/***
* Copyright (C) Microsoft. All rights reserved.
* Licensed under the MIT license. See LICENSE.txt file in the project root for full license information.
*
* =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
*
* This file defines a stream buffer that is based on a raw pointer and block size. Unlike a vector-based
* stream buffer, the buffer cannot be expanded or contracted, it has a fixed capacity.
*
* For the latest on this and related APIs, please see: https://github.com/Microsoft/cpprestsdk
*
* =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
****/
#pragma once

#ifndef _CASA_RAWPTR_STREAMS_H
#define _CASA_RAWPTR_STREAMS_H

#include <vector>
#include <queue>
#include <algorithm>
#include <iterator>

#include "pplx/pplxtasks.h"
#include "cpprest/astreambuf.h"
#include "cpprest/streams.h"

namespace Concurrency { namespace streams {

    // Forward declarations
    template <typename _CharType> class rawptr_buffer;

    namespace details {

    /// <summary>
    /// The basic_rawptr_buffer class serves as a memory-based steam buffer that supports both writing and reading
    /// sequences of characters to and from a fixed-size block.
    /// </summary>
    template<typename _CharType>
    class basic_rawptr_buffer : public streams::details::streambuf_state_manager<_CharType>
    {
    public:
        typedef _CharType char_type;

        typedef typename basic_streambuf<_CharType>::traits traits;
        typedef typename basic_streambuf<_CharType>::int_type int_type;
        typedef typename basic_streambuf<_CharType>::pos_type pos_type;
        typedef typename basic_streambuf<_CharType>::off_type off_type;

        /// <summary>
        /// Constructor
        /// </summary>
        basic_rawptr_buffer()
            : streambuf_state_manager<_CharType>(std::ios_base::in | std::ios_base::out),
              m_data(nullptr),
              m_current_position(0),
              m_size(0)
        {
        }

        /// <summary>
        /// Destructor
        /// </summary>
        virtual ~basic_rawptr_buffer()
        {
            this->_close_read();
            this->_close_write();
        }

    protected:

        /// <summary>
        /// can_seek is used to determine whether a stream buffer supports seeking.
        /// </summary>
        virtual bool can_seek() const { return this->is_open(); }

        /// <summary>
        /// <c>has_size<c/> is used to determine whether a stream buffer supports size().
        /// </summary>
        virtual bool has_size() const { return this->is_open(); }

        /// <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
        {
            return utility::size64_t(m_size);
        }

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

        /// <summary>
        /// Set 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 buffer_size().</remarks>
        virtual void set_buffer_size(size_t , std::ios_base::openmode = std::ios_base::in)
        {
            return;
        }

        /// <summary>
        /// For any input stream, in_avail returns the number of characters that are immediately available
        /// to be consumed without blocking. May be used in conjunction with <cref="::sbumpc method"/> and sgetn() to
        /// read data without incurring the overhead of using tasks.
        /// </summary>
        virtual size_t in_avail() const
        {
            // See the comment in seek around the restiction that we do not allow read head to
            // seek beyond the current size.
            _ASSERTE(m_current_position <= m_size);

            msl::safeint3::SafeInt<size_t> readhead(m_current_position);
            msl::safeint3::SafeInt<size_t> writeend(m_size);
            return (size_t)(writeend - readhead);
        }

        /// <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)
        {
            if (mode & std::ios_base::in)
            {
                this->_close_read().get(); // Safe to call get() here.
            }

            if (mode & std::ios_base::out)
            {
                this->_close_write().get(); // Safe to call get() here.
            }

            if ( !this->can_read() && !this->can_write() )
            {
                m_data = nullptr;
            }

            // Exceptions will be propagated out of _close_read or _close_write
            return pplx::task_from_result();
        }

        virtual pplx::task<bool> _sync()
        {
            return pplx::task_from_result(true);
        }

        virtual pplx::task<int_type> _putc(_CharType ch)
        {
            if (m_current_position >= m_size)
                return pplx::task_from_result<int_type>(traits::eof());
            int_type retVal = (this->write(&ch, 1) == 1) ? static_cast<int_type>(ch) : traits::eof();
            return pplx::task_from_result<int_type>(retVal);
        }

        virtual pplx::task<size_t> _putn(const _CharType *ptr, size_t count)
        {
            msl::safeint3::SafeInt<size_t> newSize = msl::safeint3::SafeInt<size_t>(count) + m_current_position;
            if ( newSize > m_size )
                return pplx::task_from_exception<size_t>(std::make_exception_ptr(std::runtime_error("Writing past the end of the buffer")));
            return pplx::task_from_result<size_t>(this->write(ptr, count));
        }

