#region Copyright notice and license
// Protocol Buffers - Google's data interchange format
// Copyright 2015 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#endregion


namespace XGame.Framework.Network.Protobuf
{
    public sealed class MapFieldCodec<TKey, TValue>
    {
        private readonly FieldCodec<TKey> keyCodec;
        private readonly FieldCodec<TValue> valueCodec;
        private readonly uint mapTag;

        /// <summary>
        /// Creates a new entry codec based on a separate key codec and value codec,
        /// and the tag to use for each map entry.
        /// </summary>
        /// <param name="keyCodec">The key codec.</param>
        /// <param name="valueCodec">The value codec.</param>
        /// <param name="mapTag">The map tag to use to introduce each map entry.</param>
        public MapFieldCodec(FieldCodec<TKey> keyCodec, FieldCodec<TValue> valueCodec, uint mapTag)
        {
            this.keyCodec = keyCodec;
            this.valueCodec = valueCodec;
            this.mapTag = mapTag;
        }

        /// <summary>
        /// The tag used in the enclosing message to indicate map entries.
        /// </summary>
        public uint MapTag { get { return mapTag; } }

        /// <summary>
        /// A mutable message class, used for parsing and serializing. This
        /// delegates the work to a codec, but implements the <see cref="IMessage"/> interface
        /// for interop with <see cref="CodedInputStream"/> and <see cref="CodedOutputStream"/>.
        /// This is nested inside Codec as it's tightly coupled to the associated codec,
        /// and it's simpler if it has direct access to all its fields.
        /// </summary>
        public class MessageAdapter : IMsgParser
        {
            private static readonly byte[] ZeroLengthMessageStreamData = new byte[] { 0 };

            private readonly MapFieldCodec<TKey, TValue> codec;
            public TKey Key { get; set; }
            public TValue Value { get; set; }

            public MessageAdapter(MapFieldCodec<TKey, TValue> codec)
            {
                this.codec = codec;
            }

            public void Reset()
            {
                Key = codec.keyCodec.DefaultValue;
                Value = codec.valueCodec.DefaultValue;
            }

            public void MergeFrom(CodedInputStream input)
            {
                uint tag;
                while ((tag = input.ReadTag()) != 0)
                {
                    if (tag == codec.keyCodec.Tag)
                    {
                        Key = codec.keyCodec.Read(input);
                    }
                    else if (tag == codec.valueCodec.Tag)
                    {
                        Value = codec.valueCodec.Read(input);
                    }
                    else
                    {
                        input.SkipLastField();
                    }
                }

                // Corner case: a map entry with a key but no value, where the value type is a message.
                // Read it as if we'd seen an input stream with no data (i.e. create a "default" message).
                if (Value == null)
                {
                    Value = codec.valueCodec.Read(new CodedInputStream(ZeroLengthMessageStreamData));
                }
            }

            public void WriteTo(CodedOutputStream output)
            {
                codec.keyCodec.WriteTagAndValue(output, Key);
                codec.valueCodec.WriteTagAndValue(output, Value);
            }

            public int CalculateSize()
            {
                return codec.keyCodec.CalculateSizeWithTag(Key) + codec.valueCodec.CalculateSizeWithTag(Value);
            }

            public void Clear() { }

            //MessageDescriptor IMessage.Descriptor { get { return null; } }
        }
    }
}