added unit test

Cargo.toml

@@ -21,6 +21,7 @@ tantivy-fst = "0.1"
 memmap = {version = "0.7", optional=true}
 lz4 = {version="1.20", optional=true}
 snap = {version="0.2"}
+derive_builder = "0.7"
 atomicwrites = {version="0.2.2", optional=true}
 tempfile = "3.0"
 log = "0.4"
@@ -30,7 +31,7 @@ serde_json = "1.0"
 num_cpus = "1.2"
 fs2={version="0.4", optional=true}
 itertools = "0.8"
-levenshtein_automata = {version="0.1", features=["fst_automaton"]}
+levenshtein_automata = "0.1"
 notify = {version="4", optional=true}
 bit-set = "0.5"
 uuid = { version = "0.7.2", features = ["v4", "serde"] }
@@ -81,7 +82,7 @@ unstable = [] # useful for benches.
 wasm-bindgen = ["uuid/wasm-bindgen"]
 
 [workspace]
-members = ["query-grammar"]
+members = ["query-grammar", "incremental-search"]
 
 [badges]
 travis-ci = { repository = "tantivy-search/tantivy" }

Makefile

@@ -1,3 +1,3 @@
 test:
 	echo "Run test only... No examples."
-	cargo test --tests --lib
+	cargo test --all --tests --lib

incremental-search/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "incremental-search"
+version = "0.11.0"
+authors = ["Paul Masurel <paul.masurel@gmail.com>"]
+edition = "2018"
+
+
+[dependencies]
+derive_builder = "0.7"
+tantivy = {path = ".."}

