using System;

namespace NHSE.Core
{
    public static class LevenshteinDistance
    {
        /// <summary>
        /// Compute the distance between two strings.
        /// http://www.dotnetperls.com/levenshtein
        /// https://stackoverflow.com/a/13793600
        /// </summary>
        public static int Compute(string s, string t)
        {
            int n = s.Length;
            int m = t.Length;
            int[,] d = new int[n + 1, m + 1];

            // Step 1
            if (n == 0)
                return m;

            if (m == 0)
                return n;

            // Step 2
            for (int i = 0; i <= n; d[i, 0] = i++) { }
            for (int j = 0; j <= m; d[0, j] = j++) { }

            // Step 3
            for (int i = 1; i <= n; i++)
            {
                //Step 4
                for (int j = 1; j <= m; j++)
                {
                    // Step 5
                    int cost = (t[j - 1] == s[i - 1]) ? 0 : 1;

                    // Step 6
                    var x1 = d[i - 1, j] + 1;
                    var x2 = d[i, j - 1] + 1;
                    var x3 = d[i - 1, j - 1] + cost;
                    d[i, j] = Math.Min(Math.Min(x1, x2), x3);
                }
            }

            // Step 7
            return d[n, m];
        }
    }
}
