patterns 0.3.2

use core::{
    marker::PhantomData,
    num::IntErrorKind,
    ops::Not,
    simd::{Mask, Simd},
    str::FromStr,
};

use crate::{const_utils, Scanner, VUNKNOWN as DEFAULT_BYTES};

/// A prepared pattern. Allows to search for a given byte sequence in data.
/// Supports masking and alignment requirements.
///
/// `BYTES` determines the LANES size.
/// Every block of data is processed in chunks of `BYTES` bytes.
/// Rust will compile this to other targets without issue, but will use
/// inner loops for that.
/// It is also the max length for patterns.
#[derive(Clone, Debug)]
#[must_use]
pub struct Pattern<const ALIGNMENT: usize = 1, const BYTES: usize = DEFAULT_BYTES> {
    /// raw pattern
    pub(crate) bytes: Simd<u8, BYTES>,
    /// pattern mask
    pub(crate) mask: Mask<i8, BYTES>,
    /// preprocessed chunk of `self.bytes` of size ALIGNMENT,
    /// repeated `BYTES / ALIGNMENT` times
    ///
    /// first aligned chunk that has the fewest wildcards
    pub(crate) first_bytes: Simd<u8, BYTES>,
    /// mask for `self.first_bytes`
    ///
    /// first bytes mask is inverted
    /// x & mask == mask === x | ^mask == -1
    pub(crate) first_bytes_mask: Mask<i8, BYTES>,
    /// offset of `self.first_bytes` from the start of the pattern
    pub(crate) first_byte_offset: u8,
    /// length of the pattern
    pub(crate) length: u8,
    phantom: PhantomData<[u8; ALIGNMENT]>,
}

impl<const ALIGNMENT: usize, const BYTES: usize> Pattern<ALIGNMENT, BYTES> {
    const _ALIGNED: () = {
        if ALIGNMENT > BYTES {
            panic!("Pattern ALIGNMENT must be less or equal to BYTES");
        }
    };

    /// Parse a pattern. Use [`Pattern::from_str`] to return an error instead of
    /// panicking.
    ///
    /// # Panics
    /// Panics if [`ParsePatternError`] is returned.
    #[inline]
    pub const fn new(pattern: &str) -> Self {
        match Self::from_str(pattern) {
            Ok(p) => p,
            Err(ParsePatternError::PatternTooLong) => panic!("PatternTooLong"),
            Err(ParsePatternError::InvalidHexNumber(..)) => panic!("InvalidHexNumber"),
            Err(ParsePatternError::MissingNonWildcardByte) => panic!("MissingNonWildcardByte"),
        }
    }

    /// Create a pattern from a byte slice and a mask.
    /// Byte slices longer than `BYTES` are cut short.
    /// Mask expects a [`u64`] bitencoding. A 0 bit marks the byte as wildcard.
    /// Mask is trimmed to `bytes.len()`.
    ///
    /// # Panics
    /// Panics when all bytes are masked as wildcards.
    pub fn from_slice(bytes: &[u8], mask: u64) -> Self {
        #[expect(
            path_statements,
            reason = "This forces evaluation of the const and emits a compile time error."
        )]
        Self::_ALIGNED;
        let mut input: [u8; BYTES] = [0; BYTES];
        let length = bytes.len().min(BYTES);
        input[..length].copy_from_slice(bytes);
        let mask = u64::MAX.checked_shr(length as u32).unwrap_or(0).not() & mask;
        let bytes = Simd::<u8, BYTES>::from_array(input);
        let mask = Mask::<i8, BYTES>::from_bitmask(mask.reverse_bits());
        let mask_array = mask.to_simd();
        let mask_array = mask_array.as_array().as_slice();

        let first_byte_offset = find_first_byte_offset::<ALIGNMENT>(mask_array).unwrap();

        let (first_bytes, first_bytes_mask) = fill_first_bytes::<ALIGNMENT, BYTES>(
            &input[first_byte_offset..],
            &mask_array[first_byte_offset..],
        );

        Self {
            bytes,
            mask,
            first_bytes,
            first_bytes_mask,
            first_byte_offset: first_byte_offset as _,
            length: length as _,
            phantom: PhantomData,
        }
    }

