/*
 * InspIRCd -- Internet Relay Chat Daemon
 *
 *   Copyright (C) 2021 Dominic Hamon
 *   Copyright (C) 2013-2016 Attila Molnar <attilamolnar@hush.com>
 *   Copyright (C) 2013-2014 Adam <Adam@anope.org>
 *   Copyright (C) 2012-2013, 2017-2023 Sadie Powell <sadie@witchery.services>
 *   Copyright (C) 2012 Robby <robby@chatbelgie.be>
 *   Copyright (C) 2009 Daniel De Graaf <danieldg@inspircd.org>
 *   Copyright (C) 2007, 2017 Robin Burchell <robin+git@viroteck.net>
 *   Copyright (C) 2007 Dennis Friis <peavey@inspircd.org>
 *   Copyright (C) 2005-2008 Craig Edwards <brain@inspircd.org>
 *
 * This file is part of InspIRCd.  InspIRCd is free software: you can
 * redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation, version 2.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */


#pragma once

#include <string>
#include "socket.h"
#include "base.h"

#ifndef _WIN32
#include <sys/uio.h>
#endif

#ifndef IOV_MAX
#define IOV_MAX 1024
#endif

/**
 * Event mask for SocketEngine events
 */
enum EventMask
{
	/** Do not test this socket for readability
	 */
	FD_WANT_NO_READ = 0x1,
	/** Give a read event at all times when reads will not block.
	 */
	FD_WANT_POLL_READ = 0x2,
	/** Give a read event when there is new data to read.
	 *
	 * An event MUST be sent if there is new data to be read, and the most
	 * recent read/recv() on this FD returned EAGAIN. An event MAY be sent
	 * at any time there is data to be read on the socket.
	 */
	FD_WANT_FAST_READ = 0x4,
	/** Give an optional read event when reads begin to unblock
	 *
	 * This state is useful if you want to leave data in the OS receive
	 * queue but not get continuous event notifications about it, because
	 * it may not require a system call to transition from FD_WANT_FAST_READ
	 */
	FD_WANT_EDGE_READ = 0x8,

	/** Mask for all read events */
	FD_WANT_READ_MASK = 0x0F,

	/** Do not test this socket for writability
	 */
	FD_WANT_NO_WRITE = 0x10,
	/** Give a write event at all times when writes will not block.
	 *
	 * You probably shouldn't use this state; if it's likely that the write
	 * will not block, try it first, then use FD_WANT_FAST_WRITE if it
	 * fails. If it's likely to block (or you are using polling-style reads)
	 * then use FD_WANT_SINGLE_WRITE.
	 */
	FD_WANT_POLL_WRITE = 0x20,
	/** Give a write event when writes don't block any more
	 *
	 * An event MUST be sent if writes will not block, and the most recent
	 * write/send() on this FD returned EAGAIN, or connect() returned
	 * EINPROGRESS. An event MAY be sent at any time that writes will not
	 * block.
	 *
	 * Before calling OnEventHandler*(), a socket engine MAY change the state of
	 * the FD back to FD_WANT_EDGE_WRITE if it is simpler (for example, if a
	 * one-shot notification was registered). If further writes are needed,
	 * it is the responsibility of the event handler to change the state to
	 * one that will generate the required notifications
	 */
	FD_WANT_FAST_WRITE = 0x40,
	/** Give an optional write event on edge-triggered write unblock.
	 *
	 * This state is useful to avoid system calls when moving to/from
	 * FD_WANT_FAST_WRITE when writing data to a mostly-unblocked socket.
	 */
	FD_WANT_EDGE_WRITE = 0x80,
	/** Request a one-shot poll-style write notification. The socket will
	 * return to the FD_WANT_NO_WRITE state before OnEventHandler*() is called.
	 */
	FD_WANT_SINGLE_WRITE = 0x100,

	/** Mask for all write events */
	FD_WANT_WRITE_MASK = 0x1F0,

	/** Add a trial read. During the next DispatchEvents invocation, this
	 * will call OnEventHandlerRead() unless reads are known to be
	 * blocking.
	 */
	FD_ADD_TRIAL_READ  = 0x1000,
	/** Assert that reads are known to block. This cancels FD_ADD_TRIAL_READ.
	 * Reset by SE before running OnEventHandlerRead().
	 */
	FD_READ_WILL_BLOCK = 0x2000,

