/**
 * Logging with call-stack capture.
 *
 * Records carry a level, message, source location and — for severe enough
 * levels — a formatted `std::stacktrace`. Capturing a trace walks the stack and
 * reads debug information, so it is only done when the record's level is at or
 * above `options::stacktrace_from`, and the whole call is skipped when the
 * level is disabled.
 *
 * `std::stacktrace` is implemented by libstdc++ only. With GCC the module has
 * to link `stdc++exp` (the static library that implements it); the CMake target
 * takes care of that. File and line numbers in the trace come from debug
 * information, so build with `-g` (Debug or RelWithDebInfo) to see them; symbol
 * names work in any build.
 */
module;

// libc++ (the OpenRA3 toolchain) has no <stacktrace>, so this vendored copy adds
// a native fallback for the frames: Windows CaptureStackBackTrace and POSIX
// execinfo. These live in the global module fragment because they are C headers.
#if defined(_WIN32)
#define WIN32_LEAN_AND_MEAN
#define NOMINMAX
#include <windows.h>
#elif (defined(__unix__) || defined(__APPLE__)) && !defined(__EMSCRIPTEN__)
#include <execinfo.h>
#endif

export module ender.log;

import std;

export namespace ender::log {
    /** Severity of a record, ordered from most to least verbose. */
    enum class level: std::uint8_t {
        trace = 0,
        debug,
        info,
        warn,
        error,
        critical,
    };

    /** Short upper-case name of a level, for output. */
    [[nodiscard]] inline auto to_string(const level severity) -> std::string_view {
        switch (severity) {
            case level::trace: return "TRACE";
            case level::debug: return "DEBUG";
            case level::info: return "INFO";
            case level::warn: return "WARN";
            case level::error: return "ERROR";
            case level::critical: return "CRITICAL";
        }
        return "?";
    }

    /** Default timestamp rendered on a record, chrono format syntax. */
    inline constexpr std::string_view default_time_format{"%Y-%m-%d %H:%M:%S"};

    /** Logger configuration. */
    struct options {
        /** Records below this level are dropped before anything is built. */
        level minimum{level::info};
        /** Capture a stack trace for records at this level and above. */
        level stacktrace_from{level::error};
        /** Maximum number of frames kept in a captured trace. */
        std::size_t stacktrace_depth{16};
        /**
         * Frames to drop from the top of a captured trace.
         *
         * The default drops `capture_stacktrace` and `emit`, which always exist
         * as frames. The level wrappers are inlined away in optimised builds, so
         * a fixed count cannot cover them; any leading frame that belongs to
         * this module is therefore stripped by name instead, which keeps the
         * caller visible whether or not the wrappers were inlined.
         */
        std::size_t stacktrace_skip{2};
    };

    /** One log record. */
    struct record {
        level severity{level::info};
        std::string message{};
        std::string file{};
        std::uint32_t line{0};
        std::string function{};
        /** Formatted call stack; empty when it was not captured. */
        std::string stacktrace{};
        std::chrono::system_clock::time_point time{};
        std::thread::id thread{};

        [[nodiscard]] auto has_stacktrace() const -> bool { return !stacktrace.empty(); }
    };

    namespace detail {
        /**
         * Render a time point with a runtime chrono format string.
         *
         * `std::format`'s format string is compile-time only, so the spec is
         * wrapped in a replacement field and fed to `std::vformat`; a bare spec
         * would be read as literal text rather than a chrono conversion.
         */
        [[nodiscard]] inline auto format_time(const std::chrono::system_clock::time_point time,
                                              const std::string_view time_format) -> std::string {
            const auto moment = std::chrono::floor<std::chrono::seconds>(time);
            const auto pattern = std::string{"{:"}.append(time_format).append("}");
            return std::vformat(pattern, std::make_format_args(moment));
        }

