using System;
using System.Collections.Generic;
using System.Linq;
using HeuristicLab.Data;

namespace HeuristicLab.Algorithms.NSGA3
{
    public static class Utility
    {
        public static List<T> Concat<T>(List<T> list1, List<T> list2)
        {
            List<T> resultList = new List<T>(list1.Count + list2.Count);

            resultList.AddRange(list1);
            resultList.AddRange(list2);

            return resultList;
        }

        /// <summary>
        /// Returns the number of possible combinations of size <paramref name="r" /> from a set of
        /// size <paramref name="n" />.
        /// </summary>
        /// <param name="n"></param>
        /// <param name="r"></param>
        /// <returns></returns>
        /// <exception cref="InvalidOperationException">
        /// Thrown, when <paramref name="r" /> &gt; <paramref name="n" /> or when <paramref name="r"
        /// /> &lt; 1.
        /// </exception>
        public static int NCR(int n, int r)
        {
            if (n < r) throw new InvalidOperationException($"Constraint was not met: n >= r (n = {n}, r = {r})");
            if (r < 0) throw new InvalidOperationException($"Constraint was not met: r >= 0 (r = {r})");
            if (n == r) return 1;

            r = Math.Max(r, n - r);

            long range1 = RangeMultiplication(r + 1, n - r);
            return (int)(range1 / Factorial(n - r));
        }

        private static long RangeMultiplication(int start, int count)
        {
            long s = 1;
            return LeftFold((long a, int b) => checked(a * b), new List<int>(Enumerable.Range(start, count)), s);
        }

        private static T2 LeftFold<T1, T2>(Func<T2, T1, T2> func, List<T1> elements, T2 start)
        {
            var item = start;
            foreach (var element in elements)
                item = func(item, element);

            return item;
        }

        public static long Factorial(long n)
        {
            if (n < 0 || n > 30) throw new InvalidOperationException($"Constraint for n was not met: 0 <= n <= 30 (n = {n})");
            long product = 1;
            for (long i = 2; i <= n; i++)
                product *= i;

            return product;
        }

        public static double[][] ToJaggedArray(this DoubleMatrix m)
        {
            if (m == null) return null;
            var a = new double[m.Rows][];
            for (int i = m.Rows - 1; i >= 0; i--)
            {
                a[i] = new double[m.Columns];
                for (int j = m.Columns - 1; j >= 0; j--) a[i][j] = m[i, j];
            }
            return a;
        }

        public static DoubleMatrix ConvertToDoubleMatrix(List<ReferencePoint> referencePoints)
        {
            return new DoubleMatrix(ToArray(referencePoints));
        }

        public static double[][] ToFitnessMatrix(this List<Solution> solutions)
        {
            double[][] data = new double[solutions.Count][];
            for (int i = 0; i < solutions.Count; i++)
            {
                Solution solution = solutions[i];
                data[i] = new double[solution.Objectives.Length];
                for (int j = 0; j < solution.Objectives.Length; j++)
                {
                    data[i][j] = solution.Objectives[j];
                }
            }

            return data;
        }

        public static DoubleMatrix ToMatrix(this IEnumerable<IReadOnlyList<double>> data)
        {
            var d2 = data.ToArray();
            var mat = new DoubleMatrix(d2.Length, d2[0].Count);
            for (var i = 0; i < mat.Rows; i++)
                for (var j = 0; j < mat.Columns; j++)
                    mat[i, j] = d2[i][j];
            return mat;
        }

        private static double[,] ToArray(List<ReferencePoint> referencePoints)
        {
            if (referencePoints == null || !referencePoints.Any()) throw new ArgumentException($"{nameof(referencePoints)} is null or empty");
            int obj = referencePoints.First().Values.Length;
            int pointCount = referencePoints.Count;
            double[,] array = new double[pointCount, obj];

            for (int p = 0; p < pointCount; p++)
                for (int d = 0; d < obj; d++)
                    array[p, d] = referencePoints[p].Values[d];

            return array;
        }

        public static TOut Min<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            return MinArgMin(func, inputs).Item2;
        }

        public static TIn ArgMin<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            return MinArgMin(func, inputs).Item1;
        }

        /// <summary>
        /// Finds the value amongst <paramref name="inputs" /> such that the output value returned
        /// by <paramref name="func" /> is minimal.
        /// </summary>
        /// <typeparam name="TIn">The input type for the function.</typeparam>
        /// <typeparam name="TOut">The comparable output type of the function.</typeparam>
        /// <param name="func">The function for which to find the minimal value.</param>
        /// <param name="inputs">
        /// The function arguments for which to find the one with the minimum output value when
        /// given to <paramref name="func" />.
        /// </param>
        /// <returns></returns>
        public static Tuple<TIn, TOut> MinArgMin<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            if (func == null) throw new ArgumentNullException(nameof(func));
            if (inputs == null) throw new ArgumentNullException(nameof(inputs));
            var it = inputs.GetEnumerator();
            var hasItems = it.MoveNext();
            if (!hasItems) throw new InvalidOperationException("No items given to find the minimum of");

            // find minimum argument and minimum value
            var minArg = it.Current;
            var minValue = func(it.Current);
            while (it.MoveNext())
            {
                var currentArg = it.Current;
                var currentValue = func(it.Current);
                if (minValue.CompareTo(currentValue) > 0)
                {
                    minArg = currentArg;
                    minValue = currentValue;
                }
            }

            return Tuple.Create(minArg, minValue);
        }

        public static TOut Max<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            return MaxArgMax(func, inputs).Item2;
        }

        public static TIn ArgMax<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            return MaxArgMax(func, inputs).Item1;
        }

        /// <summary>
        /// Finds the value amongst <paramref name="inputs" /> such that the output value returned
        /// by <paramref name="func" /> is as big as possible.
        /// </summary>
        /// <typeparam name="TIn">The input type for the function.</typeparam>
        /// <typeparam name="TOut">The comparable output type of the function.</typeparam>
        /// <param name="func">The function for which to find the biggest value.</param>
        /// <param name="inputs">
        /// The function arguments for which to find the one with the biggest output value when
        /// given to <paramref name="func" />.
        /// </param>
        /// <returns></returns>
        public static Tuple<TIn, TOut> MaxArgMax<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            if (func == null) throw new ArgumentNullException(nameof(func));
            if (inputs == null) throw new ArgumentNullException(nameof(inputs));
            var it = inputs.GetEnumerator();
            var hasItems = it.MoveNext();
            if (!hasItems) throw new InvalidOperationException("No items given to find the maximum of");

            // find maximum argument and maximum value
            var maxArg = it.Current;
            var maxValue = func(it.Current);
            while (it.MoveNext())
            {
                var currentArg = it.Current;
                var currentValue = func(it.Current);
                if (maxValue.CompareTo(currentValue) < 0)
                {
                    maxArg = currentArg;
                    maxValue = currentValue;
                }
            }

            return Tuple.Create(maxArg, maxValue);
        }
    }
}