355 lines
11 KiB
Rust
355 lines
11 KiB
Rust
use std::cmp::{min, Reverse};
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use std::collections::{BTreeMap, HashSet};
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use std::ops::{Index, IndexMut};
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use levenshtein_automata::{Distance, DFA};
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use meilisearch_tokenizer::Token;
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use super::build_dfa;
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use crate::search::query_tree::{Operation, Query};
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type IsPrefix = bool;
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/// Structure created from a query tree
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/// referencing words that match the given query tree.
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#[derive(Default)]
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pub struct MatchingWords {
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dfas: Vec<(DFA, String, u8, IsPrefix)>,
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}
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impl MatchingWords {
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pub fn from_query_tree(tree: &Operation) -> Self {
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// fetch matchable words from the query tree
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let mut dfas: Vec<_> = fetch_queries(tree)
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.into_iter()
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// create DFAs for each word
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.map(|(w, t, p)| (build_dfa(w, t, p), w.to_string(), t, p))
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.collect();
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// Sort word by len in DESC order prioritizing the longuest word,
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// in order to highlight the longuest part of the matched word.
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dfas.sort_unstable_by_key(|(_dfa, query_word, _typo, _is_prefix)| {
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Reverse(query_word.len())
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});
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Self { dfas }
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}
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/// Returns the number of matching bytes if the word matches one of the query words.
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pub fn matching_bytes(&self, word_to_highlight: &Token) -> Option<usize> {
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self.dfas.iter().find_map(|(dfa, query_word, typo, is_prefix)| {
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match dfa.eval(word_to_highlight.text()) {
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Distance::Exact(t) if t <= *typo => {
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if *is_prefix {
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let len = bytes_to_highlight(word_to_highlight.text(), query_word);
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Some(word_to_highlight.num_chars_from_bytes(len))
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} else {
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Some(word_to_highlight.num_chars_from_bytes(word_to_highlight.text().len()))
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}
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}
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_otherwise => None,
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}
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})
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}
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}
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/// Lists all words which can be considered as a match for the query tree.
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fn fetch_queries(tree: &Operation) -> HashSet<(&str, u8, IsPrefix)> {
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fn resolve_ops<'a>(tree: &'a Operation, out: &mut HashSet<(&'a str, u8, IsPrefix)>) {
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match tree {
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Operation::Or(_, ops) | Operation::And(ops) => {
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ops.as_slice().iter().for_each(|op| resolve_ops(op, out));
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}
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Operation::Query(Query { prefix, kind }) => {
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let typo = if kind.is_exact() { 0 } else { kind.typo() };
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out.insert((kind.word(), typo, *prefix));
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}
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Operation::Phrase(words) => {
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for word in words {
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out.insert((word, 0, false));
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}
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}
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}
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}
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let mut queries = HashSet::new();
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resolve_ops(tree, &mut queries);
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queries
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}
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// A simple wrapper around vec so we can get contiguous but index it like it's 2D array.
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struct N2Array<T> {
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y_size: usize,
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buf: Vec<T>,
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}
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impl<T: Clone> N2Array<T> {
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fn new(x: usize, y: usize, value: T) -> N2Array<T> {
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N2Array { y_size: y, buf: vec![value; x * y] }
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}
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}
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impl<T> Index<(usize, usize)> for N2Array<T> {
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type Output = T;
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#[inline]
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fn index(&self, (x, y): (usize, usize)) -> &T {
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&self.buf[(x * self.y_size) + y]
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}
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}
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impl<T> IndexMut<(usize, usize)> for N2Array<T> {
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#[inline]
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fn index_mut(&mut self, (x, y): (usize, usize)) -> &mut T {
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&mut self.buf[(x * self.y_size) + y]
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}
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}
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/// Returns the number of **bytes** we want to highlight in the `source` word.
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/// Basically we want to highlight as much characters as possible in the source until it has too much
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/// typos (= 2)
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/// The algorithm is a modified
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/// [Damerau-Levenshtein](https://en.wikipedia.org/wiki/Damerau%E2%80%93Levenshtein_distance)
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fn bytes_to_highlight(source: &str, target: &str) -> usize {
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let n = source.chars().count();
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let m = target.chars().count();
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if n == 0 {
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return 0;
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}
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// since we allow two typos we can send two characters even if it's completely wrong
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if m < 3 {
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return source.chars().take(m).map(|c| c.len_utf8()).sum();
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}
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if n == m && source == target {
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return source.len();
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}
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let inf = n + m;
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let mut matrix = N2Array::new(n + 2, m + 2, 0);
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matrix[(0, 0)] = inf;
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for i in 0..=n {
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matrix[(i + 1, 0)] = inf;
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matrix[(i + 1, 1)] = i;
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}
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for j in 0..=m {
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matrix[(0, j + 1)] = inf;
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matrix[(1, j + 1)] = j;
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}
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let mut last_row = BTreeMap::new();
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for (row, char_s) in source.chars().enumerate() {
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let mut last_match_col = 0;
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let row = row + 1;
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for (col, char_t) in target.chars().enumerate() {
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let col = col + 1;
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let last_match_row = *last_row.get(&char_t).unwrap_or(&0);
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let cost = if char_s == char_t { 0 } else { 1 };
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let dist_add = matrix[(row, col + 1)] + 1;
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let dist_del = matrix[(row + 1, col)] + 1;
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let dist_sub = matrix[(row, col)] + cost;
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let dist_trans = matrix[(last_match_row, last_match_col)]
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+ (row - last_match_row - 1)
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+ 1
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+ (col - last_match_col - 1);
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let dist = min(min(dist_add, dist_del), min(dist_sub, dist_trans));
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matrix[(row + 1, col + 1)] = dist;
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if cost == 0 {
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last_match_col = col;
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}
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}
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last_row.insert(char_s, row);
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}
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let mut minimum = (u32::max_value(), 0);
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for x in 0..=m {
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let dist = matrix[(n + 1, x + 1)] as u32;
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if dist < minimum.0 {
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minimum = (dist, x);
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}
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}
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// everything was done characters wise and now we want to returns a number of bytes
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source.chars().take(minimum.1).map(|c| c.len_utf8()).sum()
