/***
* Copyright (C) Microsoft. All rights reserved.
* Licensed under the MIT license. See LICENSE.txt file in the project root for full license information.
*
* =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
*
* Asynchronous I/O: stream buffer. This is an extension to the PPL concurrency features and therefore
* lives in the Concurrency namespace.
*
* For the latest on this and related APIs, please see: https://github.com/Microsoft/cpprestsdk
*
* =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
****/
#pragma once

#include <math.h>
#include <atomic>
#include <cstring>
#include <ios>
#include <memory>

#include "pplx/pplxtasks.h"
#include "cpprest/details/basic_types.h"
#include "cpprest/asyncrt_utils.h"

#if (defined(_MSC_VER) && (_MSC_VER >= 1800)) && !CPPREST_FORCE_PPLX
namespace Concurrency // since namespace pplx = Concurrency
#else
namespace pplx
#endif
{
    namespace details
    {
        template<class F, class T = bool>
        pplx::task<T> _do_while(F func)
        {
            pplx::task<T> first = func();
            return first.then([=](bool guard) -> pplx::task<T> {
                if (guard)
                    return pplx::details::_do_while<F,T>(func);
                else
                    return first;
            });
        }
    }
}

namespace Concurrency
{

/// Library for asynchronous streams.
namespace streams
{
    /// <summary>
    /// Extending the standard char_traits type with one that adds values and types
    /// that are unique to "C++ REST SDK" streams.
    /// </summary>
    /// <typeparam name="_CharType">
    /// The data type of the basic element of the stream.
    /// </typeparam>
    template<typename _CharType>
    struct char_traits : std::char_traits<_CharType>
    {
        /// <summary>
        /// Some synchronous functions will return this value if the operation
        /// requires an asynchronous call in a given situation.
        /// </summary>
        /// <returns>An <c>int_type</c> value which implies that an asynchronous call is required.</returns>
        static typename std::char_traits<_CharType>::int_type requires_async() { return std::char_traits<_CharType>::eof()-1; }
    };
#if !defined(_WIN32)
    template<>
    struct char_traits<unsigned char> : private std::char_traits<char>
    {
    public:
        typedef unsigned char char_type;

        using std::char_traits<char>::eof;
        using std::char_traits<char>::int_type;
        using std::char_traits<char>::off_type;
        using std::char_traits<char>::pos_type;

        static size_t length(const unsigned char* str)
        {
            return std::char_traits<char>::length(reinterpret_cast<const char*>(str));
        }

        static void assign(unsigned char& left, const unsigned char& right) { left = right; }
        static unsigned char* assign(unsigned char* left, size_t n, unsigned char value)
        {
            return reinterpret_cast<unsigned char*>(std::char_traits<char>::assign(reinterpret_cast<char*>(left), n, static_cast<char>(value)));
        }

        static unsigned char* copy(unsigned char* left, const unsigned char* right, size_t n)
        {
            return reinterpret_cast<unsigned char*>(std::char_traits<char>::copy(reinterpret_cast<char*>(left), reinterpret_cast<const char*>(right), n));
        }

        static unsigned char* move(unsigned char* left, const unsigned char* right, size_t n)
        {
            return reinterpret_cast<unsigned char*>(std::char_traits<char>::move(reinterpret_cast<char*>(left), reinterpret_cast<const char*>(right), n));
        }

        static int_type requires_async() { return eof() - 1; }
    };
#endif

    namespace details {

    /// <summary>
    /// Stream buffer base class.
    /// </summary>
    template<typename _CharType>
    class basic_streambuf
    {
    public:
        typedef _CharType char_type;
        typedef ::concurrency::streams::char_traits<_CharType> traits;

        typedef typename traits::int_type int_type;
        typedef typename traits::pos_type pos_type;
        typedef typename traits::off_type off_type;


        /// <summary>
        /// Virtual constructor for stream buffers.
        /// </summary>
        virtual ~basic_streambuf() { }

        /// <summary>
        /// <c>can_read</c> is used to determine whether a stream buffer will support read operations (get).
        /// </summary>
        virtual bool can_read() const = 0;

        /// <summary>
        /// <c>can_write</c> is used to determine whether a stream buffer will support write operations (put).
        /// </summary>
        virtual bool can_write() const = 0;

        /// <summary>
        /// <c>can_seek<c/> is used to determine whether a stream buffer supports seeking.
        /// </summary>
        virtual bool can_seek() const = 0;

        /// <summary>
        /// <c>has_size<c/> is used to determine whether a stream buffer supports size().
        /// </summary>
        virtual bool has_size() const = 0;

        /// <summary>
        /// <c>is_eof</c> is used to determine whether a read head has reached the end of the buffer.
        /// </summary>
        virtual bool is_eof() const = 0;

        /// <summary>
        /// Gets the stream buffer size, if one has been set.
        /// </summary>
        /// <param name="direction">The direction of buffering (in or out)</param>
        /// <returns>The size of the internal buffer (for the given direction).</returns>
        /// <remarks>An implementation that does not support buffering will always return 0.</remarks>
        virtual size_t buffer_size(std::ios_base::openmode direction = std::ios_base::in) const = 0;

        /// <summary>
        /// Sets the stream buffer implementation to buffer or not buffer.
        /// </summary>
        /// <param name="size">The size to use for internal buffering, 0 if no buffering should be done.</param>
        /// <param name="direction">The direction of buffering (in or out)</param>
        /// <remarks>An implementation that does not support buffering will silently ignore calls to this function and it will not have any effect on what is returned by subsequent calls to <see cref="::buffer_size method" />.</remarks>
        virtual void set_buffer_size(size_t size, std::ios_base::openmode direction = std::ios_base::in) = 0;

        /// <summary>
        /// For any input stream, <c>in_avail</c> returns the number of characters that are immediately available
        /// to be consumed without blocking. May be used in conjunction with <cref="::sbumpc method"/> to read data without
        /// incurring the overhead of using tasks.
        /// </summary>
        virtual size_t in_avail() const = 0;

