dsi-bitstream 0.10.1

/*
 * SPDX-FileCopyrightText: 2025 Tommaso Fontana
 * SPDX-FileCopyrightText: 2025 Inria
 * SPDX-FileCopyrightText: 2025 Sebastiano Vigna
 *
 * SPDX-License-Identifier: Apache-2.0 OR MIT
 */

//! Enumeration of all available codes, with associated read and write methods.
//!
//! This is the slower and more generic form of dispatching, mostly used for
//! testing and writing examples. For faster dispatching, consider using
//! [dynamic] or [static] dispatch.

use super::*;
#[cfg(feature = "serde")]
use alloc::string::{String, ToString};
#[cfg(feature = "mem_dbg")]
use mem_dbg::{MemDbg, MemSize};

/// An enum whose variants represent all the available codes.
///
/// This enum is kept in sync with implementations in the [`codes`] module.
///
/// Both [`Display`] and [`FromStr`] are implemented for this enum in a
/// compatible way, making it possible to store a code as a string in a
/// configuration file and then parse it back.
///
/// [`codes`]: crate::codes
/// [`Display`]: core::fmt::Display
/// [`FromStr`]: core::str::FromStr
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "mem_dbg", derive(MemDbg, MemSize))]
#[cfg_attr(feature = "mem_dbg", mem_size(flat))]
#[cfg_attr(feature = "fuzz", derive(arbitrary::Arbitrary))]
#[non_exhaustive]
pub enum Codes {
    Unary,
    Gamma,
    Delta,
    Omega,
    VByteLe,
    VByteBe,
    Zeta(usize),
    Pi(usize),
    Golomb(u64),
    ExpGolomb(usize),
    Rice(usize),
}

impl Codes {
    /// Returns the canonical form of this code.
    ///
    /// Some codes are equivalent, in the sense that they are defined
    /// differently, but they give rise to the same codewords. Among equivalent
    /// codes, there is usually one that is faster to encode and decode, which
    /// we call the _canonical representative_ of the equivalence class.
    ///
    /// The mapping is:
    ///
    /// - [`Rice(0)`], [`Golomb(1)`] → [`Unary`]
    ///
    /// - [`Zeta(1)`], [`ExpGolomb(0)`], [`Pi(0)`] → [`Gamma`]
    ///
    /// - [`Golomb(2ⁿ)`] → [`Rice(n)`]
    ///
    /// [`Rice(0)`]: Codes::Rice
    /// [`Golomb(1)`]: Codes::Golomb
    /// [`Unary`]: Codes::Unary
    /// [`Zeta(1)`]: Codes::Zeta
    /// [`ExpGolomb(0)`]: Codes::ExpGolomb
    /// [`Pi(0)`]: Codes::Pi
    /// [`Gamma`]: Codes::Gamma
    /// [`Golomb(2ⁿ)`]: Codes::Golomb
    /// [`Rice(n)`]: Codes::Rice
    #[must_use]
    pub const fn canonicalize(self) -> Self {
        match self {
            Self::Zeta(1) | Self::ExpGolomb(0) | Self::Pi(0) => Self::Gamma,
            Self::Rice(0) | Self::Golomb(1) => Self::Unary,
            Self::Golomb(b) if b.is_power_of_two() => Self::Rice(b.trailing_zeros() as usize),
            other => other,
        }
    }

    /// Delegates to the [`DynamicCodeRead`] implementation.
    ///
    /// This inherent method is provided to reduce ambiguity in method
    /// resolution.
    #[inline(always)]
    pub fn read<E: Endianness, CR: CodesRead<E> + ?Sized>(
        &self,
        reader: &mut CR,
    ) -> Result<u64, CR::Error> {
        DynamicCodeRead::read(self, reader)
    }

    /// Delegates to the [`DynamicCodeWrite`] implementation.
    ///
    /// This inherent method is provided to reduce ambiguity in method
    /// resolution.
    #[inline(always)]
    pub fn write<E: Endianness, CW: CodesWrite<E> + ?Sized>(
        &self,
        writer: &mut CW,
        n: u64,
    ) -> Result<usize, CW::Error> {
        DynamicCodeWrite::write(self, writer, n)
    }

