namespace DSALib.Auxiliary {
    public class SpellCorrect {
        public const double ErrorThreshold = 1 / 3.0;
        private const double Match = 3.0;
        private const double Gap = -1.5;
        private const double Mismatch = -2.0;

        public static double Compare(string s, string q) {
            s = s.ToLower();
            q = q.ToLower();

            int i, j;

            var matrix = new double[s.Length + 1, q.Length + 1];
            var max = 0.0;
            matrix[0, 0] = 0.0;

            for (i = 1; i < s.Length; i++)
                matrix[i, 0] = i * Gap;

            for (i = 1; i < q.Length; i++) matrix[0, i] = 0.0;


            for (i = 1; i <= s.Length; i++)
            for (j = 1; j <= q.Length; j++) {
                var decay = j / (s.Length * 1000.0);
                var add = s[i - 1] == q[j - 1] ? Match - decay : Mismatch;
                var score = matrix[i - 1, j - 1] + add;

                if (score < matrix[i - 1, j] + Gap) score = matrix[i - 1, j] + Gap;

                if (score < matrix[i, j - 1] + Gap) score = matrix[i, j - 1] + Gap;

                if (i > 1 && j > 1)
                    if (s[i - 1] == q[j - 2] && s[i - 2] == q[j - 1]) {
                        add = 3 / 2.0 * Match - decay;
                        if (score < matrix[i - 2, j - 2] + add) score = matrix[i - 2, j - 2] + add;
                    }

                if (max < score && i == s.Length) max = score;

                matrix[i, j] = score;
            }

            return max;
        }

        public static bool IsMatch(string s1, string s2) {
            var score = Compare(s1, s2);
            return score > ErrorThreshold * s1.Length;
        }
    }
}