//
// Copyright (c) 2013-2016 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef BEAST_HTTP_STREAM_H_INCLUDED
#define BEAST_HTTP_STREAM_H_INCLUDED

#include <beast/core/async_completion.hpp>
#include <beast/core/basic_streambuf.hpp>
#include <beast/http.hpp>
#include <boost/asio/io_service.hpp>
#include <boost/intrusive/list.hpp>
#include <memory>

namespace beast {
namespace http {

namespace detail {

class stream_base
{
protected:
    struct op
        : boost::intrusive::list_base_hook<
            boost::intrusive::link_mode<
                boost::intrusive::normal_link>>
    {
        virtual ~op() = default;
        virtual void operator()() = 0;
        virtual void cancel() = 0;
    };

    using op_list = typename boost::intrusive::make_list<
        op, boost::intrusive::constant_time_size<false>>::type;

    op_list wr_q_;
    bool wr_active_ = false;
};

} // detail

/** Provides message-oriented functionality using HTTP.

    The stream class template provides asynchronous and blocking
    message-oriented functionality necessary for clients and servers
    to utilize the HTTP protocol.

    @par Thread Safety
    @e Distinct @e objects: Safe.@n
    @e Shared @e objects: Unsafe. The application must ensure that
    all asynchronous operations are performed within the same
    implicit or explicit strand.

    @par Example

    To use the class template with an `ip::tcp::socket`, you would write:

    @code
    http::stream<ip::tcp::socket> hs(io_service);
    @endcode
    Alternatively, you can write:
    @code
    ip::tcp::socket sock(io_service);
    http::stream<ip::tcp::socket&> hs(sock);
    @endcode

    @note A stream object must not be destroyed while there are
    pending asynchronous operations associated with it.

    @par Concepts
    AsyncReadStream, AsyncWriteStream, Stream, SyncReadStream, SyncWriteStream.
 */
template<class NextLayer,
    class Allocator = std::allocator<char>>
class stream : public detail::stream_base
{
    NextLayer next_layer_;
    basic_streambuf<Allocator> rd_buf_;

public:
    /// The type of the next layer.
    using next_layer_type =
        typename std::remove_reference<NextLayer>::type;

    /// The type of the lowest layer.
    using lowest_layer_type =
        typename next_layer_type::lowest_layer_type;

    /// The type of endpoint of the lowest layer.
    using endpoint_type =
        typename lowest_layer_type::endpoint_type;

    /// The protocol of the next layer.
    using protocol_type =
        typename lowest_layer_type::protocol_type;

    /// The type of resolver of the next layer.
    using resolver_type =
        typename protocol_type::resolver;

    /** Destructor.

        @note A stream object must not be destroyed while there
        are pending asynchronous operations associated with it.
    */
    ~stream();

    /** Move constructor.

        Undefined behavior if operations are active or pending.
    */
    stream(stream&&) = default;

    /** Move assignment.

        Undefined behavior if operations are active or pending.
    */
    stream& operator=(stream&&) = default;

    /** Construct a HTTP stream.

        This constructor creates a HTTP stream and initialises
        the next layer.

        @throws Any exceptions thrown by the Stream constructor.

        @param args The arguments to be passed to initialise the
        next layer. The arguments are forwarded to the next layer's
        constructor.
    */
    template<class... Args>
    explicit
    stream(Args&&... args);

    /** Get the io_service associated with the stream.

        This function may be used to obtain the io_service object
        that the stream uses to dispatch handlers for asynchronous
        operations.

        @return A reference to the io_service object that the stream
        will use to dispatch handlers. Ownership is not transferred
        to the caller.
    */
    boost::asio::io_service&
    get_io_service()
    {
        return next_layer_.lowest_layer().get_io_service();
    }

    /** Get a reference to the next layer.

        This function returns a reference to the next layer
        in a stack of stream layers.

        @return A reference to the next layer in the stack of
        stream layers. Ownership is not transferred to the caller.
    */
    next_layer_type&
    next_layer()
    {
        return next_layer_;
    }

    /** Get a reference to the next layer.

        This function returns a reference to the next layer in a
        stack of stream layers.

        @return A reference to the next layer in the stack of
        stream layers. Ownership is not transferred to the caller.
    */
    next_layer_type const&
    next_layer() const
    {
        return next_layer_;
    }

    /** Get a reference to the lowest layer.

