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

import std;
import Crafter.Build;
namespace fs = std::filesystem;
using namespace Crafter;

// Builds that run at the same time share their dependencies' clones in the
// cache, and two crafter-builds can run at once. Fetching a clone that
// already exists ran `git pull` (and the CMake build) in it with nothing to
// keep a second fetch out, and the second git fails on the first one's
// index.lock. A clone's fetch and build now hold a lock of their own. Within
// one run, the configurations that declare the same dependency share one
// fetch of it instead (SharedExternalFetch).
//
// Eight threads fetch the same tracked branch of a local repository at
// once, a few rounds over, the branch moving between rounds so every pull
// has work to do; every fetch has to succeed. Each thread fetches through
// GitFetch and through BuildExternal, which every build of an
// ExternalDependency calls, each into a clone of its own. Everything is
// local; XDG_CACHE_HOME keeps the clones out of the real cache.

extern "C" int setenv(const char* name, const char* value, int overwrite);

namespace {
    std::int32_t failures = 0;

    void Check(bool cond, std::string_view msg) {
        if (!cond) {
            std::println(std::cerr, "FAIL: {}", msg);
            ++failures;
        }
    }

    void Git(const fs::path& dir, std::string_view args) {
        const std::string command = std::format("git -C {} {}", ShellQuote(dir.string()), args);
        auto result = RunCommandWithTimeout(command, std::chrono::seconds(60));
        if (result.exitCode != 0) throw std::runtime_error(std::format("{} failed: {}", command, result.output));
    }

    void Commit(const fs::path& repo, std::uint32_t round) {
        std::ofstream(repo / "round.txt", std::ios::binary | std::ios::trunc) << round;
        Git(repo, "add round.txt");
        Git(repo, std::format("commit -q -m round-{}", round));
    }

    std::uint32_t Round(const fs::path& clone) {
        std::ifstream in(clone / "round.txt");
        std::uint32_t round = 0;
        in >> round;
        return round;
    }
}

int main() {
    const fs::path scratch = fs::temp_directory_path() / "crafter-build-concurrent-external-fetch";
    fs::remove_all(scratch);
    fs::create_directories(scratch);
    setenv("XDG_CACHE_HOME", (scratch / "cache").c_str(), 1);
    setenv("GIT_CONFIG_NOSYSTEM", "1", 1);
    setenv("GIT_CONFIG_GLOBAL", "/dev/null", 1);
    for (const char* name : { "GIT_AUTHOR_NAME", "GIT_COMMITTER_NAME" }) setenv(name, "crafter-build test", 1);
    for (const char* name : { "GIT_AUTHOR_EMAIL", "GIT_COMMITTER_EMAIL" }) setenv(name, "test@example.invalid", 1);

    const fs::path repo = scratch / "shared";
    fs::create_directories(repo);
    Git(repo, "init -q -b main");
    Commit(repo, 0);
    const GitSource source { .url = std::format("file://{}", repo.string()), .branch = "main" };
    const fs::path clone = GitFetch(source);
    // A clone of its own: BuildExternal keys the cache differently.
    ExternalDependency dep;
    dep.name = "shared";
    dep.source = source;
    const std::string cloned = BuildExternal(dep, HostTarget());
    Check(cloned.empty(), std::format("BuildExternal clones the repository: {}", cloned));

    constexpr std::uint32_t threads = 8;
    constexpr std::uint32_t rounds = 4;
    std::vector<std::string> errors;
    std::mutex errorsMutex;
    for (std::uint32_t round = 1; round <= rounds; ++round) {
        Commit(repo, round);
        std::vector<std::jthread> fetchers;
        for (std::uint32_t i = 0; i < threads; ++i) {
            fetchers.emplace_back([&] {
                std::string error;
                try {
                    (void)GitFetch(source);
                    error = BuildExternal(dep, HostTarget());
                } catch (const std::exception& e) {
                    error = e.what();
                }
                if (error.empty()) return;
                std::lock_guard lock(errorsMutex);
                errors.push_back(std::move(error));
            });
        }
    }
    Check(errors.empty(), std::format("{} threads fetching at once, {} rounds: every fetch succeeds ({} failed{}{})", threads, rounds, errors.size(), errors.empty() ? "" : ", the first: ", errors.empty() ? "" : errors.front()));
    Check(Round(clone) == rounds, std::format("and GitFetch's clone ends at the last round ({})", Round(clone)));
    const fs::path externalClone = ExternalCloneDir(dep, HostTarget());
    Check(Round(externalClone) == rounds, std::format("and so does BuildExternal's ({})", Round(externalClone)));

    std::error_code ec;
    fs::remove_all(scratch, ec);
    if (failures > 0) {
        std::println(std::cerr, "{} assertions failed", failures);
        return 1;
    }
    return 0;
}