        /// <summary>
        /// Checks if the stream buffer is open.
        /// </summary>
        /// <remarks>No separation is made between open for reading and open for writing.</remarks>
        virtual bool is_open() const = 0;

        /// <summary>
        /// Closes the stream buffer, preventing further read or write operations.
        /// </summary>
        /// <param name="mode">The I/O mode (in or out) to close for.</param>
        virtual pplx::task<void> close(std::ios_base::openmode mode = (std::ios_base::in | std::ios_base::out)) = 0;

        /// <summary>
        /// Closes the stream buffer with an exception.
        /// </summary>
        /// <param name="mode">The I/O mode (in or out) to close for.</param>
        /// <param name="eptr">Pointer to the exception.</param>
        virtual pplx::task<void> close(std::ios_base::openmode mode, std::exception_ptr eptr) = 0;

        /// <summary>
        /// Writes a single character to the stream.
        /// </summary>
        /// <param name="ch">The character to write</param>
        /// <returns>A <c>task</c> that holds the value of the character. This value is EOF if the write operation fails.</returns>
        virtual pplx::task<int_type> putc(_CharType ch) = 0;

        /// <summary>
        /// Writes a number of characters to the stream.
        /// </summary>
        /// <param name="ptr">A pointer to the block of data to be written.</param>
        /// <param name="count">The number of characters to write.</param>
        /// <returns>A <c>task</c> that holds the number of characters actually written, either 'count' or 0.</returns>
        virtual pplx::task<size_t> putn(const _CharType *ptr, size_t count) = 0;

        /// <summary>
        /// Writes a number of characters to the stream. Note: callers must make sure the data to be written is valid until
        /// the returned task completes.
        /// </summary>
        /// <param name="ptr">A pointer to the block of data to be written.</param>
        /// <param name="count">The number of characters to write.</param>
        /// <returns>A <c>task</c> that holds the number of characters actually written, either 'count' or 0.</returns>
        virtual pplx::task<size_t> putn_nocopy(const _CharType *ptr, size_t count) = 0;

        /// <summary>
        /// Reads a single character from the stream and advances the read position.
        /// </summary>
        /// <returns>A <c>task</c> that holds the value of the character. This value is EOF if the read fails.</returns>
        virtual pplx::task<int_type> bumpc() = 0;

        /// <summary>
        /// Reads a single character from the stream and advances the read position.
        /// </summary>
        /// <returns>The value of the character. <c>-1</c> if the read fails. <c>-2</c> if an asynchronous read is required</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual int_type sbumpc() = 0;

        /// <summary>
        /// Reads a single character from the stream without advancing the read position.
        /// </summary>
            /// <returns>A <c>task</c> that holds the value of the byte. This value is EOF if the read fails.</returns>
        virtual pplx::task<int_type> getc() = 0;

        /// <summary>
        /// Reads a single character from the stream without advancing the read position.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails. <see cref="::requires_async method" /> if an asynchronous read is required</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual int_type sgetc() = 0;

        /// <summary>
        /// Advances the read position, then returns the next character without advancing again.
        /// </summary>
        /// <returns>A <c>task</c> that holds the value of the character. This value is EOF if the read fails.</returns>
        virtual pplx::task<int_type> nextc() = 0;

        /// <summary>
        /// Retreats the read position, then returns the current character without advancing.
        /// </summary>
        /// <returns>A <c>task</c> that holds the value of the character. This value is EOF if the read fails, <c>requires_async</c> if an asynchronous read is required</returns>
        virtual pplx::task<int_type> ungetc() = 0;

        /// <summary>
        /// Reads up to a given number of characters from the stream.
        /// </summary>
        /// <param name="ptr">The address of the target memory area.</param>
        /// <param name="count">The maximum number of characters to read.</param>
            /// <returns>A <c>task</c> that holds the number of characters read. This value is O if the end of the stream is reached.</returns>
        virtual pplx::task<size_t> getn(_Out_writes_(count) _CharType *ptr, _In_ size_t count) = 0;

        /// <summary>
        /// Copies up to a given number of characters from the stream, synchronously.
        /// </summary>
        /// <param name="ptr">The address of the target memory area.</param>
        /// <param name="count">The maximum number of characters to read.</param>
        /// <returns>The number of characters copied. O if the end of the stream is reached or an asynchronous read is required.</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual size_t scopy(_Out_writes_(count) _CharType *ptr, _In_ size_t count) = 0;

        /// <summary>
        /// Gets the current read or write position in the stream.
        /// </summary>
        /// <param name="direction">The I/O direction to seek (see remarks)</param>
        /// <returns>The current position. EOF if the operation fails.</returns>
        /// <remarks>Some streams may have separate write and read cursors.
        ///          For such streams, the direction parameter defines whether to move the read or the write cursor.</remarks>
        virtual pos_type getpos(std::ios_base::openmode direction) const = 0;

        /// <summary>
        /// Gets the size of the stream, if known. Calls to <c>has_size</c> will determine whether
        /// the result of <c>size</c> can be relied on.
        /// </summary>
        virtual utility::size64_t size() const = 0;

        /// <summary>
        /// Seeks to the given position.
        /// </summary>
        /// <param name="pos">The offset from the beginning of the stream.</param>
        /// <param name="direction">The I/O direction to seek (see remarks).</param>
        /// <returns>The position. EOF if the operation fails.</returns>
        /// <remarks>Some streams may have separate write and read cursors. For such streams, the direction parameter defines whether to move the read or the write cursor.</remarks>
        virtual pos_type seekpos(pos_type pos, std::ios_base::openmode direction) = 0;