incremental-search/src/bitset.rs

@@ -0,0 +1,395 @@
+use std::fmt;
+use std::u64;
+
+#[derive(Clone, Copy, Eq, PartialEq)]
+pub(crate) struct TinySet(u64);
+
+impl fmt::Debug for TinySet {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.into_iter().collect::<Vec<u32>>().fmt(f)
+    }
+}
+
+pub struct TinySetIterator(TinySet);
+impl Iterator for TinySetIterator {
+    type Item = u32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.pop_lowest()
+    }
+}
+
+impl IntoIterator for TinySet {
+    type Item = u32;
+    type IntoIter = TinySetIterator;
+    fn into_iter(self) -> Self::IntoIter {
+        TinySetIterator(self)
+    }
+}
+
+impl TinySet {
+    /// Returns an empty `TinySet`.
+    pub fn empty() -> TinySet {
+        TinySet(0u64)
+    }
+
+    /// Returns the complement of the set in `[0, 64[`.
+    fn complement(self) -> TinySet {
+        TinySet(!self.0)
+    }
+
+    /// Returns true iff the `TinySet` contains the element `el`.
+    pub fn contains(self, el: u32) -> bool {
+        !self.intersect(TinySet::singleton(el)).is_empty()
+    }
+
+    /// Returns the intersection of `self` and `other`
+    pub fn intersect(self, other: TinySet) -> TinySet {
+        TinySet(self.0 & other.0)
+    }
+
+    /// Creates a new `TinySet` containing only one element
+    /// within `[0; 64[`
+    #[inline(always)]
+    pub fn singleton(el: u32) -> TinySet {
+        TinySet(1u64 << u64::from(el))
+    }
+
+    /// Insert a new element within [0..64[
+    #[inline(always)]
+    pub fn insert(self, el: u32) -> TinySet {
+        self.union(TinySet::singleton(el))
+    }
+
+    /// Insert a new element within [0..64[
+    #[inline(always)]
+    pub fn insert_mut(&mut self, el: u32) -> bool {
+        let old = *self;
+        *self = old.insert(el);
+        old != *self
+    }
+
+    /// Returns the union of two tinysets
+    #[inline(always)]
+    pub fn union(self, other: TinySet) -> TinySet {
+        TinySet(self.0 | other.0)
+    }
+
+    /// Returns true iff the `TinySet` is empty.
+    #[inline(always)]
+    pub fn is_empty(self) -> bool {
+        self.0 == 0u64
+    }
+
+    /// Returns the lowest element in the `TinySet`
+    /// and removes it.
+    #[inline(always)]
+    pub fn pop_lowest(&mut self) -> Option<u32> {
+        if self.is_empty() {
+            None
+        } else {
+            let lowest = self.0.trailing_zeros() as u32;
+            self.0 ^= TinySet::singleton(lowest).0;
+            Some(lowest)
+        }
+    }
+
+    /// Returns a `TinySet` than contains all values up
+    /// to limit excluded.
+    ///
+    /// The limit is assumed to be strictly lower than 64.
+    pub fn range_lower(upper_bound: u32) -> TinySet {
+        TinySet((1u64 << u64::from(upper_bound % 64u32)) - 1u64)
+    }
+
+    /// Returns a `TinySet` that contains all values greater
+    /// or equal to the given limit, included. (and up to 63)
+    ///
+    /// The limit is assumed to be strictly lower than 64.
+    pub fn range_greater_or_equal(from_included: u32) -> TinySet {
+        TinySet::range_lower(from_included).complement()
+    }
+
+    pub fn clear(&mut self) {
+        self.0 = 0u64;
+    }
+
+    pub fn len(self) -> u32 {
+        self.0.count_ones()
+    }
+}
+
+#[derive(Clone)]
+pub struct BitSet {
+    tinysets: Box<[TinySet]>,
+    len: usize, //< Technically it should be u32, but we
+    // count multiple inserts.
+    // `usize` guards us from overflow.
+    max_value: u32,
+}
+
+fn num_buckets(max_val: u32) -> u32 {
+    (max_val + 63u32) / 64u32
+}
+
+impl BitSet {
+    /// Create a new `BitSet` that may contain elements
+    /// within `[0, max_val[`.
+    pub fn with_max_value(max_value: u32) -> BitSet {
+        let num_buckets = num_buckets(max_value);
+        let tinybisets = vec![TinySet::empty(); num_buckets as usize].into_boxed_slice();
+        BitSet {
+            tinysets: tinybisets,
+            len: 0,
+            max_value,
+        }
+    }
+
+    /// Removes all elements from the `BitSet`.
+    pub fn clear(&mut self) {
+        for tinyset in self.tinysets.iter_mut() {
+            *tinyset = TinySet::empty();
+        }
+    }
+
+    /// Returns the number of elements in the `BitSet`.
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Inserts an element in the `BitSet`
+    pub fn insert(&mut self, el: u32) {
+        // we do not check saturated els.
+        let higher = el / 64u32;
+        let lower = el % 64u32;
+        self.len += if self.tinysets[higher as usize].insert_mut(lower) {
+            1
+        } else {
+            0
+        };
+    }
+
+    /// Returns true iff the elements is in the `BitSet`.
+    pub fn contains(&self, el: u32) -> bool {
+        self.tinyset(el / 64u32).contains(el % 64)
+    }
+
+    /// Returns the first non-empty `TinySet` associated to a bucket lower
+    /// or greater than bucket.
+    ///
+    /// Reminder: the tiny set with the bucket `bucket`, represents the
+    /// elements from `bucket * 64` to `(bucket+1) * 64`.
+    pub(crate) fn first_non_empty_bucket(&self, bucket: u32) -> Option<u32> {
+        self.tinysets[bucket as usize..]
+            .iter()
+            .cloned()
+            .position(|tinyset| !tinyset.is_empty())
+            .map(|delta_bucket| bucket + delta_bucket as u32)
+    }
+
+    pub fn max_value(&self) -> u32 {
+        self.max_value
+    }
+
+    /// Returns the tiny bitset representing the
+    /// the set restricted to the number range from
+    /// `bucket * 64` to `(bucket + 1) * 64`.
+    pub(crate) fn tinyset(&self, bucket: u32) -> TinySet {
+        self.tinysets[bucket as usize]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use super::BitSet;
+    use super::TinySet;
+    use crate::docset::DocSet;
+    use crate::query::BitSetDocSet;
+    use crate::tests;
+    use crate::tests::generate_nonunique_unsorted;