        /// <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>
        _CharType* _alloc(size_t count)
        {
            if (!this->can_write()) return nullptr;

            msl::safeint3::SafeInt<size_t> readhead(m_current_position);
            msl::safeint3::SafeInt<size_t> writeend(m_size);
            size_t space_left = (size_t)(writeend - readhead);

            if (space_left < count) return nullptr;

            // Let the caller copy the data
            return (_CharType*)(m_data+m_current_position);
        }

        /// <summary>
        /// Submits a block already allocated by the stream buffer.
        /// </summary>
        /// <param name="count">The number of characters to be committed.</param>
        void _commit(size_t actual)
        {
            // Update the write position and satisfy any pending reads
            update_current_position(m_current_position+actual);
        }

        /// <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)
        {
            count = 0;
            ptr = nullptr;

            if (!this->can_read()) return false;

            count = in_avail();

            if (count > 0)
            {
                ptr = (_CharType*)(m_data+m_current_position);
                return true;
            }
            else
            {
                ptr = nullptr;

                // Can only be open for read OR write, not both. If there is no data then
                // we have reached the end of the stream so indicate such with true.
                return true;
            }
        }

        /// <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_opt_ (count) _CharType *ptr, _In_ size_t count)
        {
            if (ptr != nullptr)
                update_current_position(m_current_position + count);
        }

        virtual pplx::task<size_t> _getn(_Out_writes_ (count) _CharType *ptr, _In_ size_t count)
        {
            return pplx::task_from_result(this->read(ptr, count));
        }

        size_t _sgetn(_Out_writes_ (count) _CharType *ptr, _In_ size_t count)
        {
            return this->read(ptr, count);
        }

        virtual size_t _scopy(_Out_writes_ (count) _CharType *ptr, _In_ size_t count)
        {
            return this->read(ptr, count, false);
        }

        virtual pplx::task<int_type> _bumpc()
        {
            return pplx::task_from_result(this->read_byte(true));
        }

        virtual int_type _sbumpc()
        {
            return this->read_byte(true);
        }

        virtual pplx::task<int_type> _getc()
        {
            return pplx::task_from_result(this->read_byte(false));
        }

        int_type _sgetc()
        {
            return this->read_byte(false);
        }

        virtual pplx::task<int_type> _nextc()
        {
            if (m_current_position >= m_size-1)
                return pplx::task_from_result(basic_streambuf<_CharType>::traits::eof());

            this->read_byte(true);
            return pplx::task_from_result(this->read_byte(false));
        }

        virtual pplx::task<int_type> _ungetc()
        {
            auto pos = seekoff(-1, std::ios_base::cur, std::ios_base::in);
            if ( pos == (pos_type)traits::eof())
                return pplx::task_from_result(traits::eof());
            return this->getc();
        }

        /// <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 mode) const
        {
            if ( ((mode & std::ios_base::in) && !this->can_read()) ||
                    ((mode & std::ios_base::out) && !this->can_write()))
                    return static_cast<pos_type>(traits::eof());

            if (mode == std::ios_base::in)
                return (pos_type)m_current_position;
            else if (mode == std::ios_base::out)
                return (pos_type)m_current_position;
            else
                return (pos_type)traits::eof();
        }

        /// <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 position, std::ios_base::openmode mode)
        {
            pos_type beg(0);
            pos_type end(m_size);

            if (position >= beg)
            {
                auto pos = static_cast<size_t>(position);

                // Read head
                if ((mode & std::ios_base::in) && this->can_read())
                {
                    if (position <= end)
                    {
                        // We do not allow reads to seek beyond the end or before the start position.
                        update_current_position(pos);
                        return static_cast<pos_type>(m_current_position);
                    }
                }

