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
    {
        // NOTE: Only non-readonly to support LazyDerSequence
        internal Asn1Encodable[] elements;

        /**
         * 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 Asn1SequenceParser)
            {
                return GetInstance(((Asn1SequenceParser)obj).ToAsn1Object());
            }
            else if (obj is byte[])
            {
                try
                {
                    return GetInstance(FromByteArray((byte[])obj));
                }
                catch (IOException e)
                {
                    throw new ArgumentException("failed to construct sequence from byte[]: " + e.Message);
                }
            }
            else if (obj is Asn1Encodable)
            {
                Asn1Object primitive = ((Asn1Encodable)obj).ToAsn1Object();
                
                if (primitive is Asn1Sequence)
                {
                    return (Asn1Sequence)primitive;
                }
            }

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

        protected internal Asn1Sequence()
        {
            this.elements = Asn1EncodableVector.EmptyElements;
        }

        protected internal Asn1Sequence(Asn1Encodable element)
        {
            if (null == element)
                throw new ArgumentNullException("element");

            this.elements = new Asn1Encodable[]{ element };
        }

        protected internal Asn1Sequence(params Asn1Encodable[] elements)
        {
            if (Arrays.IsNullOrContainsNull(elements))
                throw new NullReferenceException("'elements' cannot be null, or contain null");

            this.elements = Asn1EncodableVector.CloneElements(elements);
        }

        protected internal Asn1Sequence(Asn1EncodableVector elementVector)
        {
            if (null == elementVector)
                throw new ArgumentNullException("elementVector");

            this.elements = elementVector.TakeElements();
        }

        public virtual IEnumerator GetEnumerator()
        {
            return elements.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 elements[index]; }
        }

        public virtual int Count
        {
            get { return elements.Length; }
        }

        public virtual Asn1Encodable[] ToArray()
        {
            return Asn1EncodableVector.CloneElements(elements);
        }

        protected override int Asn1GetHashCode()
        {
            //return Arrays.GetHashCode(elements);
            int i = elements.Length;
            int hc = i + 1;

            while (--i >= 0)
            {
                hc *= 257;
                hc ^= elements[i].ToAsn1Object().CallAsn1GetHashCode();
            }

            return hc;
        }

        protected override bool Asn1Equals(Asn1Object asn1Object)
        {
            Asn1Sequence that = asn1Object as Asn1Sequence;
            if (null == that)
                return false;

            int count = this.Count;
            if (that.Count != count)
                return false;

            for (int i = 0; i < count; ++i)
            {
                Asn1Object o1 = this.elements[i].ToAsn1Object();
                Asn1Object o2 = that.elements[i].ToAsn1Object();

                if (o1 != o2 && !o1.CallAsn1Equals(o2))
                    return false;
            }

            return true;
        }

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