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//! a simple fuzzy pattern matcher for filename filtering / sorting.
//! It's not meant for file contents but for small strings (less than 1000 chars)
//! such as file names.
use std::fmt::{self, Write};
use crate::patterns::Match;
// weights used in match score computing
const BONUS_MATCH: i32 = 50_000;
const BONUS_EXACT: i32 = 1_000;
const BONUS_START: i32 = 10;
const BONUS_START_WORD: i32 = 5;
const BONUS_CANDIDATE_LENGTH: i32 = -1; // per char
const BONUS_LENGTH: i32 = -10; // per char of length of the match
const BONUS_NB_HOLES: i32 = -30; // there's also a max on that number
#[derive(Debug, Clone)]
pub struct FuzzyPattern {
lc_bytes: Box<[u8]>,
lc_chars: Box<[char]>, // lowercase characters
max_nb_holes: usize,
}
impl fmt::Display for FuzzyPattern {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
for &c in self.lc_chars.iter() {
f.write_char(c)?
}
Ok(())
}
}
enum MatchSearchResult {
Perfect(Match), // no need to test other positions
Some(Match),
None,
}
enum ScoreSearchResult {
Perfect(i32), // no need to test other positions
Some(i32),
None,
}
impl FuzzyPattern {
/// build a pattern which will later be usable for fuzzy search.
/// A pattern should be reused
pub fn from(pat: &str) -> FuzzyPattern {
let lc_bytes = pat.to_lowercase().as_bytes().to_vec();
let lc_bytes = lc_bytes.into_boxed_slice();
let lc_chars: Vec<char> = pat.chars().map(|c| c.to_ascii_lowercase()).collect();
let lc_chars = lc_chars.into_boxed_slice();
let max_nb_holes = match lc_chars.len() {
1 => 0,
2 => 1,
3 => 2,
4 => 3,
5 => 3,
6 => 4,
7 => 4,
8 => 4,
_ => lc_chars.len() * 4 / 7,
};
FuzzyPattern {
lc_bytes,
lc_chars,
max_nb_holes,
}
}
/// look for a match starting at a given character
fn match_starting_at_index(
&self,
cand_chars: &[char],
start_idx: usize, // start index in candidate, in chars
) -> MatchSearchResult {
if cand_chars[start_idx] != self.lc_chars[0] {
return MatchSearchResult::None;
}
let mut pos: Vec<usize> = vec![]; // positions of matching chars in candidate
pos.push(start_idx);
let mut d = 1;
let mut nb_holes = 0;
for pat_idx in 1..self.lc_chars.len() {
let hole_start = d;
loop {
let cand_idx = start_idx + d;
if cand_idx == cand_chars.len() {
return MatchSearchResult::None;
}
d += 1;
if cand_chars[cand_idx] == self.lc_chars[pat_idx] {
pos.push(cand_idx);
break;
}
}
if hole_start + 1 != d {
// note that there's no absolute guarantee we found the minimal
// number of holes. The algorithm isn't perfect
if nb_holes >= self.max_nb_holes {
return MatchSearchResult::None;
}
nb_holes += 1;
}
}
let mut score = BONUS_MATCH;
score += BONUS_CANDIDATE_LENGTH * (cand_chars.len() as i32);
score += BONUS_NB_HOLES * (nb_holes as i32);
let match_len = (d as i32) - 1;
score += match_len * BONUS_LENGTH;
if start_idx == 0 {
score += BONUS_START;
if cand_chars.len() == self.lc_chars.len() {
score += BONUS_EXACT;
return MatchSearchResult::Perfect(Match { score, pos });
}
} else {
let previous = cand_chars[start_idx - 1];
if previous == '_' || previous == ' ' || previous == '-' {
score += BONUS_START_WORD;
if cand_chars.len() - start_idx == self.lc_chars.len() {
return MatchSearchResult::Perfect(Match { score, pos });
}
}
}
MatchSearchResult::Some(Match { score, pos })
}
/// return a match if the pattern can be found in the candidate string.
/// The algorithm tries to return the best one. For example if you search
/// "abc" in "ababca-abc", the returned match would be at the end.
pub fn find(&self, candidate: &str) -> Option<Match> {
let mut cand_chars: Vec<char> = Vec::with_capacity(candidate.len());
cand_chars.extend(candidate.chars().map(|c| c.to_ascii_lowercase()));
if cand_chars.len() < self.lc_chars.len() {
return None;
}
let mut best_score = 0;
let mut best_match: Option<Match> = None;
let n = cand_chars.len() - self.lc_chars.len();
for start_idx in 0..=n {
match self.match_starting_at_index(&cand_chars, start_idx) {
MatchSearchResult::Perfect(m) => {
return Some(m);
}
MatchSearchResult::Some(m) => {
if m.score > best_score {
best_score = m.score;
best_match = Some(m);
}
}
_ => {}
}
}
best_match
}
/// if a match starts at the given byte index, return its score.
/// Return it as "Perfect" if no better match can be found further
/// in the string.
