/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

#include <errno.h>
#include <fcntl.h>
#include <poll.h>

#include <cassert>
#include <chrono>
#include <condition_variable>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <sstream>
#include <mutex>
#include <thread>
#include <vector>

// A "fake socket" is represented by a number, a smallish integer, just like a real socket.
//
// There is one FakeSocketPair for each two sequential fake socket numbers. When you create one, you
// will always get the lower (even) number in a pair. The higher number will be returned if you
// successfully call fakeSocketConnect() from the lower number to some other fake socket.
//
// After you create a fake socket, there is basically just two things you can do with it:
//
// 1) Call fakeSocketConnect on it giving another fake socket number to connect to. Once the
// connection is successful, you can call fakeSocketRead() and fakeSocketWrite() on your original
// socket.
//
// 2) Call fakeSocketListen() on it, indicating it is a "server" socket. After that, keep calling
// fakeSocketAccept() and each time that returns successfully, it will return a new fake socket that
// is connected to another fake socket that called fakeSocketConnect() to the server socket. You can
// then call fakeSocketRead() and fakeSocketWrite() on it.
//
// This all is complicated a bit by the fact that all the API is non-blocking.

struct FakeSocketPair
{
    int fd[2];
    bool listening;
    int connectingFd;
    bool shutdown[2];
    bool readable[2];
    std::vector<std::vector<char>> buffer[2];

    FakeSocketPair()
    {
        fd[0] = -1;
        fd[1] = -1;
        listening = false;
        connectingFd = -1;
        shutdown[0] = false;
        shutdown[1] = false;
        readable[0] = false;
        readable[1] = false;
    }
};

static thread_local std::ostringstream loggingBuffer;
static void (*loggingCallback)(const std::string&) = nullptr;

static std::mutex theMutex;
static std::condition_variable theCV;

static int fakeSocketLogLevel = 0;

static void fakeSocketDumpStateImpl();

// Avoid problems with order of initialisation of static globals.
static std::vector<FakeSocketPair>& getFds()
{
    static std::vector<FakeSocketPair> fds;

    return fds;
}

static std::string flush()
{
    static bool alwaysStderr = std::getenv("FAKESOCKET_LOG_ALWAYS_STDERR") != nullptr;
    if (alwaysStderr)
        std::cerr << std::this_thread::get_id() << ':' << loggingBuffer.str() << std::endl;
    else if (loggingCallback != nullptr)
        loggingCallback(loggingBuffer.str());
    loggingBuffer.str("");
    return "";
}

#ifdef __ANDROID__
// kill the verbose logging on Android
#define FAKESOCKET_LOG(level, arg)
#else
#define FAKESOCKET_LOG(level, arg) do { if (level <= fakeSocketLogLevel) { loggingBuffer << arg; } } while (false)
#endif

void fakeSocketSetLoggingCallback(void (*callback)(const std::string&))
{
    loggingCallback = callback;
}

static int fakeSocketAllocate()
{
    if (fakeSocketLogLevel == 0)
    {
        char *logLevel = std::getenv("FAKESOCKET_LOG_LEVEL");
        if (logLevel == nullptr)
            fakeSocketLogLevel = 1;
        else
        {
            fakeSocketLogLevel = std::strtol(logLevel, nullptr, 10);
            if (fakeSocketLogLevel != 1 && fakeSocketLogLevel != 2)
                fakeSocketLogLevel = 1;
        }
    }

    std::vector<FakeSocketPair>& fds = getFds();

    std::lock_guard<std::mutex> lock(theMutex);

    // We always allocate a new FakeSocketPair struct. Let's not bother with potential issues with
    // reusing them. It isn't like we would be allocating thousands anyway during the typical
    // lifetime of an app. Also, not reusing FakeSocket fd numbers means that it is easier to set a
    // conditional breakpoint on an operation on a specific fd when debugging some problematic
    // scenario.

    const int i = fds.size();
    fds.resize(i + 1);

    FakeSocketPair& result = fds[i];

    result.fd[0] = i*2;

    return i*2;
}

int fakeSocketSocket()
{
    const int result = fakeSocketAllocate();