+    use std::collections::BTreeSet;
+    use std::collections::HashSet;
+
+    #[test]
+    fn test_tiny_set() {
+        assert!(TinySet::empty().is_empty());
+        {
+            let mut u = TinySet::empty().insert(1u32);
+            assert_eq!(u.pop_lowest(), Some(1u32));
+            assert!(u.pop_lowest().is_none())
+        }
+        {
+            let mut u = TinySet::empty().insert(1u32).insert(1u32);
+            assert_eq!(u.pop_lowest(), Some(1u32));
+            assert!(u.pop_lowest().is_none())
+        }
+        {
+            let mut u = TinySet::empty().insert(2u32);
+            assert_eq!(u.pop_lowest(), Some(2u32));
+            u.insert_mut(1u32);
+            assert_eq!(u.pop_lowest(), Some(1u32));
+            assert!(u.pop_lowest().is_none());
+        }
+        {
+            let mut u = TinySet::empty().insert(63u32);
+            assert_eq!(u.pop_lowest(), Some(63u32));
+            assert!(u.pop_lowest().is_none());
+        }
+    }
+
+    #[test]
+    fn test_bitset() {
+        let test_against_hashset = |els: &[u32], max_value: u32| {
+            let mut hashset: HashSet<u32> = HashSet::new();
+            let mut bitset = BitSet::with_max_value(max_value);
+            for &el in els {
+                assert!(el < max_value);
+                hashset.insert(el);
+                bitset.insert(el);
+            }
+            for el in 0..max_value {
+                assert_eq!(hashset.contains(&el), bitset.contains(el));
+            }
+            assert_eq!(bitset.max_value(), max_value);
+        };
+
+        test_against_hashset(&[], 0);
+        test_against_hashset(&[], 1);
+        test_against_hashset(&[0u32], 1);
+        test_against_hashset(&[0u32], 100);
+        test_against_hashset(&[1u32, 2u32], 4);
+        test_against_hashset(&[99u32], 100);
+        test_against_hashset(&[63u32], 64);
+        test_against_hashset(&[62u32, 63u32], 64);
+    }
+
+    #[test]
+    fn test_bitset_large() {
+        let arr = generate_nonunique_unsorted(100_000, 5_000);
+        let mut btreeset: BTreeSet<u32> = BTreeSet::new();
+        let mut bitset = BitSet::with_max_value(100_000);
+        for el in arr {
+            btreeset.insert(el);
+            bitset.insert(el);
+        }
+        for i in 0..100_000 {
+            assert_eq!(btreeset.contains(&i), bitset.contains(i));
+        }
+        assert_eq!(btreeset.len(), bitset.len());
+        let mut bitset_docset = BitSetDocSet::from(bitset);
+        for el in btreeset.into_iter() {
+            bitset_docset.advance();
+            assert_eq!(bitset_docset.doc(), el);
+        }
+        assert!(!bitset_docset.advance());
+    }
+
+    #[test]
+    fn test_bitset_num_buckets() {
+        use super::num_buckets;
+        assert_eq!(num_buckets(0u32), 0);
+        assert_eq!(num_buckets(1u32), 1);
+        assert_eq!(num_buckets(64u32), 1);
+        assert_eq!(num_buckets(65u32), 2);
+        assert_eq!(num_buckets(128u32), 2);
+        assert_eq!(num_buckets(129u32), 3);
+    }
+
+    #[test]
+    fn test_tinyset_range() {
+        assert_eq!(
+            TinySet::range_lower(3).into_iter().collect::<Vec<u32>>(),
+            [0, 1, 2]
+        );
+        assert!(TinySet::range_lower(0).is_empty());
+        assert_eq!(
+            TinySet::range_lower(63).into_iter().collect::<Vec<u32>>(),
+            (0u32..63u32).collect::<Vec<_>>()
+        );
+        assert_eq!(
+            TinySet::range_lower(1).into_iter().collect::<Vec<u32>>(),
+            [0]
+        );
+        assert_eq!(
+            TinySet::range_lower(2).into_iter().collect::<Vec<u32>>(),
+            [0, 1]
+        );
+        assert_eq!(
+            TinySet::range_greater_or_equal(3)
+                .into_iter()
+                .collect::<Vec<u32>>(),
+            (3u32..64u32).collect::<Vec<_>>()
+        );
+    }
+
+    #[test]
+    fn test_bitset_len() {
+        let mut bitset = BitSet::with_max_value(1_000);
+        assert_eq!(bitset.len(), 0);
+        bitset.insert(3u32);
+        assert_eq!(bitset.len(), 1);
+        bitset.insert(103u32);
+        assert_eq!(bitset.len(), 2);
+        bitset.insert(3u32);
+        assert_eq!(bitset.len(), 2);
+        bitset.insert(103u32);
+        assert_eq!(bitset.len(), 2);
+        bitset.insert(104u32);
+        assert_eq!(bitset.len(), 3);
+    }
+
+    #[test]
+    fn test_bitset_clear() {
+        let mut bitset = BitSet::with_max_value(1_000);
+        let els = tests::sample(1_000, 0.01f64);
+        for &el in &els {
+            bitset.insert(el);
+        }
+        assert!(els.iter().all(|el| bitset.contains(*el)));
+        bitset.clear();
+        for el in 0u32..1000u32 {
+            assert!(!bitset.contains(el));
+        }
+    }
+}
+
+#[cfg(all(test, feature = "unstable"))]
+mod bench {
+
+    use super::BitSet;
+    use super::TinySet;
+    use test;
+
+    #[bench]
+    fn bench_tinyset_pop(b: &mut test::Bencher) {
+        b.iter(|| {
+            let mut tinyset = TinySet::singleton(test::black_box(31u32));
+            tinyset.pop_lowest();
+            tinyset.pop_lowest();
+            tinyset.pop_lowest();
+            tinyset.pop_lowest();
+            tinyset.pop_lowest();
+            tinyset.pop_lowest();
+        });
+    }
+
+    #[bench]
+    fn bench_tinyset_sum(b: &mut test::Bencher) {
+        let tiny_set = TinySet::empty().insert(10u32).insert(14u32).insert(21u32);
+        b.iter(|| {
+            assert_eq!(test::black_box(tiny_set).into_iter().sum::<u32>(), 45u32);
+        });
+    }
+
+    #[bench]
+    fn bench_tinyarr_sum(b: &mut test::Bencher) {
+        let v = [10u32, 14u32, 21u32];
+        b.iter(|| test::black_box(v).iter().cloned().sum::<u32>());
+    }
+
+    #[bench]
+    fn bench_bitset_initialize(b: &mut test::Bencher) {
+        b.iter(|| BitSet::with_max_value(1_000_000));
+    }
+}

