#region Copyright notice and license
// Protocol Buffers - Google's data interchange format
// Copyright 2008 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 Google.Protobuf
{
    /// <summary>
    /// This class is used internally by the Protocol Buffer Library and generated
    /// message implementations. It is public only for the sake of those generated
    /// messages. Others should not use this class directly.
    /// <para>
    /// This class contains constants and helper functions useful for dealing with
    /// the Protocol Buffer wire format.
    /// </para>
    /// </summary>
    public static class WireFormat
    {
        #region Fixed sizes.

        // TODO(jonskeet): Move these somewhere else. They're messy. Consider making FieldType a smarter kind of enum
        internal const int Fixed32Size = 4;
        internal const int Fixed64Size = 8;
        internal const int SFixed32Size = 4;
        internal const int SFixed64Size = 8;
        internal const int FloatSize = 4;
        internal const int DoubleSize = 8;
        internal const int BoolSize = 1;

        #endregion

        /// <summary>
        /// Wire types within protobuf encoding.
        /// </summary>
        public enum WireType : uint
        {
            /// <summary>
            /// Variable-length integer.
            /// </summary>
            Varint = 0,
            /// <summary>
            /// A fixed-length 64-bit value.
            /// </summary>
            Fixed64 = 1,
            /// <summary>
            /// A length-delimited value, i.e. a length followed by that many bytes of data.
            /// </summary>
            LengthDelimited = 2,
            /// <summary>
            /// A "start group" value - not supported by this implementation.
            /// </summary>
            StartGroup = 3,
            /// <summary>
            /// An "end group" value - not supported by this implementation.
            /// </summary>
            EndGroup = 4,
            /// <summary>
            /// A fixed-length 32-bit value.
            /// </summary>
            Fixed32 = 5
        }
        
        private const int TagTypeBits = 3;
        private const uint TagTypeMask = (1 << TagTypeBits) - 1;

        /// <summary>
        /// Given a tag value, determines the wire type (lower 3 bits).
        /// </summary>
        public static WireType GetTagWireType(uint tag)
        {
            return (WireType) (tag & TagTypeMask);
        }

        /// <summary>
        /// Determines whether the given tag is an end group tag.
        /// </summary>
        /// <param name="tag">The tag to check.</param>
        /// <returns><c>true</c> if the given tag is an end group tag; <c>false</c> otherwise.</returns>
        public static bool IsEndGroupTag(uint tag)
        {
            return (WireType) (tag & TagTypeMask) == WireType.EndGroup;
        }

        /// <summary>
        /// Given a tag value, determines the field number (the upper 29 bits).
        /// </summary>
        public static int GetTagFieldNumber(uint tag)
        {
            return (int) tag >> TagTypeBits;
        }

        /// <summary>
        /// Makes a tag value given a field number and wire type.
        /// </summary>
        public static uint MakeTag(int fieldNumber, WireType wireType)
        {
            return (uint) (fieldNumber << TagTypeBits) | (uint) wireType;
        }        
    }
}