    /// Converts a code to the constants in the [`code_consts`] module used for
    /// [`ConstCode`]. This is mostly used to verify that the code is supported
    /// by [`ConstCode`].
    ///
    /// The code is [canonicalized] before the conversion, so equivalent codes
    /// map to the same constant.
    ///
    /// # Errors
    ///
    /// Returns [`DispatchError::UnsupportedCode`] if the (canonicalized)
    /// code has no corresponding constant in [`code_consts`].
    ///
    /// [canonicalized]: Codes::canonicalize
    pub const fn to_code_const(&self) -> Result<usize, DispatchError> {
        Ok(match self.canonicalize() {
            Self::Unary => code_consts::UNARY,
            Self::Gamma => code_consts::GAMMA,
            Self::Delta => code_consts::DELTA,
            Self::Omega => code_consts::OMEGA,
            Self::VByteLe => code_consts::VBYTE_LE,
            Self::VByteBe => code_consts::VBYTE_BE,
            Self::Zeta(2) => code_consts::ZETA2,
            Self::Zeta(3) => code_consts::ZETA3,
            Self::Zeta(4) => code_consts::ZETA4,
            Self::Zeta(5) => code_consts::ZETA5,
            Self::Zeta(6) => code_consts::ZETA6,
            Self::Zeta(7) => code_consts::ZETA7,
            Self::Zeta(8) => code_consts::ZETA8,
            Self::Zeta(9) => code_consts::ZETA9,
            Self::Zeta(10) => code_consts::ZETA10,
            Self::Rice(1) => code_consts::RICE1,
            Self::Rice(2) => code_consts::RICE2,
            Self::Rice(3) => code_consts::RICE3,
            Self::Rice(4) => code_consts::RICE4,
            Self::Rice(5) => code_consts::RICE5,
            Self::Rice(6) => code_consts::RICE6,
            Self::Rice(7) => code_consts::RICE7,
            Self::Rice(8) => code_consts::RICE8,
            Self::Rice(9) => code_consts::RICE9,
            Self::Rice(10) => code_consts::RICE10,
            Self::Pi(1) => code_consts::PI1,
            Self::Pi(2) => code_consts::PI2,
            Self::Pi(3) => code_consts::PI3,
            Self::Pi(4) => code_consts::PI4,
            Self::Pi(5) => code_consts::PI5,
            Self::Pi(6) => code_consts::PI6,
            Self::Pi(7) => code_consts::PI7,
            Self::Pi(8) => code_consts::PI8,
            Self::Pi(9) => code_consts::PI9,
            Self::Pi(10) => code_consts::PI10,
            Self::Golomb(3) => code_consts::GOLOMB3,
            Self::Golomb(5) => code_consts::GOLOMB5,
            Self::Golomb(6) => code_consts::GOLOMB6,
            Self::Golomb(7) => code_consts::GOLOMB7,
            Self::Golomb(9) => code_consts::GOLOMB9,
            Self::Golomb(10) => code_consts::GOLOMB10,
            Self::ExpGolomb(1) => code_consts::EXP_GOLOMB1,
            Self::ExpGolomb(2) => code_consts::EXP_GOLOMB2,
            Self::ExpGolomb(3) => code_consts::EXP_GOLOMB3,
            Self::ExpGolomb(4) => code_consts::EXP_GOLOMB4,
            Self::ExpGolomb(5) => code_consts::EXP_GOLOMB5,
            Self::ExpGolomb(6) => code_consts::EXP_GOLOMB6,
            Self::ExpGolomb(7) => code_consts::EXP_GOLOMB7,
            Self::ExpGolomb(8) => code_consts::EXP_GOLOMB8,
            Self::ExpGolomb(9) => code_consts::EXP_GOLOMB9,
            Self::ExpGolomb(10) => code_consts::EXP_GOLOMB10,
            _ => {
                return Err(DispatchError::UnsupportedCode(*self));
            }
        })
    }

