Introduce a basically working rkv based MeiliDB

src/automaton/dfa.rs

@@ -0,0 +1,51 @@
+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, false));
+            match setting {
+                Prefix   => builder.build_prefix_dfa(query),
+                NoPrefix => builder.build_dfa(query),
+            }
+        },
+        5 ..= 8 => {
+            let builder = LEVDIST1.get_or_init(|| LevBuilder::new(1, false));
+            match setting {
+                Prefix   => builder.build_prefix_dfa(query),
+                NoPrefix => builder.build_dfa(query),
+            }
+        },
+        _ => {
+            let builder = LEVDIST2.get_or_init(|| LevBuilder::new(2, false));
+            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)
+}