        This function returns a reference to the lowest layer
        in a stack of stream layers.

        @return A reference to the lowest layer in the stack of
        stream layers. Ownership is not transferred to the caller.
    */
    lowest_layer_type&
    lowest_layer()
    {
        return next_layer_.lowest_layer();
    }

    /** Get a reference to the lowest layer.

        This function returns a reference to the lowest layer
        in a stack of stream layers.

        @return A reference to the lowest layer in the stack of
        stream layers. Ownership is not transferred to the caller.
    */
    lowest_layer_type const&
    lowest_layer() const
    {
        return next_layer_.lowest_layer();
    }

    /** Cancel pending operations.

        This will cancel all of the asynchronous operations pending,
        including pipelined writes that have not been started. Handlers for
        canceled writes will be called with
        `boost::asio::error::operation_aborted`.

        @throws boost::system::system_error Thrown on failure.
    */
    void
    cancel()
    {
        error_code ec;
        cancel(ec);
        if(ec)
            throw system_error{ec};
    }

    /** Cancel pending operations.

        This will cancel all of the asynchronous operations pending,
        including pipelined writes that have not been started. Handlers for
        canceled writes will be called with
        `boost::asio::error::operation_aborted`.

        @param ec Set to indicate what error occurred, if any.
    */
    void
    cancel(error_code& ec);

    /** Read a HTTP message from the stream.

        This function is used to read a single HTTP message from the stream.
        The call will block until one of the followign conditions is true:

        @li A message has been read.

        @li An error occurred.

        The operation is implemented in terms of zero or more calls to the
        next layer's `read_some` function.

        @param msg An object used to store the message. The previous
        contents of the object will be overwritten.

        @throws boost::system::system_error Thrown on failure.
    */
    template<bool isRequest, class Body, class Headers>
    void
    read(message_v1<isRequest, Body, Headers>& msg)
    {
        error_code ec;
        read(msg, ec);
        if(ec)
            throw system_error{ec};
    }

    /** Read a HTTP message from the stream.

        This function is used to read a single HTTP message from the stream.
        The call will block until one of the followign conditions is true:

        @li A message has been read.

        @li An error occurred.

        The operation is implemented in terms of zero or more calls to the
        next layer's `read_some` function.

        @param msg An object used to store the message. The previous
        contents of the object will be overwritten.

        @param ec Set to indicate what error occurred, if any.
    */
    template<bool isRequest, class Body, class Headers>
    void
    read(message_v1<isRequest, Body, Headers>& msg,
        error_code& ec);

    /** Start reading a HTTP message from the stream asynchronously.

        This function is used to asynchronously read a single HTTP message
        from the stream. The function call always returns immediately. The
        asynchronous operation will continue until one of the following
        conditions is true:

        @li The message has been written.

        @li An error occurred.

        This operation is implemented in terms of zero or more calls to the
        next layer's async_read_some function, and is known as a composed
        operation. The program must ensure that the stream performs no other
        read operations or any other composed operations that perform reads
        until this operation completes.

        @param msg An object used to store the message. The previous
        contents of the object will be overwritten. Ownership of the message
        is not transferred; the caller must guarantee that the object remains
        valid until the handler is called.

        @param handler The handler to be called when the request completes.
        Copies will be made of the handler as required. The equivalent
        function signature of the handler must be:
        @code void handler(
            error_code const& error // result of operation
        ); @endcode
        Regardless of whether the asynchronous operation completes
        immediately or not, the handler will not be invoked from within
        this function. Invocation of the handler will be performed in a
        manner equivalent to using boost::asio::io_service::post().
    */
    template<bool isRequest, class Body, class Headers,
        class ReadHandler>
    #if GENERATING_DOCS
    void_or_deduced
    #else
    typename async_completion<
        ReadHandler, void(error_code)>::result_type
    #endif
    async_read(message_v1<isRequest, Body, Headers>& msg,
        ReadHandler&& handler);

    /** Write a HTTP message to the stream.

        This function is used to write a single HTTP message to the
        stream. The call will block until one of the following conditions
        is true:

        @li The entire message is sent.

        @li An error occurred.

