/* Copyright (C) 2014
 * Swift Project Community / Contributors
 *
 * This file is part of Swift Project. It is subject to the license terms in the LICENSE file found in the top-level
 * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
 * including this file, may be copied, modified, propagated, or distributed except according to the terms
 * contained in the LICENSE file.
 */

#ifndef BLACKMISC_LOGMESSAGE_H
#define BLACKMISC_LOGMESSAGE_H

//! \file

#include "blackmiscexport.h"
#include "statusmessagelist.h"
#include "statusmessage.h"
#include "logcategorylist.h"
#include "indexsequence.h"
#include <QDebug>
#include <QLoggingCategory>
#include <QList>
#include <type_traits>

namespace BlackMisc
{
    /*!
     * Trait to detect whether T contains a member toQString.
     */
    template <typename T>
    class HasToQString
    {
        // http://en.wikibooks.org/wiki/More_C++_Idioms/Member_Detector
        struct Fallback { int toQString; };
        template <int Fallback:: *> struct int_t { typedef int type; };
        template <typename U, bool = std::is_class<U>::value> struct Derived : public U, public Fallback {};
        template <typename U> struct Derived<U, false> : public Fallback {};
        template <typename U> static char test(typename int_t<&Derived<U>::toQString>::type);
        template <typename U> static int test(...);

    public:
        //! True if T contains a member toQString.
        static const bool value = sizeof(test<T>(0)) > 1;
    };

    /*!
     * Helper with static methods for dealing with metadata embedded in log message category strings.
     *
     * There are certain aspects of log messages which cannot be represented in Qt's native log message machinery.
     * Therefore we are forced to use a special encoding of the message category string to encode these aspects.
     *
     * An encoded category string consists of a plain category string with zero or more flag strings appended.
     * The plain category and the flags are all separated by forward-slash characters ('/').
     *
     * There are currently two flags:
     * \li \c "debug" Qt only has 3 ordinary severities (debug, warning, critical), so we use QtMsgDebug for both
     *                debug and info messages, and we use this flag to distinguish between them.
     * \li \c "redundant" To avoid handling the same message twice, this flag identifies a message which has already
     *                    been directly returned as the return value of the method which generated it.
     */
    class BLACKMISC_EXPORT CLogMessageHelper
    {
    public:
        //! Deleted constructor.
        CLogMessageHelper() = delete;

        //! Returns an encoded category string with the debug flag appended.
        static QString addDebugFlag(const QString &category);

        //! Returns an encoded category string with the redundant flag appended.
        static QString addRedundantFlag(const QString &category);

        //! Strips all flags from an encoded category string, returning only the plain category string.
        static QString stripFlags(const QString &category);

        //! Returns true if the given encoded category string has the debug flag.
        static bool hasDebugFlag(const QString &category);

        //! Returns true if the given encoded category string has the redundant flag.
        static bool hasRedundantFlag(const QString &category);
    };

    /*!
     * Class for emitting a log message. Works similar to the qDebug, qWarning, qCritical family of functions.
     *
     * The member functions debug, info, warning, error, and the stream operators all return a reference to <tt>*this</tt>,
     * so they can be chained together.
     *
     * The categories are arbitrary string tags which can be attached to the message to categorize it.
     * A message can have more than one category. The categories can be used for filtering by message handlers.
     */
    class BLACKMISC_EXPORT CLogMessage
    {
    public:
        //! Construct a message with the "uncategorized" category.
        CLogMessage() {}

        //! Constructor taking filename, line number, and function name, for uncategorized verbose debug messages.
        CLogMessage(const char *file, int line, const char *function) : m_logger(file, line, function) {}

        //! Construct a message with some specific category.
        CLogMessage(const CLogCategory &category) : m_categories({ category }) {}

        //! Construct a message with some specific categories.
        CLogMessage(const CLogCategoryList &categories) : m_categories(categories) {}

        //! Construct a message with some specific categories.
        CLogMessage(const CLogCategoryList &categories, const CLogCategory &extra) : CLogMessage(categories) { m_categories.push_back(extra); }

        //! Construct a message with some specific categories.
        CLogMessage(const CLogCategoryList &categories, const CLogCategoryList &extra) : CLogMessage(categories) { m_categories.push_back(extra); }

        //! Destructor. This actually emits the message.
        ~CLogMessage();

        //! Convert to CStatusMessage for returning the message directly from the function which generated it.
        operator CStatusMessage();

        //! Convert to CVariant for returning the message directly from the function which generated it.
        operator CVariant();

        //! Set the severity to debug.
        CLogMessage &debug();

        //! Set the severity to info, providing a format string.
        CLogMessage &info(QString format);

        //! Set the severity to warning, providing a format string.
        CLogMessage &warning(QString format);

        //! Set the severity to error, providing a format string.
        CLogMessage &error(QString format);

        //! Set the severity to info, providing a format string, and adding the validation category.
        CLogMessage &validationInfo(QString format);

        //! Set the severity to warning, providing a format string, and adding the validation category.
        CLogMessage &validationWarning(QString format);

        //! Set the severity to error, providing a format string, and adding the validation category.
        CLogMessage &validationError(QString format);

        //! Streaming operators.
        //! \details If the format string is empty, the message will consist of all streamed values separated by spaces.
        //!          Otherwise, the streamed values will replace the place markers %1, %2, %3... in the format string.
        //! \see QString::arg
        //! @{
        CLogMessage &operator <<(const QString &v) { return arg(v); }
        CLogMessage &operator <<(int v) { return arg(QString::number(v)); }
        CLogMessage &operator <<(uint v) { return arg(QString::number(v)); }
        CLogMessage &operator <<(long v) { return arg(QString::number(v)); }
        CLogMessage &operator <<(ulong v) { return arg(QString::number(v)); }
        CLogMessage &operator <<(qlonglong v) { return arg(QString::number(v)); }
        CLogMessage &operator <<(qulonglong v) { return arg(QString::number(v)); }
        CLogMessage &operator <<(short v) { return arg(QString::number(v)); }
        CLogMessage &operator <<(ushort v) { return arg(QString::number(v)); }
        CLogMessage &operator <<(QChar v) { return arg(v); }
        CLogMessage &operator <<(char v) { return arg(QChar(v)); }
        CLogMessage &operator <<(double v) { return arg(QString::number(v)); }
        template <class T, class = typename std::enable_if<HasToQString<T>::value>::type>
        CLogMessage &operator <<(const T &v) { return arg(v.toQString()); }
        //! @}

        //! Sends a verbatim, preformatted message to the log.
        static void preformatted(const CStatusMessage &statusMessage);

        //! Sends a list of verbatim, preformatted messages to the log.
        static void preformatted(const CStatusMessageList &statusMessages);

    private:
        QMessageLogger m_logger;
        CStatusMessage::StatusSeverity m_severity = CStatusMessage::SeverityDebug;
        CLogCategoryList m_categories = CLogCategoryList { CLogCategory::uncategorized() };
        QString m_message;
        QStringList m_args;
        bool m_redundant = false;

        CLogMessage &arg(QString value) { m_args.push_back(value); return *this; }
        QString message() const;
        QByteArray qtCategory() const;
        QDebug ostream(const QByteArray &category) const;
    };
}

/*!
 * Convenience macro to construct a CLogMessage with the filename, line number, and function name,
 * for verbose debug messages.
 */
#define BLACK_LOG (BlackMisc::CLogMessage { __FILE__, __LINE__, Q_FUNC_INFO })

#endif