        /// <summary>
        /// Seeks to a position given by a relative offset.
        /// </summary>
        /// <param name="offset">The relative position to seek to</param>
        /// <param name="way">The starting point (beginning, end, current) for the seek.</param>
        /// <param name="mode">The I/O direction to seek (see remarks)</param>
        /// <returns>The position. EOF if the operation fails.</returns>
        /// <remarks>Some streams may have separate write and read cursors.
        ///          For such streams, the mode parameter defines whether to move the read or the write cursor.</remarks>
        virtual pos_type seekoff(off_type offset, std::ios_base::seekdir way, std::ios_base::openmode mode) = 0;

        /// <summary>
        /// For output streams, flush any internally buffered data to the underlying medium.
        /// </summary>
        /// <returns>A <c>task</c> that returns <c>true</c> if the sync succeeds, <c>false</c> if not.</returns>
        virtual pplx::task<void> sync() = 0;

        //
        // Efficient read and write.
        //
        // The following routines are intended to be used for more efficient, copy-free, reading and
        // writing of data from/to the stream. Rather than having the caller provide a buffer into which
        // data is written or from which it is read, the stream buffer provides a pointer directly to the
        // internal data blocks that it is using. Since not all stream buffers use internal data structures
        // to copy data, the functions may not be supported by all. An application that wishes to use this
        // functionality should therefore first try them and check for failure to support. If there is
        // such failure, the application should fall back on the copying interfaces (putn / getn)
        //

        /// <summary>
        /// Allocates a contiguous memory block and returns it.
        /// </summary>
        /// <param name="count">The number of characters to allocate.</param>
        /// <returns>A pointer to a block to write to, null if the stream buffer implementation does not support alloc/commit.</returns>
        virtual _CharType* alloc(_In_ size_t count) = 0;

        /// <summary>
        /// Submits a block already allocated by the stream buffer.
        /// </summary>
        /// <param name="count">The number of characters to be committed.</param>
        virtual void commit(_In_ size_t count) = 0;

        /// <summary>
        /// Gets a pointer to the next already allocated contiguous block of data.
        /// </summary>
        /// <param name="ptr">A reference to a pointer variable that will hold the address of the block on success.</param>
        /// <param name="count">The number of contiguous characters available at the address in 'ptr'.</param>
        /// <returns><c>true</c> if the operation succeeded, <c>false</c> otherwise.</returns>
        /// <remarks>
        /// A return of false does not necessarily indicate that a subsequent read operation would fail, only that
        /// there is no block to return immediately or that the stream buffer does not support the operation.
        /// The stream buffer may not de-allocate the block until <see cref="::release method" /> is called.
        /// If the end of the stream is reached, the function will return <c>true</c>, a null pointer, and a count of zero;
        /// a subsequent read will not succeed.
        /// </remarks>
        virtual bool acquire(_Out_ _CharType*& ptr, _Out_ size_t& count) = 0;

        /// <summary>
        /// Releases a block of data acquired using <see cref="::acquire method"/>. This frees the stream buffer to de-allocate the
        /// memory, if it so desires. Move the read position ahead by the count.
        /// </summary>
        /// <param name="ptr">A pointer to the block of data to be released.</param>
        /// <param name="count">The number of characters that were read.</param>
        virtual void release(_Out_writes_(count) _CharType *ptr, _In_ size_t count) = 0;

        /// <summary>
        /// Retrieves the stream buffer exception_ptr if it has been set.
        /// </summary>
        /// <returns>Pointer to the exception, if it has been set; otherwise, <c>nullptr</c> will be returned</returns>
        virtual std::exception_ptr exception() const = 0;
    };


    template<typename _CharType>
    class streambuf_state_manager : public basic_streambuf<_CharType>, public std::enable_shared_from_this<streambuf_state_manager<_CharType>>
    {
    public:
        typedef typename details::basic_streambuf<_CharType>::traits traits;
        typedef typename details::basic_streambuf<_CharType>::int_type int_type;
        typedef typename details::basic_streambuf<_CharType>::pos_type pos_type;
        typedef typename details::basic_streambuf<_CharType>::off_type off_type;

        /// <summary>
        /// <c>can_read</c> is used to determine whether a stream buffer will support read operations (get).
        /// </summary>
        virtual bool can_read() const
        {
            return m_stream_can_read;
        }

        /// <summary>
        /// <c>can_write</c> is used to determine whether a stream buffer will support write operations (put).
        /// </summary>
        virtual bool can_write() const
        {
            return m_stream_can_write;
        }

        /// <summary>
        /// Checks if the stream buffer is open.
        /// </summary>
        /// <remarks>No separation is made between open for reading and open for writing.</remarks>
        virtual bool is_open() const
        {
            return can_read() || can_write();
        }

        /// <summary>
        /// Closes the stream buffer, preventing further read or write operations.
        /// </summary>
        /// <param name="mode">The I/O mode (in or out) to close for.</param>
        virtual pplx::task<void> close(std::ios_base::openmode mode = std::ios_base::in | std::ios_base::out)
        {
            pplx::task<void> closeOp = pplx::task_from_result();

            if (mode & std::ios_base::in && can_read()) {
                closeOp = _close_read();
            }

            // After the flush_internal task completed, "this" object may have been destroyed,
            // accessing the members is invalid, use shared_from_this to avoid access violation exception.
            auto this_ptr = std::static_pointer_cast<streambuf_state_manager>(this->shared_from_this());

            if (mode & std::ios_base::out && can_write()) {
                if (closeOp.is_done())
                    closeOp = closeOp && _close_write().then([this_ptr]{}); // passing down exceptions from closeOp
                else
                    closeOp = closeOp.then([this_ptr] { return this_ptr->_close_write().then([this_ptr]{}); });
            }

            return closeOp;
        }

        /// <summary>
        /// Closes the stream buffer with an exception.
        /// </summary>
        /// <param name="mode">The I/O mode (in or out) to close for.</param>
        /// <param name="eptr">Pointer to the exception.</param>
        virtual pplx::task<void> close(std::ios_base::openmode mode, std::exception_ptr eptr)
        {
            if (m_currentException == nullptr)
                m_currentException = eptr;
            return close(mode);
        }