        If the semantics of the message require that the connection is
        closed to indicate the end of the content body,
        `boost::asio::error::eof` is thrown after the message is sent.
        successfuly. The caller is responsible for actually closing the
        connection. For regular TCP/IP streams this means shutting down the
        send side, while SSL streams may call the SSL shutdown function.

        @param msg The message to send.

        @throws boost::system::system_error Thrown on failure.
    */
    template<bool isRequest, class Body, class Headers>
    void
    write(message_v1<isRequest, Body, Headers> const& msg)
    {
        error_code ec;
        write(msg, ec);
        if(ec)
            throw system_error{ec};
    }

    /** Write a HTTP message to the stream.

        This function is used to write a single HTTP message to the
        stream. The call will block until one of the following conditions
        is true:

        @li The entire message is sent.

        @li An error occurred.

        If the semantics of the message require that the connection is
        closed to indicate the end of the content body,
        `boost::asio::error::eof` is returned after the message is sent.
        successfuly. The caller is responsible for actually closing the
        connection. For regular TCP/IP streams this means shutting down the
        send side, while SSL streams may call the SSL shutdown function.

        @param msg The message to send.

        @param ec Set to the error, if any occurred.
    */
    template<bool isRequest, class Body, class Headers>
    void
    write(message_v1<isRequest, Body, Headers> const& msg,
        error_code& ec);

    /** Start pipelining a HTTP message to the stream asynchronously.

        This function is used to queue a message to be sent on the stream.
        Unlike the free function, this version will place the message on an
        outgoing message queue if there is already a write pending.

        If the semantics of the message require that the connection is
        closed to indicate the end of the content body, the handler
        is called with the error `boost::asio::error::eof` after the message
        has been sent successfully. The caller is responsible for actually
        closing the connection. For regular TCP/IP streams this means
        shutting down the send side, while SSL streams may call the SSL
        `async_shutdown` function.

        @param msg The message to send. A copy of the message will be made.

        @param handler The handler to be called when the request completes.
        Copies will be made of the handler as required. The equivalent
        function signature of the handler must be:
        @code void handler(
            error_code const& error // result of operation
        ); @endcode
        Regardless of whether the asynchronous operation completes
        immediately or not, the handler will not be invoked from within
        this function. Invocation of the handler will be performed in a
        manner equivalent to using boost::asio::io_service::post().
    */
    template<bool isRequest, class Body, class Headers,
        class WriteHandler>
    #if GENERATING_DOCS
    void_or_deduced
    #else
    typename async_completion<
        WriteHandler, void(error_code)>::result_type
    #endif
    async_write(message_v1<isRequest, Body, Headers> const& msg,
        WriteHandler&& handler);

    /** Start pipelining a HTTP message to the stream asynchronously.

        This function is used to queue a message to be sent on the stream.
        Unlike the free function, this version will place the message on an
        outgoing message queue if there is already a write pending.

        If the semantics of the message require that the connection is
        closed to indicate the end of the content body, the handler
        is called with the error boost::asio::error::eof. The caller is
        responsible for actually closing the connection. For regular
        TCP/IP streams this means shutting down the send side, while SSL
        streams may call the SSL async_shutdown function.

        @param msg The message to send. Ownership of the message, which
        must be movable, is transferred to the implementation. The message
        will not be destroyed until the asynchronous operation completes.

        @param handler The handler to be called when the request completes.
        Copies will be made of the handler as required. The equivalent
        function signature of the handler must be:
        @code void handler(
            error_code const& error // result of operation
        ); @endcode
        Regardless of whether the asynchronous operation completes
        immediately or not, the handler will not be invoked from within
        this function. Invocation of the handler will be performed in a
        manner equivalent to using boost::asio::io_service::post().
    */
    template<bool isRequest, class Body, class Headers,
        class WriteHandler>
    #if GENERATING_DOCS
    void_or_deduced
    #else
    typename async_completion<
        WriteHandler, void(error_code)>::result_type
    #endif
    async_write(message_v1<isRequest, Body, Headers>&& msg,
        WriteHandler&& handler);

private:
    template<bool, class, class, class> class read_op;
    template<bool, class, class, class> class write_op;

    void
    cancel_all();
};

} // http
} // beast

#include "http_stream.ipp"

#endif