incremental-search/src/lib.rs

@@ -0,0 +1,266 @@
+use tantivy::query::{BooleanQuery, FuzzyTermQuery, EmptyQuery};
+use derive_builder::Builder;
+use std::str::FromStr;
+use tantivy::query::{FuzzyConfiguration, FuzzyConfigurationBuilder, Query, Occur};
+use tantivy::schema::Field;
+use tantivy::{Searcher, TantivyError, DocAddress, Term, Document};
+use tantivy::collector::TopDocs;
+use std::ops::Deref;
+
+
+#[derive(Debug)]
+pub struct IncrementalSearchQuery {
+    pub terms: Vec<String>,
+    pub last_is_prefix: bool,
+}
+
+impl IncrementalSearchQuery {
+    pub fn fuzzy_configurations(&self) -> Vec<FuzzyConfigurations> {
+        if self.terms.is_empty() {
+            return Vec::default();
+        }
+        let single_term_confs: Vec<FuzzyConfigurationBuilder> = (0u8..3u8)
+            .map(|d: u8| {
+                let mut builder = FuzzyConfigurationBuilder::default();
+                builder.distance(d).transposition_cost_one(true);
+                builder
+            })
+            .collect();
+        let mut configurations: Vec<Vec<FuzzyConfigurationBuilder>> = single_term_confs
+            .iter()
+            .map(|conf| vec![conf.clone()])
+            .collect();
+        let mut new_configurations = Vec::new();
+        for _ in 1..self.terms.len() {
+            new_configurations.clear();
+            for single_term_conf in &single_term_confs {
+                for configuration in &configurations {
+                    let mut new_configuration: Vec<FuzzyConfigurationBuilder> = configuration.clone();
+                    new_configuration.push(single_term_conf.clone());
+                    new_configurations.push(new_configuration);
+                }
+            }
+            std::mem::swap(&mut configurations, &mut new_configurations);
+        }
+        if self.last_is_prefix {
+            for configuration in &mut configurations {
+                if let Some(last_conf) = configuration.last_mut() {
+                    last_conf.prefix(true);
+                }
+            }
+        }
+        let mut fuzzy_configurations: Vec<FuzzyConfigurations> = configurations
+            .into_iter()
+            .map(FuzzyConfigurations::from)
+            .collect();
+        fuzzy_configurations.sort_by(|left, right| left.cost.partial_cmp(&right.cost).unwrap());
+        fuzzy_configurations
+    }
+
+    fn search_query(&self, fields: &[Field], configurations: FuzzyConfigurations) -> Box<dyn Query> {
+        if self.terms.is_empty() {
+            Box::new(EmptyQuery)
+        } else if self.terms.len() == 1 {
+            build_query_for_fields(fields, &self.terms[0], &configurations.configurations[0])
+        } else {
+            Box::new(BooleanQuery::from(self.terms.iter()
+                .zip(configurations.configurations.iter())
+                .map(|(term, configuration)|
+                         (Occur::Must, build_query_for_fields(fields, &term, &configuration))
+                )
+                .collect::<Vec<_>>()))
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct FuzzyConfigurations {
+    configurations: Vec<FuzzyConfiguration>,
+    cost: f64,
+}
+
+
+fn compute_cost(fuzzy_confs: &[FuzzyConfiguration]) -> f64 {
+    fuzzy_confs
+        .iter()
+        .map(|fuzzy_conf| {
+            let weight = if fuzzy_conf.prefix { 30f64 } else { 5f64 };
+            weight * f64::from(fuzzy_conf.distance)
+        })
+        .sum()
+}
+
+impl From<Vec<FuzzyConfigurationBuilder>> for FuzzyConfigurations {
+    fn from(fuzzy_conf_builder: Vec<FuzzyConfigurationBuilder>) -> FuzzyConfigurations {
+        let configurations = fuzzy_conf_builder
+            .into_iter()
+            .map(|conf| conf.build().unwrap())
+            .collect::<Vec<FuzzyConfiguration>>();
+        let cost = compute_cost(&configurations);
+        FuzzyConfigurations {
+            configurations,
+            cost,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct ParseIncrementalQueryError;
+
+impl Into<TantivyError> for ParseIncrementalQueryError {
+    fn into(self) -> TantivyError {
+        TantivyError::InvalidArgument(format!("Invalid query: {:?}", self))
+    }
+}
+
+impl FromStr for IncrementalSearchQuery {
+    type Err = ParseIncrementalQueryError;
+
+    fn from_str(query_str: &str) -> Result<Self, Self::Err> {
+        let terms: Vec<String> = query_str
+            .split_whitespace()
+            .map(ToString::to_string)
+            .collect();
+        Ok(IncrementalSearchQuery {
+            terms,
+            last_is_prefix: query_str
+                .chars()
+                .last()
+                .map(|c| !c.is_whitespace())
+                .unwrap_or(false),
+        })
+    }
+}
+