        /// <summary>
        /// <c>is_eof</c> is used to determine whether a read head has reached the end of the buffer.
        /// </summary>
        virtual bool is_eof() const
        {
            return m_stream_read_eof;
        }

        /// <summary>
        /// Writes a single character to the stream.
        /// </summary>
        /// <param name="ch">The character to write</param>
        /// <returns>The value of the character. EOF if the write operation fails</returns>
        virtual pplx::task<int_type> putc(_CharType ch)
        {
            if (!can_write())
                return create_exception_checked_value_task<int_type>(traits::eof());

            return create_exception_checked_task<int_type>(_putc(ch), [](int_type) {
                return false; // no EOF for write
            });
        }

        /// <summary>
        /// Writes a number of characters to the stream.
        /// </summary>
        /// <param name="ptr">A pointer to the block of data to be written.</param>
        /// <param name="count">The number of characters to write.</param>
        /// <returns>The number of characters actually written, either 'count' or 0.</returns>
        CASABLANCA_DEPRECATED("This API in some cases performs a copy. It is deprecated and will be removed in a future release. Use putn_nocopy instead.")
        virtual pplx::task<size_t> putn(const _CharType *ptr, size_t count)
        {
            if (!can_write())
                return create_exception_checked_value_task<size_t>(0);
            if (count == 0)
                return pplx::task_from_result<size_t>(0);

            return create_exception_checked_task<size_t>(_putn(ptr, count, true), [](size_t) {
                return false; // no EOF for write
            });
        }

        /// <summary>
        /// Writes a number of characters to the stream. Note: callers must make sure the data to be written is valid until
        /// the returned task completes.
        /// </summary>
        /// <param name="ptr">A pointer to the block of data to be written.</param>
        /// <param name="count">The number of characters to write.</param>
        /// <returns>A <c>task</c> that holds the number of characters actually written, either 'count' or 0.</returns>
        virtual pplx::task<size_t> putn_nocopy(const _CharType *ptr, size_t count)
        {
            if (!can_write())
                return create_exception_checked_value_task<size_t>(0);
            if (count == 0)
                return pplx::task_from_result<size_t>(0);

            return create_exception_checked_task<size_t>(_putn(ptr, count), [](size_t) {
                return false; // no EOF for write
            });
        }

        /// <summary>
        /// Reads a single character from the stream and advances the read position.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails.</returns>
        virtual pplx::task<int_type> bumpc()
        {
            if (!can_read())
                return create_exception_checked_value_task<int_type>(streambuf_state_manager<_CharType>::traits::eof());

            return create_exception_checked_task<int_type>(_bumpc(), [](int_type val) {
                return val == streambuf_state_manager<_CharType>::traits::eof();
            });
        }

        /// <summary>
        /// Reads a single character from the stream and advances the read position.
        /// </summary>
        /// <returns>The value of the character. <c>-1</c> if the read fails. <c>-2</c> if an asynchronous read is required</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual int_type sbumpc()
        {
            if ( !(m_currentException == nullptr) )
                std::rethrow_exception(m_currentException);
            if (!can_read())
                return traits::eof();
            return check_sync_read_eof(_sbumpc());
        }

        /// <summary>
        /// Reads a single character from the stream without advancing the read position.
        /// </summary>
        /// <returns>The value of the byte. EOF if the read fails.</returns>
        virtual pplx::task<int_type> getc()
        {
            if (!can_read())
                return create_exception_checked_value_task<int_type>(traits::eof());

            return create_exception_checked_task<int_type>(_getc(), [](int_type val) {
                return val == streambuf_state_manager<_CharType>::traits::eof();
            });
        }

        /// <summary>
        /// Reads a single character from the stream without advancing the read position.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails. <see cref="::requires_async method" /> if an asynchronous read is required</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual int_type sgetc()
        {
            if ( !(m_currentException == nullptr) )
                std::rethrow_exception(m_currentException);
            if (!can_read())
                return traits::eof();
            return check_sync_read_eof(_sgetc());
        }

        /// <summary>
        /// Advances the read position, then returns the next character without advancing again.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails.</returns>
        virtual pplx::task<int_type> nextc()
        {
            if (!can_read())
                return create_exception_checked_value_task<int_type>(traits::eof());

            return create_exception_checked_task<int_type>(_nextc(), [](int_type val) {
                return val == streambuf_state_manager<_CharType>::traits::eof();
            });
        }

        /// <summary>
        /// Retreats the read position, then returns the current character without advancing.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails. <see cref="::requires_async method" /> if an asynchronous read is required</returns>
        virtual pplx::task<int_type> ungetc()
        {
            if (!can_read())
                return create_exception_checked_value_task<int_type>(traits::eof());

            return create_exception_checked_task<int_type>(_ungetc(), [](int_type) {
                return false;
            });
        }

        /// <summary>
        /// Reads up to a given number of characters from the stream.
        /// </summary>
        /// <param name="ptr">The address of the target memory area.</param>
        /// <param name="count">The maximum number of characters to read.</param>
        /// <returns>The number of characters read. O if the end of the stream is reached.</returns>
        virtual pplx::task<size_t> getn(_Out_writes_(count) _CharType *ptr, _In_ size_t count)
        {
            if (!can_read())
                return create_exception_checked_value_task<size_t>(0);
            if (count == 0)
                return pplx::task_from_result<size_t>(0);

            return create_exception_checked_task<size_t>(_getn(ptr, count), [](size_t val) {
                return val == 0;
            });
        }