    /// Converts a value from [`code_consts`] to a code.
    ///
    /// # Errors
    ///
    /// Returns [`DispatchError::UnsupportedCodeConst`] if the value
    /// does not correspond to any known code constant.
    pub const fn from_code_const(const_code: usize) -> Result<Self, DispatchError> {
        Ok(match const_code {
            code_consts::UNARY => Self::Unary,
            code_consts::GAMMA => Self::Gamma,
            code_consts::DELTA => Self::Delta,
            code_consts::OMEGA => Self::Omega,
            code_consts::VBYTE_LE => Self::VByteLe,
            code_consts::VBYTE_BE => Self::VByteBe,
            code_consts::ZETA2 => Self::Zeta(2),
            code_consts::ZETA3 => Self::Zeta(3),
            code_consts::ZETA4 => Self::Zeta(4),
            code_consts::ZETA5 => Self::Zeta(5),
            code_consts::ZETA6 => Self::Zeta(6),
            code_consts::ZETA7 => Self::Zeta(7),
            code_consts::ZETA8 => Self::Zeta(8),
            code_consts::ZETA9 => Self::Zeta(9),
            code_consts::ZETA10 => Self::Zeta(10),
            code_consts::RICE1 => Self::Rice(1),
            code_consts::RICE2 => Self::Rice(2),
            code_consts::RICE3 => Self::Rice(3),
            code_consts::RICE4 => Self::Rice(4),
            code_consts::RICE5 => Self::Rice(5),
            code_consts::RICE6 => Self::Rice(6),
            code_consts::RICE7 => Self::Rice(7),
            code_consts::RICE8 => Self::Rice(8),
            code_consts::RICE9 => Self::Rice(9),
            code_consts::RICE10 => Self::Rice(10),
            code_consts::PI1 => Self::Pi(1),
            code_consts::PI2 => Self::Pi(2),
            code_consts::PI3 => Self::Pi(3),
            code_consts::PI4 => Self::Pi(4),
            code_consts::PI5 => Self::Pi(5),
            code_consts::PI6 => Self::Pi(6),
            code_consts::PI7 => Self::Pi(7),
            code_consts::PI8 => Self::Pi(8),
            code_consts::PI9 => Self::Pi(9),
            code_consts::PI10 => Self::Pi(10),
            code_consts::GOLOMB3 => Self::Golomb(3),
            code_consts::GOLOMB5 => Self::Golomb(5),
            code_consts::GOLOMB6 => Self::Golomb(6),
            code_consts::GOLOMB7 => Self::Golomb(7),
            code_consts::GOLOMB9 => Self::Golomb(9),
            code_consts::GOLOMB10 => Self::Golomb(10),
            code_consts::EXP_GOLOMB1 => Self::ExpGolomb(1),
            code_consts::EXP_GOLOMB2 => Self::ExpGolomb(2),
            code_consts::EXP_GOLOMB3 => Self::ExpGolomb(3),
            code_consts::EXP_GOLOMB4 => Self::ExpGolomb(4),
            code_consts::EXP_GOLOMB5 => Self::ExpGolomb(5),
            code_consts::EXP_GOLOMB6 => Self::ExpGolomb(6),
            code_consts::EXP_GOLOMB7 => Self::ExpGolomb(7),
            code_consts::EXP_GOLOMB8 => Self::ExpGolomb(8),
            code_consts::EXP_GOLOMB9 => Self::ExpGolomb(9),
            code_consts::EXP_GOLOMB10 => Self::ExpGolomb(10),
            _ => return Err(DispatchError::UnsupportedCodeConst(const_code)),
        })
    }
}

impl DynamicCodeRead for Codes {
    #[inline]
    fn read<E: Endianness, CR: CodesRead<E> + ?Sized>(
        &self,
        reader: &mut CR,
    ) -> Result<u64, CR::Error> {
        Ok(match self.canonicalize() {
            Codes::Unary => reader.read_unary()?,
            Codes::Gamma => reader.read_gamma()?,
            Codes::Delta => reader.read_delta()?,
            Codes::Omega => reader.read_omega()?,
            Codes::VByteBe => reader.read_vbyte_be()?,
            Codes::VByteLe => reader.read_vbyte_le()?,
            Codes::Zeta(3) => reader.read_zeta3()?,
            Codes::Zeta(k) => reader.read_zeta(k)?,
            Codes::Pi(2) => reader.read_pi2()?,
            Codes::Pi(k) => reader.read_pi(k)?,
            Codes::Golomb(b) => reader.read_golomb(b)?,
            Codes::ExpGolomb(k) => reader.read_exp_golomb(k)?,
            Codes::Rice(log2_b) => reader.read_rice(log2_b)?,
        })
    }
}

