meilisearch/meilidb-core/src/automaton/dfa.rs

use once_cell::sync::OnceCell;
use levenshtein_automata::{
    LevenshteinAutomatonBuilder as LevBuilder,
    DFA,
};

static LEVDIST0: OnceCell<LevBuilder> = OnceCell::new();
static LEVDIST1: OnceCell<LevBuilder> = OnceCell::new();
static LEVDIST2: OnceCell<LevBuilder> = OnceCell::new();

#[derive(Copy, Clone)]
enum PrefixSetting {
    Prefix,
    NoPrefix,
}

fn build_dfa_with_setting(query: &str, setting: PrefixSetting) -> DFA {
    use PrefixSetting::{Prefix, NoPrefix};

    match query.len() {
        0 ..= 4 => {
            let builder = LEVDIST0.get_or_init(|| LevBuilder::new(0, true));
            match setting {
                Prefix   => builder.build_prefix_dfa(query),
                NoPrefix => builder.build_dfa(query),
            }
        },
        5 ..= 8 => {
            let builder = LEVDIST1.get_or_init(|| LevBuilder::new(1, true));
            match setting {
                Prefix   => builder.build_prefix_dfa(query),
                NoPrefix => builder.build_dfa(query),
            }
        },
        _ => {
            let builder = LEVDIST2.get_or_init(|| LevBuilder::new(2, true));
            match setting {
                Prefix   => builder.build_prefix_dfa(query),
                NoPrefix => builder.build_dfa(query),
            }
        },
    }
}

pub fn build_prefix_dfa(query: &str) -> DFA {
    build_dfa_with_setting(query, PrefixSetting::Prefix)
}

pub fn build_dfa(query: &str) -> DFA {
    build_dfa_with_setting(query, PrefixSetting::NoPrefix)
}