        /// <summary>
        /// Copies up to a given number of characters from the stream, synchronously.
        /// </summary>
        /// <param name="ptr">The address of the target memory area.</param>
        /// <param name="count">The maximum number of characters to read.</param>
        /// <returns>The number of characters copied. O if the end of the stream is reached or an asynchronous read is required.</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual size_t scopy(_Out_writes_(count) _CharType *ptr, _In_ size_t count)
        {
            if ( !(m_currentException == nullptr) )
                std::rethrow_exception(m_currentException);
            if (!can_read())
                return 0;

            return _scopy(ptr, count);
        }

        /// <summary>
        /// For output streams, flush any internally buffered data to the underlying medium.
        /// </summary>
        /// <returns><c>true</c> if the flush succeeds, <c>false</c> if not</returns>
        virtual pplx::task<void> sync()
        {
            if (!can_write())
            {
                if (m_currentException == nullptr)
                    return pplx::task_from_result();
                else
                    return pplx::task_from_exception<void>(m_currentException);
            }
            return create_exception_checked_task<bool>(_sync(), [](bool) {
                return false;
            }).then([](bool){});
        }

        /// <summary>
        /// Retrieves the stream buffer exception_ptr if it has been set.
        /// </summary>
        /// <returns>Pointer to the exception, if it has been set; otherwise, <c>nullptr</c> will be returned.</returns>
        virtual std::exception_ptr exception() const
        {
            return m_currentException;
        }

        /// <summary>
        /// Allocates a contiguous memory block and returns it.
        /// </summary>
        /// <param name="count">The number of characters to allocate.</param>
        /// <returns>A pointer to a block to write to, null if the stream buffer implementation does not support alloc/commit.</returns>
        /// <remarks>This is intended as an advanced API to be used only when it is important to avoid extra copies.</remarks>
        _CharType* alloc(size_t count)
        {
            if (m_alloced)
                throw std::logic_error("The buffer is already allocated, this maybe caused by overlap of stream read or write");

            _CharType* alloc_result = _alloc(count);

            if (alloc_result)
                m_alloced = true;

            return alloc_result;
        }

        /// <summary>
        /// Submits a block already allocated by the stream buffer.
        /// </summary>
        /// <param name="count">The number of characters to be committed.</param>
        /// <remarks>This is intended as an advanced API to be used only when it is important to avoid extra copies.</remarks>
        void commit(size_t count)
        {
            if (!m_alloced)
                throw std::logic_error("The buffer needs to allocate first");

            _commit(count);
            m_alloced = false;
        }

    public:
        virtual bool can_seek() const = 0;
        virtual bool has_size() const = 0;
        virtual utility::size64_t size() const { return 0; }
        virtual size_t buffer_size(std::ios_base::openmode direction = std::ios_base::in) const = 0;
        virtual void set_buffer_size(size_t size, std::ios_base::openmode direction = std::ios_base::in) = 0;
        virtual size_t in_avail() const = 0;
        virtual pos_type getpos(std::ios_base::openmode direction) const = 0;
        virtual pos_type seekpos(pos_type pos, std::ios_base::openmode direction) = 0;
        virtual pos_type seekoff(off_type offset, std::ios_base::seekdir way, std::ios_base::openmode mode) = 0;
        virtual bool acquire(_Out_writes_(count) _CharType*& ptr, _In_ size_t& count) = 0;
        virtual void release(_Out_writes_(count) _CharType *ptr, _In_ size_t count) = 0;
    protected:
        virtual pplx::task<int_type> _putc(_CharType ch) = 0;

        // This API is only needed for file streams and until we remove the deprecated stream buffer putn overload.
        virtual pplx::task<size_t> _putn(const _CharType *ptr, size_t count, bool)
        {
            // Default to no copy, only the file streams API overloads and performs a copy.
            return _putn(ptr, count);
        }
        virtual pplx::task<size_t> _putn(const _CharType *ptr, size_t count) = 0;

        virtual pplx::task<int_type> _bumpc() = 0;
        virtual int_type _sbumpc() = 0;
        virtual pplx::task<int_type> _getc() = 0;
        virtual int_type _sgetc() = 0;
        virtual pplx::task<int_type> _nextc() = 0;
        virtual pplx::task<int_type> _ungetc() = 0;
        virtual pplx::task<size_t> _getn(_Out_writes_(count) _CharType *ptr, _In_ size_t count) = 0;
        virtual size_t _scopy(_Out_writes_(count) _CharType *ptr, _In_ size_t count) = 0;
        virtual pplx::task<bool> _sync() = 0;
        virtual _CharType* _alloc(size_t count) = 0;
        virtual void _commit(size_t count) = 0;

        /// <summary>
        /// The real read head close operation, implementation should override it if there is any resource to be released.
        /// </summary>
        virtual pplx::task<void> _close_read()
        {
            m_stream_can_read = false;
            return pplx::task_from_result();
        }

        /// <summary>
        /// The real write head close operation, implementation should override it if there is any resource to be released.
        /// </summary>
        virtual pplx::task<void> _close_write()
        {
            m_stream_can_write = false;
            return pplx::task_from_result();
        }

    protected:
        streambuf_state_manager(std::ios_base::openmode mode)
        {
            m_stream_can_read = (mode & std::ios_base::in) != 0;
            m_stream_can_write = (mode & std::ios_base::out) != 0;
            m_stream_read_eof = false;
            m_alloced = false;
        }

        std::exception_ptr m_currentException;
        // The in/out mode for the buffer
        std::atomic<bool> m_stream_can_read;
        std::atomic<bool> m_stream_can_write;
        std::atomic<bool> m_stream_read_eof;
        std::atomic<bool> m_alloced;


    private:
        template<typename _CharType1>
        pplx::task<_CharType1> create_exception_checked_value_task(const _CharType1 &val) const
        {
            if (this->exception() == nullptr)
                return pplx::task_from_result<_CharType1>(static_cast<_CharType1>(val));
            else
                return pplx::task_from_exception<_CharType1>(this->exception());
        }

