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

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

// The machine as the driver sees it: whether it runs inside the Flatpak's
// sandbox, its environment, the files it shares with other drivers and how
// they are locked, /proc, and the identity it is known by on the seat board.
//
// The sandbox is decided once, by Init(). Everything that reads /proc or the
// sandbox's instance files goes through Paths(), which a test points at a
// fake tree: flatpak-builder runs the suite inside `flatpak build`, where
// /.flatpak-info exists, and a test that read the real files would test the
// build sandbox instead of the code.
export namespace Crafter::Review::Platform {
    enum class Mode {
        Native,
        // Inside a Flatpak: its own PID namespace, XDG directories under
        // ~/.var/app, a private /tmp unless the manifest shares the host's.
        Sandbox,
    };

    struct SystemPaths {
        std::filesystem::path proc = "/proc";
        std::filesystem::path flatpakInfo = "/.flatpak-info";
        // $XDG_RUNTIME_DIR, where the instance's bwrapinfo.json is mounted:
        // /run/user/<uid>/.flatpak/<instance-id>/bwrapinfo.json.
        std::filesystem::path runtimeDir;
    };

    // Decides the mode from /.flatpak-info and, in the sandbox, restores the
    // host's XDG directories (RestoreHostXdg) before any thread starts.
    void Init();
    Mode CurrentMode();
    bool InSandbox();
    // For tests: pin the mode and the paths the identity code reads.
    void SetMode(Mode mode);
    const SystemPaths& Paths();
    void SetPaths(SystemPaths paths);

    // ---- environment -----------------------------------------------------------
    std::optional<std::string> GetEnv(std::string_view name);
    // The process environment.
    std::map<std::string, std::string> Environment();
    // $HOME, else the password database's.
    std::string Home();
    // Flatpak points XDG_{CONFIG,CACHE,DATA,STATE}_HOME at ~/.var/app/<id>/…;
    // they go back to the host's (HOST_XDG_*, else the XDG defaults under
    // $HOME), so git reads ~/.config/git/config, Playwright finds
    // ~/.cache/ms-playwright, and claude and npx behave as on the host.
    void RestoreHostXdg();
    // The absolute path of the running binary (/proc/self/exe).
    std::filesystem::path SelfExe();

    // ---- time ----------------------------------------------------------------------
    // time.time()
    double Now();
    // time.strftime(format) in local time.
    std::string LocalTime(std::string_view format);
    // time.strftime(format, time.localtime(epochSeconds))
    std::string LocalTime(std::string_view format, double epochSeconds);
    // date.today().isoformat()
    std::string TodayIso();

    // ---- files ------------------------------------------------------------------------
    // The file's bytes, or nullopt when it cannot be read.
    std::optional<std::string> ReadFile(const std::filesystem::path& path);
    // `content` into `<path>.<pid>.tmp`, created with `mode` (the umask
    // applies), then renamed over `path`: a reader never sees half a file, and
    // two writers never share a temp name. The pid is PublishedPid(), which in
    // the sandbox is a host pid, where every driver would otherwise be pid 2.
    // Directories are created as needed.
    void WriteAtomic(const std::filesystem::path& path, std::string_view content, std::uint32_t mode = 0644);

    // `path` and its missing parents: the parents made as mkdir makes them,
    // the last directory with `mode`, both less the umask; a directory that is
    // there keeps its mode. Throws with the errno text ("[Errno 13] Permission
    // denied: '/x'").
    void MakeDirs(const std::filesystem::path& path, std::uint32_t mode = 0777);

    // An exclusive flock(2) on `lockPath`, held while the object lives. flock,
    // not fcntl or OFD locks: every driver on the machine takes flock on the
    // same side files, and on Linux the two kinds do not exclude each other. A
    // missing lock file is created 0666 less the umask.
    class FileLock {
    public:
        explicit FileLock(const std::filesystem::path& lockPath);
        ~FileLock();
        FileLock(const FileLock&) = delete;
        FileLock& operator=(const FileLock&) = delete;
        // False when the lock file could not be opened or locked; the caller
        // carries on best-effort.
        bool Held() const;
        // Why not, when it is not held.
        const std::string& Problem() const;

    private:
        std::int32_t fd = -1;
        std::string problem;
    };

