str-distance 0.1.0

/// Return the shorter str as first index
#[inline]
pub(crate) fn order_by_len_asc<'a>(s1: &'a str, s2: &'a str) -> (&'a str, &'a str) {
    if s1.len() <= s2.len() {
        (s1, s2)
    } else {
        (s2, s1)
    }
}

#[inline]
pub(crate) fn count_eq<S, T>(mut s1_iter: S, mut s2_iter: T) -> usize
where
    S: Iterator,
    T: Iterator,
    <S as Iterator>::Item: PartialEq<<T as Iterator>::Item>,
{
    let mut match_ctn = 0;
    loop {
        let c1 = match s1_iter.next() {
            None => {
                // s2 ends with completely with s1
                break;
            }
            Some(val) => val,
        };

        let c2 = match s2_iter.next() {
            None => {
                // s1 ends completely with s2
                break;
            }
            Some(val) => val,
        };
        if c1 == c2 {
            match_ctn += 1;
        } else {
            break;
        }
    }
    match_ctn
}

pub(crate) struct DelimDistinct<S, T>
where
    S: Iterator + Clone,
    T: Iterator + Clone,
    <S as Iterator>::Item: PartialEq<<T as Iterator>::Item>,
{
    /// The amount of items both iter share at their beginning.
    pub prefix_len: usize,
    /// Iterator over the distinct items of s1
    pub distinct_s1: S,
    /// The amount of distinct items left in iter 1
    pub s1_len: usize,
    /// Iterator over the distinct items of s2
    pub distinct_s2: T,
    /// The amount of distinct items left in iter 2
    pub s2_len: usize,
    /// The amount of items both iters share at their end.
    pub suffix_len: usize,
}

#[allow(unused)]
impl<S, T> DelimDistinct<S, T>
where
    S: Iterator + Clone,
    T: Iterator + Clone,
    <S as Iterator>::Item: PartialEq<<T as Iterator>::Item>,
{
    /// Amount of chars both str share at their tails.
    #[inline]
    pub fn common(&self) -> usize {
        self.prefix_len + self.suffix_len
    }

    /// The amount of distinct chars for each str
    #[inline]
    pub fn remaining(&self) -> (usize, usize) {
        (self.s1_len, self.s2_len)
    }

    /// Whether both str are identical.
    #[inline]
    pub fn is_eq(&self) -> bool {
        self.remaining() == (0, 0)
    }

    #[inline]
    pub fn remaining_s2(&self) -> usize {
        self.s2_len
    }

    #[inline]
    pub fn remaining_s1(&self) -> usize {
        self.s1_len
    }

    /// Return the len of common prefix and suffix items, and the distinct left
    /// elements in between.
    #[inline]
    pub(crate) fn new_skip_take(
        a: S,
        b: T,
    ) -> DelimDistinct<std::iter::Skip<std::iter::Take<S>>, std::iter::Skip<std::iter::Take<T>>>
    {
        // collecting is a little tedious here, but we can't rely on the iters also
        // being DoubleEnded
        let a_vec: Vec<_> = a.clone().collect();
        let b_vec: Vec<_> = b.clone().collect();

        let a_len = a_vec.len();
        let b_len = b_vec.len();

        let suffix_len = count_eq(a_vec.into_iter().rev(), b_vec.into_iter().rev());

        let a_iter = a.take(a_len - suffix_len);
        let b_iter = b.take(b_len - suffix_len);

        let prefix_len = count_eq(a_iter.clone(), b_iter.clone());

        let common_len = prefix_len + suffix_len;
        DelimDistinct {
            suffix_len,
            prefix_len,
            s1_len: a_len - common_len,
            s2_len: b_len - common_len,
            distinct_s1: a_iter.skip(prefix_len),
            distinct_s2: b_iter.skip(prefix_len),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn delim_different() {
        let s1 = "kitten";
        let s2 = "sitting";

        let delim = DelimDistinct::new_skip_take(s1.chars(), s2.chars());
        assert_eq!(delim.prefix_len, 0);
        assert_eq!(delim.suffix_len, 0);
        assert_eq!(delim.s1_len, 6);
        assert_eq!(delim.s2_len, 7);
    }

    #[test]
    fn delim_eq() {
        let s1 = "kitten";
        let s2 = "kitten";

        let delim = DelimDistinct::new_skip_take(s1.chars(), s2.chars());
        assert_eq!(delim.common(), 6);
        assert_eq!(delim.remaining(), (0, 0));
        assert!(delim.is_eq());
    }

    #[test]
    fn delim_eq_suffix() {
        let s1 = "cute kitten";
        let s2 = "kitten";

        let delim = DelimDistinct::new_skip_take(s1.chars(), s2.chars());
        assert_eq!(delim.common(), 6);
        assert_eq!(delim.remaining(), (5, 0));
        assert_eq!(delim.distinct_s1.collect::<String>(), String::from("cute "));

        let s1 = "k cute kitten";
        let s2 = "kitten";
        let delim = DelimDistinct::new_skip_take(s1.chars(), s2.chars());
        assert_eq!(delim.common(), 6);
        assert_eq!(delim.remaining(), (7, 0));
        assert_eq!(
            delim.distinct_s1.collect::<String>(),
            String::from("k cute ")
        );
    }

    #[test]
    fn delim_eq_prefix() {
        let s1 = "hungry kitten";
        let s2 = "hungry hippo";

        let delim = DelimDistinct::new_skip_take(s1.chars(), s2.chars());
        assert_eq!(delim.common(), 7);
        assert_eq!(delim.remaining(), (6, 5));
        assert_eq!(
            delim.distinct_s1.collect::<String>(),
            String::from("kitten")
        );
        assert_eq!(delim.distinct_s2.collect::<String>(), String::from("hippo"));
    }

    #[test]
    fn delim_eq_prefix_suffix() {
        let s1 = "hungry kitten is hungry";
        let s2 = "hungry hippo is hungry";

        let delim = DelimDistinct::new_skip_take(s1.chars(), s2.chars());
        assert_eq!(delim.common(), 17);
        assert_eq!(delim.remaining(), (6, 5));
        assert_eq!(
            delim.distinct_s1.collect::<String>(),
            String::from("kitten")
        );
        assert_eq!(delim.distinct_s2.collect::<String>(), String::from("hippo"));
    }
}