        /**
         * Render one record as a human-readable block: a header line and, when
         * present, the indented stack frames. Shared by the stream sinks.
         *
         * @param time_format A chrono format string applied to the record's
         *        timestamp; defaults to the date and time of day.
         */
        [[nodiscard]] inline auto format_record(const record &entry,
                                                const std::string_view time_format = default_time_format)
            -> std::string {
            const auto stamp = format_time(entry.time, time_format);
            auto text = std::format("[{}] {:<8} {}", stamp, to_string(entry.severity), entry.message);
            if (!entry.file.empty()) {
                text += std::format("  ({}:{})", entry.file, entry.line);
            }
            text += '\n';
            if (entry.has_stacktrace()) {
                text += entry.stacktrace;
            }
            return text;
        }
    }

    /** Where records go. */
    class sink {
    public:
        virtual ~sink() = default;

        /** Receive one record; called with the logger's mutex held. */
        virtual auto write(const record &entry) -> void = 0;

        /** Flush any buffering. */
        virtual auto flush() -> void {}
    };

    /** Writes a human-readable line per record to a stream (stderr by default). */
    class console_sink final: public sink {
    public:
        explicit console_sink(std::ostream &stream = std::cerr,
                              std::string time_format = std::string{default_time_format})
            : stream_(&stream), time_format_(std::move(time_format)) {}

        auto write(const record &entry) -> void override {
            *stream_ << detail::format_record(entry, time_format_);
            stream_->flush();
        }

    private:
        std::ostream *stream_;
        std::string time_format_;
    };

    /** Keeps every record in memory; useful for tests and in-game consoles. */
    class memory_sink final: public sink {
    public:
        auto write(const record &entry) -> void override {
            const auto lock = std::scoped_lock{mutex_};
            records_.push_back(entry);
        }

        [[nodiscard]] auto records() const -> std::vector<record> {
            const auto lock = std::scoped_lock{mutex_};
            return records_;
        }

        [[nodiscard]] auto size() const -> std::size_t {
            const auto lock = std::scoped_lock{mutex_};
            return records_.size();
        }

        auto clear() -> void {
            const auto lock = std::scoped_lock{mutex_};
            records_.clear();
        }

    private:
        mutable std::mutex mutex_;
        std::vector<record> records_;
    };

    /** Configuration for `file_sink`. */
    struct file_options {
        /** Move an existing log file aside to an archive when the sink opens it. */
        bool archive_on_open{true};
        /** Flush after every record, so the tail survives a crash. */
        bool flush_each_record{true};
        /** Rotate once the active file would grow past this many bytes; 0 disables. */
        std::size_t max_file_size{0};
        /** Keep at most this many archives, dropping the oldest first; 0 keeps them all. */
        std::size_t max_archives{0};
        /** Timestamp format used on each record's header line (chrono syntax). */
        std::string timestamp_format{std::string{default_time_format}};
        /** Chrono format for the timestamp inserted into archive names. */
        std::string archive_time_format{"%Y%m%d-%H%M%S"};
    };

    /**
     * Writes records to a file, archiving the previous one on open.
     *
     * `path` is the active file. When the sink opens it and the file already
     * holds data, that file is renamed to a timestamped archive first, so a run
     * never appends onto a previous run's log: every start begins a fresh file
     * and the old one is preserved as `<stem>.<timestamp><extension>` (`.log`
     * when the active file has no extension), where the timestamp is rendered by
     * `file_options::archive_time_format` (default `<YYYYmmdd-HHMMSS>`). The same
     * happens mid-run once the active file passes `file_options::max_file_size`.
     * `file_options::max_archives` bounds how many archives are kept.
     *
     * As with every sink, `write` is called with the logger's mutex held, so one
     * sink is safe to share; it is not safe for two processes to point at the
     * same file.
     */
    class file_sink final: public sink {
    public:
        explicit file_sink(std::filesystem::path path, const file_options options = {})
            : path_(std::move(path)), options_(options) {
            if (options_.archive_on_open && std::filesystem::exists(path_)) {
                if (std::filesystem::file_size(path_) > 0) {
                    archive_current();
                } else {
                    std::filesystem::remove(path_);
                }
            }
            open();
        }

        auto write(const record &entry) -> void override {
            const auto block = detail::format_record(entry, options_.timestamp_format);
            // Rotate before writing, but never rotate an empty file: that would
            // archive nothing and lose the record that is about to be written.
            if (options_.max_file_size > 0 && size_ > 0 && size_ + block.size() > options_.max_file_size) {
                archive_current();
                open();
            }
            stream_ << block;
            size_ += block.size();
            if (options_.flush_each_record) stream_.flush();
        }

        auto flush() -> void override {
            if (stream_.is_open()) stream_.flush();
        }

