chore: Move index related things to the meilidb-core workspace member

meilidb-core/src/automaton.rs

@@ -0,0 +1,91 @@
+use fst::Automaton;
+use lazy_static::lazy_static;
+use levenshtein_automata::{
+    LevenshteinAutomatonBuilder as LevBuilder,
+    DFA, Distance,
+};
+
+lazy_static! {
+    static ref LEVDIST0: LevBuilder = LevBuilder::new(0, false);
+    static ref LEVDIST1: LevBuilder = LevBuilder::new(1, false);
+    static ref LEVDIST2: LevBuilder = LevBuilder::new(2, false);
+}
+
+pub struct DfaExt {
+    query_len: usize,
+    automaton: DFA,
+}
+
+impl Automaton for DfaExt {
+    type State = <DFA as Automaton>::State;
+
+    fn start(&self) -> Self::State {
+        self.automaton.start()
+    }
+
+    fn is_match(&self, state: &Self::State) -> bool {
+        self.automaton.is_match(state)
+    }
+
+    fn can_match(&self, state: &Self::State) -> bool {
+        self.automaton.can_match(state)
+    }
+
+    fn will_always_match(&self, state: &Self::State) -> bool {
+        self.automaton.will_always_match(state)
+    }
+
+    fn accept(&self, state: &Self::State, byte: u8) -> Self::State {
+        self.automaton.accept(state, byte)
+    }
+}
+
+impl AutomatonExt for DfaExt {
+    fn eval<B: AsRef<[u8]>>(&self, s: B) -> Distance {
+        self.automaton.eval(s)
+    }
+
+    fn query_len(&self) -> usize {
+        self.query_len
+    }
+}
+
+#[derive(Copy, Clone)]
+enum PrefixSetting {
+    Prefix,
+    NoPrefix,
+}
+
+fn build_dfa_with_setting(query: &str, setting: PrefixSetting) -> DfaExt {
+    use self::PrefixSetting::{Prefix, NoPrefix};
+
+    let dfa = match query.len() {
+        0 ..= 4 => match setting {
+            Prefix   => LEVDIST0.build_prefix_dfa(query),
+            NoPrefix => LEVDIST0.build_dfa(query),
+        },
+        5 ..= 8 => match setting {
+            Prefix   => LEVDIST1.build_prefix_dfa(query),
+            NoPrefix => LEVDIST1.build_dfa(query),
+        },
+        _ => match setting {
+            Prefix   => LEVDIST2.build_prefix_dfa(query),
+            NoPrefix => LEVDIST2.build_dfa(query),
+        },
+    };
+
+    DfaExt { query_len: query.len(), automaton: dfa }
+}
+
+pub fn build_prefix_dfa(query: &str) -> DfaExt {
+    build_dfa_with_setting(query, PrefixSetting::Prefix)
+}
+
+pub fn build_dfa(query: &str) -> DfaExt {
+    build_dfa_with_setting(query, PrefixSetting::NoPrefix)
+}
+
+pub trait AutomatonExt: Automaton {
+    fn eval<B: AsRef<[u8]>>(&self, s: B) -> Distance;
+    fn query_len(&self) -> usize;
+}