using System;
using System.Runtime.CompilerServices;
using System.Text.RegularExpressions;
using BenchmarkDotNet.Attributes;

namespace Benchmark
{
    [MemoryDiagnoser]
    public class TrailingNumberFromString
    {
        private readonly Regex _regex = new Regex(@"^\d$", RegexOptions.Compiled);

        [Benchmark]
        public int? GetTrailingNumberFromString1()
        {
            const string foo = "Test1234";
            string sValue = null;

            for (var i = foo.Length - 1; i >= 0; i--)
            {
                var regex = new Regex(@"^\d$");

                if (regex.IsMatch(foo[i].ToString()))
                    sValue = foo[i] + sValue;
                else
                    break;
            }

            if (sValue != null)
                return Convert.ToInt32(sValue);

            return null;
        }

        [Benchmark]
        public int? GetTrailingNumberFromString2()
        {
            const string foo = "Test1234";
            string sValue = null;

            for (var i = foo.Length - 1; i >= 0; i--)
            {
                if (_regex.IsMatch(foo[i].ToString()))
                    sValue = foo[i] + sValue;
                else
                    break;
            }
            if (sValue != null)
                return Convert.ToInt32(sValue);

            return null;
        }

        [Benchmark]
        public int? GetTrailingNumberFromString3()
        {
            const string foo = "Test1234";
            var result = 0;

            for (var i = foo.Length - 1; i >= 0; i--)
            {
                if (foo[i] >= 48 && foo[i] <= 58)
                {
                    var value = foo[i] - 48;
                    result += value * (int) Math.Pow(10, foo.Length - i - 1);
                    continue;
                }

                break;
            }

            return result;
        }

        [Benchmark]
        public int? GetTrailingNumberFromString4()
        {
            const string foo = "Test1234";
            var result = 0;
            
            for (var i = foo.Length - 1; i >= 0; i--)
            {
                if (foo[i] >= 48 && foo[i] <= 58)
                {
                    var value = foo[i] - 48;
                    result += value * IntegerPow(10, foo.Length - i - 1);
                    continue;
                }

                break;
            }

            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static int IntegerPow(int x, int y)
        {
            if (y == 0) return 1;
            var result = x;
            for (var i = 1; i < y; i++)
            {
                result *= x;
            }

            return result;
        }
        
        [Benchmark]
        public int? GetTrailingNumberFromString5()
        {
            const string foo = "Test1234";
            var regex = new Regex(@"\d+$");
            var match = regex.Match(foo);
            return match.Success && int.TryParse(match.Value, out var result) ? result : default(int?);
        }
    }
}