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//! Prefix similarity
use crate::{Algorithm, Result};
/// Prefix similarity is the length of the longest common prefix for the given sequences.
///
/// It's a very dumb metric but it can be surprisingly effective for comparing words
/// in languages with an extensive use of [suffixes](https://en.wikipedia.org/wiki/Suffix).
#[derive(Default)]
pub struct Prefix {}
impl Algorithm<usize> for Prefix {
fn for_iter<C, E>(&self, mut s1: C, mut s2: C) -> Result<usize>
where
C: Iterator<Item = E>,
E: Eq,
{
let mut result = 0;
let mut prev_match: bool = true;
let mut l1 = 0;
let mut l2 = 0;
loop {
match (s1.next(), s2.next()) {
(Some(c1), Some(c2)) => {
l1 += 1;
l2 += 1;
if c1 != c2 {
prev_match = false;
} else if prev_match {
result += 1;
}
}
(Some(_), None) => {
l1 += 1;
}
(None, Some(_)) => {
l2 += 1;
}
(None, None) => {
break;
}
}
}
Result {
abs: result,
is_distance: false,
max: l1.max(l2),
len1: l1,
len2: l2,
}
}
}
#[cfg(test)]
mod tests {
use crate::str::prefix;
use assert2::assert;
use rstest::rstest;
#[rstest]
#[case("", "", 0)]
#[case("", "a", 0)]
#[case("a", "", 0)]
#[case("a", "a", 1)]
#[case("a", "b", 0)]
#[case("abcde", "abcef", 3)]
#[case("abcde", "abcfde", 3)]
#[case("abcd", "bcd", 0)]
fn function_str(#[case] s1: &str, #[case] s2: &str, #[case] exp: usize) {
assert!(prefix(s1, s2) == exp);
}
}