    /// Parses a string to a pattern.
    ///
    /// Expected format:
    /// ```text
    /// ? 1A . B4 ?? e0 .. 5f
    /// ```
    /// `?` and `.` mark wildcards. Only the first character is checked for
    /// wildcards. `10 .error 00` is equivalent to `10 ? 00`.
    pub const fn from_str(s: &str) -> Result<Self, ParsePatternError> {
        #[expect(
            path_statements,
            reason = "This forces evaluation of the const and emits a compile time error."
        )]
        Self::_ALIGNED;
        let bytes = const_utils::SplitAsciiWhitespace::new(s);

        let length = bytes.clone().count();
        if length > BYTES {
            return Err(ParsePatternError::PatternTooLong);
        }

        let (buffer, mask) = {
            let mut buffer = [0_u8; BYTES];
            let mut mask = [0_i8; BYTES];
            let mut index = 0;
            let mut bytes = bytes;

            loop {
                let byte;
                (bytes, byte) = bytes.next();
                let byte = match byte {
                    Some(b) => b,
                    None => break,
                };

                if !const_utils::is_wildcard(byte) {
                    let parsed = match const_utils::hex_to_u8(byte) {
                        Ok(parsed) => parsed,
                        Err(e) => return Err(ParsePatternError::InvalidHexNumber(e)),
                    };
                    buffer[index] = parsed;
                    mask[index] = -1;
                }

                index += 1;
            }

            (buffer, mask)
        };

        let first_byte_offset = match find_first_byte_offset::<ALIGNMENT>(&mask) {
            Ok(offset) => offset,
            Err(e) => return Err(e),
        };

        let (_, chunk) = buffer.split_at(first_byte_offset);
        let (_, mask_chunk) = mask.split_at(first_byte_offset);
        let (first_bytes, first_bytes_mask) =
            fill_first_bytes::<ALIGNMENT, BYTES>(chunk, mask_chunk);

        // There is no const way to create a Mask
        // # Safety: Mask is defined as repr transparent over Simd<T>
        //
        // transmute doesn't accept types with sizes depending on BYTES
        let mask = Simd::from_array(mask);
        let mask = unsafe { *(&mask as *const _ as *const _) };

        Ok(Self {
            bytes: Simd::<u8, BYTES>::from_array(buffer),
            mask,
            first_bytes,
            first_bytes_mask,
            first_byte_offset: first_byte_offset as _,
            length: length as _,
            phantom: PhantomData,
        })
    }

    /// Creates an [`Iterator`] over data.
    #[inline]
    pub fn matches<'pattern, 'data>(
        &'pattern self,
        data: &'data [u8],
    ) -> Scanner<'pattern, 'data, ALIGNMENT, BYTES> {
        Scanner::new(self, data)
    }
}

const fn find_first_byte_offset<const ALIGNMENT: usize>(
    mut mask: &[i8],
) -> Result<usize, ParsePatternError> {
    let mut i = 0;
    let mut smallest = 0;
    let mut highest_count = 0;
    loop {
        if mask.len() < ALIGNMENT {
            break;
        }
        let chunk;
        (chunk, mask) = mask.split_at(ALIGNMENT);

        let mut j = 0;
        let mut count = 0;
        while j < chunk.len() {
            count += (chunk[j] != 0) as usize;
            j += 1;
        }

        let chunk_count = count;
        if chunk_count > highest_count {
            highest_count = chunk_count;
            smallest = i;
        }

        i += 1;
    }

    if highest_count == 0 {
        Err(ParsePatternError::MissingNonWildcardByte)
    } else {
        Ok(smallest * ALIGNMENT)
    }
}

const fn fill_first_bytes<const ALIGNMENT: usize, const BYTES: usize>(
    chunk: &[u8],
    mask: &[i8],
) -> (Simd<u8, BYTES>, Mask<i8, BYTES>) {
    let mut first = [0u8; BYTES];
    let mut first_mask = [0i8; BYTES];

    let mut i = 0;

    while i < BYTES / ALIGNMENT {
        let mut j = 0;
        while j < ALIGNMENT {
            first[i * ALIGNMENT + j] = chunk[j];
            first_mask[i * ALIGNMENT + j] = !mask[j];
            j += 1;
        }
        i += 1;
    }

    let bytes = Simd::from_array(first);
    // There is no const way to create a Mask
    // # Safety: Mask is defined as repr transparent over Simd<T>
    //
    // transmute doesn't accept types with sizes depending on BYTES
    let mask = Simd::from_array(first_mask);
    let mask = unsafe { *(&mask as *const _ as *const _) };

    (bytes, mask)
}

impl<const ALIGNMENT: usize, const BYTES: usize> FromStr for Pattern<ALIGNMENT, BYTES> {
    type Err = ParsePatternError;

    #[inline]
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::from_str(s)
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
#[non_exhaustive]
pub enum ParsePatternError {
    PatternTooLong,
    InvalidHexNumber(IntErrorKind),
    MissingNonWildcardByte,
}

impl From<IntErrorKind> for ParsePatternError {
    #[inline]
    fn from(value: IntErrorKind) -> Self {
        Self::InvalidHexNumber(value)
    }
}