    FAKESOCKET_LOG(1, "FakeSocket Create #" << result << flush());

    return result;
}

int fakeSocketPipe2(int pipefd[2])
{
    pipefd[0] = fakeSocketAllocate();
    assert(pipefd[0] >= 0);

    std::vector<FakeSocketPair>& fds = getFds();
    FakeSocketPair& pair = fds[pipefd[0]/2];

    std::unique_lock<std::mutex> lock(theMutex);

    assert(pair.fd[0] == pipefd[0]);

    pair.fd[1] = pair.fd[0] + 1;
    pipefd[1] = pair.fd[1];

    FAKESOCKET_LOG(1, "FakeSocket Pipe created (#" << pipefd[0] << ",#" << pipefd[1] << ')' << flush());

    return 0;
}

static std::string pollBits(int bits)
{
    if (bits == 0)
        return "-";

    std::string result;

    if (bits & POLLERR)
    {
        if (result != "")
            result += '+';
        result += "ERR";
    }
    if (bits & POLLHUP)
    {
        if (result != "")
            result += '+';
        result += "HUP";
    }
    if (bits & POLLIN)
    {
        if (result != "")
            result += '+';
        result += "IN";
    }
    if (bits & POLLNVAL)
    {
        if (result != "")
            result += '+';
        result += "NVAL";
    }
    if (bits & POLLOUT)
    {
        if (result != "")
            result += '+';
        result += "OUT";
    }
    if (bits & POLLPRI)
    {
        if (result != "")
            result += '+';
        result += "PRI";
    }

    return result;
}

static bool checkForPoll(std::vector<FakeSocketPair>& fds, struct pollfd *pollfds, int nfds)
{
    bool retval = false;
    for (int i = 0; i < nfds; i++)
    {
        const int K = ((pollfds[i].fd)&1);
        const int N = 1 - K;

        if (pollfds[i].fd < 0 || static_cast<unsigned>(pollfds[i].fd/2) >= fds.size())
        {
            pollfds[i].revents = POLLNVAL;
            retval = true;
        }
        else
        {
            if (fds[pollfds[i].fd/2].fd[K] == -1)
            {
                pollfds[i].revents = POLLNVAL;
                retval = true;
            }
            else
                pollfds[i].revents = 0;
        }

        if (pollfds[i].revents == 0)
        {
            if (pollfds[i].events & POLLIN)
            {
                if (fds[pollfds[i].fd/2].readable[K] ||
                    (K == 0 && fds[pollfds[i].fd/2].listening && fds[pollfds[i].fd/2].connectingFd != -1))
                {
                    pollfds[i].revents |= POLLIN;
                    retval = true;
                }
            }
            // With multiple buffers, a socket is always writable unless the peer is closed or shut down
            if (pollfds[i].events & POLLOUT)
            {
                if (fds[pollfds[i].fd/2].fd[N] != -1 && !fds[pollfds[i].fd/2].shutdown[N])
                {
                    pollfds[i].revents |= POLLOUT;
                    retval = true;
                }
            }
            if (fds[pollfds[i].fd/2].shutdown[N])
            {
                    pollfds[i].revents |= POLLHUP;
                    retval = true;
            }
        }
    }
    return retval;
}

int fakeSocketPoll(struct pollfd *pollfds, int nfds, int timeout)
{
    FAKESOCKET_LOG(2, "FakeSocket Poll ");
    for (int i = 0; i < nfds; i++)
    {
        if (i > 0)
            FAKESOCKET_LOG(2, ',');
        FAKESOCKET_LOG(2, '#' << pollfds[i].fd << ':' << pollBits(pollfds[i].events));
    }
    FAKESOCKET_LOG(2, ", timeout:" << timeout << flush());

    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);

    if (timeout > 0)
    {
        auto const now = std::chrono::steady_clock::now();
        auto const end = now + std::chrono::milliseconds(timeout);

        while (!checkForPoll(fds, pollfds, nfds))
            if (theCV.wait_until(lock, end) == std::cv_status::timeout)
            {
                FAKESOCKET_LOG(2, "FakeSocket Poll timeout: 0" << flush());
                return 0;
            }
    }
    else if (timeout == 0)
    {
        checkForPoll(fds, pollfds, nfds);
    }
    else // timeout < 0
    {
        while (!checkForPoll(fds, pollfds, nfds))
            theCV.wait(lock);
    }

    int result = 0;
    for (int i = 0; i < nfds; i++)
    {
        if (pollfds[i].revents != 0)
            result++;
    }