+fn build_query_for_fields(fields: &[Field], term_text: &str, conf: &FuzzyConfiguration) -> Box<dyn Query> {
+    assert!(fields.len() > 0);
+    if fields.len() > 1 {
+        let term_queries: Vec<(Occur, Box<dyn Query>)> = fields
+            .iter()
+            .map(|&field| {
+                let term = Term::from_field_text(field, term_text);
+                let query = FuzzyTermQuery::new_from_configuration(term, conf.clone());
+                let boxed_query: Box<dyn Query> = Box::new(query);
+                (Occur::Must, boxed_query)
+            })
+            .collect();
+        Box::new(BooleanQuery::from(term_queries))
+    } else {
+        let term = Term::from_field_text(fields[0], term_text);
+        Box::new( FuzzyTermQuery::new_from_configuration(term, conf.clone()))
+    }
+
+}
+
+pub struct IncrementalSearchResult {
+    pub docs: Vec<Document>
+}
+
+#[derive(Builder, Default)]
+pub struct IncrementalSearch {
+    nhits: usize,
+    #[builder(default)]
+    search_fields: Vec<Field>,
+    #[builder(default)]
+    return_fields: Vec<Field>,
+}
+
+impl IncrementalSearch {
+
+    pub fn search<S: Deref<Target=Searcher>>(
+        &self,
+        query: &str,
+        searcher: &S,
+    ) -> tantivy::Result<IncrementalSearchResult> {
+        let searcher = searcher.deref();
+        let inc_search_query: IncrementalSearchQuery =
+            FromStr::from_str(query).map_err(Into::<TantivyError>::into)?;
+
+        let mut results: Vec<DocAddress> = Vec::default();
+        let mut remaining = self.nhits;
+        for fuzzy_conf in inc_search_query.fuzzy_configurations() {
+            if remaining == 0 {
+                break;
+            }
+            let query = inc_search_query.search_query(&self.search_fields[..], fuzzy_conf);
+            let new_docs = searcher.search(query.as_ref(), &TopDocs::with_limit(remaining))?;
+            // TODO(pmasurel) remove already added docs.
+            results.extend(new_docs.into_iter()
+                .map(|(_, doc_address)| doc_address));
+            remaining = self.nhits - results.len();
+            if remaining == 0 {
+                break;
+            }
+        }
+        let docs: Vec<Document> = results.into_iter()
+            .map(|doc_address: DocAddress| searcher.doc(doc_address))
+            .collect::<tantivy::Result<_>>()?;
+        Ok(IncrementalSearchResult {
+            docs
+        })
+    }
+}
+#[cfg(test)]
+mod tests {
+    use tantivy::doc;
+    use crate::{IncrementalSearch, IncrementalSearchBuilder, IncrementalSearchQuery};
+    use std::str::FromStr;
+    use tantivy::schema::{SchemaBuilder, TEXT, STORED};
+    use tantivy::Index;
+
+    #[test]
+    fn test_incremental_search() {
+        let incremental_search = IncrementalSearchBuilder::default()
+            .nhits(10)
+            .build()
+            .unwrap();
+    }
+
+    #[test]
+    fn test_incremental_search_query_parse_empty() {
+        let query = IncrementalSearchQuery::from_str("").unwrap();
+        assert_eq!(query.terms, Vec::<String>::new());
+        assert!(!query.last_is_prefix);
+    }
+
+    #[test]
+    fn test_incremental_search_query_parse_trailing_whitespace() {
+        let query = IncrementalSearchQuery::from_str("hello happy tax pa ").unwrap();
+        assert_eq!(query.terms, vec!["hello", "happy", "tax", "pa"]);
+        assert!(!query.last_is_prefix);
+    }
+
+    #[test]
+    fn test_incremental_search_query_parse_unicode_whitespace() {
+        let query = IncrementalSearchQuery::from_str("hello  happy tax pa ").unwrap();
+        assert_eq!(query.terms, vec!["hello", "happy", "tax", "pa"]);
+        assert!(!query.last_is_prefix);
+    }
+
+    #[test]
+    fn test_incremental_search_query_parse() {
+        let query = IncrementalSearchQuery::from_str("hello happy tax pa").unwrap();
+        assert_eq!(query.terms, vec!["hello", "happy", "tax", "pa"]);
+        assert!(query.last_is_prefix);
+    }
+
+    #[test]
+    fn test_blop() {
+        let mut schema_builder = SchemaBuilder::new();
+        let body = schema_builder.add_text_field("body", TEXT | STORED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_with_num_threads(1, 30_000_000).unwrap();
+        index_writer.add_document(doc!(body=> "hello happy tax payer"));
+        index_writer.commit().unwrap();
+        let reader = index.reader().unwrap();
+        let searcher = reader.searcher();
+        let incremental_search: IncrementalSearch = IncrementalSearchBuilder::default()
+            .nhits(1)
+            .search_fields(vec![body])
+            .build()
+            .unwrap();
+        let top_docs = incremental_search.search("hello hapy t", &searcher).unwrap();
+        assert_eq!(top_docs.docs.len(), 1);
+    }
+}

