// Copyright (C) 2021 The Qt Company Ltd.
// Copyright (C) 2019 Luxoft Sweden AB
// Copyright (C) 2018 Pelagicore AG
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only

#if defined(_WIN32) && (_WIN32_WINNT-0 < _WIN32_WINNT_VISTA)
// needed for QueryFullProcessImageNameW
#  undef WINVER
#  undef _WIN32_WINNT
#  define WINVER _WIN32_WINNT_VISTA
#  define _WIN32_WINNT _WIN32_WINNT_VISTA
#endif

#include <QThreadStorage>
#include <QAtomicInteger>
#include <QCoreApplication>
#include <QMutexLocker>

#include "global.h"
#include "logging.h"
#include "utilities.h"
#include "unixsignalhandler.h"

#include <stdio.h>

#if defined(Q_OS_WIN)
#  include <windows.h>
#  include <io.h>
#  include <QOperatingSystemVersion>
#  include <QThread>

Q_CORE_EXPORT void qWinMsgHandler(QtMsgType t, const char* str);
#else
#  include <unistd.h>
#  include <sys/ioctl.h>
#  include <termios.h>
#  include <signal.h>
#  if defined(Q_OS_MACOS)
#    include <libproc.h>
#  endif
#endif
#if defined(Q_OS_ANDROID)
#  include <QCoreApplication>
#  include <android/log.h>
#endif

#if defined(AM_USE_DLTLOGGING)
#  include <QtDltLogging/QtDlt>
#  include <QtDltLogging/QDltRegistration>
#else
#  define QDLT_LOGGING_CATEGORY(a,b,c,d) Q_LOGGING_CATEGORY(a,b)
#  define QDLT_FALLBACK_CATEGORY(a)
#  define QDLT_REGISTER_APPLICATION(a,b)
#endif

#ifndef QDLT_REGISTER_CONTEXT_ON_FIRST_USE
#  define QDLT_REGISTER_CONTEXT_ON_FIRST_USE(a)
#endif

QT_BEGIN_NAMESPACE_AM

#if defined(AM_USE_DLTLOGGING)
static constexpr const char *s_defaultSystemUiDltId = "QTAM";
static constexpr const char *s_defaultSystemUiDltDescription = "Qt Application Manager";
#endif

/*
//! [am-logging-categories]
\table
\header
    \li Category
    \li DLT Context ID
    \li Description
\row
    \li \c am.system
    \li \c SYS
    \li General system messages
\row
    \li \c am.installer
    \li \c INST
    \li Installer sub-system messages
\row
    \li \c am.graphics
    \li \c GRPH
    \li OpenGL/UI related messages
\row
    \li \c am.wayland.debug
    \li \c WAYL
    \li Wayland related messages
\row
    \li \c am.qml
    \li \c QML
    \li General QML related messages
\row
    \li \c am.runtime
    \li \c RT
    \li Runtime messages
\row
    \li \c am.runtime.qml
    \li \c QMRT
    \li QML runtime messages
\row
    \li \c am.notify
    \li \c NTFY
    \li Notification sub-system messages
\row
    \li \c am.deployment
    \li \c DPLM
    \li Deployment hints
\row
    \li \c am.intent
    \li \c INTN
    \li Intent sub-system messages
\row
    \li \c am.cache
    \li \c CACH
    \li Cache sub-system messages
\row
    \li \c general
    \li \c GEN
    \li Used for DLT logging only and enabled by default. Categories that have no context ID
        mapping in DLT default to \c GEN; this includes uncategorized logging.
\endtable
//! [am-logging-categories]
*/
QDLT_REGISTER_CONTEXT_ON_FIRST_USE(true)
QDLT_REGISTER_APPLICATION(s_defaultSystemUiDltId, s_defaultSystemUiDltDescription)
QDLT_LOGGING_CATEGORY(LogSystem, "am.system", "SYS", "General system messages")
QDLT_LOGGING_CATEGORY(LogInstaller, "am.installer", "INST", "Installer sub-system messages")
QDLT_LOGGING_CATEGORY(LogGraphics, "am.graphics", "GRPH", "OpenGL/UI related messages")
QDLT_LOGGING_CATEGORY(LogWaylandDebug, "am.wayland.debug", "WAYL", "Wayland related messages")
QDLT_LOGGING_CATEGORY(LogQml, "am.qml", "QML", "General QML related messages")
QDLT_LOGGING_CATEGORY(LogRuntime, "am.runtime", "RT", "Runtime messages")
QDLT_LOGGING_CATEGORY(LogQmlRuntime, "am.runtime.qml", "QMRT", "QML runtime messages")
QDLT_LOGGING_CATEGORY(LogNotifications, "am.notify", "NTFY", "Notifications sub-system messages")
QDLT_LOGGING_CATEGORY(LogDeployment, "am.deployment", "DPLM", "Deployment hints")
QDLT_LOGGING_CATEGORY(LogIntents, "am.intent", "INTN", "Intents sub-system messages")
QDLT_LOGGING_CATEGORY(LogCache, "am.cache", "CACH", "Cache sub-system messages")
QDLT_LOGGING_CATEGORY(LogGeneral, "general", "GEN", "Messages without dedicated context ID (fallback)")
QDLT_FALLBACK_CATEGORY(LogGeneral)


