skim 4.6.1

Fuzzy Finder in rust!
Documentation 
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use std::cmp::min;
use std::fmt::{Display, Error, Formatter};
use std::sync::Arc;

use crate::fuzzy_matcher::arinae::ArinaeMatcher;
#[cfg(frizbee)]
use crate::fuzzy_matcher::frizbee::FrizbeeMatcher;
use crate::fuzzy_matcher::{FuzzyMatcher, clangd::ClangdMatcher, fzy::FzyMatcher, skim::SkimMatcherV2};

use crate::item::RankBuilder;
use crate::{CaseMatching, MatchEngine, Typos};
use crate::{MatchRange, MatchResult, SkimItem};

//------------------------------------------------------------------------------
/// Fuzzy matching algorithm to use
#[derive(Debug, Copy, Clone, Default, PartialEq)]
#[cfg_attr(feature = "cli", derive(clap::ValueEnum))]
#[cfg_attr(feature = "cli", clap(rename_all = "snake_case"))]
pub enum FuzzyAlgorithm {
    /// Arinae: typo-resistant & natural algorithm, default
    #[cfg_attr(feature = "cli", clap(alias = "ari"))]
    #[default]
    Arinae,
    /// Clangd fuzzy matching algorithm
    Clangd,
    /// Fzy matching algorithm (<https://github.com/jhawthorn/fzy>)
    Fzy,
    /// Frizbee matching algorithm, typo resistant (`x86_64` and `aarch64` only)
    #[cfg(frizbee)]
    Frizbee,
    /// Previous skim fuzzy matching algorithm (v2)
    SkimV2,
}

const BYTES_1M: usize = 1024 * 1024 * 1024;

//------------------------------------------------------------------------------
// Fuzzy engine
#[derive(Default)]
pub struct FuzzyEngineBuilder {
    query: String,
    case: CaseMatching,
    algorithm: FuzzyAlgorithm,
    rank_builder: Arc<RankBuilder>,
    /// Typo tolerance configuration:
    /// - `Typos::Disabled`: no typo tolerance
    /// - `Typos::Smart`: adaptive (`pattern_length` / 4)
    /// - `Typos::Fixed(n)`: exactly n typos allowed
    typos: Typos,
    /// When true, prefer the last (rightmost) occurrence on tied scores.
    last_match: bool,
}

impl FuzzyEngineBuilder {
    pub fn query(mut self, query: &str) -> Self {
        self.query = query.to_string();
        self
    }

    pub fn case(mut self, case: CaseMatching) -> Self {
        self.case = case;
        self
    }

    pub fn algorithm(mut self, algorithm: FuzzyAlgorithm) -> Self {
        self.algorithm = algorithm;
        self
    }

    pub fn rank_builder(mut self, rank_builder: Arc<RankBuilder>) -> Self {
        self.rank_builder = rank_builder;
        self
    }

    pub fn typos(mut self, typos: Typos) -> Self {
        self.typos = typos;
        self
    }

    /// No-op: `fuzzy_match_range` is now always used (`ByteRange`).
    /// Kept for API backward compatibility.
    pub fn filter_mode(self, _filter_mode: bool) -> Self {
        self
    }

    pub fn last_match(mut self, last_match: bool) -> Self {
        self.last_match = last_match;
        self
    }

    /// Compute the effective `max_typos` for the given query.
    ///
    /// - `Typos::Disabled` → `None` (no typo tolerance)
    /// - `Typos::Smart` → adaptive: `Some(query.chars().count() / 4)`
    /// - `Typos::Fixed(n)` → `Some(n)`
    fn effective_max_typos(&self) -> Option<usize> {
        match self.typos {
            Typos::Disabled => None,
            Typos::Smart => Some(self.query.chars().count().saturating_div(4)),
            Typos::Fixed(n) => Some(n),
        }
    }