    FAKESOCKET_LOG(2, "FakeSocket Poll result: ");
    for (int i = 0; i < nfds; i++)
    {
        if (i > 0)
            FAKESOCKET_LOG(2, ',');
        FAKESOCKET_LOG(2, '#' << pollfds[i].fd << ':' << pollBits(pollfds[i].revents));
    }
    FAKESOCKET_LOG(2, ": " << result << flush());

    return result;
}

int fakeSocketListen(int fd)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd < 0 || static_cast<unsigned>(fd/2) >= fds.size() || fds[fd/2].fd[fd&1] == -1)
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Listening on #" << fd << flush());
        errno = EBADF;
        return -1;
    }

    FakeSocketPair& pair = fds[fd/2];

    if (fd&1 || pair.fd[1] != -1)
    {
        FAKESOCKET_LOG(1, "FakeSocket EISCONN: Listening on #" << fd << flush());
        errno = EISCONN;
        return -1;
    }

    if (pair.listening)
    {
        FAKESOCKET_LOG(1, "FakeSocket EIO: Listening on #" << fd << flush());
        errno = EIO;
        return -1;
    }

    pair.listening = true;
    pair.connectingFd = -1;

    FAKESOCKET_LOG(1, "FakeSocket Listen #" << fd << flush());

    return 0;
}

int fakeSocketConnect(int fd1, int fd2)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd1 < 0 || fd2 < 0 || static_cast<unsigned>(fd1/2) >= fds.size() || static_cast<unsigned>(fd2/2) >= fds.size())
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Connect #" << fd1 << " to #" << fd2 << flush());
        errno = EBADF;
        return -1;
    }
    if (fd1/2 == fd2/2)
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Connect #" << fd1 << " to #" << fd2 << flush());
        errno = EBADF;
        return -1;
    }

    FakeSocketPair& pair1 = fds[fd1/2];
    FakeSocketPair& pair2 = fds[fd2/2];

    if ((fd1&1) || (fd2&1))
    {
        FAKESOCKET_LOG(1, "FakeSocket EISCONN: Connect #" << fd1 << " to #" << fd2 << flush());
        errno = EISCONN;
        return -1;
    }

    if (!pair2.listening || pair2.connectingFd != -1)
    {
        FAKESOCKET_LOG(1, "FakeSocket ECONNREFUSED: Connect #" << fd1 << " to #" << fd2 << flush());
        errno = ECONNREFUSED;
        return -1;
    }

    pair2.connectingFd = fd1;
    theCV.notify_all();

    while (pair1.fd[1] == -1)
        theCV.wait(lock);

    assert(pair1.fd[1] == pair1.fd[0] + 1);

    FAKESOCKET_LOG(1, "FakeSocket Connect #" << fd1 << " to #" << fd2 << ": #" << pair1.fd[1] << flush());

    return 0;
}

int fakeSocketAccept4(int fd)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd < 0 || static_cast<unsigned>(fd/2) >= fds.size())
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Accept #" << fd << flush());
        errno = EBADF;
        return -1;
    }

    if (fd & 1)
    {
        FAKESOCKET_LOG(1, "FakeSocket EISCONN: Accept #" << fd << flush());
        errno = EISCONN;
        return -1;
    }

    FakeSocketPair& pair = fds[fd/2];

    if (!pair.listening)
    {
        FAKESOCKET_LOG(1, "FakeSocket EIO: Accept #" << fd << flush());
        errno = EIO;
        return -1;
    }

    while (pair.connectingFd == -1)
        theCV.wait(lock);

    assert(pair.connectingFd >= 0);
    assert(static_cast<unsigned>(pair.connectingFd/2) < fds.size());
    assert((pair.connectingFd&1) == 0);

    FakeSocketPair& pair2 = fds[pair.connectingFd/2];

    assert(pair2.fd[1] == -1);
    assert(pair2.fd[0] == pair.connectingFd);

    pair.connectingFd = -1;

    pair2.fd[1] = pair2.fd[0] + 1;

    theCV.notify_all();