	/** Add a trial write. During the next DispatchEvents invocation, this
	 * will call OnEventHandlerWrite() unless writes are known to be
	 * blocking.
	 *
	 * This could be used to group several writes together into a single
	 * send() syscall, or to ensure that writes are blocking when attempting
	 * to use FD_WANT_FAST_WRITE.
	 */
	FD_ADD_TRIAL_WRITE = 0x4000,
	/** Assert that writes are known to block. This cancels FD_ADD_TRIAL_WRITE.
	 * Reset by SE before running OnEventHandlerWrite().
	 */
	FD_WRITE_WILL_BLOCK = 0x8000,

	/** Mask for trial read/trial write */
	FD_TRIAL_NOTE_MASK = 0x5000
};

/** This class is a basic I/O handler class.
 * Any object which wishes to receive basic I/O events
 * from the socketengine must derive from this class and
 * implement the OnEventHandler*() methods. The derived class
 * must then be added to SocketEngine using the method
 * SocketEngine::AddFd(), after which point the derived
 * class will receive events to its OnEventHandler*() methods.
 * The event mask passed to SocketEngine::AddFd() determines
 * what events the EventHandler gets notified about and with
 * what semantics. SocketEngine::ChangeEventMask() can be
 * called to update the event mask later. The only
 * requirement beyond this for an event handler is that it
 * must have a file descriptor. What this file descriptor
 * is actually attached to is completely up to you.
 */
class CoreExport EventHandler
	: public Cullable
{
private:
	/** Private state maintained by socket engine */
	int event_mask = 0;

	void SetEventMask(int mask) { event_mask = mask; }

	/** File descriptor.
	 * All events which can be handled must have a file descriptor.  This
	 * allows you to add events for sockets, fifo's, pipes, and various
	 * other forms of IPC.  Do not change this while the object is
	 * registered with the SocketEngine
	 */
	int fd = -1;

public:
	/** Get the current file descriptor
	 * @return The file descriptor of this handler
	 */
	inline int GetFd() const { return fd; }

	/** Checks if this event handler has a fd associated with it. */
	inline bool HasFd() const { return fd >= 0; }

	inline int GetEventMask() const { return event_mask; }

	/** Set a new file descriptor
	 * @param FD The new file descriptor. Do not call this method without
	 * first deleting the object from the SocketEngine if you have
	 * added it to a SocketEngine instance.
	 */
	void SetFd(int FD);

	/** Called by the socket engine in case of a read event
	 */
	virtual void OnEventHandlerRead() = 0;

	/** Called by the socket engine in case of a write event.
	 * The default implementation does nothing.
	 */
	virtual void OnEventHandlerWrite();

	/** Called by the socket engine in case of an error event.
	 * The default implementation does nothing.
	 * @param errornum Error code
	 */
	virtual void OnEventHandlerError(int errornum);

	friend class SocketEngine;
};

/** Provides basic file-descriptor-based I/O support.
 * The actual socketengine class presents the
 * same interface on all operating systems, but
 * its private members and internal behaviour
 * should be treated as blackboxed, and vary
 * from system to system and upon the config
 * settings chosen by the server admin.
 */
class CoreExport SocketEngine final
{
public:
	/** Socket engine statistics: count of various events, bandwidth usage
	 */
	class Statistics
	{
		mutable size_t indata = 0;
		mutable size_t outdata = 0;
		mutable time_t lastempty = 0;

		/** Reset the byte counters and lastempty if there wasn't a reset in this second.
		 */
		void CheckFlush() const;

	public:
		/** Update counters for network data received.
		 * This should be called after every read-type syscall.
		 * @param len_in Number of bytes received, or -1 for error, as typically
		 * returned by a read-style syscall.
		 */
		void UpdateReadCounters(ssize_t len_in);

		/** Update counters for network data sent.
		 * This should be called after every write-type syscall.
		 * @param len_out Number of bytes sent, or -1 for error, as typically
		 * returned by a read-style syscall.
		 */
		void UpdateWriteCounters(ssize_t len_out);