struct DeferredMessage
{
    DeferredMessage(QtMsgType _msgType, const QMessageLogContext &_context, const QString &_message);
    DeferredMessage(DeferredMessage &&other) Q_DECL_NOEXCEPT;
    ~DeferredMessage();

    QtMsgType msgType;
    int line;
    const char *file;
    const char *function;
    const char *category;
    const QString message;
};

struct LoggingGlobal
{
    bool dltEnabled =
#if defined(AM_USE_DLTLOGGING)
            true;
#else
            false;
#endif
    bool messagePatternDefined = false;
    bool useAMConsoleLogger = false;
    bool noCustomLogging = false;
    QStringList rules;
    QtMessageHandler defaultQtHandler = nullptr;
    QByteArray applicationId;
    QVariant useAMConsoleLoggerConfig;
    QString dltLongMessageBehavior;

    QMutex deferredMessagesMutex;
    std::vector<DeferredMessage> deferredMessages;

    ~LoggingGlobal();
};

Q_GLOBAL_STATIC(LoggingGlobal, lg)

DeferredMessage::DeferredMessage(QtMsgType _msgType, const QMessageLogContext &_context, const QString &_message)
    : msgType(_msgType)
    , line(_context.line)
    , message(_message)
{
    file = qstrdup(_context.file);
    function = qstrdup(_context.function);
    category = qstrdup(_context.category);
}

DeferredMessage::DeferredMessage(DeferredMessage &&other) Q_DECL_NOEXCEPT
    : msgType(other.msgType)
    , line(other.line)
    , file(other.file)
    , function(other.function)
    , category(other.category)
    , message(other.message)
{
    other.file = nullptr;
    other.function = nullptr;
    other.category = nullptr;
}

DeferredMessage::~DeferredMessage()
{
    delete[] file;
    delete[] function;
    delete[] category;
}


static void colorLogToStderr(QtMsgType msgType, const QMessageLogContext &context, const QString &message)
{
    if (msgType < QtDebugMsg || msgType > QtInfoMsg)
        msgType = QtCriticalMsg;

    // Try to re-use a 512 byte buffer per thread as much as possible to avoid allocations.
    static QThreadStorage<QByteArray> outBuffers;
    QByteArray &out = outBuffers.localData();
    if (out.capacity() > 512)
        out.clear();
    if (!out.capacity())
        out.reserve(512);
    out.resize(0);

    int consoleWidth = Console::width();

    // Find out, if we have a valid code location and prepare the output strings
    const char *filename = nullptr;
    int filenameLength = 0;
    char linenumber[8];
    int linenumberLength = 0;

    if (context.line > 0 && context.file && context.file[0]) {
        QByteArray ba = QByteArray::fromRawData(context.file, int(qstrlen(context.file)));
        int pos = -1;
#if defined(Q_OS_WIN)
        pos = ba.lastIndexOf('\\');
#endif
        if (pos < 0)
            pos = ba.lastIndexOf('/');

        filename = context.file + pos + 1;
        filenameLength = ba.size() - pos - 1;

        linenumberLength = qsnprintf(linenumber, 8, "%d", qMin(context.line, 9999999));
        if (linenumberLength < 0 || linenumberLength >= int(sizeof(linenumber)))
            linenumberLength = 0;
        linenumber[linenumberLength] = 0;
    }

    static const char *msgTypeStr[] = { "DBG ", "WARN", "CRIT", "FATL", "INFO" };
    static const Console::Color msgTypeColor[] = { Console::Green, Console::Yellow, Console::Red,
                                                   Console::Magenta, Console::Blue };
    int categoryLength = int(qstrlen(context.category));
    QByteArray msg = message.toLocal8Bit(); // sadly this allocates, but there's no other way in Qt