        /** The active log file. */
        [[nodiscard]] auto path() const -> const std::filesystem::path & { return path_; }

        /** Archives this sink created, oldest first. */
        [[nodiscard]] auto archives() const -> const std::vector<std::filesystem::path> & { return archives_; }

    private:
        auto open() -> void {
            stream_.clear();
            stream_.open(path_, std::ios::out | std::ios::trunc | std::ios::binary);
            size_ = 0;
        }

        auto archive_current() -> void {
            if (stream_.is_open()) stream_.close();
            const auto stamp = detail::format_time(std::chrono::system_clock::now(), options_.archive_time_format);
            // Keep the extension last: `<stem>.<timestamp><extension>`, falling
            // back to `.log` when the active file has none.
            const auto stem = path_.stem().string();
            const auto extension = path_.has_extension() ? path_.extension().string() : std::string{".log"};
            auto archive = path_.parent_path() / (stem + "." + stamp + extension);
            // Two rotations can land in the same second; disambiguate with a
            // counter rather than overwrite the earlier archive.
            for (auto counter = 1; std::filesystem::exists(archive); ++counter) {
                archive = path_.parent_path() /
                          (stem + "." + stamp + "." + std::to_string(counter) + extension);
            }
            std::filesystem::rename(path_, archive);
            archives_.push_back(archive);
            prune_archives();
        }

        auto prune_archives() -> void {
            if (options_.max_archives == 0) return;
            while (archives_.size() > options_.max_archives) {
                auto ignored = std::error_code{};
                std::filesystem::remove(archives_.front(), ignored);
                archives_.erase(archives_.begin());
            }
        }

        std::filesystem::path path_;
        file_options options_;
        std::ofstream stream_;
        std::size_t size_{0};
        std::vector<std::filesystem::path> archives_;
    };

    /*
     * <stacktrace> is not portable: libc++ has never implemented it, and only
     * libstdc++ provides it here. Where it is missing, records still carry their
     * call site through std::source_location - they simply carry no stack, and
     * everything below degrades to an empty string rather than the module
     * refusing to compile.
     *
     * CMake decides this and passes it in, rather than the module testing
     * `__cpp_lib_stacktrace` itself: feature-test macros come from the standard
     * library's headers, and `import std;` does not export them, so probing for
     * one here silently reports "absent" even on libstdc++, which has it.
     */
#ifndef ENDERLOG_HAS_STACKTRACE
#define ENDERLOG_HAS_STACKTRACE 0
#endif

#if ENDERLOG_HAS_STACKTRACE
    /** True when a frame belongs to the logging module itself. */
    [[nodiscard]] inline auto is_logger_frame(const std::stacktrace_entry &entry) -> bool {
        if (entry.description().find("ender::log") != std::string::npos) return true;
        return entry.source_file().find("ender.log.cppm") != std::string::npos;
    }

    /**
     * Render a trace as one indented line per frame.
     *
     * @param skip_logger_frames Drop leading frames belonging to this module, so
     *        the first reported frame is the caller. This is what makes the
     *        output stable across optimisation levels: in a release build the
     *        level wrappers are inlined into the caller, so counting frames
     *        alone would either over- or under-skip.
     */
    [[nodiscard]] inline auto format_stacktrace(const std::stacktrace &trace,
                                                const bool skip_logger_frames = true) -> std::string {
        if (trace.empty()) return "    <empty stacktrace>\n";

        auto first = std::size_t{0};
        if (skip_logger_frames) {
            while (first < trace.size() && is_logger_frame(trace.at(first))) ++first;
            if (first >= trace.size()) first = 0; // never hide the whole trace
        }

        auto text = std::string{};
        for (auto index = first; index < trace.size(); ++index) {
            const auto &entry = trace.at(index);
            auto description = entry.description();
            if (description.empty()) description = "<unknown>";

            auto location = std::string{};
            if (!entry.source_file().empty()) {
                location = std::format(" ({}:{})", entry.source_file(), entry.source_line());
            }
            text += std::format("    #{:<3}{}{}\n", index - first, description, location);
        }
        return text;
    }