impl DynamicCodeWrite for Codes {
    #[inline]
    fn write<E: Endianness, CW: CodesWrite<E> + ?Sized>(
        &self,
        writer: &mut CW,
        n: u64,
    ) -> Result<usize, CW::Error> {
        Ok(match self.canonicalize() {
            Codes::Unary => writer.write_unary(n)?,
            Codes::Gamma => writer.write_gamma(n)?,
            Codes::Delta => writer.write_delta(n)?,
            Codes::Omega => writer.write_omega(n)?,
            Codes::VByteBe => writer.write_vbyte_be(n)?,
            Codes::VByteLe => writer.write_vbyte_le(n)?,
            Codes::Zeta(3) => writer.write_zeta3(n)?,
            Codes::Zeta(k) => writer.write_zeta(n, k)?,
            Codes::Pi(2) => writer.write_pi2(n)?,
            Codes::Pi(k) => writer.write_pi(n, k)?,
            Codes::Golomb(b) => writer.write_golomb(n, b)?,
            Codes::ExpGolomb(k) => writer.write_exp_golomb(n, k)?,
            Codes::Rice(log2_b) => writer.write_rice(n, log2_b)?,
        })
    }
}

impl<E: Endianness, CR: CodesRead<E> + ?Sized> StaticCodeRead<E, CR> for Codes {
    #[inline(always)]
    fn read(&self, reader: &mut CR) -> Result<u64, CR::Error> {
        <Self as DynamicCodeRead>::read(self, reader)
    }
}

impl<E: Endianness, CW: CodesWrite<E> + ?Sized> StaticCodeWrite<E, CW> for Codes {
    #[inline(always)]
    fn write(&self, writer: &mut CW, n: u64) -> Result<usize, CW::Error> {
        <Self as DynamicCodeWrite>::write(self, writer, n)
    }
}

impl CodeLen for Codes {
    #[inline]
    fn len(&self, n: u64) -> usize {
        match self.canonicalize() {
            // The checked conversion avoids truncation on 32-bit platforms
            Codes::Unary => n
                .checked_add(1)
                .and_then(|len| usize::try_from(len).ok())
                .expect("unary code length does not fit in a usize"),
            Codes::Gamma => len_gamma(n),
            Codes::Delta => len_delta(n),
            Codes::Omega => len_omega(n),
            Codes::VByteLe | Codes::VByteBe => bit_len_vbyte(n),
            Codes::Zeta(k) => len_zeta(n, k),
            Codes::Pi(k) => len_pi(n, k),
            Codes::Golomb(b) => len_golomb(n, b),
            Codes::ExpGolomb(k) => len_exp_golomb(n, k),
            Codes::Rice(log2_b) => len_rice(n, log2_b),
        }
    }
}

#[cfg(feature = "serde")]
impl serde::Serialize for Codes {
    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        serializer.serialize_str(&self.to_string())
    }
}

#[cfg(feature = "serde")]
impl<'de> serde::Deserialize<'de> for Codes {
    fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        let s = String::deserialize(deserializer)?;
        s.parse().map_err(serde::de::Error::custom)
    }
}

impl core::fmt::Display for Codes {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        match self {
            Codes::Unary => write!(f, "Unary"),
            Codes::Gamma => write!(f, "Gamma"),
            Codes::Delta => write!(f, "Delta"),
            Codes::Omega => write!(f, "Omega"),
            Codes::VByteBe => write!(f, "VByteBe"),
            Codes::VByteLe => write!(f, "VByteLe"),
            Codes::Zeta(k) => write!(f, "Zeta({})", k),
            Codes::Pi(k) => write!(f, "Pi({})", k),
            Codes::Golomb(b) => write!(f, "Golomb({})", b),
            Codes::ExpGolomb(k) => write!(f, "ExpGolomb({})", k),
            Codes::Rice(log2_b) => write!(f, "Rice({})", log2_b),
        }
    }
}

