module strings

// #-js
// use levenshtein distance algorithm to calculate
// the distance between between two strings (lower is closer)
pub fn levenshtein_distance(a string, b string) int {
    mut f := [0].repeat(b.len + 1)
    for j in 0 .. f.len {
        f[j] = j
    }
    for ca in a {
        mut j := 1
        mut fj1 := f[0]
        f[0]++
        for cb in b {
            mut mn := if f[j] + 1 <= f[j - 1] + 1 { f[j] + 1 } else { f[j - 1] + 1 }
            if cb != ca {
                mn = if mn <= fj1 + 1 { mn } else { fj1 + 1 }
            } else {
                mn = if mn <= fj1 { mn } else { fj1 }
            }
            fj1 = f[j]
            f[j] = mn
            j++
        }
    }
    return f[f.len - 1]
}

// use levenshtein distance algorithm to calculate
// how similar two strings are as a percentage (higher is closer)
pub fn levenshtein_distance_percentage(a string, b string) f32 {
    d := levenshtein_distance(a, b)
    l := if a.len >= b.len { a.len } else { b.len }
    return (1.00 - f32(d) / f32(l)) * 100.00
}

// implementation of Sørensen–Dice coefficient.
// find the similarity between two strings.
// returns coefficient between 0.0 (not similar) and 1.0 (exact match).
pub fn dice_coefficient(s1 string, s2 string) f32 {
    if s1.len == 0 || s2.len == 0 {
        return 0.0
    }
    if s1 == s2 {
        return 1.0
    }
    if s1.len < 2 || s2.len < 2 {
        return 0.0
    }
    a := if s1.len > s2.len { s1 } else { s2 }
    b := if a == s1 { s2 } else { s1 }
    mut first_bigrams := map[string]int{}
    for i in 0 .. a.len - 1 {
        bigram := a[i..i + 2]
        q := if bigram in first_bigrams { first_bigrams[bigram] + 1 } else { 1 }
        first_bigrams[bigram] = q
    }
    mut intersection_size := 0
    for i in 0 .. b.len - 1 {
        bigram := b[i..i + 2]
        count := if bigram in first_bigrams { first_bigrams[bigram] } else { 0 }
        if count > 0 {
            first_bigrams[bigram] = count - 1
            intersection_size++
        }
    }
    return (2.0 * f32(intersection_size)) / (f32(a.len) + f32(b.len) - 2)
}