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}
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#[cfg(test)]
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mod tests {
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use std::borrow::Cow;
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use std::str::from_utf8;
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use meilisearch_tokenizer::TokenKind;
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use super::*;
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use crate::search::query_tree::{Operation, Query, QueryKind};
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use crate::MatchingWords;
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#[test]
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fn test_bytes_to_highlight() {
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struct TestBytesToHighlight {
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query: &'static str,
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text: &'static str,
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length: usize,
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}
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let tests = [
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TestBytesToHighlight { query: "bip", text: "bip", length: "bip".len() },
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TestBytesToHighlight { query: "bip", text: "boup", length: "bip".len() },
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TestBytesToHighlight {
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query: "Levenshtein",
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text: "Levenshtein",
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length: "Levenshtein".len(),
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},
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// we get to the end of our word with only one typo
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TestBytesToHighlight {
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query: "Levenste",
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text: "Levenshtein",
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length: "Levenste".len(),
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},
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// we get our third and last authorized typo right on the last character
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TestBytesToHighlight {
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query: "Levenstein",
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text: "Levenshte",
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length: "Levenste".len(),
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},
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// we get to the end of our word with only two typos at the beginning
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TestBytesToHighlight {
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query: "Bavenshtein",
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text: "Levenshtein",
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length: "Bavenshtein".len(),
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},
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TestBytesToHighlight {
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query: "Альфа", text: "Альфой", length: "Альф".len()
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},
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TestBytesToHighlight {
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query: "Go💼", text: "Go💼od luck.", length: "Go💼".len()
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},
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TestBytesToHighlight {
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query: "Go💼od", text: "Go💼od luck.", length: "Go💼od".len()
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},
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TestBytesToHighlight {
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query: "chäräcters",
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text: "chäräcters",
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length: "chäräcters".len(),
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},
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TestBytesToHighlight { query: "ch", text: "chäräcters", length: "ch".len() },
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TestBytesToHighlight { query: "chär", text: "chäräcters", length: "chär".len() },
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];
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for test in &tests {
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let length = bytes_to_highlight(test.text, test.query);
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assert_eq!(length, test.length, r#"lenght between: "{}" "{}""#, test.query, test.text);
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assert!(
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from_utf8(&test.query.as_bytes()[..length]).is_ok(),
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r#"converting {}[..{}] to an utf8 str failed"#,
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test.query,
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length
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);
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}
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}
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#[test]
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fn matching_words() {
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let query_tree = Operation::Or(
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false,
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vec![Operation::And(vec![
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Operation::Query(Query {
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prefix: true,
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kind: QueryKind::exact("split".to_string()),
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}),
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Operation::Query(Query {
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prefix: false,
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kind: QueryKind::exact("this".to_string()),
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}),
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Operation::Query(Query {
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prefix: true,
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kind: QueryKind::tolerant(1, "world".to_string()),
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}),
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])],
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);
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let matching_words = MatchingWords::from_query_tree(&query_tree);
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assert_eq!(
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matching_words.matching_bytes(&Token {
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kind: TokenKind::Word,
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word: Cow::Borrowed("word"),
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byte_start: 0,
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char_index: 0,
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byte_end: "word".len(),
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char_map: None,
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}),
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Some(3)
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);
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assert_eq!(
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matching_words.matching_bytes(&Token {
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kind: TokenKind::Word,
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word: Cow::Borrowed("nyc"),
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byte_start: 0,
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char_index: 0,
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byte_end: "nyc".len(),
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char_map: None,
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}),
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None
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);
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assert_eq!(
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matching_words.matching_bytes(&Token {
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kind: TokenKind::Word,
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word: Cow::Borrowed("world"),
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byte_start: 0,
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char_index: 0,
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byte_end: "world".len(),
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char_map: None,
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}),
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Some(5)
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);
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assert_eq!(
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matching_words.matching_bytes(&Token {
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kind: TokenKind::Word,
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word: Cow::Borrowed("splitted"),
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byte_start: 0,
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char_index: 0,
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byte_end: "splitted".len(),
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char_map: None,
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}),
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Some(5)
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);
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assert_eq!(
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matching_words.matching_bytes(&Token {
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kind: TokenKind::Word,
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word: Cow::Borrowed("thisnew"),
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byte_start: 0,
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char_index: 0,
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byte_end: "thisnew".len(),
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char_map: None,
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}),
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None
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);
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assert_eq!(
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matching_words.matching_bytes(&Token {
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kind: TokenKind::Word,
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word: Cow::Borrowed("borld"),
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byte_start: 0,
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char_index: 0,
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byte_end: "borld".len(),
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char_map: None,
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}),
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Some(5)
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);
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assert_eq!(
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matching_words.matching_bytes(&Token {
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kind: TokenKind::Word,
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word: Cow::Borrowed("wordsplit"),
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byte_start: 0,
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char_index: 0,
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byte_end: "wordsplit".len(),
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char_map: None,
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}),
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Some(4)
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);
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}
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}
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