using System;
using System.Collections;
using System.Diagnostics;

using Org.BouncyCastle.Utilities;

namespace Org.BouncyCastle.Asn1
{
    public class BerOctetString
        : DerOctetString, IEnumerable
    {
        private const int DefaultSegmentLimit = 1000;

        public static BerOctetString FromSequence(Asn1Sequence seq)
        {
            int count = seq.Count;
            Asn1OctetString[] v = new Asn1OctetString[count];
            for (int i = 0; i < count; ++i)
            {
                v[i] = GetInstance(seq[i]);
            }
            return new BerOctetString(v);
        }

        internal static byte[] FlattenOctetStrings(Asn1OctetString[] octetStrings)
        {
            int count = octetStrings.Length;
            switch (count)
            {
            case 0:
                return EmptyOctets;
            case 1:
                return octetStrings[0].contents;
            default:
            {
                int totalOctets = 0;
                for (int i = 0; i < count; ++i)
                {
                    totalOctets += octetStrings[i].contents.Length;
                }

                byte[] str = new byte[totalOctets];
                int pos = 0;
                for (int i = 0; i < count; ++i)
                {
                    byte[] octets = octetStrings[i].contents;
                    Array.Copy(octets, 0, str, pos, octets.Length);
                    pos += octets.Length;
                }

                Debug.Assert(pos == totalOctets);
                return str;
            }
            }
        }

        private static Asn1OctetString[] ToOctetStringArray(IEnumerable e)
        {
            IList list = Platform.CreateArrayList(e);

            int count = list.Count;
            Asn1OctetString[] v = new Asn1OctetString[count];
            for (int i = 0; i < count; ++i)
            {
                v[i] = GetInstance(list[i]);
            }
            return v;
        }

        private readonly int segmentLimit;
        private readonly Asn1OctetString[] elements;

        public BerOctetString(byte[] contents)
			: this(contents, DefaultSegmentLimit)
		{
		}

        public BerOctetString(Asn1OctetString[] elements)
            : this(elements, DefaultSegmentLimit)
        {
        }

        public BerOctetString(byte[] contents, int segmentLimit)
            : this(contents, null, segmentLimit)
        {
        }

        public BerOctetString(Asn1OctetString[] elements, int segmentLimit)
            : this(FlattenOctetStrings(elements), elements, segmentLimit)
        {
        }

        private BerOctetString(byte[] contents, Asn1OctetString[] elements, int segmentLimit)
            : base(contents)
        {
            this.elements = elements;
            this.segmentLimit = segmentLimit;
        }

        /**
         * return the DER octets that make up this string.
         */
		public IEnumerator GetEnumerator()
		{
			if (elements == null)
                return new ChunkEnumerator(contents, segmentLimit);

			return elements.GetEnumerator();
		}

        internal override IAsn1Encoding GetEncoding(int encoding)
        {
            if (Asn1OutputStream.EncodingBer != encoding)
                return base.GetEncoding(encoding);

            if (null == elements)
                return new PrimitiveEncoding(Asn1Tags.Universal, Asn1Tags.OctetString, contents);

            return new ConstructedILEncoding(Asn1Tags.Universal, Asn1Tags.OctetString,
                Asn1OutputStream.GetContentsEncodings(encoding, elements));
        }

        internal override IAsn1Encoding GetEncodingImplicit(int encoding, int tagClass, int tagNo)
        {
            if (Asn1OutputStream.EncodingBer != encoding)
                return base.GetEncodingImplicit(encoding, tagClass, tagNo);

            if (null == elements)
                return new PrimitiveEncoding(tagClass, tagNo, contents);

            return new ConstructedILEncoding(tagClass, tagNo,
                Asn1OutputStream.GetContentsEncodings(encoding, elements));
        }

        private class ChunkEnumerator
            : IEnumerator
        {
            private readonly byte[] octets;
            private readonly int segmentLimit;

            private DerOctetString currentSegment = null;
            private int nextSegmentPos = 0;

            internal ChunkEnumerator(byte[] octets, int segmentLimit)
            {
                this.octets = octets;
                this.segmentLimit = segmentLimit;
            }

            public object Current
            {
                get
                {
                    if (null == currentSegment)
                        throw new InvalidOperationException();

                    return currentSegment;
                }
            }

            public bool MoveNext()
            {
                if (nextSegmentPos >= octets.Length)
                {
                    this.currentSegment = null;
                    return false;
                }

                int length = System.Math.Min(octets.Length - nextSegmentPos, segmentLimit);
                byte[] segment = new byte[length];
                Array.Copy(octets, nextSegmentPos, segment, 0, length);
                this.currentSegment = new DerOctetString(segment);
                this.nextSegmentPos += length;
                return true;
            }

            public void Reset()
            {
                this.currentSegment = null;
                this.nextSegmentPos = 0;
            }
        }
    }
}