    // the visible character length
    int outLength = 10 + int(qstrlen(context.category)) + msg.length(); // 10 = strlen("[XXXX | ] ")
    out.append('[');

    Console::colorize(out, Console::BrightFlag | msgTypeColor[msgType]);
    out.append(msgTypeStr[msgType], 4); // all msgTypeStrs are 4 characters
    Console::colorize(out, Console::Off);

    out.append(" | ");

    Console::colorize(out, Console::Red + qHash(QByteArray::fromRawData(context.category, categoryLength)) % 7);
    out.append(context.category, categoryLength);
    Console::colorize(out, Console::Off);

    const QByteArray appId = Logging::applicationId();
    if (!appId.isEmpty()) {
        out.append(" | ");

        Console::colorize(out, Console::Red + qHash(appId) % 7);
        out.append(appId);
        Console::colorize(out, Console::Off);

        outLength += (3 + appId.length()); // 3 == strlen(" | ")
    }

    out.append("] ");
    out.append(msg);

    if (filenameLength && linenumberLength) {
        int spacing = 1;
        if (consoleWidth > 0) {
            // right-align the location mark
            spacing = consoleWidth - outLength - linenumberLength - filenameLength - 4; // 4 == strlen(" [:]")

            // keep the location mark right-aligned, even if the message contains newlines
            int lastNewline = msg.lastIndexOf('\n');
            if (lastNewline >= 0)
                spacing += (outLength - msg.length() + lastNewline + 1);

            // keep the location mark right-aligned, even if the message is longer than the window width
            while (spacing < 0)
                spacing += consoleWidth;
        }
        out.append(spacing, ' ');
        out.append('[');

        Console::colorize(out, Console::Magenta);
        out.append(filename, filenameLength);
        Console::colorize(out, Console::Off);

        out.append(':');

        Console::colorize(out, Console::BrightFlag | Console::Magenta);
        out.append(linenumber, linenumberLength);
        Console::colorize(out, Console::Off);

        out.append("]\n");
    } else {
        out.append('\n');
    }

    if (consoleWidth <= 0) {
#if defined(Q_OS_WIN)
        OutputDebugStringA(out.constData());
        return;

#elif defined(Q_OS_ANDROID)
        android_LogPriority pri = ANDROID_LOG_DEBUG;
        switch (msgType) {
        default:
        case QtDebugMsg:    pri = ANDROID_LOG_DEBUG; break;
        case QtWarningMsg:  pri = ANDROID_LOG_WARN; break;
        case QtCriticalMsg: pri = ANDROID_LOG_ERROR; break;
        case QtFatalMsg:    pri = ANDROID_LOG_FATAL; break;
        };

        static QByteArray appName = QCoreApplication::applicationName().toLocal8Bit();

        __android_log_write(pri, appName.constData(), out.constData());
        return;
#endif
    }
    fputs(out.constData(), stderr);
}

void Logging::messageHandler(QtMsgType msgType, const QMessageLogContext &context, const QString &message)
{
#if defined(AM_USE_DLTLOGGING)
    if (lg()->dltEnabled)
        QDltRegistration::messageHandler(msgType, context, message);
#endif
    if (Q_UNLIKELY(!lg()->useAMConsoleLogger))
        lg()->defaultQtHandler(msgType, context, message);
    else
        colorLogToStderr(msgType, context, message);
}

void Logging::deferredMessageHandler(QtMsgType msgType, const QMessageLogContext &context, const QString &message)
{
    QMutexLocker lock(&lg()->deferredMessagesMutex);
    lg()->deferredMessages.emplace_back(msgType, context, message);
}

void Logging::initialize()
{
    initialize(0, nullptr);
}

void Logging::initialize(int argc, const char * const *argv)
{
    if (qEnvironmentVariableIntValue("AM_NO_CUSTOM_LOGGING") == 1) {
        lg()->noCustomLogging = true;
        lg()->dltEnabled = false;
        return;
    }

