Collapse overlapped highlighted ranges (#1473)

src/snippet/mod.rs

@@ -79,7 +79,7 @@ impl Snippet {
         let mut html = String::new();
         let mut start_from: usize = 0;
 
-        for item in self.highlighted.iter() {
+        for item in collapse_overlapped_ranges(&self.highlighted) {
             html.push_str(&encode_minimal(&self.fragment[start_from..item.start]));
             html.push_str(HIGHLIGHTEN_PREFIX);
             html.push_str(&encode_minimal(&self.fragment[item.clone()]));
@@ -186,6 +186,53 @@ fn select_best_fragment_combination(fragments: &[FragmentCandidate], text: &str)
     }
 }
 
+/// Returns ranges that are collapsed into non-overlapped ranges.
+///
+/// ## Examples
+/// - [0..1, 2..3] -> [0..1, 2..3]  # no overlap
+/// - [0..1, 1..2] -> [0..1, 1..2]  # no overlap
+/// - [0..2, 1..2] -> [0..2]  # collapsed
+/// - [0..2, 1..3] -> [0..3]  # collapsed
+/// - [0..3, 1..2] -> [0..3]  # second range's end is also inside of the first range
+///
+/// Note: This function assumes `ranges` is sorted by `Range.start` in ascending order.
+fn collapse_overlapped_ranges(ranges: &[Range<usize>]) -> Vec<Range<usize>> {
+    debug_assert!(is_sorted(ranges.iter().map(|range| range.start)));
+
+    let mut result = Vec::new();
+    let mut ranges_it = ranges.iter();
+
+    let mut current = match ranges_it.next() {
+        Some(range) => range.clone(),
+        None => return result,
+    };
+
+    for range in ranges {
+        if current.end > range.start {
+            current = current.start..std::cmp::max(current.end, range.end);
+        } else {
+            result.push(current);
+            current = range.clone();
+        }
+    }
+
+    result.push(current);
+    result
+}
+
+fn is_sorted(mut it: impl Iterator<Item = usize>) -> bool {
+    if let Some(first) = it.next() {
+        let mut prev = first;
+        for item in it {
+            if item < prev {
+                return false;
+            }
+            prev = item;
+        }
+    }
+    true
+}
+
 /// `SnippetGenerator`
 ///
 /// # Example
@@ -320,10 +367,10 @@ mod tests {
 
     use maplit::btreemap;
 
-    use super::{search_fragments, select_best_fragment_combination};
+    use super::{collapse_overlapped_ranges, search_fragments, select_best_fragment_combination};
     use crate::query::QueryParser;
     use crate::schema::{IndexRecordOption, Schema, TextFieldIndexing, TextOptions, TEXT};
-    use crate::tokenizer::SimpleTokenizer;
+    use crate::tokenizer::{NgramTokenizer, SimpleTokenizer};
     use crate::{Index, SnippetGenerator};
 
     const TEST_TEXT: &str = r#"Rust is a systems programming language sponsored by
@@ -588,4 +635,47 @@ Survey in 2016, 2017, and 2018."#;
         }
         Ok(())
     }
+
+    #[test]
+    fn test_collapse_overlapped_ranges() {
+        assert_eq!(
+            collapse_overlapped_ranges(&vec![0..1, 2..3,]),
+            vec![0..1, 2..3]
+        );
+        assert_eq!(
+            collapse_overlapped_ranges(&vec![0..1, 1..2,]),
+            vec![0..1, 1..2]
+        );
+        assert_eq!(collapse_overlapped_ranges(&vec![0..2, 1..2,]), vec![0..2]);
+        assert_eq!(collapse_overlapped_ranges(&vec![0..2, 1..3,]), vec![0..3]);
+        assert_eq!(collapse_overlapped_ranges(&vec![0..3, 1..2,]), vec![0..3]);
+    }
+
+    #[test]
+    fn test_snippet_with_overlapped_highlighted_ranges() {
+        let text = "abc";
+
+        let mut terms = BTreeMap::new();
+        terms.insert(String::from("ab"), 0.9);
+        terms.insert(String::from("bc"), 1.0);
+
+        let fragments = search_fragments(
+            &From::from(NgramTokenizer::all_ngrams(2, 2)),
+            text,
+            &terms,
+            3,
+        );
+
+        assert_eq!(fragments.len(), 1);
+        {
+            let first = &fragments[0];
+            assert_eq!(first.score, 1.9);
+            assert_eq!(first.start_offset, 0);
+            assert_eq!(first.stop_offset, 3);
+        }
+
+        let snippet = select_best_fragment_combination(&fragments[..], text);
+        assert_eq!(snippet.fragment, "abc");
+        assert_eq!(snippet.to_html(), "<b>abc</b>");
+    }
 }