src/query/fuzzy_query.rs

@@ -1,12 +1,14 @@
 use crate::error::TantivyError::InvalidArgument;
 use crate::query::{AutomatonWeight, Query, Weight};
 use crate::schema::Term;
+use crate::termdict::WrappedDFA;
 use crate::Result;
 use crate::Searcher;
-use levenshtein_automata::{LevenshteinAutomatonBuilder, DFA};
+use levenshtein_automata::{Distance, LevenshteinAutomatonBuilder, DFA};
 use once_cell::sync::Lazy;
 use std::collections::HashMap;
 use std::ops::Range;
+use derive_builder::Builder;
 
 /// A range of Levenshtein distances that we will build DFAs for our terms
 /// The computation is exponential, so best keep it to low single digits
@@ -24,6 +26,38 @@ static LEV_BUILDER: Lazy<HashMap<(u8, bool), LevenshteinAutomatonBuilder>> = Laz
     lev_builder_cache
 });
 
+
+#[derive(Builder, Default, Clone, Debug)]
+pub struct FuzzyConfiguration {
+    /// How many changes are we going to allow
+    pub distance: u8,
+    /// Should a transposition cost 1 or 2?
+    #[builder(default)]
+    pub transposition_cost_one: bool,
+    #[builder(default)]
+    pub prefix: bool,
+    /// If true, only the term with a levenshtein of exactly `distance` will match.
+    /// If false, terms at a distance `<=` to `distance` will match.
+    #[builder(default)]
+    pub exact_distance: bool,
+}
+
+fn build_dfa(fuzzy_configuration: &FuzzyConfiguration, term_text: &str) -> Result<DFA> {
+    let automaton_builder = LEV_BUILDER
+        .get(&(fuzzy_configuration.distance, fuzzy_configuration.transposition_cost_one))
+        .ok_or_else(|| {
+            InvalidArgument(format!(
+                "Levenshtein distance of {} is not allowed. Choose a value in the {:?} range",
+                fuzzy_configuration.distance, VALID_LEVENSHTEIN_DISTANCE_RANGE
+            ))
+        })?;
+    if fuzzy_configuration.prefix {
+        Ok(automaton_builder.build_prefix_dfa(term_text))
+    } else {
+        Ok(automaton_builder.build_dfa(term_text))
+    }
+}
+
 /// A Fuzzy Query matches all of the documents
 /// containing a specific term that is within
 /// Levenshtein distance
@@ -41,32 +75,19 @@ static LEV_BUILDER: Lazy<HashMap<(u8, bool), LevenshteinAutomatonBuilder>> = Laz
 ///     let index = Index::create_in_ram(schema);
 ///     {
 ///         let mut index_writer = index.writer(3_000_000)?;
-///         index_writer.add_document(doc!(
-///             title => "The Name of the Wind",
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "The Diary of Muadib",
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "A Dairy Cow",
-///         ));
-///         index_writer.add_document(doc!(
-///             title => "The Diary of a Young Girl",
-///         ));
+///         index_writer.add_document(doc!(title => "The Name of the Wind"));
+///         index_writer.add_document(doc!(title => "The Diary of Muadib"));
+///         index_writer.add_document(doc!(title => "A Dairy Cow"));
+///         index_writer.add_document(doc!(title => "The Diary of a Young Girl"));
 ///         index_writer.commit().unwrap();
 ///     }
 ///     let reader = index.reader()?;
 ///     let searcher = reader.searcher();
-///
-///     {
-///
-///         let term = Term::from_field_text(title, "Diary");
-///         let query = FuzzyTermQuery::new(term, 1, true);
-///         let (top_docs, count) = searcher.search(&query, &(TopDocs::with_limit(2), Count)).unwrap();
-///         assert_eq!(count, 2);
-///         assert_eq!(top_docs.len(), 2);
-///     }
-///
+///     let term = Term::from_field_text(title, "Diary");
+///     let query = FuzzyTermQuery::new(term, 1, true);
+///     let (top_docs, count) = searcher.search(&query, &(TopDocs::with_limit(2), Count)).unwrap();
+///     assert_eq!(count, 2);
+///     assert_eq!(top_docs.len(), 2);
 ///     Ok(())
 /// }
 /// ```
@@ -74,54 +95,58 @@ static LEV_BUILDER: Lazy<HashMap<(u8, bool), LevenshteinAutomatonBuilder>> = Laz
 pub struct FuzzyTermQuery {
     /// What term are we searching
     term: Term,
-    /// How many changes are we going to allow
-    distance: u8,
-    /// Should a transposition cost 1 or 2?
-    transposition_cost_one: bool,
-    ///
-    prefix: bool,
+    configuration: FuzzyConfiguration
 }
 