    /** Capture and render the current call stack, innermost frame first. */
    [[nodiscard]] inline auto capture_stacktrace(const std::size_t skip = 2, const std::size_t depth = 16)
        -> std::string {
        return format_stacktrace(std::stacktrace::current(skip, depth));
    }
#else
    /**
     * libc++ fallback: capture the current call stack with the platform's own
     * backtrace API and render one indented line per frame.
     *
     * On Windows a frame is reported as `module.dll+0xRVA` (a MinGW release build
     * has DWARF, not the PDB symbols dbghelp resolves, so a module+offset is the
     * practical answer). On POSIX `backtrace_symbols` is used, which names a
     * frame when the executable was linked with `-rdynamic`.
     */
#if defined(_WIN32)
    [[nodiscard]] inline auto symbolicate_frame(void *address) -> std::string {
        const auto value = reinterpret_cast<std::uintptr_t>(address);
        HMODULE module = nullptr;
        if (GetModuleHandleExW(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
                               reinterpret_cast<LPCWSTR>(address), &module)) {
            wchar_t wide[260] = L"?";
            GetModuleFileNameW(module, wide, 260U);
            char narrow[260] = "?";
            WideCharToMultiByte(CP_UTF8, 0, wide, -1, narrow, sizeof(narrow), nullptr, nullptr);
            const char *base = std::strrchr(narrow, '\\');
            return std::format("{}+0x{:X}", base != nullptr ? base + 1 : narrow, value - reinterpret_cast<std::uintptr_t>(module));
        }
        return std::format("0x{:X}", value);
    }
#endif

    [[nodiscard]] inline auto capture_stacktrace(const std::size_t skip = 2, const std::size_t depth = 16) -> std::string {
        constexpr std::size_t max_frames = 64;
#if defined(_WIN32)
        void *frames[max_frames] = {};
        const auto want = static_cast<DWORD>(std::min(max_frames, skip + std::max<std::size_t>(depth, 1U)));
        const USHORT count = CaptureStackBackTrace(static_cast<DWORD>(skip), want, frames, nullptr);
        auto text = std::string{};
        for (USHORT index = 0; index < count; ++index) {
            text += std::format("    #{:<3}{}\n", index, symbolicate_frame(frames[index]));
        }
        return text;
#elif (defined(__unix__) || defined(__APPLE__)) && !defined(__EMSCRIPTEN__)
        void *frames[max_frames] = {};
        const int count = ::backtrace(frames, static_cast<int>(std::min(max_frames, skip + std::max<std::size_t>(depth, 1U))));
        char **symbols = ::backtrace_symbols(frames, count);
        auto text = std::string{};
        for (int index = static_cast<int>(std::min<std::size_t>(skip, static_cast<std::size_t>(count))); index < count; ++index) {
            text += std::format("    #{:<3}{}\n", index - static_cast<int>(skip),
                                symbols != nullptr ? symbols[index] : std::format("0x{:X}", reinterpret_cast<std::uintptr_t>(frames[index])));
        }
        if (symbols != nullptr) std::free(symbols);
        return text;
#else
        (void) skip;
        (void) depth;
        return {};
#endif
    }
#endif

    /**
     * The process-wide logger.
     *
     * `enabled` is an atomic read so hot paths can guard expensive message
     * construction; everything else takes the mutex.
     */
    class logger {
    public:
        [[nodiscard]] static auto instance() -> logger & {
            static logger shared;
            return shared;
        }

        auto configure(const options &config) -> void {
            const auto lock = std::scoped_lock{mutex_};
            options_ = config;
            minimum_.store(static_cast<std::uint8_t>(config.minimum), std::memory_order_relaxed);
        }

        [[nodiscard]] auto configuration() const -> options {
            const auto lock = std::scoped_lock{mutex_};
            return options_;
        }