        // Set exception and eof states for async read
        template<typename _CharType1>
        pplx::task<_CharType1> create_exception_checked_task(pplx::task<_CharType1> result, std::function<bool(_CharType1)> eof_test, std::ios_base::openmode mode = std::ios_base::in | std::ios_base::out)
        {
            auto thisPointer = this->shared_from_this();

            auto func1 = [=](pplx::task<_CharType1> t1) -> pplx::task<_CharType1> {
                try {
                    thisPointer->m_stream_read_eof = eof_test(t1.get());
                } catch (...) {
                    thisPointer->close(mode, std::current_exception()).get();
                    return pplx::task_from_exception<_CharType1>(thisPointer->exception(), pplx::task_options());
                }
                if (thisPointer->m_stream_read_eof && !(thisPointer->exception() == nullptr))
                    return pplx::task_from_exception<_CharType1>(thisPointer->exception(), pplx::task_options());
                return t1;
            };

            if ( result.is_done() )
            {
                // If the data is already available, we should avoid scheduling a continuation, so we do it inline.
                return func1(result);
            }
            else
            {
                return result.then(func1);
            }
        }

        // Set eof states for sync read
        int_type check_sync_read_eof(int_type ch)
        {
            m_stream_read_eof = ch == traits::eof();
            return ch;
        }

    };

    } // namespace details

    // Forward declarations
    template<typename _CharType> class basic_istream;
    template<typename _CharType> class basic_ostream;

    /// <summary>
    /// Reference-counted stream buffer.
    /// </summary>
    /// <typeparam name="_CharType">
    /// The data type of the basic element of the <c>streambuf.</c>
    /// </typeparam>
    /// <typeparam name="_CharType2">
    /// The data type of the basic element of the <c>streambuf.</c>
    /// </typeparam>
    template<typename _CharType>
    class streambuf : public details::basic_streambuf<_CharType>
    {
    public:
        typedef typename details::basic_streambuf<_CharType>::traits    traits;
        typedef typename details::basic_streambuf<_CharType>::int_type  int_type;
        typedef typename details::basic_streambuf<_CharType>::pos_type  pos_type;
        typedef typename details::basic_streambuf<_CharType>::off_type  off_type;
        typedef typename details::basic_streambuf<_CharType>::char_type char_type;

        template <typename _CharType2> friend class streambuf;

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="ptr">A pointer to the concrete stream buffer implementation.</param>
        streambuf(_In_ const std::shared_ptr<details::basic_streambuf<_CharType>> &ptr) : m_buffer(ptr) {}

        /// <summary>
        /// Default constructor.
        /// </summary>
        streambuf() { }

        /// <summary>
        /// Converter Constructor.
        /// </summary>
        /// <typeparam name="AlterCharType">
        /// The data type of the basic element of the source <c>streambuf</c>.
        /// </typeparam>
        /// <param name="other">The source buffer to be converted.</param>
        template <typename AlterCharType>
        streambuf(const streambuf<AlterCharType> &other) :
            m_buffer(std::static_pointer_cast<details::basic_streambuf<_CharType>>(std::static_pointer_cast<void>(other.m_buffer)))
        {
            static_assert(std::is_same<pos_type, typename details::basic_streambuf<AlterCharType>::pos_type>::value
                && std::is_same<off_type, typename details::basic_streambuf<AlterCharType>::off_type>::value
                && std::is_integral<_CharType>::value && std::is_integral<AlterCharType>::value
                && std::is_integral<int_type>::value && std::is_integral<typename details::basic_streambuf<AlterCharType>::int_type>::value
                && sizeof(_CharType) == sizeof(AlterCharType)
                && sizeof(int_type) == sizeof(typename details::basic_streambuf<AlterCharType>::int_type),
                "incompatible stream character types");
        }

        /// <summary>
        /// Constructs an input stream head for this stream buffer.
        /// </summary>
        /// <returns><c>basic_istream</c>.</returns>
        concurrency::streams::basic_istream<_CharType> create_istream() const
        {
            if (!can_read()) throw std::runtime_error("stream buffer not set up for input of data");
            return concurrency::streams::basic_istream<_CharType>(*this);
        }

        /// <summary>
        /// Constructs an output stream for this stream buffer.
        /// </summary>
        /// <returns>basic_ostream</returns>
        concurrency::streams::basic_ostream<_CharType> create_ostream() const
        {
            if (!can_write()) throw std::runtime_error("stream buffer not set up for output of data");
            return concurrency::streams::basic_ostream<_CharType>(*this);
        }

        /// <summary>
        /// Checks if the stream buffer has been initialized or not.
        /// </summary>
        operator bool() const { return (bool)m_buffer; }

        /// <summary>
        /// Destructor
        /// </summary>
        virtual ~streambuf() { }

        const std::shared_ptr<details::basic_streambuf<_CharType>> & get_base() const
        {
            if (!m_buffer)
            {
                throw std::invalid_argument("Invalid streambuf object");
            }

            return m_buffer;
        }

        /// <summary>
        /// <c>can_read</c> is used to determine whether a stream buffer will support read operations (get).
        /// </summary>
        virtual bool can_read() const { return get_base()->can_read(); }

        /// <summary>
        /// <c>can_write</c> is used to determine whether a stream buffer will support write operations (put).
        /// </summary>
        virtual bool can_write() const { return  get_base()->can_write(); }

        /// <summary>
        /// <c>can_seek</c> is used to determine whether a stream buffer supports seeking.
        /// </summary>
        /// <returns>True if seeking is supported, false otherwise.</returns>
        virtual bool can_seek() const { return get_base()->can_seek(); }

        /// <summary>
        /// <c>has_size</c> is used to determine whether a stream buffer supports size().
        /// </summary>
        /// <returns>True if the <c>size</c> API is supported, false otherwise.</returns>
        virtual bool has_size() const { return get_base()->has_size(); }

        /// <summary>
        /// Gets the total number of characters in the stream buffer, if known. Calls to <c>has_size</c> will determine whether
        /// the result of <c>size</c> can be relied on.
        /// </summary>
        /// <returns>The total number of characters in the stream buffer.</returns>
        virtual utility::size64_t size() const { return get_base()->size(); }