    if (qEnvironmentVariableIntValue("AM_NO_DLT_LOGGING") == 1)
        lg()->dltEnabled = false;

    bool instantLogging = false;
    if (argc > 0 && argv) {
        for (int i = 1; i < argc; ++i) {
            if (strcmp("--no-dlt-logging", argv[i]) == 0)
                lg()->dltEnabled = false;
            else if (strcmp("--log-instant", argv[i]) == 0)
                instantLogging = true;
        }
    }

    lg()->messagePatternDefined = qEnvironmentVariableIsSet("QT_MESSAGE_PATTERN");
    lg()->defaultQtHandler = instantLogging ? qInstallMessageHandler(messageHandler)
                                            : qInstallMessageHandler(deferredMessageHandler);
}

LoggingGlobal::~LoggingGlobal()
{
    // we do an unnecessary (but cheap) qInstallMessageHandler() at program exit, but this way
    // we cannot forget to dump the deferred messages whenever we exit
    Logging::completeSetup();
}

QStringList Logging::filterRules()
{
    return lg()->rules;
}

void Logging::setFilterRules(const QStringList &rules)
{
    lg()->rules = rules;
    QString rulesStr = rules.join(qL1C('\n'));
#if defined(AM_USE_DLTLOGGING)
    if (lg()->dltEnabled)
        rulesStr += qSL("\ngeneral=true");
#endif
    QLoggingCategory::setFilterRules(rulesStr);
}

void Logging::setMessagePattern(const QString &pattern)
{
    if (!pattern.isEmpty() && !lg()->messagePatternDefined && !lg()->noCustomLogging) {
        qputenv("QT_MESSAGE_PATTERN", pattern.toLocal8Bit()); // pass on to application processes, however for the
        qSetMessagePattern(pattern);  // System UI this might be too late, so set pattern explicitly here.
        lg()->messagePatternDefined = true;
    }
}

QVariant Logging::useAMConsoleLogger()
{
    return lg()->useAMConsoleLoggerConfig;
}

void Logging::setUseAMConsoleLogger(const QVariant &config)
{
    lg()->useAMConsoleLoggerConfig = config;
    if (lg()->useAMConsoleLoggerConfig.userType() == QMetaType::Bool)
        lg()->useAMConsoleLogger = lg()->useAMConsoleLoggerConfig.toBool();
    else
        lg()->useAMConsoleLogger = !lg()->messagePatternDefined;
}

void Logging::completeSetup()
{
    if (!lg()->noCustomLogging) {
        qInstallMessageHandler(messageHandler);

        QMutexLocker lock(&lg()->deferredMessagesMutex);
        for (const DeferredMessage &msg : lg()->deferredMessages) {
            QLoggingCategory cat(msg.category);
            if (cat.isEnabled(msg.msgType)) {
                QMessageLogContext context(msg.file, msg.line, msg.function, msg.category);
                messageHandler(msg.msgType, context, msg.message);
            }
        }
        std::vector<DeferredMessage>().swap(lg()->deferredMessages);
    }
}

QByteArray Logging::applicationId()
{
    return lg()->applicationId;
}

void Logging::setApplicationId(const QByteArray &appId)
{
    lg()->applicationId = appId;
}

bool Logging::hasDeferredMessages()
{
    QMutexLocker lock(&lg()->deferredMessagesMutex);
    return !lg()->deferredMessages.empty();
}

bool Logging::isDltEnabled()
{
    return lg()->dltEnabled;
}

void Logging::setDltEnabled(bool enabled)
{
    lg()->dltEnabled = enabled;
}

void Logging::registerUnregisteredDltContexts()
{
#if defined(AM_USE_DLTLOGGING)
    if (lg()->dltEnabled)
        globalDltRegistration()->registerUnregisteredContexts();
#endif
}

void Logging::setSystemUiDltId(const QByteArray &dltAppId, const QByteArray &dltAppDescription)
{
#if defined(AM_USE_DLTLOGGING)
    if (lg()->dltEnabled) {
        const QByteArray id = dltAppId.isEmpty() ? QByteArray(s_defaultSystemUiDltId) : dltAppId;
        const QByteArray description = dltAppDescription.isEmpty() ? QByteArray(s_defaultSystemUiDltDescription)
                                                                   : dltAppDescription;
        globalDltRegistration()->registerApplication(id, description);
    }
#else
    Q_UNUSED(dltAppId)
    Q_UNUSED(dltAppDescription)
#endif
}

