// SPDX-License-Identifier: LGPL-3.0-only
// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

// The timeline: what the app logged, the checks that failed, the events it
// emitted, and what the agent did, in one sequence stamped with frame
// numbers and source locations, so `crafter-debug log` shows cause next to
// effect:
//
//     1790  AGENT  call Player_Fire {}
//     1838  WARN   physics  brace 17 strain 4.2 > limit      Forts3D-Brace.cpp:212
//
//     Debug::Log("net", "peer {} joined slot {}", peerId, slot);    // also LogWarn, LogError
//     Debug::Emit("MatchEnded", MatchEnded{ .winnerSlot = 1 });
//     if (!Debug::Check(mass > 0, "physics", "body {} has mass {}", id, mass)) return;
//
// The format string is checked at compile time, as std::format's is, and the
// caller's location is captured without a macro (macros don't cross
// `import`). Every function here is safe from any thread. The timeline
// keeps the last 8192 entries.
export module Crafter.Debug:Timeline;
import std;
import Crafter.Debug.Core;
import :Registry;

export namespace Crafter::Debug {
    enum class EntryKind : std::uint8_t {
        Log,
        Warn,
        Error,
        Check,
        Event,
        Agent,
        Pause,
        Stdio,
    };

    // "log", "warn", "error", "check", "event", "agent", "pause", "stdio".
    std::string_view EntryKindName(EntryKind kind);

    struct TimelineEntry {
        // 0 for a check failure that was counted but not stored (see Check).
        std::uint64_t sequence = 0;
        std::uint64_t frame = 0;
        // Since the timeline started, on the steady clock.
        double seconds = 0;
        EntryKind kind = EntryKind::Log;
        // The log category, or an event's name.
        std::string category;
        std::string message;
        std::string file;
        std::uint32_t line = 0;
        // An event's payload.
        Value payload;
        // For a check: its site's failures so far, this one included.
        std::uint64_t count = 1;
    };

    // A format string and where it was written, captured at the call site.
    template<class... A>
    struct LocFmt {
        std::format_string<A...> format;
        std::source_location location;

        template<class S>
            requires std::convertible_to<const S&, std::string_view>
        consteval LocFmt(const S& text, std::source_location where = std::source_location::current()) : format(text), location(where) {}
    };
}

export namespace Crafter::Debug::Detail {
    // 0 for information (log, event, agent, pause, stdio), 1 for warn, 2 for
    // error and check: what `log --level` compares against.
    std::uint8_t Level(EntryKind kind);

    struct TimelineQuery {
        // Only entries after this sequence number: what a follower has seen.
        std::uint64_t afterSequence = 0;
        std::optional<std::uint64_t> sinceFrame;
        // The newest this many of the matches; 0 for all of them.
        std::size_t last = 0;
        std::uint8_t minLevel = 0;
        // A glob on the category; empty for any.
        std::string category;
        // A substring of the message or the category; empty for any.
        std::string grep;
        // Empty for any kind.
        std::vector<EntryKind> kinds;
    };

    // Whether one entry passes a query's filters (all but `last`), for a
    // follower that sees entries one at a time.
    bool Matches(const TimelineQuery& query, const TimelineEntry& entry);

    struct CheckSite {
        std::string file;
        std::uint32_t line = 0;
        std::string category;
        std::uint64_t failures = 0;
    };

    class Timeline {
    public:
        static Timeline& Instance();

        // Stamps the entry with its sequence, frame and time, stores it and
        // tells the listener. Returns its sequence number.
        std::uint64_t Append(TimelineEntry entry);
        // A failed Check. Counted per site; stored while the site has failed
        // at most ten times and then at every power of two, so a check that
        // fails every frame cannot push everything else out. The listener
        // hears every failure, stored or not.
        void RecordCheck(std::string_view category, std::string message, const std::source_location& location);

        std::vector<TimelineEntry> Query(const TimelineQuery& query) const;
        std::uint64_t LastSequence() const;
        std::vector<CheckSite> CheckSites() const;

        // Called with every stored entry and every check failure, on the
        // thread that recorded it, after the timeline's lock is released:
        // the session uses it to pause on a check and to wake followers.
        void SetListener(std::function<void(const TimelineEntry&)> listener);

    private:
        mutable std::mutex mutex;
        std::deque<TimelineEntry> entries;
        std::uint64_t nextSequence = 1;
        struct SiteCount {
            std::string category;
            std::uint64_t failures = 0;
        };
        std::map<std::pair<std::string, std::uint32_t>, SiteCount> checks;
        std::shared_ptr<const std::function<void(const TimelineEntry&)>> listener;
        std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();

        void Notify(const TimelineEntry& entry) const;
    };

    TimelineEntry MakeEntry(EntryKind kind, std::string_view category, std::string message, const std::source_location& location, Value payload = {});
}

export namespace Crafter::Debug {
    template<class... A>
    void Log(std::string_view category, LocFmt<std::type_identity_t<A>...> format, A&&... args) {
        Detail::Timeline::Instance().Append(Detail::MakeEntry(EntryKind::Log, category, std::format(format.format, std::forward<A>(args)...), format.location));
    }

    template<class... A>
    void LogWarn(std::string_view category, LocFmt<std::type_identity_t<A>...> format, A&&... args) {
        Detail::Timeline::Instance().Append(Detail::MakeEntry(EntryKind::Warn, category, std::format(format.format, std::forward<A>(args)...), format.location));
    }

    template<class... A>
    void LogError(std::string_view category, LocFmt<std::type_identity_t<A>...> format, A&&... args) {
        Detail::Timeline::Instance().Append(Detail::MakeEntry(EntryKind::Error, category, std::format(format.format, std::forward<A>(args)...), format.location));
    }

    // A soft assert: returns `ok`, and when it is false records the failure
    // (the message is only formatted then, so a Check in hot code is cheap).
    // An agent can make a failure pause the app (`pause --on-check`) or stop
    // it in an attached debugger (`--trap`).
    template<class... A>
    bool Check(bool ok, std::string_view category, LocFmt<std::type_identity_t<A>...> format, A&&... args) {
        if (!ok) Detail::Timeline::Instance().RecordCheck(category, std::format(format.format, std::forward<A>(args)...), format.location);
        return ok;
    }

    // A structured event, which `crafter-debug wait --event <name>` waits for.
    template<class T>
    void Emit(std::string_view event, const T& payload, std::source_location location = std::source_location::current()) {
        Detail::Timeline::Instance().Append(Detail::MakeEntry(EntryKind::Event, event, {}, location, Debug::Encode(payload)));
    }

    inline void Emit(std::string_view event, std::source_location location = std::source_location::current()) {
        Detail::Timeline::Instance().Append(Detail::MakeEntry(EntryKind::Event, event, {}, location));
    }
}