 impl FuzzyTermQuery {
+    pub fn new_from_configuration(term: Term, configuration: FuzzyConfiguration) -> FuzzyTermQuery {
+        FuzzyTermQuery {
+            term,
+            configuration
+        }
+    }
+
     /// Creates a new Fuzzy Query
     pub fn new(term: Term, distance: u8, transposition_cost_one: bool) -> FuzzyTermQuery {
         FuzzyTermQuery {
             term,
-            distance,
-            transposition_cost_one,
-            prefix: false,
-        }
-    }
-
-    /// Creates a new Fuzzy Query that treats transpositions as cost one rather than two
-    pub fn new_prefix(term: Term, distance: u8, transposition_cost_one: bool) -> FuzzyTermQuery {
-        FuzzyTermQuery {
-            term,
-            distance,
-            transposition_cost_one,
-            prefix: true,
-        }
-    }
-
-    fn specialized_weight(&self) -> Result<AutomatonWeight<DFA>> {
-        // LEV_BUILDER is a HashMap, whose `get` method returns an Option
-        match LEV_BUILDER.get(&(self.distance, false)) {
-            // Unwrap the option and build the Ok(AutomatonWeight)
-            Some(automaton_builder) => {
-                let automaton = automaton_builder.build_dfa(self.term.text());
-                Ok(AutomatonWeight::new(self.term.field(), automaton))
+            configuration: FuzzyConfiguration {
+                distance,
+                transposition_cost_one,
+                prefix: false,
+                exact_distance: false
             }
-            None => Err(InvalidArgument(format!(
-                "Levenshtein distance of {} is not allowed. Choose a value in the {:?} range",
-                self.distance, VALID_LEVENSHTEIN_DISTANCE_RANGE
-            ))),
         }
     }
 }
 
 impl Query for FuzzyTermQuery {
     fn weight(&self, _searcher: &Searcher, _scoring_enabled: bool) -> Result<Box<dyn Weight>> {
-        Ok(Box::new(self.specialized_weight()?))
+        let dfa = build_dfa(&self.configuration, self.term.text())?;
+        // TODO optimize for distance = 0 and possibly prefix
+        if self.configuration.exact_distance {
+            let target_distance = self.configuration.distance;
+            let wrapped_dfa = WrappedDFA {
+                dfa,
+                condition: move |distance: Distance| distance == Distance::Exact(target_distance),
+            };
+            Ok(Box::new(AutomatonWeight::new(
+                self.term.field(),
+                wrapped_dfa,
+            )))
+        } else {
+            let wrapped_dfa = WrappedDFA {
+                dfa,
+                condition: move |distance: Distance| match distance {
+                    Distance::Exact(_) => true,
+                    Distance::AtLeast(_) => false,
+                },
+            };
+            Ok(Box::new(AutomatonWeight::new(
+                self.term.field(),
+                wrapped_dfa,
+            )))
+        }
     }
 }
 
@@ -134,6 +159,7 @@ mod test {
     use crate::tests::assert_nearly_equals;
     use crate::Index;
     use crate::Term;
+    use super::FuzzyConfigurationBuilder;
 
