using System;
using System.Collections.Generic;
using System.Linq;
using NUnit.Framework;

namespace Pangrams
{
    public class Pangrams
    {
        public List<List<string>> FindPangrams(List<string> input)
        {
            var powerset = GetPowerSet(input);
            var returnValue = new List<List<string>>();

            foreach (var set in powerset)
            {
                if (GetSetLength(set) == 26 && ContainsAllLetters(set))
                {
                    returnValue.Add(set);
                }
            }
            return returnValue;
        }

        private int GetSetLength(List<string> list)
        {
            return list.Sum(x => x.Length);
        }

        // bitmask & 1 (101 & 1) === 1 / (100 & 1) === 0
        // bitmask >> 1
        // biitmask << 1
        // {quick, brown}
        public List<List<string>> GetPowerSet(List<string> input)
        {
            var returnValue = new List<List<string>>();
            for (int i = 0; i < Math.Pow(2,input.Count) ; i++)
            {
                var currentSet = new List<string>();
                for (var j = 0; j < input.Count; j++)
                {
                    var pow = (int)Math.Pow(2,j);
                    if ((pow & i) == pow)
                    {
                        currentSet.Add(input[j]);
                    }
                }
                returnValue.Add(currentSet);
            }
            return returnValue;
        }

        bool ContainsAllLetters(List<string> input)
        {
            for (char c = 'a'; c <= 'z'; c++)
            {
                if (!input.Any(x=>x.ToLower().Contains(c.ToString())))
                {
                    return false;
                }
            }
            return true;
        }

    }


    [TestFixture]
    public class PangramsTests
    {
        [Test]
        public void GetPowerSet_GetsCorrectPowerset()
        {
            var pangram = new Pangrams();
            List<string> input=new List<string>{"a", "b"};
            var powerset = pangram.GetPowerSet(input);
            // powerset should be {}, {"a"}, {"b"}, {"a", "b"}
            Assert.AreEqual(4, powerset.Count);
        }

        [Test]
        public void FindPangrams_FindsJockNymphs()
        {
            var pangram=new Pangrams();
            List<string> input = "Jock nymphs waqf drug vex blitz".Split(' ').ToList();
            var result = pangram.FindPangrams(input);
            Assert.AreEqual(1,result.Count);
        }

        [Test]
        public void FindPangrams_FindsTwoForJcokJockNymphs()
        {
            var pangram = new Pangrams();
            List<string> input = "Jock Jcok nymphs waqf drug vex blitz".Split(' ').ToList();
            var result = pangram.FindPangrams(input);
            Assert.AreEqual(2, result.Count);
        }
    }
}