		/** Get data transfer statistics.
		 * @param kbitpersec_in Filled with incoming traffic in this second in kbit/s.
		 * @param kbitpersec_out Filled with outgoing traffic in this second in kbit/s.
		 * @param kbitpersec_total Filled with total traffic in this second in kbit/s.
		 */
		void CoreExport GetBandwidth(float& kbitpersec_in, float& kbitpersec_out, float& kbitpersec_total) const;

		unsigned long TotalEvents = 0;
		unsigned long ReadEvents = 0;
		unsigned long WriteEvents = 0;
		unsigned long ErrorEvents = 0;
	};

private:
	/** Reference table, contains all current handlers
	 **/
	static std::vector<EventHandler*> ref;

	/** Current number of descriptors in the engine. */
	static size_t CurrentSetSize;

	/** The maximum number of descriptors in the engine. */
	static size_t MaxSetSize;

	/** List of handlers that want a trial read/write
	 */
	static std::set<int> trials;

	/** Socket engine statistics: count of various events, bandwidth usage
	 */
	static Statistics stats;

	/** Look up the fd limit using rlimit. */
	static void LookupMaxFds();

	/** Terminates the program when the socket engine fails to initialize. */
	[[noreturn]]
	static void InitError();

	static void OnSetEvent(EventHandler* eh, int old_mask, int new_mask) ATTR_NOT_NULL(1);

	/** Add an event handler to the base socket engine. AddFd(EventHandler*, int) should call this.
	 */
	static bool AddFdRef(EventHandler* eh) ATTR_NOT_NULL(1);

	static void DelFdRef(EventHandler* eh) ATTR_NOT_NULL(1);

	template <typename T>
	static void ResizeDouble(std::vector<T>& vect)
	{
		if (SocketEngine::CurrentSetSize > vect.size())
			vect.resize(SocketEngine::CurrentSetSize * 2);
	}

public:
#ifndef _WIN32
	typedef iovec IOVector;
#else
	typedef WindowsIOVec IOVector;
#endif

	/** Constructor.
	 * The constructor transparently initializes
	 * the socket engine which the ircd is using.
	 * Please note that if there is a catastrophic
	 * failure (for example, you try and enable
	 * epoll on a 2.4 linux kernel) then this
	 * function may bail back to the shell.
	 */
	static void Init();

	/** Destructor.
	 * The destructor transparently tidies up
	 * any resources used by the socket engine.
	 */
	static void Deinit();

	/** Add an EventHandler object to the engine.  Use AddFd to add a file
	 * descriptor to the engine and have the socket engine monitor it. You
	 * must provide an object derived from EventHandler which implements
	 * the required OnEventHandler*() methods.
	 * @param eh An event handling object to add
	 * @param event_mask The initial event mask for the object
	 */
	static bool AddFd(EventHandler* eh, int event_mask) ATTR_NOT_NULL(1);

	/** If you call this function and pass it an
	 * event handler, that event handler will
	 * receive the next available write event,
	 * even if the socket is a readable socket only.
	 * Developers should avoid constantly keeping
	 * an eventhandler in the writeable state,
	 * as this will consume large amounts of
	 * CPU time.
	 * @param eh The event handler to change
	 * @param event_mask The changes to make to the wait state
	 */
	static void ChangeEventMask(EventHandler* eh, int event_mask) ATTR_NOT_NULL(1);

	/** Returns the number of file descriptors reported by the system this program may use
	 * when it was started.
	 * @return If non-zero the number of file descriptors that the system reported that we
	 * may use.
	 */
	static size_t GetMaxFds() { return MaxSetSize; }

	/** Returns the number of file descriptors being queried
	 * @return The set size
	 */
	static size_t GetUsedFds() { return CurrentSetSize; }

	/** Delete an event handler from the engine.
	 * This function call deletes an EventHandler
	 * from the engine, returning true if it succeeded
	 * and false if it failed. This does not free the
	 * EventHandler pointer using delete, if this is
	 * required you must do this yourself.
	 * @param eh The event handler object to remove
	 */
	static void DelFd(EventHandler* eh) ATTR_NOT_NULL(1);