     #[test]
     pub fn test_fuzzy_term() {
@@ -155,7 +181,6 @@ mod test {
         let searcher = reader.searcher();
         {
             let term = Term::from_field_text(country_field, "japon");
-
             let fuzzy_query = FuzzyTermQuery::new(term, 1, true);
             let top_docs = searcher
                 .search(&fuzzy_query, &TopDocs::with_limit(2))
@@ -164,5 +189,73 @@ mod test {
             let (score, _) = top_docs[0];
             assert_nearly_equals(1f32, score);
         }
+        {
+            let term = Term::from_field_text(country_field, "japon");
+            let fuzzy_conf = FuzzyConfigurationBuilder::default()
+                .distance(2)
+                .exact_distance(true)
+                .build()
+                .unwrap();
+            let fuzzy_query = FuzzyTermQuery::new_from_configuration(term, fuzzy_conf);
+            let top_docs = searcher
+                .search(&fuzzy_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert!(top_docs.is_empty());
+        }
+        {
+            let term = Term::from_field_text(country_field, "japon");
+            let fuzzy_conf = FuzzyConfigurationBuilder::default()
+                .distance(1)
+                .exact_distance(true)
+                .build()
+                .unwrap();
+            let fuzzy_query = FuzzyTermQuery::new_from_configuration(term, fuzzy_conf);
+            let top_docs = searcher
+                .search(&fuzzy_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert_eq!(top_docs.len(), 1);
+        }
+        {
+            let term = Term::from_field_text(country_field, "jpp");
+            let fuzzy_conf = FuzzyConfigurationBuilder::default()
+                .distance(1)
+                .prefix(true)
+                .build()
+                .unwrap();
+            let fuzzy_query = FuzzyTermQuery::new_from_configuration(term, fuzzy_conf);
+            let top_docs = searcher
+                .search(&fuzzy_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert_eq!(top_docs.len(), 1);
+        }
+        {
+            let term = Term::from_field_text(country_field, "jpaan");
+            let fuzzy_conf = FuzzyConfigurationBuilder::default()
+                .distance(1)
+                .exact_distance(true)
+                .transposition_cost_one(true)
+                .build()
+                .unwrap();
+            let fuzzy_query = FuzzyTermQuery::new_from_configuration(term, fuzzy_conf);
+            let top_docs = searcher
+                .search(&fuzzy_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert_eq!(top_docs.len(), 1);
+        }
+        {
+            let term = Term::from_field_text(country_field, "jpaan");
+            let fuzzy_conf = FuzzyConfigurationBuilder::default()
+                .distance(2)
+                .exact_distance(true)
+                .transposition_cost_one(false)
+                .build()
+                .unwrap();
+            let fuzzy_query = FuzzyTermQuery::new_from_configuration(term, fuzzy_conf);
+            let top_docs = searcher
+                .search(&fuzzy_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert_eq!(top_docs.len(), 1);
+        }
     }
+
 }

src/query/mod.rs

@@ -40,7 +40,7 @@ pub use self::boolean_query::BooleanQuery;
 pub use self::empty_query::{EmptyQuery, EmptyScorer, EmptyWeight};
 pub use self::exclude::Exclude;
 pub use self::explanation::Explanation;
-pub use self::fuzzy_query::FuzzyTermQuery;
+pub use self::fuzzy_query::{FuzzyTermQuery, FuzzyConfiguration, FuzzyConfigurationBuilder};
 pub use self::intersection::intersect_scorers;
 pub use self::phrase_query::PhraseQuery;
 pub use self::query::Query;

src/termdict/mod.rs

@@ -31,14 +31,43 @@ mod termdict;
 pub use self::merger::TermMerger;
 pub use self::streamer::{TermStreamer, TermStreamerBuilder};
 pub use self::termdict::{TermDictionary, TermDictionaryBuilder};
+use levenshtein_automata::{Distance, DFA, SINK_STATE};
+use tantivy_fst::Automaton;
+
+pub(crate) struct WrappedDFA<Cond> {
+    pub dfa: DFA,
+    pub condition: Cond,
+}
+
+impl<Cond: Fn(Distance) -> bool> Automaton for WrappedDFA<Cond> {
+    type State = u32;
+
+    fn start(&self) -> Self::State {
+        self.dfa.initial_state()
+    }
+
+    fn is_match(&self, state: &Self::State) -> bool {
+        let distance = self.dfa.distance(*state);
+        (self.condition)(distance)
+    }
+
+    fn can_match(&self, state: &Self::State) -> bool {
+        *state != SINK_STATE
+    }
+
+    fn accept(&self, state: &Self::State, byte: u8) -> Self::State {
+        self.dfa.transition(*state, byte)
+    }
+}
 
 #[cfg(test)]
 mod tests {
-    use super::{TermDictionary, TermDictionaryBuilder, TermStreamer};
+    use super::{TermDictionary, TermDictionaryBuilder, TermStreamer, WrappedDFA};
     use crate::core::Index;
     use crate::directory::{Directory, RAMDirectory, ReadOnlySource};
     use crate::postings::TermInfo;
     use crate::schema::{Document, FieldType, Schema, TEXT};
+    use levenshtein_automata::Distance;
     use std::path::PathBuf;
     use std::str;
 
@@ -423,9 +452,14 @@ mod tests {
 
         // We can now build an entire dfa.
         let lev_automaton_builder = LevenshteinAutomatonBuilder::new(2, true);
-        let automaton = lev_automaton_builder.build_dfa("Spaen");
-
-        let mut range = term_dict.search(automaton).into_stream();
+        let wrapped_dfa = WrappedDFA {
+            dfa: lev_automaton_builder.build_dfa("Spaen"),
+            condition: |distance| match distance {
+                Distance::Exact(_) => true,
+                Distance::AtLeast(_) => false,
+            },
+        };
+        let mut range = term_dict.search(wrapped_dfa).into_stream();
 
         // get the first finding
         assert!(range.advance());