    // The one shape every file shared between drivers is written in (the
    // board, the ledger, memory.json, unit-state.json): lock `<path>.lock`,
    // re-read the file, let `change` edit it in place — a false return leaves
    // the file as it is — write it back atomically with `mode`, release.
    // A file that does not parse as a JSON object hands `change` a copy of
    // `fallback`. Without the lock the write is still made, best-effort;
    // `warn` hears about that and about a write that failed. Returns what
    // `change` saw.
    Json LockedUpdate(const std::filesystem::path& path, const std::function<bool(Json&)>& change, const Json& fallback,
                      std::uint32_t mode, const std::function<void(const std::string&)>& warn);

    // ---- /proc ----------------------------------------------------------------------------
    // The start time of a live process, in clock ticks since boot (field 22
    // of /proc/<pid>/stat, read after the last ')' because the command name
    // may hold spaces and parentheses); nullopt for no such process or a
    // zombie. Under Paths().proc.
    std::optional<std::int64_t> ProcStart(std::int64_t pid);
    // The first 8 characters of /proc/sys/kernel/random/boot_id, "" when
    // unreadable.
    std::string BootId();
    // /proc/meminfo as {field: MB}; a field without a kB unit keeps its value.
    std::map<std::string, std::int64_t> MemInfo(const std::filesystem::path& path = "/proc/meminfo");
    // {ppid: [pids]} of every process now, from one read of each
    // /proc/<pid>/stat. Always the real /proc: a process tree is this
    // driver's own business.
    std::map<std::int64_t, std::vector<std::int64_t>> PpidMap();
    // The pid and every descendant in `kids`.
    std::vector<std::int64_t> Tree(std::int64_t pid, const std::map<std::int64_t, std::vector<std::int64_t>>& kids);
    // The summed Pss of the processes, in MB; one that is gone counts nothing.
    double PssMb(std::span<const std::int64_t> pids);

    // ---- identity -------------------------------------------------------------------------
    // How the other drivers on this machine know a driver: `<pid>:<start>`.
    struct Identity {
        std::int64_t pid = 0;
        std::int64_t start = 0;
        std::string Key() const;
    };
    // This process as every driver on the machine can check it. Natively its
    // own pid and start time. In the sandbox its pid means nothing outside
    // (every Flatpak driver is pid 2), so it is the instance's: the host pid
    // of the sandbox's init (`child-pid` in bwrapinfo.json) and the start time
    // of /proc/1 inside, which is the same process — a driver outside that
    // checks the pid then sees it alive exactly as long as the sandbox runs.
    // nullopt in a sandbox without bwrapinfo.json (`flatpak build`), after
    // waiting up to 2 s for flatpak to write it.
    std::optional<Identity> Self();
    // The pid to put in temp names and lock information: Self()'s, else
    // getpid().
    std::int64_t PublishedPid();

    // The lifetime lock of a driver: an exclusive flock on
    // `<dir>/<pid>-<start>.lock`, held as long as the driver lives. It is
    // created under a temporary name, locked, then renamed into place, so a
    // prober never finds the file unlocked while its owner lives. Another
    // driver tells a live one from a dead one by it across sandboxes, where
    // pids are not comparable.
    class LifetimeLock {
    public:
        // Throws std::runtime_error when the name is already held by a live
        // driver: a second full run in one sandbox instance.
        LifetimeLock(const std::filesystem::path& dir, const Identity& identity);
        ~LifetimeLock();
        LifetimeLock(const LifetimeLock&) = delete;
        LifetimeLock& operator=(const LifetimeLock&) = delete;
        const std::filesystem::path& File() const;

    private:
        std::int32_t fd = -1;
        std::filesystem::path file;
    };
    std::filesystem::path LifetimeLockFile(const std::filesystem::path& dir, std::int64_t pid, std::int64_t start);
    // true: a live driver holds the lock; false: the file is there and nobody
    // holds it (its driver died); nullopt: there is no lock file (a driver
    // that takes none).
    std::optional<bool> ProbeLifetimeLock(const std::filesystem::path& dir, std::int64_t pid, std::int64_t start);
}