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

module;
#include <errno.h>
#include <fcntl.h>
#include <sys/file.h>
#include <unistd.h>
module Crafter.Debug.Core:Discovery_impl;
import std;
import :Value;
import :Codec;
import :Discovery;

using namespace Crafter::Debug;
namespace fs = std::filesystem;

namespace {
    std::string RandomId() {
        std::random_device random;
        return std::format("{:08x}{:08x}", random(), random());
    }

    std::string ReadFile(const fs::path& path) {
        std::ifstream in(path, std::ios::binary);
        if (!in) return {};
        return std::string((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
    }

    // The value of `key` in `section` of an INI-style file such as /.flatpak-info.
    std::string IniValue(std::string_view text, std::string_view section, std::string_view key) {
        bool inSection = false;
        for (const auto part : std::views::split(text, '\n')) {
            const std::string_view line(std::ranges::data(part), std::ranges::size(part));
            if (line.starts_with('[')) {
                inSection = line.size() == section.size() + 2 && line.substr(1, section.size()) == section && line.back() == ']';
                continue;
            }
            if (inSection && line.size() > key.size() && line.starts_with(key) && line[key.size()] == '=') return std::string(line.substr(key.size() + 1));
        }
        return {};
    }

    // The host pid of the sandbox's init: child-pid in the bwrapinfo.json
    // Flatpak keeps for the instance under $XDG_RUNTIME_DIR, or 0.
    std::int64_t SandboxInitPid(std::string_view instance) {
        if (instance.empty()) return 0;
        const char* runtime = std::getenv("XDG_RUNTIME_DIR");
        const fs::path base = runtime != nullptr && *runtime != 0 ? fs::path(runtime) : fs::path(std::format("/run/user/{}", ::getuid()));
        const std::string text = ReadFile(base / ".flatpak" / std::string(instance) / "bwrapinfo.json");
        if (text.empty()) return 0;
        try {
            const Value info = Value::Parse(text);
            const Value* pid = info.Find("child-pid");
            return pid != nullptr && pid->IsInteger() ? pid->AsInteger() : 0;
        } catch (const ParseError&) {
            return 0;
        }
    }

    std::system_error Failure(std::string_view what) {
        return std::system_error(errno, std::generic_category(), std::string(what));
    }

    // Through a temporary name and a rename, so a reader never sees half
    // a file. Created with `mode`, before the umask.
    void WriteAtomically(const fs::path& path, std::string_view text, std::uint32_t mode) {
        fs::path temp = path;
        temp += std::format(".{}.tmp", RandomId());
        const std::int32_t fd = ::open(temp.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, mode);
        if (fd < 0) throw Failure(std::format("creating {}", temp.string()));
        std::size_t written = 0;
        while (written < text.size()) {
            const auto count = ::write(fd, text.data() + written, text.size() - written);
            if (count < 0 && errno == EINTR) continue;
            if (count <= 0) {
                const std::system_error error = Failure(std::format("writing {}", temp.string()));
                ::close(fd);
                ::unlink(temp.c_str());
                throw error;
            }
            written += static_cast<std::size_t>(count);
        }
        ::close(fd);
        fs::rename(temp, path);
    }
}

fs::path Crafter::Debug::DiscoveryDirectory() {
    if (const char* dir = std::getenv("CRAFTER_DEBUG_DIR"); dir != nullptr && *dir != 0) return fs::path(dir);
    const char* home = std::getenv("HOME");
    return fs::path(home != nullptr && *home != 0 ? home : "/tmp") / ".cache" / "crafter-debug" / "instances";
}

Registration::Registration(InstanceRecord given) : record(std::move(given)) {
    const fs::path dir = DiscoveryDirectory();
    fs::create_directories(dir);
    std::error_code ignored;
    fs::permissions(dir, fs::perms::owner_all, ignored);

    record.instanceId = RandomId();
    record.pid = ::getpid();
    record.exe = fs::read_symlink("/proc/self/exe", ignored).string();
    record.startedAt = std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now().time_since_epoch()).count();
    const std::string info = ReadFile("/.flatpak-info");
    if (!info.empty()) {
        record.flatpakInstance = IniValue(info, "Instance", "instance-id");
        record.hostInitPid = SandboxInitPid(record.flatpakInstance);
    }

    // The lock first, made under a temporary name, locked, then renamed into
    // place, so nothing ever finds it unlocked while this instance lives;
    // then the record, which a lister only reads once the lock is there.
    lockPath = dir / std::format("{}.lock", record.instanceId);
    recordPath = dir / std::format("{}.json", record.instanceId);
    fs::path tempLock = lockPath;
    tempLock += ".tmp";
    lockFd = ::open(tempLock.c_str(), O_CREAT | O_EXCL | O_RDWR | O_CLOEXEC, 0600);
    if (lockFd < 0) throw Failure(std::format("creating {}", tempLock.string()));
    if (::flock(lockFd, LOCK_EX | LOCK_NB) != 0) {
        const std::system_error error = Failure(std::format("locking {}", tempLock.string()));
        ::close(lockFd);
        ::unlink(tempLock.c_str());
        throw error;
    }
    fs::rename(tempLock, lockPath);
    WriteAtomically(recordPath, Encode(record).Dump(), 0600);
}

Registration::~Registration() {
    std::error_code ignored;
    fs::remove(recordPath, ignored);
    fs::remove(lockPath, ignored);
    if (lockFd >= 0) ::close(lockFd);
}

std::vector<Instance> Crafter::Debug::ListInstances() {
    std::vector<Instance> live;
    std::error_code ec;
    for (const fs::directory_entry& entry : fs::directory_iterator(DiscoveryDirectory(), ec)) {
        const fs::path path = entry.path();
        if (path.extension() != ".json") continue;
        fs::path lock = path;
        lock.replace_extension(".lock");
        bool alive = false;
        const std::int32_t fd = ::open(lock.c_str(), O_RDONLY | O_CLOEXEC);
        if (fd >= 0) {
            alive = ::flock(fd, LOCK_EX | LOCK_NB) != 0 && errno == EWOULDBLOCK;
            ::close(fd);
        }
        if (!alive) {
            std::error_code ignored;
            fs::remove(path, ignored);
            fs::remove(lock, ignored);
            continue;
        }
        Value parsed;
        try {
            parsed = Value::Parse(ReadFile(path));
        } catch (const ParseError&) {
            continue;
        }
        // A newer app may add fields; what this client knows still decodes.
        InstanceRecord record;
        DecodeContext context;
        Decode(parsed, record, context);
        live.push_back({ std::move(record), path });
    }
    std::ranges::sort(live, [](const Instance& a, const Instance& b) { return a.record.startedAt > b.record.startedAt; });
    return live;
}