// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_LOGGING_H
#define BITCOIN_LOGGING_H

#include <crypto/siphash.h>
#include <logging/categories.h> // IWYU pragma: export
#include <span.h>
#include <util/byte_units.h>
#include <util/fs.h>
#include <util/log.h> // IWYU pragma: export
#include <util/stdmutex.h>
#include <util/string.h>
#include <util/time.h>

#include <atomic>
#include <cstdint>
#include <cstring>
#include <functional>
#include <list>
#include <memory>
#include <optional>
#include <string>
#include <unordered_map>
#include <vector>

static const bool DEFAULT_LOGTIMEMICROS = false;
static const bool DEFAULT_LOGIPS        = false;
static const bool DEFAULT_LOGTIMESTAMPS = true;
static const bool DEFAULT_LOGTHREADNAMES = false;
static const bool DEFAULT_LOGSOURCELOCATIONS = false;
static constexpr bool DEFAULT_LOGLEVELALWAYS = false;
extern const char * const DEFAULT_DEBUGLOGFILE;

extern bool fLogIPs;

struct SourceLocationEqual {
    bool operator()(const SourceLocation& lhs, const SourceLocation& rhs) const noexcept
    {
        return lhs.line() == rhs.line() && std::string_view(lhs.file_name()) == std::string_view(rhs.file_name());
    }
};

struct SourceLocationHasher {
    size_t operator()(const SourceLocation& s) const noexcept
    {
        // Use CSipHasher(0, 0) as a simple way to get uniform distribution.
        return size_t(CSipHasher(0, 0)
                      .Write(s.line())
                      .Write(MakeUCharSpan(std::string_view{s.file_name()}))
                      .Finalize());
    }
};

struct LogCategory {
    std::string category;
    bool active;
};

namespace BCLog {
    constexpr auto DEFAULT_LOG_LEVEL{Level::Debug};
    constexpr size_t DEFAULT_MAX_LOG_BUFFER{1'000'000}; // buffer up to 1MB of log data prior to StartLogging
    constexpr uint64_t RATELIMIT_MAX_BYTES{1_MiB}; // maximum number of bytes per source location that can be logged within the RATELIMIT_WINDOW
    constexpr auto RATELIMIT_WINDOW{1h}; // time window after which log ratelimit stats are reset
    constexpr bool DEFAULT_LOGRATELIMIT{true};

    //! Fixed window rate limiter for logging.
    class LogRateLimiter
    {
    public:
        //! Keeps track of an individual source location and how many available bytes are left for logging from it.
        struct Stats {
            //! Remaining bytes
            uint64_t m_available_bytes;
            //! Number of bytes that were consumed but didn't fit in the available bytes.
            uint64_t m_dropped_bytes{0};

            Stats(uint64_t max_bytes) : m_available_bytes{max_bytes} {}
            //! Updates internal accounting and returns true if enough available_bytes were remaining
            bool Consume(uint64_t bytes);
        };

    private:
        mutable StdMutex m_mutex;

        //! Stats for each source location that has attempted to log something.
        std::unordered_map<SourceLocation, Stats, SourceLocationHasher, SourceLocationEqual> m_source_locations GUARDED_BY(m_mutex);
        //! Whether any log locations are suppressed. Cached view on m_source_locations for performance reasons.
        std::atomic<bool> m_suppression_active{false};
        LogRateLimiter(uint64_t max_bytes, std::chrono::seconds reset_window);

    public:
        using SchedulerFunction = std::function<void(std::function<void()>, std::chrono::milliseconds)>;
        /**
         * @param scheduler_func    Callable object used to schedule resetting the window. The first
         *                          parameter is the function to be executed, and the second is the
         *                          reset_window interval.
         * @param max_bytes         Maximum number of bytes that can be logged for each source
         *                          location.
         * @param reset_window      Time window after which the stats are reset.
         */
        static std::shared_ptr<LogRateLimiter> Create(
            SchedulerFunction&& scheduler_func,
            uint64_t max_bytes,
            std::chrono::seconds reset_window);
        //! Maximum number of bytes logged per location per window.
        const uint64_t m_max_bytes;
        //! Interval after which the window is reset.
        const std::chrono::seconds m_reset_window;
        //! Suppression status of a source log location.
        enum class Status {
            UNSUPPRESSED,     // string fits within the limit
            NEWLY_SUPPRESSED, // suppression has started since this string
            STILL_SUPPRESSED, // suppression is still ongoing
        };
        //! Consumes `source_loc`'s available bytes corresponding to the size of the (formatted)
        //! `str` and returns its status.
        [[nodiscard]] Status Consume(
            const SourceLocation& source_loc,
            const std::string& str) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
        //! Resets all usage to zero. Called periodically by the scheduler.
        void Reset() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
        //! Returns true if any log locations are currently being suppressed.
        bool SuppressionsActive() const { return m_suppression_active; }
    };

    class Logger
    {
    private:
        mutable StdMutex m_cs; // Can not use Mutex from sync.h because in debug mode it would cause a deadlock when a potential deadlock was detected

        FILE* m_fileout GUARDED_BY(m_cs) = nullptr;
        std::list<util::log::Entry> m_msgs_before_open GUARDED_BY(m_cs);
        bool m_buffering GUARDED_BY(m_cs) = true; //!< Buffer messages before logging can be started.
        size_t m_max_buffer_memusage GUARDED_BY(m_cs){DEFAULT_MAX_LOG_BUFFER};
        size_t m_cur_buffer_memusage GUARDED_BY(m_cs){0};
        size_t m_buffer_lines_discarded GUARDED_BY(m_cs){0};

        //! Manages the rate limiting of each log location.
        std::shared_ptr<LogRateLimiter> m_limiter GUARDED_BY(m_cs);

