matcher_rs 0.15.1

//! Compiled single-step transforms for the text-processing pipeline.
//!
//! Each [`TransformStep`] variant wraps a low-level matcher (VariantNorm,
//! Delete, Normalize, Romanize) and provides a uniform
//! [`apply`](TransformStep::apply) interface. Returns `Option<String>` — `None`
//! when the input is unaffected.
//!
//! The registry is a fixed-size array of [`OnceLock`] slots — one per bit
//! position in [`ProcessType`]. Each slot is lazily initialized on first
//! access.

use std::sync::OnceLock;

use crate::process::{
    process_type::ProcessType,
    transform::{
        constants::*,
        delete::{DeleteFilter, DeleteMatcher},
        filter::FilterIterator,
        normalize::{NormalizeFilter, NormalizeMatcher},
        romanize::{RomanizeFilter, RomanizeMatcher},
        variant_norm::{VariantNormFilter, VariantNormMatcher},
    },
};

/// Compiled single-bit transformation step.
///
/// Each variant wraps the corresponding low-level matcher from
/// [`super::transform`]. Instances are created by `build_transform_step` and
/// cached in `TRANSFORM_STEP_CACHE` for the lifetime of the process. The
/// [`apply`](Self::apply) method provides a uniform dispatch point.
#[derive(Clone)]
pub(crate) enum TransformStep {
    /// Raw-text path; returns the input unchanged.
    None,
    /// CJK variant normalization via page-table lookup.
    VariantNorm(VariantNormMatcher),
    /// Codepoint deletion using a bitset, with optional SIMD acceleration.
    Delete(DeleteMatcher),
    /// Multi-character normalization replacements via Aho-Corasick.
    Normalize(NormalizeMatcher),
    /// CJK romanization with inter-syllable spaces preserved.
    Romanize(RomanizeMatcher),
    /// CJK romanization with inter-syllable spaces stripped.
    RomanizeChar(RomanizeMatcher),
    /// Emoji → English words via CLDR short names; strips modifiers.
    EmojiNorm(RomanizeMatcher),
}

/// Streaming byte iterator wrapping one of the four fusible
/// [`FilterIterator`] specializations.
///
/// Returned by [`TransformStep::filter_bytes`] for steps that support the
/// fused transform-scan path (Delete, Normalize, VariantNorm, Romanize,
/// RomanizeChar). `EmojiNorm` and `None` return `Option::None` from
/// `filter_bytes`.
pub(crate) enum TransformFilter<'a> {
    Delete(FilterIterator<'a, DeleteFilter<'a>>),
    Normalize(FilterIterator<'a, NormalizeFilter<'a>>),
    VariantNorm(FilterIterator<'a, VariantNormFilter<'a>>),
    Romanize(FilterIterator<'a, RomanizeFilter<'a>>),
}

impl Iterator for TransformFilter<'_> {
    type Item = u8;

    #[inline(always)]
    fn next(&mut self) -> Option<u8> {
        match self {
            Self::Delete(i) => i.next(),
            Self::Normalize(i) => i.next(),
            Self::VariantNorm(i) => i.next(),
            Self::Romanize(i) => i.next(),
        }
    }
}

impl TransformStep {
    /// Returns whether this step is guaranteed to be a no-op on ASCII input.
    ///
    /// - **VariantNorm / Romanize / RomanizeChar / EmojiNorm**: no-op — all
    ///   keys are non-ASCII.
    /// - **Delete / Normalize**: may change ASCII input (punctuation deletion,
    ///   casefold).
    #[inline(always)]
    pub(crate) fn is_noop_on_ascii_input(&self) -> bool {
        matches!(
            self,
            Self::None
                | Self::VariantNorm(_)
                | Self::Romanize(_)
                | Self::RomanizeChar(_)
                | Self::EmojiNorm(_)
        )
    }

    /// Returns a streaming byte iterator for the fused transform-scan path.
    ///
    /// The iterator applies this step's codepoint-level transformation on the
    /// fly, yielding output bytes one at a time without materializing an
    /// intermediate `String`. Used when the DFA is unavailable or text density
    /// is too high for the DFA path.
    ///
    /// Returns `None` for non-fusible steps (`None`, `EmojiNorm`).
    #[inline(always)]
    pub(crate) fn filter_bytes<'a>(&'a self, text: &'a str) -> Option<TransformFilter<'a>> {
        match self {
            Self::Delete(m) => Some(TransformFilter::Delete(m.filter_bytes(text))),
            Self::Normalize(m) => Some(TransformFilter::Normalize(m.filter_bytes(text))),
            Self::VariantNorm(m) => Some(TransformFilter::VariantNorm(m.filter_bytes(text))),
            Self::Romanize(m) | Self::RomanizeChar(m) => {
                Some(TransformFilter::Romanize(m.filter_bytes(text)))
            }
            Self::None | Self::EmojiNorm(_) => None,
        }
    }