/// Otherwise return None.
fn score_starting_at(
&self,
cand: &[u8],
start_idx: usize, // start index in candidate, in bytes
) -> ScoreSearchResult {
if cand[start_idx].to_ascii_lowercase() != self.lc_bytes[0] {
return ScoreSearchResult::None;
}
let mut d = 1;
let mut nb_holes = 0;
for pat_idx in 1..self.lc_bytes.len() {
let hole_start = d;
loop {
let cand_idx = start_idx + d;
if cand_idx == cand.len() {
return ScoreSearchResult::None;
}
d += 1;
if cand[cand_idx].to_ascii_lowercase() == self.lc_bytes[pat_idx] {
break;
}
}
if hole_start + 1 != d {
// note that there's no absolute guarantee we found the minimal
// number of holes. The algorithm isn't perfect
if nb_holes >= self.max_nb_holes {
return ScoreSearchResult::None;
}
nb_holes += 1;
}
}
let match_len = (d as i32) - 1;
let mut score = BONUS_MATCH
+ BONUS_CANDIDATE_LENGTH * (cand.len() as i32)
+ BONUS_NB_HOLES * (nb_holes as i32)
+ match_len * BONUS_LENGTH;
if start_idx == 0 {
score += BONUS_START;
if cand.len() == self.lc_bytes.len() {
score += BONUS_EXACT;
return ScoreSearchResult::Perfect(score);
}
} else {
let previous = cand[start_idx - 1];
if previous == b'_' || previous == b' ' || previous == b'-' {
score += BONUS_START_WORD;
if cand.len() - start_idx == self.lc_bytes.len() {
return ScoreSearchResult::Perfect(score);
}
}
}
ScoreSearchResult::Some(score)
}
/// compute the score of the best match, in a way mostly similar to `find` but
/// much faster by
/// - working on bytes instead of chars
/// - not storing match positions
/// The result is about the same, but the values are often a little different
/// (because lengths of parts are in bytes instead of chars). The test module
/// cares of ensuring the results are the same when all chars are one byte (i.e.
/// there's no big bug) and that orderings are consistent (what matters for the
/// app is scores orderings).
pub fn score_of(&self, candidate: &str) -> Option<i32> {
if candidate.len() < self.lc_bytes.len() {
return None;
}
let mut best_score = 0;
let n = candidate.len() - self.lc_bytes.len();
for start_idx in 0..=n {
match self.score_starting_at(candidate.as_bytes(), start_idx) {
ScoreSearchResult::Perfect(s) => {
return Some(s);
}
ScoreSearchResult::Some(score) => {
if score > best_score {
best_score = score;
}
}
_ => {}
}
}
if best_score > 0 {
Some(best_score)
} else {
None
}
}
/// return the number of results we should find before starting to
/// sort them (unless time is runing out).
pub const fn optimal_result_number(&self, targeted_size: usize) -> usize {
10 * targeted_size
}
}
#[cfg(test)]
mod fuzzy_pattern_tests {
use super::*;
/// check that the scores obtained using score_of and find are equal at least for ascii strings
/// (scores are slightly different for strings having multibytes chars due to the notes given
/// to various lengths)
#[test]
fn check_equal_scores() {
static PATTERNS: &[&str] = &["reveil", "dystroy", "broot", "AB"];
static NAMES: &[&str] = &[
" brr ooT",
"Reveillon",
"dys",
"test",
" a reveil",
"a rbrroot",
"Ab",
];
for pattern in PATTERNS {
let fp = FuzzyPattern::from(pattern);
for name in NAMES {
println!("checking pattern {:?} on name {:?}", pattern, name);
assert_eq!(fp.score_of(name), fp.find(name).map(|m| m.score));
}
}
}
/// check that the scores of all names are strictly decreasing
/// (pattern is first tested against itself).
/// We verify this property with both computation functions.
fn check_ordering_for(pattern: &str, names: &[&str]) {
let fp = FuzzyPattern::from(pattern);
// checking using score_of
let mut last_score = fp.score_of(pattern);
let mut last_name = pattern;
for name in names {
let score = fp.score_of(name);
assert!(
score < last_score,
"score({:?}) should be lower than score({:?}) (using score_of)",
name,
last_name
);
last_name = name;
last_score = score;
}
// checking using find
let mut last_score = fp.find(pattern).map(|m| m.score);
let mut last_name = pattern;
for name in names {
let score = fp.find(name).map(|m| m.score);
assert!(
score < last_score,
"score({:?}) should be lower than score({:?}) (using find)",
name,
last_name
);
last_name = name;
last_score = score;
}
}
#[test]
fn check_orderings() {
check_ordering_for(
"broot",
&[
"a broot",
"abbroot",
"abcbroot",
" abdbroot",
"1234broot1",
"12345brrrroooottt",
"12345brrr roooottt",
"brot",
],
);
check_ordering_for(
"Abc",
&["abCd", "aBdc", " abdc", " abdbccccc", " a b c", "nothing"],
);
check_ordering_for(
"réveil",
&[
"Réveillon",
"Réveillons",
" réveils",
"πréveil",
"déréveil",
" rêves",
],
);
}
}