TimeParser.cs

using System.Collections.Generic;
using System.Linq;
using System.Text;
using ScheduleBusiness.Models;

namespace ScheduleBusiness
{
    public static class TimeParser
    {
        public static Time Parse(string timeText)
        {
            if (string.IsNullOrWhiteSpace(timeText))
            {
                return null;
            }

            bool isAm = true;

            if (timeText.ToUpper().Contains("A"))
            {
                isAm = true;
            }
            else if (timeText.ToUpper().Contains("P"))
            {
                isAm = false;
            }

            List<string> pieces;
            if (timeText.Contains(":"))
            {
                pieces = timeText.Split(':').ToList();
            }
            else
            {
                pieces = timeText.Split(' ').ToList();
            }

            pieces = pieces.Where(queryPiece => !string.IsNullOrWhiteSpace(queryPiece)).ToList();

            if (pieces.Count == 1)
            {
                string onlyDigits = FilterOutNonDigits(pieces[0]);
                if (string.IsNullOrWhiteSpace(onlyDigits))
                {
                    return null;
                }

                int timeInt;
                decimal timeNum;
                if (!int.TryParse(onlyDigits, out timeInt))
                {
                    timeInt = 0;
                }

                timeNum = timeInt;

                while (timeNum > 100)
                {
                    timeNum /= 100;
                }

                int hours = (int)timeNum;
                if (hours < 0 || hours == 24)
                {
                    hours = 0;
                }

                if (hours < 12 && !isAm)
                {
                    hours += 12;
                    timeNum += 12;
                }

                if (hours == 24)
                {
                    hours -= 24;
                }

                timeNum -= hours;

                if (hours == 12 && isAm)
                {
                    hours -= 12;
                }

                decimal minutes = timeNum * 100;
                if (minutes < 0)
                {
                    minutes = 0;
                }

                if (hours > 24)
                {
                    minutes = hours % 10;
                    hours /= 10;
                }

                return IsTimeValid(hours, (int)minutes) ? new Time(hours, (int)minutes) : null;
            }
            else if (pieces.Count >= 2)
            {
                string hoursDigits = FilterOutNonDigits(pieces[0]);
                if (string.IsNullOrWhiteSpace(hoursDigits))
                {
                    pieces[0] = pieces[1];
                    pieces[1] = "0";

                    hoursDigits = FilterOutNonDigits(pieces[0]);
                }

                int timeInt;
                decimal timeNum;
                if (!int.TryParse(hoursDigits, out timeInt))
                {
                    timeInt = 0;
                }

                timeNum = timeInt;

                while (timeNum > 100)
                {
                    timeNum /= 100;
                }

                int hour = (int)timeNum;
                if (hour < 12 && !isAm)
                {
                    hour += 12;
                }

                timeNum -= hour;
                decimal minutes = timeNum * 100;

                if (minutes > 0)
                {
                    return new Time(hour, (int)minutes);
                }

                string minutesDigits = FilterOutNonDigits(pieces[1]);
                int minutesInt;
                if (!int.TryParse(minutesDigits, out minutesInt))
                {
                    minutesInt = 0;
                }

                minutes = minutesInt;

                if (minutes < 0)
                {
                    minutes = 0;
                }

                while (minutes > 100)
                {
                    minutes /= 100;
                }

                // The 12:00 AM case
                if (hour == 12 && isAm && minutes == 0)
                {
                    hour = 0;
                }

                return IsTimeValid(hour, (int)minutes) ? new Time(hour, (int)minutes) : null;
            }

            return null;
        }

        public static bool IsTimeValid(int hours, int minutes)
        {
            return hours >= 0 && hours < 24 && minutes >= 0 && minutes < 60;
        }

        public static string FilterOutNonDigits(string text)
        {
            StringBuilder filteredText = new StringBuilder();
            foreach (char ch in text)
            {
                if (char.IsDigit(ch))
                {
                    filteredText.Append(ch);
                }
            }

            return filteredText.ToString();
        }
    }
}