    FAKESOCKET_LOG(1, "FakeSocket Accept #" << fd << ": #" << pair2.fd[1] << flush());

    fakeSocketDumpStateImpl();

    return pair2.fd[1];
}

int fakeSocketPeer(int fd)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd < 0 || static_cast<unsigned>(fd/2) >= fds.size())
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Peer of #" << fd << flush());
        errno = EBADF;
        return -1;
    }

    FakeSocketPair& pair = fds[fd/2];

    const int K = (fd&1);
    const int N = 1 - K;

    FAKESOCKET_LOG(1, "FakeSocket Peer of #" << fd << ": #" << pair.fd[N] << flush());

    return pair.fd[N];
}

ssize_t fakeSocketAvailableDataLength(int fd)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd < 0 || static_cast<unsigned>(fd/2) >= fds.size())
    {
        errno = EBADF;
        return -1;
    }

    FakeSocketPair& pair = fds[fd/2];

    // K: for this fd
    const int K = (fd&1);

    if (!pair.readable[K])
    {
        FAKESOCKET_LOG(2, "FakeSocket EAGAIN: Available data on #" << fd << flush());
        errno = EAGAIN;
        return -1;
    }

    ssize_t result = 0;
    if (pair.buffer[K].size() > 0)
        result = pair.buffer[K][0].size();

    FAKESOCKET_LOG(2, "FakeSocket Available data on #" << fd << ": " << result << flush());

    return result;
}

ssize_t fakeSocketRead(int fd, void *buf, size_t nbytes)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd < 0 || static_cast<unsigned>(fd/2) >= fds.size())
    {
        FAKESOCKET_LOG(2, "FakeSocket EBADF: Read from #" << fd << ", " << nbytes << (nbytes == 1 ? " byte" : " bytes") << flush());
        errno = EBADF;
        return -1;
    }

    FakeSocketPair& pair = fds[fd/2];

    // K: for this fd
    const int K = (fd&1);
    // N: for its peer
    const int N = 1 - K;

    if (pair.fd[K] == -1)
    {
        FAKESOCKET_LOG(2, "FakeSocket EBADF: Read from #" << fd << ", " << nbytes << (nbytes == 1 ? " byte" : " bytes") << flush());
        errno = EBADF;
        return -1;
    }

    if (pair.shutdown[K])
    {
        FAKESOCKET_LOG(2, "FakeSocket Read from #" << fd << " (shut down) got 0 bytes" << flush());
        return 0;
    }

    if (!pair.readable[K])
    {
        FAKESOCKET_LOG(2, "FakeSocket EAGAIN: Read from #" << fd << ", " << nbytes << (nbytes == 1 ? " byte" : " bytes") << flush());
        errno = EAGAIN;
        return -1;
    }

    ssize_t result = 0;
    if (pair.buffer[K].size() > 0)
    {
        // These sockets are record-oriented. It won't work to read less than the whole record in
        // turn to be read.
        result = pair.buffer[K][0].size();
        if (nbytes < static_cast<unsigned>(result))
        {
            FAKESOCKET_LOG(2, "FakeSocket EAGAIN: Read from #" << fd << ", " << nbytes << (nbytes == 1 ? " byte" : " bytes") << flush());
            errno = EAGAIN; // Not the right errno, but what would be?
            return -1;
        }

        memmove(buf, pair.buffer[K][0].data(), result);
        pair.buffer[K].erase(pair.buffer[K].begin());
    }

    // If peer is closed or shut down, we continue to be readable
    if (pair.fd[N] == -1 || pair.shutdown[N])
        pair.readable[K] = true;
    else if (pair.buffer[K].size() == 0)
        pair.readable[K] = false;

    FAKESOCKET_LOG(2, "FakeSocket Read from #" << fd << " got " << result << (result == 1 ? " byte" : " bytes") << flush());

    return result;
}

ssize_t fakeSocketWrite(int fd, const void *buf, size_t nbytes)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd < 0 || static_cast<unsigned>(fd/2) >= fds.size())
    {
        FAKESOCKET_LOG(2, "FakeSocket EBADF: Write to #" << fd << ", " << nbytes << (nbytes == 1 ? " byte" : " bytes") << flush());
        errno = EBADF;
        return -1;
    }

    FakeSocketPair& pair = fds[fd/2];