        /// <summary>
        /// Gets the stream buffer size, if one has been set.
        /// </summary>
        /// <param name="direction">The direction of buffering (in or out)</param>
        /// <returns>The size of the internal buffer (for the given direction).</returns>
        /// <remarks>An implementation that does not support buffering will always return 0.</remarks>
        virtual size_t buffer_size(std::ios_base::openmode direction = std::ios_base::in) const { return get_base()->buffer_size(direction); }

        /// <summary>
        /// Sets the stream buffer implementation to buffer or not buffer.
        /// </summary>
        /// <param name="size">The size to use for internal buffering, 0 if no buffering should be done.</param>
        /// <param name="direction">The direction of buffering (in or out)</param>
        /// <remarks>An implementation that does not support buffering will silently ignore calls to this function and it will not have any effect on what is returned by subsequent calls to <see cref="::buffer_size method" />.</remarks>
        virtual void set_buffer_size(size_t size, std::ios_base::openmode direction = std::ios_base::in) { get_base()->set_buffer_size(size,direction); }

        /// <summary>
        /// For any input stream, <c>in_avail</c> returns the number of characters that are immediately available
        /// to be consumed without blocking. May be used in conjunction with <cref="::sbumpc method"/> to read data without
        /// incurring the overhead of using tasks.
        /// </summary>
        /// <returns>Number of characters that are ready to read.</returns>
        virtual size_t in_avail() const { return get_base()->in_avail(); }

        /// <summary>
        /// Checks if the stream buffer is open.
        /// </summary>
        /// <remarks>No separation is made between open for reading and open for writing.</remarks>
        /// <returns>True if the stream buffer is open for reading or writing, false otherwise.</returns>
        virtual bool is_open() const { return get_base()->is_open(); }

        /// <summary>
        /// <c>is_eof</c> is used to determine whether a read head has reached the end of the buffer.
        /// </summary>
        /// <returns>True if at the end of the buffer, false otherwise.</returns>
        virtual bool is_eof() const { return get_base()->is_eof(); }

        /// <summary>
        /// Closes the stream buffer, preventing further read or write operations.
        /// </summary>
        /// <param name="mode">The I/O mode (in or out) to close for.</param>
        virtual pplx::task<void> close(std::ios_base::openmode mode = (std::ios_base::in | std::ios_base::out))
        {
            // We preserve the check here to workaround a Dev10 compiler crash
            auto buffer = get_base();
            return buffer ? buffer->close(mode) : pplx::task_from_result();
        }

        /// <summary>
        /// Closes the stream buffer with an exception.
        /// </summary>
        /// <param name="mode">The I/O mode (in or out) to close for.</param>
        /// <param name="eptr">Pointer to the exception.</param>
        virtual pplx::task<void> close(std::ios_base::openmode mode, std::exception_ptr eptr)
        {
            // We preserve the check here to workaround a Dev10 compiler crash
            auto buffer = get_base();
            return buffer ? buffer->close(mode, eptr) : pplx::task_from_result();
        }

        /// <summary>
        /// Writes a single character to the stream.
        /// </summary>
        /// <param name="ch">The character to write</param>
        /// <returns>The value of the character. EOF if the write operation fails</returns>
        virtual pplx::task<int_type> putc(_CharType ch)
        {
            return get_base()->putc(ch);
        }

        /// <summary>
        /// Allocates a contiguous memory block and returns it.
        /// </summary>
        /// <param name="count">The number of characters to allocate.</param>
        /// <returns>A pointer to a block to write to, null if the stream buffer implementation does not support alloc/commit.</returns>
        virtual _CharType* alloc(size_t count)
        {
            return get_base()->alloc(count);
        }

        /// <summary>
        /// Submits a block already allocated by the stream buffer.
        /// </summary>
        /// <param name="count">The number of characters to be committed.</param>
        virtual void commit(size_t count)
        {
            get_base()->commit(count);
        }

        /// <summary>
        /// Gets a pointer to the next already allocated contiguous block of data.
        /// </summary>
        /// <param name="ptr">A reference to a pointer variable that will hold the address of the block on success.</param>
        /// <param name="count">The number of contiguous characters available at the address in 'ptr'.</param>
        /// <returns><c>true</c> if the operation succeeded, <c>false</c> otherwise.</returns>
        /// <remarks>
        /// A return of false does not necessarily indicate that a subsequent read operation would fail, only that
        /// there is no block to return immediately or that the stream buffer does not support the operation.
        /// The stream buffer may not de-allocate the block until <see cref="::release method" /> is called.
        /// If the end of the stream is reached, the function will return <c>true</c>, a null pointer, and a count of zero;
        /// a subsequent read will not succeed.
        /// </remarks>
        virtual bool acquire(_Out_ _CharType*& ptr, _Out_ size_t& count)
        {
            ptr = nullptr;
            count = 0;
            return get_base()->acquire(ptr, count);
        }

        /// <summary>
        /// Releases a block of data acquired using <see cref="::acquire method"/>. This frees the stream buffer to de-allocate the
        /// memory, if it so desires. Move the read position ahead by the count.
        /// </summary>
        /// <param name="ptr">A pointer to the block of data to be released.</param>
        /// <param name="count">The number of characters that were read.</param>
        virtual void release(_Out_writes_(count) _CharType *ptr, _In_ size_t count)
        {
            get_base()->release(ptr, count);
        }

        /// <summary>
        /// Writes a number of characters to the stream.
        /// </summary>
        /// <param name="ptr">A pointer to the block of data to be written.</param>
        /// <param name="count">The number of characters to write.</param>
        /// <returns>The number of characters actually written, either 'count' or 0.</returns>
        CASABLANCA_DEPRECATED("This API in some cases performs a copy. It is deprecated and will be removed in a future release. Use putn_nocopy instead.")
        virtual pplx::task<size_t> putn(const _CharType *ptr, size_t count)
        {
            return get_base()->putn(ptr, count);
        }

