package com.infendro.cli.util

internal const val threshold = 2

/**
 * Calculates the Damerau-Levenshtein distance between two strings.
 *
 * The distance is the minimum number of operations (insertion, deletion, substitution, and transposition) required to transform one string into another.
 *
 * @param a The source string.
 * @param b The target string.
 * @return The minimum number of operations to transform [a] into [b].
 */
internal fun distance(a: String, b: String): Int {
    if (a == b) return 0

    val n = a.length
    val m = b.length

    if (n == 0) return m
    if (m == 0) return n

    var prev2 = IntArray(m + 1)
    var prev1 = IntArray(m + 1) { it }
    var curr = IntArray(m + 1)

    for (i in 1..n) {
        curr[0] = i
        for (j in 1..m) {
            val cost = if (a[i - 1] == b[j - 1]) 0 else 1

            curr[j] = minOf(
                prev1[j] + 1,        // deletion
                curr[j - 1] + 1,     // insertion
                prev1[j - 1] + cost, // substitution
            )

            // transposition
            if (i > 1 && j > 1 && a[i - 1] == b[j - 2] && a[i - 2] == b[j - 1]) {
                curr[j] = minOf(
                    curr[j],
                    prev2[j - 2] + 1,
                )
            }
        }

        val tmp = prev2
        prev2 = prev1
        prev1 = curr
        curr = tmp
    }

    return prev1[m]
}