    // K: for this fd
    // N: for its peer, whose read buffer we want to write into
    const int K = (fd&1);
    const int N = 1 - K;

    if (pair.fd[K] == -1)
    {
        FAKESOCKET_LOG(2, "FakeSocket EBADF: Write to #" << fd << ", " << nbytes << (nbytes == 1 ? " byte" : " bytes") << flush());
        errno = EBADF;
        return -1;
    }

    if (pair.shutdown[K])
    {
        // Should we raise(SIGPIPE)? Probably not, Online code does not expect SIGPIPE at all...
        FAKESOCKET_LOG(2, "FakeSocket EPIPE: Write to #" << fd << " (shut down), " << nbytes << (nbytes == 1 ? " byte" : " bytes") << flush());
        errno = EPIPE;
        return -1;
    }

    pair.buffer[N].emplace_back(std::vector<char>(nbytes));
    memmove(pair.buffer[N].back().data(), buf, nbytes);
    pair.readable[N] = true;

    theCV.notify_all();

    FAKESOCKET_LOG(2, "FakeSocket Write to #" << fd << ": " << nbytes << (nbytes == 1 ? " byte" : " bytes") << flush());
    return nbytes;
}

int fakeSocketShutdown(int fd)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd < 0 || static_cast<unsigned>(fd/2) >= fds.size())
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Shutdown #" << fd << flush());
        errno = EBADF;
        return -1;
    }

    FakeSocketPair& pair = fds[fd/2];

    const int K = (fd&1);
    const int N = 1 - K;

    if (pair.fd[K] == -1)
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Shutdown #" << fd << flush());
        errno = EBADF;
        return -1;
    }

    if (pair.fd[N] == -1)
    {
        FAKESOCKET_LOG(1, "FakeSocket ENOTCONN: Shutdown #" << fd << flush());
        errno = ENOTCONN;
        return -1;
    }

    pair.shutdown[K] = true;
    pair.readable[K] = true;

    theCV.notify_all();

    FAKESOCKET_LOG(1, "FakeSocket Shutdown #" << fd << flush());

    return 0;
}

int fakeSocketClose(int fd)
{
    std::vector<FakeSocketPair>& fds = getFds();
    std::unique_lock<std::mutex> lock(theMutex);
    if (fd < 0 || static_cast<unsigned>(fd/2) >= fds.size())
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Close #" << fd << flush());
        errno = EBADF;
        return -1;
    }

    FakeSocketPair& pair = fds[fd/2];

    const int K = (fd&1);
    const int N = 1 - K;

    if (pair.fd[K] == -1)
    {
        FAKESOCKET_LOG(1, "FakeSocket EBADF: Close #" << fd << flush());
        errno = EBADF;
        return -1;
    }

    assert(pair.fd[K] == fd);

    pair.fd[K] = -1;
    pair.buffer[K].resize(0);
    pair.readable[N] = true;

    theCV.notify_all();

    FAKESOCKET_LOG(1, "FakeSocket Close #" << fd << flush());

    fakeSocketDumpStateImpl();

    return 0;
}

static void fakeSocketDumpStateImpl()
{
    std::vector<FakeSocketPair>& fds = getFds();
    FAKESOCKET_LOG(1, "FakeSocket open sockets:" << flush());
    for (int i = 0; i < static_cast<int>(fds.size()); i++)
    {
        if (fds[i].fd[0] != -1)
        {
            assert(fds[i].fd[0] == i*2);
            FAKESOCKET_LOG(1, "  #" << fds[i].fd[0]);
            if (fds[i].fd[1] != -1)
            {
                assert(fds[i].fd[1] == i*2+1);
                assert(!fds[i].listening);
                FAKESOCKET_LOG(1, " <=> #" << fds[i].fd[1]);
            }
            else if (fds[i].listening)
            {
                FAKESOCKET_LOG(1, " listening");
            }
            FAKESOCKET_LOG(1, flush());
        }
        else if (fds[i].fd[1] != -1)
        {
            assert(fds[i].fd[1] == i*2+1);
            assert(!fds[i].listening);
            FAKESOCKET_LOG(1, "  #" << fds[i].fd[1] << flush());
        }
    }
}

void fakeSocketDumpState()
{
    std::unique_lock<std::mutex> lock(theMutex);
    fakeSocketDumpStateImpl();
}

/* vim:set shiftwidth=4 softtabstop=4 expandtab: */