                // Write head
                if ((mode & std::ios_base::out) && this->can_write())
                {
                    // Update write head and satisfy read requests if any
                    update_current_position(pos);

                    return static_cast<pos_type>(m_current_position);
                }
            }

            return static_cast<pos_type>(traits::eof());
        }

        /// <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)
        {
            pos_type beg = 0;
            pos_type cur = static_cast<pos_type>(m_current_position);
            pos_type end = static_cast<pos_type>(m_size);

            switch ( way )
            {
            case std::ios_base::beg:
                return seekpos(beg + offset, mode);

            case std::ios_base::cur:
                return seekpos(cur + offset, mode);

            case std::ios_base::end:
                return seekpos(end + offset, mode);

            default:
                return static_cast<pos_type>(traits::eof());
            }
        }

    private:
        template<typename _CharType1> friend class ::concurrency::streams::rawptr_buffer;

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="data">The address (pointer to) the memory block.</param>
        /// <param name="size">The memory block size, measured in number of characters.</param>
        basic_rawptr_buffer(const _CharType* data, size_t size)
            : streambuf_state_manager<_CharType>(std::ios_base::in),
              m_data(const_cast<_CharType*>(data)),
              m_size(size),
              m_current_position(0)
        {
            validate_mode(std::ios_base::in);
        }

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="data">The address (pointer to) the memory block.</param>
        /// <param name="size">The memory block size, measured in number of characters.</param>
        /// <param name="mode">The stream mode (in, out, etc.).</param>
        basic_rawptr_buffer(_CharType* data, size_t size, std::ios_base::openmode mode)
            : streambuf_state_manager<_CharType>(mode),
              m_data(data),
              m_size(size),
              m_current_position(0)
        {
            validate_mode(mode);
        }

        static void validate_mode(std::ios_base::openmode mode)
        {
            // Disallow simultaneous use of the stream buffer for writing and reading.
            if ((mode & std::ios_base::in) && (mode & std::ios_base::out))
                throw std::invalid_argument("this combination of modes on raw pointer stream not supported");
        }

        /// <summary>
        /// Determines if the request can be satisfied.
        /// </summary>
        bool can_satisfy(size_t) const
        {
            // We can always satisfy a read, at least partially, unless the
            // read position is at the very end of the buffer.
            return (in_avail() > 0);
        }

        /// <summary>
        /// Reads a byte from the stream and returns it as int_type.
        /// Note: This routine must only be called if can_satisfy() returns true.
        /// </summary>
        int_type read_byte(bool advance = true)
        {
            _CharType value;
            auto read_size = this->read(&value, 1, advance);
            return read_size == 1 ? static_cast<int_type>(value) : traits::eof();
        }

        /// <summary>
        /// Reads up to count characters into ptr and returns the count of characters copied.
        /// The return value (actual characters copied) could be <= count.
        /// Note: This routine must only be called if can_satisfy() returns true.
        /// </summary>
        size_t read(_Out_writes_ (count) _CharType *ptr, _In_ size_t count, bool advance = true)
        {
            if (!can_satisfy(count))
                return 0;

            msl::safeint3::SafeInt<size_t> request_size(count);
            msl::safeint3::SafeInt<size_t> read_size = request_size.Min(in_avail());

            size_t newPos = m_current_position + read_size;

            auto readBegin = m_data + m_current_position;
            auto readEnd = m_data + newPos;

#ifdef _WIN32
            // Avoid warning C4996: Use checked iterators under SECURE_SCL
            std::copy(readBegin, readEnd, stdext::checked_array_iterator<_CharType *>(ptr, count));
#else
            std::copy(readBegin, readEnd, ptr);
#endif // _WIN32

            if (advance)
            {
                update_current_position(newPos);
            }

            return (size_t) read_size;
        }

        /// <summary>
        /// Write count characters from the ptr into the stream buffer
        /// </summary>
        size_t write(const _CharType *ptr, size_t count)
        {
            if (!this->can_write() || (count == 0)) return 0;

            msl::safeint3::SafeInt<size_t> newSize = msl::safeint3::SafeInt<size_t>(count) +m_current_position;

            if ( newSize > m_size )
                throw std::runtime_error("Writing past the end of the buffer");

            // Copy the data
#ifdef _WIN32
            // Avoid warning C4996: Use checked iterators under SECURE_SCL
            std::copy(ptr, ptr + count, stdext::checked_array_iterator<_CharType *>(m_data, m_size, m_current_position));
#else
            std::copy(ptr, ptr + count, m_data+m_current_position);
#endif // _WIN32

