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

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

		/**
         * return an UTC Time from the passed in object.
         *
         * @exception ArgumentException if the object cannot be converted.
         */
        public static DerUtcTime GetInstance(
            object obj)
        {
            if (obj == null || obj is DerUtcTime)
            {
                return (DerUtcTime)obj;
            }

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

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

        /**
         * return an UTC Time 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 DerUtcTime GetInstance(
            Asn1TaggedObject	obj,
            bool				explicitly)
        {
            return GetInstance(obj.GetObject());
        }

        /**
         * The correct format for this is YYMMDDHHMMSSZ (it used to be that seconds were
         * never encoded. When you're creating one of these objects from scratch, that's
         * what you want to use, otherwise we'll try to deal with whatever Gets read from
         * the input stream... (this is why the input format is different from the GetTime()
         * method output).
         * <p>
         * @param time the time string.</p>
         */
        public DerUtcTime(
            string time)
        {
			if (time == null)
				throw new ArgumentNullException("time");

			this.time = time;

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

		/**
         * base constructor from a DateTime object
         */
        public DerUtcTime(
            DateTime time)
        {
            this.time = time.ToString("yyMMddHHmmss") + "Z";
        }

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

//		public DateTime ToDateTime()
//		{
//			string tm = this.AdjustedTimeString;
//
//			return new DateTime(
//				Int16.Parse(tm.Substring(0, 4)),
//				Int16.Parse(tm.Substring(4, 2)),
//				Int16.Parse(tm.Substring(6, 2)),
//				Int16.Parse(tm.Substring(8, 2)),
//				Int16.Parse(tm.Substring(10, 2)),
//				Int16.Parse(tm.Substring(12, 2)));
//		}

		/**
		 * return the time as a date based on whatever a 2 digit year will return. For
		 * standardised processing use ToAdjustedDateTime().
		 *
		 * @return the resulting date
		 * @exception ParseException if the date string cannot be parsed.
		 */
		public DateTime ToDateTime()
		{
			return ParseDateString(TimeString, @"yyMMddHHmmss'GMT'zzz");
		}

		/**
		* return the time as an adjusted date
		* in the range of 1950 - 2049.
		*
		* @return a date in the range of 1950 to 2049.
		* @exception ParseException if the date string cannot be parsed.
		*/
		public DateTime ToAdjustedDateTime()
		{
			return ParseDateString(AdjustedTimeString, @"yyyyMMddHHmmss'GMT'zzz");
		}

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

			return dt.ToUniversalTime();
		}

		/**
         * return the time - always in the form of
         *  YYMMDDhhmmssGMT(+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("yyMMddHHmmssz");
         * </pre>
         * To read in the time and Get a date which is compatible with our local
         * time zone.</p>
         * <p>
         * <b>Note:</b> In some cases, due to the local date processing, this
         * may lead to unexpected results. If you want to stick the normal
         * convention of 1950 to 2049 use the GetAdjustedTime() method.</p>
         */
        public string TimeString
        {
			get
			{
				//
				// standardise the format.
				//
				if (time.IndexOf('-') < 0 && time.IndexOf('+') < 0)
				{
					if (time.Length == 11)
					{
						return time.Substring(0, 10) + "00GMT+00:00";
					}
					else
					{
						return time.Substring(0, 12) + "GMT+00:00";
					}
				}
				else
				{
					int index = time.IndexOf('-');
					if (index < 0)
					{
						index = time.IndexOf('+');
					}
					string d = time;

					if (index == time.Length - 3)
					{
						d += "00";
					}

					if (index == 10)
					{
						return d.Substring(0, 10) + "00GMT" + d.Substring(10, 3) + ":" + d.Substring(13, 2);
					}
					else
					{
						return d.Substring(0, 12) + "GMT" + d.Substring(12, 3) + ":" +  d.Substring(15, 2);
					}
				}
			}
        }

		[Obsolete("Use 'AdjustedTimeString' property instead")]
		public string AdjustedTime
		{
			get { return AdjustedTimeString; }
		}

		/// <summary>
		/// Return a time string as an adjusted date with a 4 digit year.
		/// This goes in the range of 1950 - 2049.
		/// </summary>
		public string AdjustedTimeString
		{
			get
			{
				string d = TimeString;
				string c = d[0] < '5' ? "20" : "19";

				return c + d;
			}
		}

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

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

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

			if (other == null)
				return false;

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

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

		public override string ToString()
		{
			return time;
		}
	}
}