void Logging::setDltApplicationId(const QByteArray &dltAppId, const QByteArray &dltAppDescription)
{
#if defined(AM_USE_DLTLOGGING)
    if (lg()->dltEnabled)
        globalDltRegistration()->registerApplication(dltAppId, dltAppDescription);
#else
    Q_UNUSED(dltAppId)
    Q_UNUSED(dltAppDescription)
#endif
}

QString Logging::dltLongMessageBehavior()
{
    return lg()->dltLongMessageBehavior;
}

void Logging::setDltLongMessageBehavior(const QString &behaviorString)
{
    if (!lg()->dltEnabled)
        return;

    lg()->dltLongMessageBehavior = behaviorString;

#if defined(AM_USE_DLTLOGGING)
    QDltRegistration::LongMessageBehavior behavior = QDltRegistration::LongMessageBehavior::Truncate;
    if (behaviorString == qL1S("split"))
        behavior = QDltRegistration::LongMessageBehavior::Split;
    else if (behaviorString == qL1S("pass"))
        behavior = QDltRegistration::LongMessageBehavior::Pass;

    globalDltRegistration()->setLongMessageBehavior(behavior);
#endif
}

void Logging::logToDlt(QtMsgType msgType, const QMessageLogContext &context, const QString &message)
{
#if defined(AM_USE_DLTLOGGING)
    if (lg()->dltEnabled)
        QDltRegistration::messageHandler(msgType, context, message);
#else
    Q_UNUSED(msgType)
    Q_UNUSED(context)
    Q_UNUSED(message)
#endif
}

void am_trace(QDebug)
{ }

struct ConsoleGlobal
{
    bool supportsAnsiColor = false;
    bool hasConsoleWindow = false;
    bool isRunningInQtCreator = false;
    QAtomicInt consoleWidthCached = 0;

    ConsoleGlobal();
};

Q_GLOBAL_STATIC(ConsoleGlobal, cg)

ConsoleGlobal::ConsoleGlobal()
{
    enum { ColorAuto, ColorOff, ColorOn } forceColor = ColorAuto;
    const QByteArray forceColorOutput = qgetenv("AM_FORCE_COLOR_OUTPUT");
    if (forceColorOutput == "off" || forceColorOutput == "0")
        forceColor = ColorOff;
    else if (forceColorOutput == "on" || forceColorOutput == "1")
        forceColor = ColorOn;

#if defined(Q_OS_UNIX)
    if (::isatty(STDERR_FILENO)) {
        hasConsoleWindow = true;
        supportsAnsiColor = true;
    }

#elif defined(Q_OS_WIN)
    HANDLE h = GetStdHandle(STD_ERROR_HANDLE);
    if (h != INVALID_HANDLE_VALUE) {
        // enable ANSI mode on Windows 10
        DWORD mode = 0;
        if (GetConsoleMode(h, &mode)) {
            mode |= 0x04;
            if (SetConsoleMode(h, mode)) {
                supportsAnsiColor = true;
                hasConsoleWindow = true;
            }
        }
    }
#endif

    qint64 pid = QCoreApplication::applicationPid();
    for (int level = 0; level < 5; ++level) { // only check 5 levels deep
        pid = getParentPid(pid);
        if (pid <= 1)
            break;

#if defined(Q_OS_LINUX)
        static QString checkCreator = qSL("/proc/%1/exe");
        QFileInfo fi(checkCreator.arg(pid));
        if (fi.symLinkTarget().contains(qSL("qtcreator"))) {
            isRunningInQtCreator = true;
            break;
        }
#elif defined(Q_OS_MACOS)
        static char buffer[PROC_PIDPATHINFO_MAXSIZE + 1];
        int len = proc_pidpath(pid, buffer, sizeof(buffer) - 1);
        if ((len > 0) && QByteArray::fromRawData(buffer, len).contains("Qt Creator")) {
            isRunningInQtCreator = true;
            break;
        }
#elif defined(Q_OS_WIN)
        HANDLE hProcess = OpenProcess(PROCESS_QUERY_INFORMATION | PROCESS_VM_READ, false, pid);
        if (hProcess) {
            wchar_t exeName[1024] = { 0 };
            DWORD exeNameSize = sizeof(exeName) - 1;
            if (QueryFullProcessImageNameW(hProcess, 0, exeName, &exeNameSize)) {
                if (QString::fromWCharArray(exeName, exeNameSize).contains(qSL("qtcreator.exe"))) {
                    isRunningInQtCreator = true;
                    break;
                }
            }
        }
#endif
    }