            // Update write head and satisfy pending reads if any
            update_current_position(newSize);

            return count;
        }

        /// <summary>
        /// Updates the current read or write position
        /// </summary>
        void update_current_position(size_t newPos)
        {
            // The new write head
            m_current_position = newPos;

            _ASSERTE(m_current_position <= m_size);
        }

        // The actual memory block
        _CharType* m_data;

        // The size of the memory block
        size_t m_size;

        // Read/write head
        size_t m_current_position;
    };

    } // namespace details

    /// <summary>
    /// The <c>rawptr_buffer</c> class serves as a memory-based stream buffer that supports reading
    /// sequences of characters to or from a fixed-size block. Note that it cannot be used simultaneously for reading as well as writing.
    /// </summary>
    /// <typeparam name="_CharType">
    /// The data type of the basic element of the <c>rawptr_buffer</c>.
    /// </typeparam>
    template<typename _CharType>
    class rawptr_buffer : public streambuf<_CharType>
    {
    public:
        typedef _CharType char_type;

        /// <summary>
        /// Create a rawptr_buffer given a pointer to a memory block and the size of the block.
        /// </summary>
        /// <param name="data">The address (pointer to) the memory block.</param>
        /// <param name="size">The memory block size, measured in number of characters.</param>
        rawptr_buffer(const char_type* data, size_t size)
            : streambuf<char_type>(std::shared_ptr<details::basic_rawptr_buffer<char_type>>(new details::basic_rawptr_buffer<char_type>(data, size)))
        {
        }

        /// <summary>
        /// Create a rawptr_buffer given a pointer to a memory block and the size of the block.
        /// </summary>
        /// <param name="data">The address (pointer to) the memory block.</param>
        /// <param name="size">The memory block size, measured in number of characters.</param>
        rawptr_buffer(char_type* data, size_t size, std::ios_base::openmode mode = std::ios::out)
            : streambuf<char_type>(std::shared_ptr<details::basic_rawptr_buffer<char_type>>(new details::basic_rawptr_buffer<char_type>(data, size, mode)))
        {
        }

        /// <summary>
        /// Default constructor.
        /// </summary>
        rawptr_buffer()
        {
        }
    };

    /// <summary>
    /// The rawptr_stream class is used to create memory-backed streams that support writing or reading
    /// sequences of characters to / from a fixed-size block.
    /// </summary>
    /// <typeparam name="_CharType">
    /// The data type of the basic element of the <c>rawptr_stream</c>.
    /// </typeparam>
    template<typename _CharType>
    class rawptr_stream
    {
    public:
        typedef _CharType char_type;
        typedef rawptr_buffer<_CharType>  buffer_type;

        /// <summary>
        /// Create a rawptr-stream given a pointer to a read-only memory block and the size of the block.
        /// </summary>
        /// <param name="data">The address (pointer to) the memory block.</param>
        /// <param name="size">The memory block size, measured in number of characters.</param>
        /// <returns>An opened input stream.</returns>
        static concurrency::streams::basic_istream<char_type> open_istream(const char_type* data, size_t size)
        {
            return concurrency::streams::basic_istream<char_type>(buffer_type(data, size));
        }

        /// <summary>
        /// Create a rawptr-stream given a pointer to a writable memory block and the size of the block.
        /// </summary>
        /// <param name="data">The address (pointer to) the memory block.</param>
        /// <param name="size">The memory block size, measured in number of characters.</param>
        /// <returns>An opened input stream.</returns>
        static concurrency::streams::basic_istream<char_type> open_istream(char_type* data, size_t size)
        {
            return concurrency::streams::basic_istream<char_type>(buffer_type(data, size, std::ios::in));
        }

        /// <summary>
        /// Create a rawptr-stream given a pointer to a writable memory block and the size of the block.
        /// </summary>
        /// <param name="data">The address (pointer to) the memory block.</param>
        /// <param name="size">The memory block size, measured in number of characters.</param>
        /// <returns>An opened output stream.</returns>
        static concurrency::streams::basic_ostream<char_type> open_ostream(char_type* data, size_t size)
        {
            return concurrency::streams::basic_ostream<char_type>(buffer_type(data, size, std::ios::out));
        }
    };

}} // namespaces

#endif