fn array_format_error(s: &str) -> [u8; 32] {
    let mut error_buffer = [0u8; 32];
    let len = s.len().min(32);
    error_buffer[..len].copy_from_slice(&s.as_bytes()[..len]);
    error_buffer
}

impl core::str::FromStr for Codes {
    type Err = CodeError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "Unary" => Ok(Codes::Unary),
            "Gamma" => Ok(Codes::Gamma),
            "Delta" => Ok(Codes::Delta),
            "Omega" => Ok(Codes::Omega),
            "VByteBe" => Ok(Codes::VByteBe),
            "VByteLe" => Ok(Codes::VByteLe),

            _ => {
                // Strict grammar: exactly `Name(param)` with `param` a single
                // integer and nothing after the closing parenthesis. The former
                // `split` accepted trailing/incomplete text (e.g. `Zeta(3)x`).
                let inner = s
                    .strip_suffix(')')
                    .ok_or_else(|| CodeError::UnknownCode(array_format_error(s)))?;
                let (name, param) = inner
                    .split_once('(')
                    .ok_or_else(|| CodeError::UnknownCode(array_format_error(s)))?;
                if param.contains('(') || param.contains(')') {
                    return Err(CodeError::UnknownCode(array_format_error(s)));
                }
                let invalid = || CodeError::InvalidParameter(array_format_error(s));
                match name {
                    // zeta is defined for k in [1..64).
                    "Zeta" => {
                        let k: usize = param.parse()?;
                        if k == 0 || k >= 64 {
                            return Err(invalid());
                        }
                        Ok(Codes::Zeta(k))
                    }
                    // pi, exponential Golomb and Rice shift by their parameter,
                    // so it must stay below 64.
                    "Pi" => {
                        let k: usize = param.parse()?;
                        if k >= 64 {
                            return Err(invalid());
                        }
                        Ok(Codes::Pi(k))
                    }
                    "ExpGolomb" => {
                        let k: usize = param.parse()?;
                        if k >= 64 {
                            return Err(invalid());
                        }
                        Ok(Codes::ExpGolomb(k))
                    }
                    "Rice" => {
                        let k: usize = param.parse()?;
                        if k >= 64 {
                            return Err(invalid());
                        }
                        Ok(Codes::Rice(k))
                    }
                    // Golomb divides by its modulus, which must be positive.
                    "Golomb" => {
                        let b: u64 = param.parse()?;
                        if b == 0 {
                            return Err(invalid());
                        }
                        Ok(Codes::Golomb(b))
                    }
                    _ => Err(CodeError::UnknownCode(array_format_error(name))),
                }
            }
        }
    }
}

/// Error type for parsing a code from a string.
#[derive(Debug, Clone)]
pub enum CodeError {
    /// Error parsing an integer parameter.
    ParseError(core::num::ParseIntError),
    /// Unknown code name. Uses a fixed-size array instead of `String` for `no_std` compatibility.
    UnknownCode([u8; 32]),
    /// A parameter is outside the valid range for its code (for example
    /// `Golomb(0)`, `Zeta(0)`, or a shift parameter `>= 64`).
    InvalidParameter([u8; 32]),
}
impl core::error::Error for CodeError {}
impl core::fmt::Display for CodeError {
    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
        match self {
            CodeError::ParseError(e) => write!(f, "parse error: {}", e),
            CodeError::UnknownCode(s) => {
                write!(f, "unknown code: ")?;
                for c in s {
                    if *c == 0 {
                        break;
                    }
                    write!(f, "{}", *c as char)?;
                }
                Ok(())
            }
            CodeError::InvalidParameter(s) => {
                write!(f, "invalid parameter for code: ")?;
                for c in s {
                    if *c == 0 {
                        break;
                    }
                    write!(f, "{}", *c as char)?;
                }
                Ok(())
            }
        }
    }
}

impl From<core::num::ParseIntError> for CodeError {
    fn from(e: core::num::ParseIntError) -> Self {
        CodeError::ParseError(e)
    }
}