        [[nodiscard]] auto enabled(const level severity) const -> bool {
            return static_cast<std::uint8_t>(severity) >= minimum_.load(std::memory_order_relaxed);
        }

        auto add_sink(std::shared_ptr<sink> destination) -> void {
            const auto lock = std::scoped_lock{mutex_};
            sinks_.push_back(std::move(destination));
        }

        auto set_sinks(std::vector<std::shared_ptr<sink>> destinations) -> void {
            const auto lock = std::scoped_lock{mutex_};
            sinks_ = std::move(destinations);
        }

        auto dispatch(const record &entry) -> void {
            const auto lock = std::scoped_lock{mutex_};
            for (const auto &destination: sinks_) {
                destination->write(entry);
            }
        }

    private:
        logger() { sinks_.push_back(std::make_shared<console_sink>()); }

        mutable std::mutex mutex_;
        options options_{};
        std::atomic<std::uint8_t> minimum_{static_cast<std::uint8_t>(options{}.minimum)};
        std::vector<std::shared_ptr<sink>> sinks_;
    };

    /** Apply a configuration to the process-wide logger. */
    inline auto configure(const options &config) -> void { logger::instance().configure(config); }

    /** Current configuration of the process-wide logger. */
    [[nodiscard]] inline auto current_options() -> options { return logger::instance().configuration(); }

    /** Route records to an additional sink. */
    inline auto add_sink(std::shared_ptr<sink> destination) -> void {
        logger::instance().add_sink(std::move(destination));
    }

    /**
     * Create a file sink, route records to it, and hand it back.
     *
     * The previous log at `path` is archived on open, so this never appends onto
     * an earlier run.
     *
     * @return The sink, so the caller can inspect the archives it creates.
     */
    inline auto add_file_sink(std::filesystem::path path, const file_options &options = {})
        -> std::shared_ptr<file_sink> {
        auto destination = std::make_shared<file_sink>(std::move(path), options);
        logger::instance().add_sink(destination);
        return destination;
    }

    /** Replace every sink. */
    inline auto set_sinks(std::vector<std::shared_ptr<sink>> destinations) -> void {
        logger::instance().set_sinks(std::move(destinations));
    }

    /** True when a record at this level would be emitted. */
    [[nodiscard]] inline auto enabled(const level severity) -> bool { return logger::instance().enabled(severity); }

    namespace detail {
        /** Build and dispatch one record. Not for direct use. */
        inline auto emit(const level severity, std::string message, const std::source_location location) -> void {
            auto &target = logger::instance();
            if (!target.enabled(severity)) return;

            const auto config = target.configuration();
            auto entry = record{
                .severity = severity,
                .message = std::move(message),
                .file = location.file_name(),
                .line = static_cast<std::uint32_t>(location.line()),
                .function = location.function_name(),
                .time = std::chrono::system_clock::now(),
                .thread = std::this_thread::get_id(),
            };
            if (severity >= config.stacktrace_from) {
                entry.stacktrace = capture_stacktrace(config.stacktrace_skip, config.stacktrace_depth);
            }
            target.dispatch(entry);
        }
    }

    /**
     * Emit a record.
     *
     * The source location defaults to the call site, so this reports exactly
     * where it was called from.
     */
    inline auto log(const level severity,
                    std::string message,
                    const std::source_location location = std::source_location::current()) -> void {
        detail::emit(severity, std::move(message), location);
    }

    inline auto trace(std::string message, const std::source_location location = std::source_location::current())
        -> void {
        detail::emit(level::trace, std::move(message), location);
    }

    inline auto debug(std::string message, const std::source_location location = std::source_location::current())
        -> void {
        detail::emit(level::debug, std::move(message), location);
    }

    inline auto info(std::string message, const std::source_location location = std::source_location::current())
        -> void {
        detail::emit(level::info, std::move(message), location);
    }

    inline auto warn(std::string message, const std::source_location location = std::source_location::current())
        -> void {
        detail::emit(level::warn, std::move(message), location);
    }

    /** Emits at `error`, which captures a call stack by default. */
    inline auto error(std::string message, const std::source_location location = std::source_location::current())
        -> void {
        detail::emit(level::error, std::move(message), location);
    }

    inline auto critical(std::string message, const std::source_location location = std::source_location::current())
        -> void {
        detail::emit(level::critical, std::move(message), location);
    }
}