	/** Returns true if a file descriptor exists in
	 * the socket engine's list.
	 * @param fd The event handler to look for
	 * @return True if this fd has an event handler
	 */
	static bool HasFd(int fd);

	/** Returns the EventHandler attached to a specific fd.
	 * If the fd isn't in the socketengine, returns NULL.
	 * @param fd The event handler to look for
	 * @return A pointer to the event handler, or NULL
	 */
	static EventHandler* GetRef(int fd);

	/** Waits for events and dispatches them to handlers.  Please note that
	 * this doesn't wait long, only a couple of milliseconds. It returns the
	 * number of events which occurred during this call.  This method will
	 * dispatch events to their handlers by calling their
	 * EventHandler::OnEventHandler*() methods.
	 * @return The number of events which have occurred.
	 */
	static int DispatchEvents();

	/** Dispatch trial reads and writes. This causes the actual socket I/O
	 * to happen when writes have been pre-buffered.
	 */
	static void DispatchTrialWrites();

	/** Abstraction for BSD sockets accept(2).
	 * This function should emulate its namesake system call exactly.
	 * @param eh This version of the call takes an EventHandler instead of a bare file descriptor.
	 * @param addr The client IP address and port
	 * @param addrlen The size of the sockaddr parameter.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static int Accept(EventHandler* eh, sockaddr* addr, socklen_t* addrlen) ATTR_NOT_NULL(1, 2, 3);

	/** Close the underlying fd of an event handler, remove it from the socket engine and set the fd to -1.
	 * @param eh The EventHandler to close.
	 * @return 0 on success, a negative value on error
	 */
	static int Close(EventHandler* eh) ATTR_NOT_NULL(1);

	/** Abstraction for BSD sockets close(2).
	 * This function should emulate its namesake system call exactly.
	 * This function should emulate its namesake system call exactly.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static int Close(int fd);

	/** Abstraction for BSD sockets send(2).
	 * This function should emulate its namesake system call exactly.
	 * @param eh This version of the call takes an EventHandler instead of a bare file descriptor.
	 * @param buf The buffer in which the data that is sent is stored.
	 * @param len The size of the buffer.
	 * @param flags A flag value that controls the sending of the data.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static ssize_t Send(EventHandler* eh, const void* buf, size_t len, int flags) ATTR_NOT_NULL(1, 2);

	/** Abstraction for vector write function writev().
	 * This function should emulate its namesake system call exactly.
	 * @param eh EventHandler to send data with
	 * @param iov Array of IOVectors containing the buffers to send and their lengths in the platform's
	 * native format.
	 * @param count Number of elements in iov.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static ssize_t WriteV(EventHandler* eh, const IOVector* iov, int count) ATTR_NOT_NULL(1, 2);

#ifdef _WIN32
	/** Abstraction for vector write function writev() that accepts a POSIX format iovec.
	 * This function should emulate its namesake system call exactly.
	 * @param eh EventHandler to send data with
	 * @param iov Array of iovecs containing the buffers to send and their lengths in POSIX format.
	 * @param count Number of elements in iov.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static int WriteV(EventHandler* eh, const iovec* iov, int count) ATTR_NOT_NULL(1, 2);
#endif

	/** Abstraction for BSD sockets recv(2).
	 * This function should emulate its namesake system call exactly.
	 * @param eh This version of the call takes an EventHandler instead of a bare file descriptor.
	 * @param buf The buffer in which the data that is read is stored.
	 * @param len The size of the buffer.
	 * @param flags A flag value that controls the reception of the data.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static ssize_t Recv(EventHandler* eh, void* buf, size_t len, int flags) ATTR_NOT_NULL(1);

	/** Abstraction for BSD sockets recvfrom(2).
	 * This function should emulate its namesake system call exactly.
	 * @param eh This version of the call takes an EventHandler instead of a bare file descriptor.
	 * @param buf The buffer in which the data that is read is stored.
	 * @param len The size of the buffer.
	 * @param flags A flag value that controls the reception of the data.
	 * @param from The remote IP address and port.
	 * @param fromlen The size of the from parameter.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static ssize_t RecvFrom(EventHandler* eh, void* buf, size_t len, int flags, sockaddr* from, socklen_t* fromlen) ATTR_NOT_NULL(1, 2, 5, 6);