/// Structure representing minimal binary coding with a fixed upper bound.
///
/// [Minimal binary coding] does not fit the [`Codes`] enum because it is not
/// defined for all integers.
///
/// Instances of this structure can be used in contexts in which a
/// [`DynamicCodeRead`], [`DynamicCodeWrite`], [`StaticCodeRead`],
/// [`StaticCodeWrite`] or [`CodeLen`] implementing minimal binary coding
/// is necessary.
///
/// [Minimal binary coding]: crate::codes::minimal_binary
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct MinimalBinary(
    /// The upper bound of the minimal binary code.
    pub u64,
);

impl DynamicCodeRead for MinimalBinary {
    fn read<E: Endianness, R: CodesRead<E> + ?Sized>(
        &self,
        reader: &mut R,
    ) -> Result<u64, R::Error> {
        reader.read_minimal_binary(self.0)
    }
}

impl DynamicCodeWrite for MinimalBinary {
    fn write<E: Endianness, W: CodesWrite<E> + ?Sized>(
        &self,
        writer: &mut W,
        n: u64,
    ) -> Result<usize, W::Error> {
        writer.write_minimal_binary(n, self.0)
    }
}

impl<E: Endianness, CR: CodesRead<E> + ?Sized> StaticCodeRead<E, CR> for MinimalBinary {
    fn read(&self, reader: &mut CR) -> Result<u64, CR::Error> {
        <Self as DynamicCodeRead>::read(self, reader)
    }
}

impl<E: Endianness, CW: CodesWrite<E> + ?Sized> StaticCodeWrite<E, CW> for MinimalBinary {
    fn write(&self, writer: &mut CW, n: u64) -> Result<usize, CW::Error> {
        <Self as DynamicCodeWrite>::write(self, writer, n)
    }
}

impl CodeLen for MinimalBinary {
    fn len(&self, n: u64) -> usize {
        len_minimal_binary(n, self.0)
    }
}

#[cfg(test)]
mod parse_tests {
    use super::Codes;
    use core::str::FromStr;

    #[test]
    fn test_parses_valid_parameterized_codes() {
        assert_eq!(Codes::from_str("Unary").unwrap(), Codes::Unary);
        assert_eq!(Codes::from_str("Zeta(3)").unwrap(), Codes::Zeta(3));
        assert_eq!(Codes::from_str("Pi(2)").unwrap(), Codes::Pi(2));
        assert_eq!(Codes::from_str("Golomb(7)").unwrap(), Codes::Golomb(7));
        assert_eq!(
            Codes::from_str("ExpGolomb(0)").unwrap(),
            Codes::ExpGolomb(0)
        );
        assert_eq!(Codes::from_str("Rice(0)").unwrap(), Codes::Rice(0));
        assert_eq!(Codes::from_str("Rice(63)").unwrap(), Codes::Rice(63));
    }

    #[test]
    fn test_rejects_out_of_range_parameters() {
        // These previously deserialized into values that panic on first use
        // (divide-by-zero) or shift by >= 64.
        assert!(Codes::from_str("Golomb(0)").is_err());
        assert!(Codes::from_str("Zeta(0)").is_err());
        assert!(Codes::from_str("Zeta(64)").is_err());
        assert!(Codes::from_str("Rice(64)").is_err());
        assert!(Codes::from_str("Pi(64)").is_err());
        assert!(Codes::from_str("ExpGolomb(64)").is_err());
    }

    #[test]
    fn test_rejects_malformed_grammar() {
        assert!(Codes::from_str("Zeta(3").is_err());
        assert!(Codes::from_str("Zeta(3)x").is_err());
        assert!(Codes::from_str("Zeta(3)(4)").is_err());
        assert!(Codes::from_str("Zeta()").is_err());
        assert!(Codes::from_str("Nope(1)").is_err());
    }
}