    #[allow(deprecated)]
    pub fn build(self) -> FuzzyEngine {
        #[allow(unused_mut)]
        let mut algorithm = self.algorithm;
        let max_typos = self.effective_max_typos();
        let matcher: Box<dyn FuzzyMatcher> = match algorithm {
            FuzzyAlgorithm::SkimV2 => {
                let matcher = SkimMatcherV2::default().element_limit(BYTES_1M);
                let matcher = match self.case {
                    CaseMatching::Respect => matcher.respect_case(),
                    CaseMatching::Ignore => matcher.ignore_case(),
                    CaseMatching::Smart => matcher.smart_case(),
                };
                debug!("Initialized SkimV2 algorithm");
                Box::new(matcher)
            }
            FuzzyAlgorithm::Clangd => {
                let matcher = ClangdMatcher::default();
                let matcher = match self.case {
                    CaseMatching::Respect => matcher.respect_case(),
                    CaseMatching::Ignore => matcher.ignore_case(),
                    CaseMatching::Smart => matcher.smart_case(),
                };
                debug!("Initialized Clangd algorithm");
                Box::new(matcher)
            }
            #[cfg(frizbee)]
            FuzzyAlgorithm::Frizbee => Box::new(FrizbeeMatcher::default().case(self.case).max_typos(max_typos)),
            FuzzyAlgorithm::Fzy => {
                let matcher = FzyMatcher::default().max_typos(max_typos);
                let matcher = match self.case {
                    CaseMatching::Respect => matcher.respect_case(),
                    CaseMatching::Ignore => matcher.ignore_case(),
                    CaseMatching::Smart => matcher.smart_case(),
                };
                debug!("Initialized Fzy algorithm (max_typos: {max_typos:?})");
                Box::new(matcher)
            }
            FuzzyAlgorithm::Arinae => {
                let matcher = ArinaeMatcher::new(self.case, !matches!(self.typos, Typos::Disabled), self.last_match);
                debug!("Initialized Arinae algorithm");
                Box::new(matcher)
            }
        };

        FuzzyEngine {
            matcher,
            query: self.query,
            rank_builder: self.rank_builder,
        }
    }
}

/// The fuzzy matching engine
pub struct FuzzyEngine {
    query: String,
    matcher: Box<dyn FuzzyMatcher>,
    rank_builder: Arc<RankBuilder>,
}

impl FuzzyEngine {
    /// Returns a default builder for chaining
    #[must_use]
    pub fn builder() -> FuzzyEngineBuilder {
        FuzzyEngineBuilder::default()
    }
}

impl MatchEngine for FuzzyEngine {
    fn match_item(&self, item: &dyn SkimItem) -> Option<MatchResult> {
        let item_text = item.text();
        let default_range = [(0, item_text.len())];

        // Always use fuzzy_match_range which returns (score, begin, end)
        // without computing per-character match indices.  This avoids an
        // O(pattern_len) Vec allocation per matched item and skips the full
        // traceback in the DP.  The renderer handles ByteRange directly for
        // both horizontal scrolling and match highlighting.
        let mut best: Option<(i64, usize, usize)> = None;
        for &(start, end) in item.get_matching_ranges().unwrap_or(&default_range) {
            let start = min(start, item_text.len());
            let end = min(end, item_text.len());

            let result = if self.query.is_empty() {
                Some((0i64, 0, 0))
            } else if item_text[start..end].is_empty() {
                None
            } else {
                self.matcher
                    .fuzzy_match_range(&item_text[start..end], &self.query)
                    .map(|(s, b, e)| {
                        let offset = if start != 0 {
                            item_text[..start].chars().count()
                        } else {
                            0
                        };
                        (s, b + offset, e + offset)
                    })
            };

            if result.is_some() {
                best = result;
                break;
            }
        }

        let (score, begin, end) = best?;
        // `fuzzy_match_range` returns `end` as the inclusive index of the last
        // matched character.  Convert to exclusive upper bound for CharRange.
        let end_excl = if self.query.is_empty() { end } else { end + 1 };

        // When the span length equals the query length, the match is
        // contiguous and CharRange is a perfect representation (no gaps).
        // When the span is wider than the query, there are gaps between
        // matched characters; fall back to fuzzy_indices for accurate
        // per-character highlighting (only ~25 visible items need this).
        let query_len = self.query.chars().count();
        let matched_range = if end_excl - begin == query_len {
            // Contiguous match — CharRange is exact.
            MatchRange::CharRange(begin, end_excl)
        } else {
            // Non-contiguous match — compute exact indices for correct highlighting.
            match self.matcher.fuzzy_indices(&item_text, &self.query) {
                Some((_s, indices)) => MatchRange::Chars(indices),
                None => MatchRange::CharRange(begin, end_excl),
            }
        };

        Some(MatchResult {
            rank: self
                .rank_builder
                .build_rank(i32::try_from(score).unwrap_or(i32::MAX), begin, end_excl, &item_text),
            matched_range,
        })
    }
}

impl Display for FuzzyEngine {
    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
        write!(f, "(Fuzzy: {})", self.query)
    }
}