using System;
using System.Collections;
using System.IO;

using Org.BouncyCastle.Utilities;
using Org.BouncyCastle.Utilities.Collections;

namespace Org.BouncyCastle.Asn1
{
    public abstract class Asn1Sequence
		: Asn1Object, IEnumerable
    {
        private readonly IList seq;

		/**
         * return an Asn1Sequence from the given object.
         *
         * @param obj the object we want converted.
         * @exception ArgumentException if the object cannot be converted.
         */
        public static Asn1Sequence GetInstance(
            object obj)
        {
            if (obj == null || obj is Asn1Sequence)
            {
                return (Asn1Sequence)obj;
            }
			else if (obj is byte[])
			{
				try
				{
					return Asn1Sequence.GetInstance(Asn1Object.FromByteArray((byte[])obj));
				}
				catch (IOException e)
				{
					throw new ArgumentException("Failed to construct sequence from byte[]", e);
				}
			}

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

		/**
         * Return an ASN1 sequence from a tagged object. There is a special
         * case here, if an object appears to have been explicitly tagged on
         * reading but we were expecting it to be implicitly tagged in the
         * normal course of events it indicates that we lost the surrounding
         * sequence - so we need to add it back (this will happen if the tagged
         * object is a sequence that contains other sequences). If you are
         * dealing with implicitly tagged sequences you really <b>should</b>
         * be using this method.
         *
         * @param obj the tagged object.
         * @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 Asn1Sequence GetInstance(
            Asn1TaggedObject	obj,
            bool				explicitly)
        {
			Asn1Object inner = obj.GetObject();

			if (explicitly)
            {
                if (!obj.IsExplicit())
                    throw new ArgumentException("object implicit - explicit expected.");

				return (Asn1Sequence) inner;
            }

			//
            // constructed object which appears to be explicitly tagged
            // when it should be implicit means we have to add the
            // surrounding sequence.
            //
            if (obj.IsExplicit())
            {
                if (obj is BerTaggedObject)
                {
                    return new BerSequence(inner);
                }

				return new DerSequence(inner);
            }

			if (inner is Asn1Sequence)
            {
                return (Asn1Sequence) inner;
            }

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

		protected internal Asn1Sequence(
			int capacity)
		{
            seq = Platform.CreateArrayList(capacity);
		}

		public virtual IEnumerator GetEnumerator()
		{
			return seq.GetEnumerator();
		}

		[Obsolete("Use GetEnumerator() instead")]
		public IEnumerator GetObjects()
        {
            return GetEnumerator();
        }

		private class Asn1SequenceParserImpl
			: Asn1SequenceParser
		{
			private readonly Asn1Sequence outer;
			private readonly int max;
			private int index;

			public Asn1SequenceParserImpl(
				Asn1Sequence outer)
			{
				this.outer = outer;
				this.max = outer.Count;
			}

			public IAsn1Convertible ReadObject()
			{
				if (index == max)
					return null;

				Asn1Encodable obj = outer[index++];

				if (obj is Asn1Sequence)
					return ((Asn1Sequence)obj).Parser;

				if (obj is Asn1Set)
					return ((Asn1Set)obj).Parser;

				// NB: Asn1OctetString implements Asn1OctetStringParser directly
//				if (obj is Asn1OctetString)
//					return ((Asn1OctetString)obj).Parser;

				return obj;
			}

			public Asn1Object ToAsn1Object()
			{
				return outer;
			}
		}

		public virtual Asn1SequenceParser Parser
		{
			get { return new Asn1SequenceParserImpl(this); }
		}

        /**
         * return the object at the sequence position indicated by index.
         *
         * @param index the sequence number (starting at zero) of the object
         * @return the object at the sequence position indicated by index.
         */
		public virtual Asn1Encodable this[int index]
		{
			get { return (Asn1Encodable) seq[index]; }
		}

		[Obsolete("Use 'object[index]' syntax instead")]
        public Asn1Encodable GetObjectAt(
            int index)
        {
             return this[index];
        }

		[Obsolete("Use 'Count' property instead")]
		public int Size
        {
			get { return Count; }
        }

		public virtual int Count
		{
			get { return seq.Count; }
		}

		protected override int Asn1GetHashCode()
		{
			int hc = Count;

			foreach (object o in this)
			{
				hc *= 17;
				if (o == null)
				{
					hc ^= DerNull.Instance.GetHashCode();
				}
				else
                {
					hc ^= o.GetHashCode();
                }
            }

			return hc;
        }

		protected override bool Asn1Equals(
			Asn1Object asn1Object)
		{
			Asn1Sequence other = asn1Object as Asn1Sequence;

			if (other == null)
                return false;

			if (Count != other.Count)
                return false;

			IEnumerator s1 = GetEnumerator();
            IEnumerator s2 = other.GetEnumerator();

			while (s1.MoveNext() && s2.MoveNext())
			{
				Asn1Object o1 = GetCurrent(s1).ToAsn1Object();
				Asn1Object o2 = GetCurrent(s2).ToAsn1Object();

				if (!o1.Equals(o2))
					return false;
			}

			return true;
        }

		private Asn1Encodable GetCurrent(IEnumerator e)
		{
			Asn1Encodable encObj = (Asn1Encodable)e.Current;

			// unfortunately null was allowed as a substitute for DER null
			if (encObj == null)
				return DerNull.Instance;

			return encObj;
		}

		protected internal void AddObject(
            Asn1Encodable obj)
        {
            seq.Add(obj);
        }

		public override string ToString()
		{
			return CollectionUtilities.ToString(seq);
		}
    }
}
