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

export module Crafter.Review:Memory;
import std;
import :Json;

// Memory (2026-10-22, Jorijn: "make the concurrency limit from free memory,
// instead of just guessing"): what the machine has free, what a pass costs,
// and the budget the pool admits passes against.
//
// - Free: the kernel's MemAvailable, read at the start of every gate and
//   before every launch: the whole machine's, which is right for a budget and
//   wrong for a cost.
// - Cost: the peak PSS of a pass's own process tree (claude, and for the
//   browser environments the Playwright server and Chromium under it), sampled
//   by the driver on its own passes and kept per repository and environment
//   (Calibration); a pass is admitted at the highest of its environment's
//   recent peaks, or at the measured default before any is recorded.
// - Reserve: what is left for the desktop and the page cache —
//   REVIEW_GATES_MEM_RESERVE_MB, by default 10 % of MemTotal, at least 2 GB.
//   A policy, not a measurement.
export namespace Crafter::Review::Memory {
    // Recent peaks kept per repository and environment.
    constexpr std::size_t Keep = 30;

    // MemAvailable in MB; nullopt without /proc/meminfo.
    std::optional<std::int64_t> Available(const std::filesystem::path& path = "/proc/meminfo");
    // REVIEW_GATES_MEM_RESERVE_MB, else 10 % of MemTotal, at least 2048.
    // std::invalid_argument for a value that is no number.
    std::int64_t Reserve(const std::optional<std::string>& configured, const std::filesystem::path& path = "/proc/meminfo");
    std::int64_t Reserve();

    // The peak tree PSS of every watched pass, on one thread. A sweep makes one
    // ppid map, then reads smaps_rollup for every process of every watched tree
    // — the costly read, it walks the page tables. The pause after a sweep is
    // `interval` or three times the sweep's own length, whichever is longer, so
    // sampling holds at most a quarter of one core whatever the number of
    // passes (2026-10-22). A pass shorter than one pause may go unmeasured.
    class Sampler {
    public:
        using Measure = std::function<double(std::int64_t pid, const std::map<std::int64_t, std::vector<std::int64_t>>& kids)>;
        using Scan = std::function<std::map<std::int64_t, std::vector<std::int64_t>>()>;
        explicit Sampler(double interval = 3.0, Measure measure = {}, Scan scan = {});
        ~Sampler();
        Sampler(const Sampler&) = delete;
        Sampler& operator=(const Sampler&) = delete;
        void Watch(const std::string& key, std::int64_t pid);
        // One sweep over every watched pass; its length in seconds.
        double Sample();
        // Stop watching; the peak in MB, rounded to 0.1, or nullopt when
        // nothing was measured.
        std::optional<double> Done(const std::string& key);
        static double Pause(double interval, double sweep);

    private:
        struct State;
        std::shared_ptr<State> state;
    };

    // Recent peaks per repository and environment, in one JSON file next to the
    // seat ledger: {repo: {env: [MB]}}. A record, never a dependency
    // (2026-10-22): a damaged file reads as empty, a part of the wrong shape as
    // absent, and a peak that cannot be written is dropped.
    class Calibration {
    public:
        Calibration(std::filesystem::path path, const std::filesystem::path& repo, std::map<std::string, std::int64_t> defaults);
        std::vector<Json> Peaks(std::string_view environment) const;
        struct Cost {
            // MB, an int or a float as the file holds it.
            Json megabytes;
            std::string source;
        };
        Cost CostOf(std::string_view environment) const;
        // Keep a pass's peak; whether it was stored. The file is every
        // driver's on this machine: the re-read and the write are one section
        // under its lock (2026-10-31), so a peak another driver wrote between
        // them is kept.
        bool Record(std::string_view environment, double megabytes);

    private:
        std::filesystem::path path;
        std::string repo;
        std::map<std::string, std::int64_t> defaults;
        mutable std::mutex lock;
        Json Load() const;
    };
}