using System;
using System.Globalization;
using System.Text;

namespace Org.BouncyCastle.Asn1
{
    /**
     * Generalized time object.
     */
    public class DerGeneralizedTime
        : Asn1Object
    {
        private readonly string time;

		/**
         * return a generalized time from the passed in object
         *
         * @exception ArgumentException if the object cannot be converted.
         */
        public static DerGeneralizedTime GetInstance(
            object obj)
        {
			if (obj == null || obj is DerGeneralizedTime)
            {
                return (DerGeneralizedTime)obj;
            }

			if (obj is Asn1OctetString)
            {
                return new DerGeneralizedTime(((Asn1OctetString)obj).GetOctets());
            }

			throw new ArgumentException("illegal object in GetInstance: " + obj.GetType().Name, "obj");
        }

		/**
         * return a Generalized Time object from a tagged object.
         *
         * @param obj the tagged object holding the object we want
         * @param explicitly true if the object is meant to be explicitly
         *              tagged false otherwise.
         * @exception ArgumentException if the tagged object cannot
         *               be converted.
         */
        public static DerGeneralizedTime GetInstance(
            Asn1TaggedObject	obj,
            bool				explicitly)
        {
            return GetInstance(obj.GetObject());
        }

		/**
		 * The correct format for this is YYYYMMDDHHMMSS[.f]Z, or without the Z
		 * for local time, or Z+-HHMM on the end, for difference between local
		 * time and UTC time. The fractional second amount f must consist of at
		 * least one number with trailing zeroes removed.
		 *
		 * @param time the time string.
		 * @exception ArgumentException if string is an illegal format.
		 */
		public DerGeneralizedTime(
			string time)
		{
			this.time = time;

			try
			{
				ToDateTime();
			}
			catch (FormatException e)
			{
				throw new ArgumentException("invalid date string: " + e.Message);
			}
		}

		/**
         * base constructor from a local time object
         */
        public DerGeneralizedTime(
            DateTime time)
        {
            this.time = time.ToString(@"yyyyMMddHHmmss\Z");
        }

		internal DerGeneralizedTime(
            byte[] bytes)
        {
            //
            // explicitly convert to characters
            //
			this.time = Encoding.ASCII.GetString(bytes, 0, bytes.Length);
        }

		/**
		 * Return the time.
		 * @return The time string as it appeared in the encoded object.
		 */
		public string TimeString
		{
			get { return time; }
		}

		/**
         * return the time - always in the form of
         *  YYYYMMDDhhmmssGMT(+hh:mm|-hh:mm).
         * <p>
         * Normally in a certificate we would expect "Z" rather than "GMT",
         * however adding the "GMT" means we can just use:
         * <pre>
         *     dateF = new SimpleDateFormat("yyyyMMddHHmmssz");
         * </pre>
         * To read in the time and Get a date which is compatible with our local
         * time zone.</p>
         */
        public string GetTime()
        {
            //
            // standardise the format.
            //
            if (time[time.Length - 1] == 'Z')
            {
                return time.Substring(0, time.Length - 1) + "GMT+00:00";
            }
            else
            {
                int signPos = time.Length - 5;
                char sign = time[signPos];
                if (sign == '-' || sign == '+')
                {
                    return time.Substring(0, signPos)
                        + "GMT"
                        + time.Substring(signPos, 3)
                        + ":"
                        + time.Substring(signPos + 3);
                }
                else
                {
                    signPos = time.Length - 3;
                    sign = time[signPos];
                    if (sign == '-' || sign == '+')
                    {
                        return time.Substring(0, signPos)
                            + "GMT"
                            + time.Substring(signPos)
                            + ":00";
                    }
                }
            }

            return time + CalculateGmtOffset();
        }

		private string CalculateGmtOffset()
		{
			char sign = '+';

			// Note: GetUtcOffset incorporates Daylight Savings offset
			int minutes = TimeZone.CurrentTimeZone.GetUtcOffset(ToDateTime()).Minutes;
			if (minutes < 0)
			{
				sign = '-';
				minutes = -minutes;
			}
			int hours = minutes / 60;
			minutes %= 60;

			return "GMT" + sign + Convert(hours) + ":" + Convert(minutes);
		}

		private static string Convert(
			int time)
		{
			if (time < 10)
			{
				return "0" + time;
			}

			return time.ToString();
		}

		public DateTime ToDateTime()
		{
			string formatStr;
			string d = time;
			bool makeUniversal = false;

			if (d.EndsWith("Z"))
			{
				if (HasFractionalSeconds)
				{
					int fCount = d.Length - d.IndexOf('.') - 2;
					formatStr = @"yyyyMMddHHmmss." + FString(fCount) + @"\Z";
				}
				else
				{
					formatStr = @"yyyyMMddHHmmss\Z";
				}
			}
			else if (time.IndexOf('-') > 0 || time.IndexOf('+') > 0)
			{
				d = GetTime();
				makeUniversal = true;

				if (HasFractionalSeconds)
				{
					int fCount = d.IndexOf("GMT") - 1 - d.IndexOf('.');
					formatStr = @"yyyyMMddHHmmss." + FString(fCount) + @"'GMT'zzz";
				}
				else
				{
					formatStr = @"yyyyMMddHHmmss'GMT'zzz";
				}
			}
			else
			{
				if (HasFractionalSeconds)
				{
					int fCount = d.Length - 1 - d.IndexOf('.');
					formatStr = @"yyyyMMddHHmmss." + FString(fCount);
				}
				else
				{
					formatStr = @"yyyyMMddHHmmss";
				}

				// TODO?
//				dateF.setTimeZone(new SimpleTimeZone(0, TimeZone.getDefault().getID()));
			}

			return ParseDateString(d, formatStr, makeUniversal);
		}

		private string FString(
			int count)
		{
			StringBuilder sb = new StringBuilder();
			for (int i = 0; i < count; ++i)
			{
				sb.Append('f');
			}
			return sb.ToString();
		}

		private DateTime ParseDateString(
			string	dateStr,
			string	formatStr,
			bool	makeUniversal)
		{
			DateTime dt = DateTime.ParseExact(
				dateStr,
				formatStr,
				DateTimeFormatInfo.InvariantInfo);

			return makeUniversal ? dt.ToUniversalTime() : dt;
		}

		private bool HasFractionalSeconds
		{
			get { return time.IndexOf('.') == 14; }
		}

		private byte[] GetOctets()
        {
			return Encoding.ASCII.GetBytes(time);
        }

		internal override void Encode(
            DerOutputStream derOut)
        {
            derOut.WriteEncoded(Asn1Tags.GeneralizedTime, GetOctets());
        }

		protected override bool Asn1Equals(
			Asn1Object asn1Object)
        {
			DerGeneralizedTime other = asn1Object as DerGeneralizedTime;

			if (other == null)
				return false;

			return this.time.Equals(other.time);
        }

		protected override int Asn1GetHashCode()
		{
            return time.GetHashCode();
        }
    }
}