	/** Abstraction for BSD sockets sendto(2).
	 * This function should emulate its namesake system call exactly.
	 * @param eh This version of the call takes an EventHandler instead of a bare file descriptor.
	 * @param buf The buffer in which the data that is sent is stored.
	 * @param len The size of the buffer.
	 * @param flags A flag value that controls the sending of the data.
	 * @param address The remote IP address and port.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static ssize_t SendTo(EventHandler* eh, const void* buf, size_t len, int flags, const irc::sockets::sockaddrs& address) ATTR_NOT_NULL(1, 2);

	/** Abstraction for BSD sockets connect(2).
	 * This function should emulate its namesake system call exactly.
	 * @param eh This version of the call takes an EventHandler instead of a bare file descriptor.
	 * @param address The server IP address and port.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static int Connect(EventHandler* eh, const irc::sockets::sockaddrs& address) ATTR_NOT_NULL(1);

	/** Make a file descriptor blocking.
	 * @param fd a file descriptor to set to blocking mode
	 * @return 0 on success, -1 on failure, errno is set appropriately.
	 */
	static int Blocking(int fd);

	/** Make a file descriptor nonblocking.
	 * @param fd A file descriptor to set to nonblocking mode
	 * @return 0 on success, -1 on failure, errno is set appropriately.
	 */
	static int NonBlocking(int fd);

	/** Abstraction for BSD sockets shutdown(2).
	 * This function should emulate its namesake system call exactly.
	 * @param eh This version of the call takes an EventHandler instead of a bare file descriptor.
	 * @param how What part of the socket to shut down
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static int Shutdown(EventHandler* eh, int how) ATTR_NOT_NULL(1);

	/** Abstraction for BSD sockets bind(2).
	 * This function should emulate its namesake system call exactly.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static int Bind(EventHandler* eh, const irc::sockets::sockaddrs& addr) ATTR_NOT_NULL(1);

	/** Abstraction for BSD sockets listen(2).
	 * This function should emulate its namesake system call exactly.
	 * @return This method should return exactly the same values as the system call it emulates.
	 */
	static int Listen(EventHandler* eh, int backlog) ATTR_NOT_NULL(1);

	/** Sets the value of a socket option.
	 * @param fd The file descriptor to change the options of.
	 * @param level The level at which to change the socket options.
	 * @param name The option to change the value of.
	 * @param value The value to set.
	 * @return The system result of the socket operation.
	 */
	template <typename Value>
	static int SetOption(int fd, int level, int name, Value value)
	{
		return setsockopt(fd, level, name, reinterpret_cast<char*>(&value), sizeof(value));
	}

	/** Sets the value of a socket option.
	 * @param eh The socket to change the options of.
	 * @param level The level at which to change the socket options.
	 * @param name The option to change the value of.
	 * @param value The value to set.
	 * @return The system result of the socket operation.
	 */
	template <typename Value>
	static int SetOption(EventHandler* eh, int level, int name, Value value)
	{
		return SetOption<Value>(eh->GetFd(), level, name, value);
	}

	/** This function is called immediately after fork().
	 * Some socket engines (notably kqueue) cannot have their
	 * handles inherited by forked processes. This method
	 * allows for the socket engine to re-create its handle
	 * after the daemon forks as the socket engine is created
	 * long BEFORE the daemon forks.
	 */
	static void RecoverFromFork();

	/** Get data transfer and event statistics
	 */
	static const Statistics& GetStats() { return stats; }

	/** Should we ignore the error in errno?
	 * Checks EAGAIN and WSAEWOULDBLOCK
	 */
	static bool IgnoreError();

	/** Return the last socket related error. strrerror(errno) on *nix
	 */
	static std::string LastError();

	/** Returns the error for the given error num, strerror(errnum) on *nix
	 */
	static std::string GetError(int errnum);
};

inline bool SocketEngine::IgnoreError()
{
	if ((errno == EAGAIN) || (errno == EWOULDBLOCK))
		return true;

#ifdef _WIN32
	if (WSAGetLastError() == WSAEWOULDBLOCK)
		return true;
#endif

	return false;
}