    /// Applies this step to `text`. Returns `Some((new_string,
    /// output_density))` if the text was modified, `None` if the step is a
    /// no-op for this input.
    ///
    /// `parent_density` is the non-ASCII byte density of `text` (0.0 = pure
    /// ASCII). The returned density is an estimate for engine dispatch:
    /// - **VariantNorm**: CJK→CJK, density unchanged → `parent_density`
    /// - **Delete / Normalize**: density approximately unchanged →
    ///   `parent_density`
    /// - **Romanize / RomanizeChar**: CJK→ASCII, density drops → `0.0`
    ///
    /// When `parent_density == 0.0` the ASCII fast path fires:
    /// VariantNorm/Romanize/RomanizeChar are guaranteed no-ops on ASCII input,
    /// and Delete/Normalize produce ASCII output from ASCII input (proven by
    /// process map analysis).
    #[inline(always)]
    pub(crate) fn apply(&self, text: &str, parent_density: f32) -> Option<(String, f32)> {
        if parent_density == 0.0 {
            return match self {
                Self::None
                | Self::VariantNorm(_)
                | Self::Romanize(_)
                | Self::RomanizeChar(_)
                | Self::EmojiNorm(_) => None,
                Self::Delete(matcher) => matcher.delete(text).map(|s| (s, 0.0)),
                Self::Normalize(matcher) => matcher.replace(text).map(|s| (s, 0.0)),
            };
        }

        match self {
            Self::None => None,
            Self::VariantNorm(matcher) => matcher.replace(text).map(|s| (s, parent_density)),
            Self::Delete(matcher) => matcher.delete(text).map(|s| (s, parent_density)),
            Self::Normalize(matcher) => matcher.replace(text).map(|s| (s, parent_density)),
            Self::Romanize(matcher) | Self::RomanizeChar(matcher) | Self::EmojiNorm(matcher) => {
                matcher.replace(text).map(|s| (s, 0.0))
            }
        }
    }
}

// ---------------------------------------------------------------------------
// Lazy registry
// ---------------------------------------------------------------------------

static TRANSFORM_STEP_CACHE: [OnceLock<TransformStep>; 8] = [
    OnceLock::new(),
    OnceLock::new(),
    OnceLock::new(),
    OnceLock::new(),
    OnceLock::new(),
    OnceLock::new(),
    OnceLock::new(),
    OnceLock::new(),
];

/// Returns the cached [`TransformStep`] for a single-bit [`ProcessType`] flag.
///
/// The step is lazily initialized on first access via [`OnceLock`] and reused
/// for all subsequent calls with the same flag.
///
/// # Panics
///
/// In debug builds, panics if `process_type_bit` is not a single-bit flag
/// (i.e., not a power of two) or exceeds the cache size. Callers must iterate
/// [`ProcessType`] to extract individual bits before calling this function.
pub(crate) fn get_transform_step(process_type_bit: ProcessType) -> &'static TransformStep {
    debug_assert!(
        process_type_bit.bits().is_power_of_two() || process_type_bit == ProcessType::None,
        "get_transform_step requires a single-bit ProcessType, got {:?}",
        process_type_bit
    );
    let index = process_type_bit.bits().trailing_zeros() as usize;
    debug_assert!(index < TRANSFORM_STEP_CACHE.len());

    TRANSFORM_STEP_CACHE[index].get_or_init(|| build_transform_step(process_type_bit))
}

fn build_transform_step(process_type_bit: ProcessType) -> TransformStep {
    match process_type_bit {
        ProcessType::None => TransformStep::None,
        ProcessType::VariantNorm => TransformStep::VariantNorm(VariantNormMatcher::new(
            VARIANT_NORM_L1_BYTES,
            VARIANT_NORM_L2_BYTES,
        )),
        ProcessType::Delete => TransformStep::Delete(DeleteMatcher::new(DELETE_BITSET_BYTES)),
        ProcessType::Normalize => TransformStep::Normalize(NormalizeMatcher::new(
            NORMALIZE_L1_BYTES,
            NORMALIZE_L2_BYTES,
            NORMALIZE_STR_BYTES,
        )),
        ProcessType::Romanize => TransformStep::Romanize(RomanizeMatcher::new(
            ROMANIZE_L1_BYTES,
            ROMANIZE_L2_BYTES,
            ROMANIZE_STR_BYTES,
            false,
        )),
        ProcessType::RomanizeChar => TransformStep::RomanizeChar(RomanizeMatcher::new(
            ROMANIZE_L1_BYTES,
            ROMANIZE_L2_BYTES,
            ROMANIZE_STR_BYTES,
            true,
        )),
        ProcessType::EmojiNorm => TransformStep::EmojiNorm(RomanizeMatcher::new(
            EMOJI_NORM_L1_BYTES,
            EMOJI_NORM_L2_BYTES,
            EMOJI_NORM_STR_BYTES,
            false,
        )),
        _ => unreachable!("unsupported single-bit ProcessType"),
    }
}