        //! Category-specific log level. Overrides `m_log_level`.
        std::unordered_map<LogFlags, Level> m_category_log_levels GUARDED_BY(m_cs);

        //! If there is no category-specific log level, all logs with a severity
        //! level lower than `m_log_level` will be ignored.
        std::atomic<Level> m_log_level{DEFAULT_LOG_LEVEL};

        /** Log categories bitfield. */
        std::atomic<CategoryMask> m_categories{BCLog::NONE};

        std::string Format(const util::log::Entry& entry) const;

        std::string LogTimestampStr(SystemClock::time_point now, std::chrono::seconds mocktime) const;

        /** Slots that connect to the print signal */
        std::list<std::function<void(const std::string&)>> m_print_callbacks GUARDED_BY(m_cs){};

        /** Send an entry to the log output (internal) */
        void LogPrint_(util::log::Entry log_entry) EXCLUSIVE_LOCKS_REQUIRED(m_cs);

        std::string GetLogPrefix(LogFlags category, Level level) const;

    public:
        bool m_print_to_console = false;
        bool m_print_to_file = false;

        bool m_log_timestamps = DEFAULT_LOGTIMESTAMPS;
        bool m_log_time_micros = DEFAULT_LOGTIMEMICROS;
        bool m_log_threadnames = DEFAULT_LOGTHREADNAMES;
        bool m_log_sourcelocations = DEFAULT_LOGSOURCELOCATIONS;
        bool m_always_print_category_level = DEFAULT_LOGLEVELALWAYS;

        fs::path m_file_path;
        std::atomic<bool> m_reopen_file{false};

        /** Send an entry to the log output */
        void LogPrint(util::log::Entry log_entry) EXCLUSIVE_LOCKS_REQUIRED(!m_cs);

        /** Returns whether logs will be written to any output */
        bool Enabled() const EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
        {
            STDLOCK(m_cs);
            return m_buffering || m_print_to_console || m_print_to_file || !m_print_callbacks.empty();
        }

        /** Connect a slot to the print signal and return the connection */
        std::list<std::function<void(const std::string&)>>::iterator PushBackCallback(std::function<void(const std::string&)> fun) EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
        {
            STDLOCK(m_cs);
            m_print_callbacks.push_back(std::move(fun));
            return --m_print_callbacks.end();
        }

        /** Delete a connection */
        void DeleteCallback(std::list<std::function<void(const std::string&)>>::iterator it) EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
        {
            STDLOCK(m_cs);
            m_print_callbacks.erase(it);
        }

        size_t NumConnections() EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
        {
            STDLOCK(m_cs);
            return m_print_callbacks.size();
        }

        /** Start logging (and flush all buffered messages) */
        bool StartLogging() EXCLUSIVE_LOCKS_REQUIRED(!m_cs);
        /** Only for testing */
        void DisconnectTestLogger() EXCLUSIVE_LOCKS_REQUIRED(!m_cs);

        void SetRateLimiting(std::shared_ptr<LogRateLimiter> limiter) EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
        {
            STDLOCK(m_cs);
            m_limiter = std::move(limiter);
        }

        /** Disable logging
         * This offers a slight speedup and slightly smaller memory usage
         * compared to leaving the logging system in its default state.
         * Mostly intended for libbitcoin-kernel apps that don't want any logging.
         * Should be used instead of StartLogging().
         */
        void DisableLogging() EXCLUSIVE_LOCKS_REQUIRED(!m_cs);

        void ShrinkDebugFile() EXCLUSIVE_LOCKS_REQUIRED(!m_cs);

        std::unordered_map<LogFlags, Level> CategoryLevels() const EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
        {
            STDLOCK(m_cs);
            return m_category_log_levels;
        }
        void SetCategoryLogLevel(const std::unordered_map<LogFlags, Level>& levels) EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
        {
            STDLOCK(m_cs);
            m_category_log_levels = levels;
        }
        void AddCategoryLogLevel(LogFlags category, Level level) EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
        {
            STDLOCK(m_cs);
            m_category_log_levels[category] = level;
        }
        bool SetCategoryLogLevel(std::string_view category_str, std::string_view level_str) EXCLUSIVE_LOCKS_REQUIRED(!m_cs);

        Level LogLevel() const { return m_log_level.load(); }
        void SetLogLevel(Level level) { m_log_level = level; }
        bool SetLogLevel(std::string_view level);

        CategoryMask GetCategoryMask() const { return m_categories.load(); }

        void EnableCategory(LogFlags flag);
        bool EnableCategory(std::string_view str);
        void DisableCategory(LogFlags flag);
        bool DisableCategory(std::string_view str);

        bool WillLogCategory(LogFlags category) const;
        bool WillLogCategoryLevel(LogFlags category, Level level) const EXCLUSIVE_LOCKS_REQUIRED(!m_cs);

        /** Returns a vector of the log categories in alphabetical order. */
        std::vector<LogCategory> LogCategoriesList() const;
        /** Returns a string with the log categories in alphabetical order. */
        std::string LogCategoriesString() const
        {
            return util::Join(LogCategoriesList(), ", ", [&](const LogCategory& i) { return i.category; });
        };

        //! Returns a string with all user-selectable log levels.
        std::string LogLevelsString() const;

        //! Returns the string representation of a log level.
        static std::string LogLevelToStr(BCLog::Level level);

        bool DefaultShrinkDebugFile() const;

        //! Return log flag if str parses as a log category.
        static std::optional<BCLog::LogFlags> GetLogCategory(std::string_view str);
    };
} // namespace BCLog

BCLog::Logger& LogInstance();

#endif // BITCOIN_LOGGING_H
