytes.len() > 21 {
        return Err(ProtocolError::TtcDecode("encoded NUMBER too long"));
    }
    let Some(&first) = bytes.first() else {
        return Err(ProtocolError::TtcDecode("empty NUMBER"));
    };
    let is_positive = first & 0x80 != 0;
    if bytes.len() == 1 {
        return Ok(DecodedNumberStack::Sentinel {
            text: if is_positive { "0" } else { "-1e126" },
            is_integer: true,
        });
    }

    let exponent_byte = if is_positive { first } else { !first };
    let exponent = i16::from(exponent_byte) - 193;
    let mut decimal_point_index = exponent * 2 + 2;
    let mut end = bytes.len();
    if !is_positive && bytes[end - 1] == 102 {
        end -= 1;
    }

    let mut len = 0usize;
    // FUSED i128 coefficient (bead rust-oracledb-shh): folded as each significant
    // digit is emitted, removing the second `digits_to_i128` walk over the digit
    // buffer for the common in-range NUMBER. `Some(acc)` accumulates `acc*10 + d`
    // over the SAME digit sequence, in the SAME order, that `digits_to_i128`
    // walks — so the result is byte-identical. On overflow it latches to `None`
    // and the digit buffer (still filled below) drives the unchanged spill path.
    let mut coeff: Option<i128> = Some(0);
    // The digit count is provably <= MAX_DIGITS for valid wire forms; guard
    // defensively so a crafted oversize input cannot index out of bounds. Each
    // emitted digit is also folded into the i128 accumulator.
    let push = |buf: &mut [u8], d: u8, len: &mut usize, coeff: &mut Option<i128>| {
        if *len < buf.len() {
            buf[*len] = d;
            *len += 1;
        }
        *coeff = coeff
            .and_then(|acc| acc.checked_mul(10))
            .and_then(|acc| acc.checked_add(i128::from(d)));
    };

    for (index, encoded) in bytes.iter().enumerate().take(end).skip(1) {
        let value = if is_positive {
            encoded.saturating_sub(1)
        } else {
            101u8.saturating_sub(*encoded)
        };

        let first_digit = value / 10;
        if first_digit == 0 && len == 0 {
            decimal_point_index -= 1;
        } else if first_digit == 10 {
            push(digit_buf, 1, &mut len, &mut coeff);
            push(digit_buf, 0, &mut len, &mut coeff);
            decimal_point_index += 1;
        } else if first_digit != 0 || index > 0 {
            push(digit_buf, first_digit, &mut len, &mut coeff);
        }

        let second_digit = value % 10;
        if second_digit != 0 || index < end - 1 {
            push(digit_buf, second_digit, &mut len, &mut coeff);
        }
    }

    let len_i16 = i16::try_from(len).unwrap_or(i16::MAX);
    let is_integer = decimal_point_index > 0 && decimal_point_index >= len_i16;

    // Apply the sign to the fused coefficient, matching `digits_to_i128`'s
    // `if is_negative { -acc }`. Negating a non-overflowed magnitude can itself
    // never overflow i128 here (the magnitude already fit), so this preserves the
    // exact spill boundary.
    let coefficient = coeff.map(|acc| if is_positive { acc } else { -acc });

    Ok(DecodedNumberStack::Parts {
        digit_len: len,
        is_negative: !is_positive,
        decimal_point_index,
        is_integer,
        coefficient,
    })
}

/// Append the canonical decimal text for `digits` (significant decimal digits,
/// each 0..=9) positioned by `decimal_point_index`, with the given sign. This is
/// the legacy `decode_number_text_into` formatting tail, factored out so the
/// inline [`super::number::OracleNumber`] formatter is the same logic. Keep it
/// byte-for-byte aligned with `super::number::fmt_inline_into`.
pub(crate) fn format_number_digits(
    digits: &[u8],
    is_negative: bool,
    decimal_point_index: i16,
    text: &mut String,
) {
    if is_negative {
        text.push('-');
    }
    if decimal_point_index <= 0 {
        text.push_str("0.");
        for _ in decimal_point_index..0 {
            text.push('0');
        }
    }
    for (index, digit) in digits.iter().enumerate() {
        if index > 0
            && matches!(
                i16::try_from(index)
                    .unwrap_or(i16::MAX)
                    .cmp(&decimal_point_index),
                std::cmp::Ordering::Equal
            )
        {
            text.push('.');
        }
        text.push(char::from(b'0' + *digit));
    }
    if decimal_point_index > i16::try_from(digits.len()).unwrap_or(i16::MAX) {
        for _ in i16::try_from(digits.len()).unwrap_or(i16::MAX)..decimal_point_index {
            text.push('0');
        }
    }
}

pub(crate) fn decode_text_value(bytes: &[u8], csfrm: u8) -> Result<String> {
    if csfrm == CS_FORM_NCHAR {
        let units = bytes
            .chunks_exact(2)
            .map(|chunk| u16::from_be_bytes([chunk[0], chunk[1]]))
            .collect::<Vec<_>>();
        if units.len() * 2 != bytes.len() {
            return Err(ProtocolError::TtcDecode("invalid UTF-16 text length"));
        }
        String::from_utf16(&units).map_err(|_| ProtocolError::TtcDecode("invalid UTF-16 text"))
    } else {
        String::from_utf8(bytes.to_vec())
            .map_err(|_| ProtocolError::TtcDecode("invalid UTF-8 text"))
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // Regression: bead rust-oracledb-jmc. A crafted BindValue::Number whose
    // text packs many leading digits and a huge exponent (within the
    // NUMBER_AS_TEXT_CHARS cap) used to overflow `decimal_point_index +=
    // exponent`, panicking in debug builds. The reference rejects such values;
    // we must too (clean Err, never a panic).
    #[test]
    fn number_text_huge_exponent_rejected_not_panicked() {
        // 160 digits + "e+2147483647" == 172 bytes == NUMBER_AS_TEXT_CHARS.
        let crafted = format!("{}e+2147483647", "1".repeat(160));
        assert_eq!(crafted.len(), NUMBER_AS_TEXT_CHARS);
        assert!(encode_number_text(&crafted).is_err());

        // Negative-exponent counterpart must also reject without panicking.
        let crafted_neg = format!("0.{}e-2147483647", "0".repeat(158));
        assert!(encode_number_text(&crafted_neg).is_err());
    }

    #[test]
    fn number_text_ordinary_values_still_encode() {
        for ok in [
            "0",
            "1",
            "-1",
            "3.14159",
            "1e10",
            "-2.5e-3",
            "12345678901234567890",
        ] {
            assert!(encode_number_text(ok).is_ok(), "expected {ok} to encode");
        }
    }

    #[test]
    fn interval_ds_roundtrip_preserves_nanoseconds() {
        let wire = encode_interval_ds(2, 3 * 3600 + 4 * 60 + 5, 123_456_789)
            .expect("encode nanosecond interval");
        assert_eq!(
            decode_interval_ds(&wire).expect("decode nanosecond interval"),
            QueryValue::IntervalDS {
                days: 2,
                hours: 3,
                minutes: 4,
                seconds: 5,
                fseconds: 123_456_789,
            }
        );
    }
}