    if (forceColor != ColorAuto)
        supportsAnsiColor = (forceColor == ColorOn);
    else if (!supportsAnsiColor)
        supportsAnsiColor = isRunningInQtCreator;

#if defined(Q_OS_UNIX) && defined(SIGWINCH)
    UnixSignalHandler::instance()->install(UnixSignalHandler::RawSignalHandler, SIGWINCH, [](int) {
        // we are in a signal handler, so we just clear the cached value in the atomic int
        cg()->consoleWidthCached = 0;
    });
#elif defined(Q_OS_WIN)
    class ConsoleThread : public QThread
    {
    public:
        ConsoleThread(QObject *parent)
            : QThread(parent)
        { }

        ~ConsoleThread()
        {
            terminate();
            wait();
        }

    protected:
        void run() override
        {
            HANDLE h = GetStdHandle(STD_INPUT_HANDLE);
            DWORD mode = 0;
            if (!GetConsoleMode(h, &mode))
                return;
            if (!SetConsoleMode(h, mode | ENABLE_WINDOW_INPUT))
                return;

            INPUT_RECORD ir;
            DWORD irRead = 0;
            while (ReadConsoleInputW(h, &ir, 1, &irRead)) {
                if ((irRead == 1) && (ir.EventType == WINDOW_BUFFER_SIZE_EVENT))
                    cg()->consoleWidthCached = 0;
            }
        }
    };
    qAddPreRoutine([]() { (new ConsoleThread(QCoreApplication::instance()))->start(); });
#endif // Q_OS_WIN
}

bool Console::ensureInitialized()
{
    return cg();
}

bool Console::supportsAnsiColor()
{
    return cg()->supportsAnsiColor;
}

bool Console::isRunningInQtCreator()
{
    return cg()->isRunningInQtCreator;
}

bool Console::hasConsoleWindow()
{
    return cg()->hasConsoleWindow;
}

int Console::width()
{
    int consoleWidthCalculated = cg()->consoleWidthCached;

    if (consoleWidthCalculated <= 0) {
        if (cg()->hasConsoleWindow) {
#if defined(Q_OS_UNIX)
            struct ::winsize ws;
            if ((::ioctl(STDERR_FILENO, TIOCGWINSZ, &ws) == 0) && (ws.ws_col > 0))
                consoleWidthCalculated = ws.ws_col;
#elif defined(Q_OS_WIN)
            HANDLE h = GetStdHandle(STD_ERROR_HANDLE);
            CONSOLE_SCREEN_BUFFER_INFO csbi;
            if (GetConsoleScreenBufferInfo(h, &csbi))
                consoleWidthCalculated = csbi.dwSize.X;
#endif
        }
        cg()->consoleWidthCached = consoleWidthCalculated;
    }
    if ((consoleWidthCalculated <= 0) && cg()->isRunningInQtCreator)
        return 120;
    else
        return consoleWidthCalculated;
}

QByteArray &Console::colorize(QByteArray &out, int ansiColor, bool forceNoColor)
{
    static const char *ansiColors[] = {
        "\x1b[1m",  // bright
        "\x1b[0m",  // off
        "\x1b[30m", // black
        "\x1b[31m", // red
        "\x1b[32m", // green
        "\x1b[33m", // yellow
        "\x1b[34m", // blue
        "\x1b[35m", // magenta
        "\x1b[36m", // cyan
        "\x1b[37m" // gray
    };

    if (forceNoColor || !cg()->supportsAnsiColor)
        return out;
    if (ansiColor & BrightFlag)
        out.append(ansiColors[0]);
    if (ansiColor != BrightFlag)
        out.append(ansiColors[1 + (ansiColor & ~BrightFlag)]);
    return out;
}

QT_END_NAMESPACE_AM