/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;

namespace Avro.IO
{
    /// <summary>
    /// Utility to present <see cref="MemoryStream"/>s as an <see cref="InputStream"/>.
    /// </summary>
    /// <seealso cref="ByteBufferOutputStream"/>
    public class ByteBufferInputStream : InputStream
    {
        private readonly IList<MemoryStream> _buffers;
        private int _currentBuffer;

        /// <summary>
        /// Initializes a new instance of a <see cref="ByteBufferInputStream"/>.
        /// </summary>
        /// <param name="buffers"></param>
        public ByteBufferInputStream(IList<MemoryStream> buffers)
        {
            _buffers = buffers;
        }

        /// <inheritdoc/>
        public override int Read(byte[] b, int off, int len)
        {
            if (len == 0) return 0;
            MemoryStream buffer = GetNextNonEmptyBuffer();
            long remaining = buffer.Length - buffer.Position;
            if (len > remaining)
            {
                int remainingCheck = buffer.Read(b, off, (int) remaining);

                if(remainingCheck != remaining)
                    throw new InvalidDataException(string.Format(CultureInfo.InvariantCulture,
                        "remainingCheck [{0}] and remaining[{1}] are different.",
                        remainingCheck, remaining));
                return (int)remaining;
            }

            int lenCheck = buffer.Read(b, off, len);

            if (lenCheck != len)
                throw new InvalidDataException(string.Format(CultureInfo.InvariantCulture,
                    "lenCheck [{0}] and len[{1}] are different.", lenCheck, len));

            return len;
        }

        private MemoryStream GetNextNonEmptyBuffer()
        {
            while (_currentBuffer < _buffers.Count)
            {
                MemoryStream buffer = _buffers[_currentBuffer];
                if (buffer.Position < buffer.Length)
                    return buffer;

                _currentBuffer++;
            }
            throw new EndOfStreamException();
        }

        /// <summary>
        /// Throws a <see cref="NotSupportedException"/>.
        /// </summary>
        /// <exception cref="NotSupportedException">
        /// Always thows.
        /// </exception>
        public override long Length
        {
            get { throw new NotSupportedException(); }
        }
    }
}