        /// <summary>
        /// Writes a number of characters to the stream. Note: callers must make sure the data to be written is valid until
        /// the returned task completes.
        /// </summary>
        /// <param name="ptr">A pointer to the block of data to be written.</param>
        /// <param name="count">The number of characters to write.</param>
        /// <returns>The number of characters actually written, either 'count' or 0.</returns>
        virtual pplx::task<size_t> putn_nocopy(const _CharType *ptr, size_t count)
        {
            return get_base()->putn_nocopy(ptr, count);
        }

        /// <summary>
        /// Reads a single character from the stream and advances the read position.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails.</returns>
        virtual pplx::task<int_type> bumpc()
        {
            return get_base()->bumpc();
        }

        /// <summary>
        /// Reads a single character from the stream and advances the read position.
        /// </summary>
        /// <returns>The value of the character. <c>-1</c> if the read fails. <c>-2</c> if an asynchronous read is required</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual typename details::basic_streambuf<_CharType>::int_type sbumpc()
        {
            return get_base()->sbumpc();
        }

        /// <summary>
        /// Reads a single character from the stream without advancing the read position.
        /// </summary>
        /// <returns>The value of the byte. EOF if the read fails.</returns>
        virtual pplx::task<int_type> getc()
        {
            return get_base()->getc();
        }

        /// <summary>
        /// Reads a single character from the stream without advancing the read position.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails. <see cref="::requires_async method" /> if an asynchronous read is required</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual typename details::basic_streambuf<_CharType>::int_type sgetc()
        {
            return get_base()->sgetc();
        }

        /// <summary>
        /// Advances the read position, then returns the next character without advancing again.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails.</returns>
        pplx::task<int_type> nextc()
        {
            return get_base()->nextc();
        }

        /// <summary>
        /// Retreats the read position, then returns the current character without advancing.
        /// </summary>
        /// <returns>The value of the character. EOF if the read fails. <see cref="::requires_async method" /> if an asynchronous read is required</returns>
        pplx::task<int_type> ungetc()
        {
            return get_base()->ungetc();
        }

        /// <summary>
        /// Reads up to a given number of characters from the stream.
        /// </summary>
        /// <param name="ptr">The address of the target memory area.</param>
        /// <param name="count">The maximum number of characters to read.</param>
        /// <returns>The number of characters read. O if the end of the stream is reached.</returns>
        virtual pplx::task<size_t> getn(_Out_writes_(count) _CharType *ptr, _In_ size_t count)
        {
            return get_base()->getn(ptr, count);
        }

        /// <summary>
        /// Copies up to a given number of characters from the stream, synchronously.
        /// </summary>
        /// <param name="ptr">The address of the target memory area.</param>
        /// <param name="count">The maximum number of characters to read.</param>
        /// <returns>The number of characters copied. O if the end of the stream is reached or an asynchronous read is required.</returns>
        /// <remarks>This is a synchronous operation, but is guaranteed to never block.</remarks>
        virtual size_t scopy(_Out_writes_(count) _CharType *ptr, _In_ size_t count)
        {
            return get_base()->scopy(ptr, count);
        }

        /// <summary>
        /// Gets the current read or write position in the stream.
        /// </summary>
        /// <param name="direction">The I/O direction to seek (see remarks)</param>
        /// <returns>The current position. EOF if the operation fails.</returns>
        /// <remarks>Some streams may have separate write and read cursors.
        ///          For such streams, the direction parameter defines whether to move the read or the write cursor.</remarks>
        virtual typename details::basic_streambuf<_CharType>::pos_type getpos(std::ios_base::openmode direction) const
        {
            return get_base()->getpos(direction);
        }

        /// <summary>
        /// Seeks to the given position.
        /// </summary>
        /// <param name="pos">The offset from the beginning of the stream.</param>
        /// <param name="direction">The I/O direction to seek (see remarks).</param>
        /// <returns>The position. EOF if the operation fails.</returns>
        /// <remarks>Some streams may have separate write and read cursors. For such streams, the direction parameter defines whether to move the read or the write cursor.</remarks>
        virtual typename details::basic_streambuf<_CharType>::pos_type seekpos(typename details::basic_streambuf<_CharType>::pos_type pos, std::ios_base::openmode direction)
        {
            return get_base()->seekpos(pos, direction);
        }

        /// <summary>
        /// Seeks to a position given by a relative offset.
        /// </summary>
        /// <param name="offset">The relative position to seek to</param>
        /// <param name="way">The starting point (beginning, end, current) for the seek.</param>
        /// <param name="mode">The I/O direction to seek (see remarks)</param>
        /// <returns>The position. EOF if the operation fails.</returns>
        /// <remarks>Some streams may have separate write and read cursors.
        ///          For such streams, the mode parameter defines whether to move the read or the write cursor.</remarks>
        virtual typename details::basic_streambuf<_CharType>::pos_type seekoff(typename details::basic_streambuf<_CharType>::off_type offset, std::ios_base::seekdir way, std::ios_base::openmode mode)
        {
            return get_base()->seekoff(offset, way, mode);
        }

        /// <summary>
        /// For output streams, flush any internally buffered data to the underlying medium.
        /// </summary>
        /// <returns><c>true</c> if the flush succeeds, <c>false</c> if not</returns>
        virtual pplx::task<void> sync()
        {
            return get_base()->sync();
        }

        /// <summary>
        /// Retrieves the stream buffer exception_ptr if it has been set.
        /// </summary>
        /// <returns>Pointer to the exception, if it has been set; otherwise, <c>nullptr</c> will be returned</returns>
        virtual std::exception_ptr exception() const
        {
            return get_base()->exception();
        }

    private:
        std::shared_ptr<details::basic_streambuf<_CharType>> m_buffer;

    };

}}