module;

#include <json.hpp>

module cargoxx.resolver;

import std;
import cargoxx.exec;
import cargoxx.util;

namespace cargoxx::resolver {

namespace fs = std::filesystem;

namespace {

auto network_error(std::string msg) -> util::Error {
    return util::Error{util::ErrorCode::ResolutionNetworkError, std::move(msg),
                       "", std::nullopt, std::nullopt};
}

auto fetch_tree_paths(const std::string& url) -> util::Result<std::vector<std::string>> {
    auto r = exec::run("curl", {"-fsSL", "--max-time", "20", url},
                       exec::ExecOptions{
                           .cwd = {},
                           .env_overrides = {},
                           .timeout = std::chrono::seconds{30},
                           .inherit_stdio = false,
                       });
    if (!r) {
        return std::unexpected(r.error());
    }
    if (r->exit_code != 0) {
        return std::unexpected(network_error(std::format(
            "curl failed (exit {}): {}", r->exit_code, r->stderr_text)));
    }
    nlohmann::json j;
    try {
        j = nlohmann::json::parse(r->stdout_text);
    } catch (const nlohmann::json::parse_error& e) {
        return std::unexpected(
            network_error(std::format("tree listing not valid JSON: {}", e.what())));
    }
    if (!j.contains("tree") || !j["tree"].is_array()) {
        return std::unexpected(network_error("tree listing missing 'tree' array"));
    }
    std::vector<std::string> out;
    for (const auto& entry : j["tree"]) {
        if (entry.contains("path") && entry["path"].is_string()) {
            out.push_back(entry["path"].get<std::string>());
        }
    }
    return out;
}

auto cache_root() -> fs::path {
    if (auto* xdg = std::getenv("XDG_CACHE_HOME"); xdg && *xdg) {
        return fs::path{xdg} / "cargoxx";
    }
    if (auto* home = std::getenv("HOME"); home && *home) {
        return fs::path{home} / ".cache" / "cargoxx";
    }
    return fs::temp_directory_path() / "cargoxx";
}

constexpr auto INDEX_TTL = std::chrono::hours{24};

auto load_or_fetch(const std::string& cache_key, const std::string& url)
    -> util::Result<std::vector<std::string>> {
    auto path = cache_root() / std::format("{}-index.txt", cache_key);
    std::error_code ec;
    if (fs::exists(path, ec) && !ec) {
        auto age = std::chrono::system_clock::now() -
                   std::chrono::file_clock::to_sys(fs::last_write_time(path));
        if (age < INDEX_TTL) {
            std::ifstream in{path};
            if (in) {
                std::vector<std::string> out;
                std::string line;
                while (std::getline(in, line)) {
                    if (!line.empty()) {
                        out.push_back(std::move(line));
                    }
                }
                if (!out.empty()) {
                    return out;
                }
            }
        }
    }
    auto fresh = fetch_tree_paths(url);
    if (!fresh) {
        return std::unexpected(fresh.error());
    }
    fs::create_directories(path.parent_path(), ec);
    if (std::ofstream out{path}; out) {
        for (const auto& p : *fresh) {
            out << p << '\n';
        }
    }
    return fresh;
}

// Levenshtein top-k filter with a max-distance gate of ⌈len/4⌉ (min 1).
auto top_fuzzy(std::string_view query, const std::vector<std::string>& corpus,
               std::size_t k) -> std::vector<std::string> {
    const std::size_t cap = std::max<std::size_t>(1, (query.size() + 3) / 4);
    struct Scored {
        std::size_t dist;
        std::string name;
    };
    std::vector<Scored> scored;
    scored.reserve(corpus.size());
    for (const auto& c : corpus) {
        auto d = util::levenshtein(query, c);
        if (d <= cap) {
            scored.push_back({d, c});
        }
    }
    std::ranges::sort(scored, [](const auto& a, const auto& b) {
        if (a.dist != b.dist) {
            return a.dist < b.dist;
        }
        return a.name < b.name;
    });
    std::vector<std::string> out;
    for (std::size_t i = 0; i < std::min(k, scored.size()); ++i) {
        out.push_back(std::move(scored[i].name));
    }
    return out;
}

constexpr auto FUZZY_K = std::size_t{3};

} // namespace

auto conan_probe_fuzzy(const std::string& name) -> util::Result<ConanRecipe> {
    if (auto exact = conan_probe(name); exact) {
        return exact;
    }
    auto index = load_or_fetch(
        "conan",
        "https://api.github.com/repos/conan-io/conan-center-index/git/trees/master:recipes");
    if (!index) {
        return std::unexpected(util::Error{
            util::ErrorCode::ResolutionUnknownPackage,
            std::format("no Conan recipe for '{}' and index fetch failed", name),
            "", std::nullopt, std::nullopt,
        });
    }
    auto candidates = top_fuzzy(name, *index, FUZZY_K);
    for (const auto& cand : candidates) {
        if (auto r = conan_probe(cand); r) {
            return r;
        }
    }
    return std::unexpected(util::Error{
        util::ErrorCode::ResolutionUnknownPackage,
        std::format("no Conan recipe matches '{}' (tried exact + fuzzy top-{})",
                    name, FUZZY_K),
        "", std::nullopt, std::nullopt,
    });
}

auto vcpkg_probe_fuzzy(const std::string& name) -> util::Result<VcpkgRecipe> {
    if (auto exact = vcpkg_probe(name); exact) {
        return exact;
    }
    auto index = load_or_fetch(
        "vcpkg",
        "https://api.github.com/repos/microsoft/vcpkg/git/trees/master:ports");
    if (!index) {
        return std::unexpected(util::Error{
            util::ErrorCode::ResolutionUnknownPackage,
            std::format("no vcpkg port for '{}' and index fetch failed", name),
            "", std::nullopt, std::nullopt,
        });
    }
    auto candidates = top_fuzzy(name, *index, FUZZY_K);
    for (const auto& cand : candidates) {
        if (auto r = vcpkg_probe(cand); r) {
            return r;
        }
    }
    return std::unexpected(util::Error{
        util::ErrorCode::ResolutionUnknownPackage,
        std::format("no vcpkg port matches '{}' (tried exact + fuzzy top-{})",
                    name, FUZZY_K),
        "", std::nullopt, std::nullopt,
    });
}

} // namespace cargoxx::resolver