#include <algorithm>
#include <chrono>
#include <set>
#include <memory>
#include <tuple>
#if __APPLE__
#include <sys/time.h>
#endif

#include "lix/libstore/machines.hh"
#include "lix/libmain/shared.hh"
#include "lix/libstore/pathlocks.hh"
#include "lix/libstore/globals.hh"
#include "lix/libutil/serialise.hh"
#include "lix/libstore/build-result.hh"
#include "lix/libstore/store-api.hh"
#include "lix/libstore/derivations.hh"
#include "lix/libutil/strings.hh"
#include "lix/libstore/local-store.hh"
#include "lix/libcmd/legacy.hh"
#include "lix/libutil/experimental-features.hh"
#include "lix/libutil/hash.hh"
#include "build-remote.hh"

namespace nix {

std::string escapeUri(std::string uri)
{
    std::replace(uri.begin(), uri.end(), '/', '_');
    return uri;
}

static std::string currentLoad;

static std::string makeLockFilename(const std::string & storeUri) {
    // We include 48 bytes of escaped URI to give an idea of what the lock
    // is on, then 16 bytes of hash to disambiguate.
    // This avoids issues with the escaped URI being very long and causing
    // path too long errors, while also avoiding any possibility of collision
    // caused by simple truncation.
    auto hash = hashString(HashType::SHA256, storeUri).to_string(Base::Base32, false);
    return escapeUri(storeUri).substr(0, 48) + "-" + hash.substr(0, 16);
}

static AutoCloseFD openSlotLock(const Machine & m, uint64_t slot)
{
    return openLockFile(fmt("%s/%s-%d", currentLoad, makeLockFilename(m.storeUri), slot), true);
}

static bool allSupportedLocally(Store & store, const std::set<std::string>& requiredFeatures) {
    for (auto & feature : requiredFeatures)
        if (!store.config().systemFeatures.get().count(feature)) return false;
    return true;
}

static int main_build_remote(AsyncIoRoot & aio, std::string programName, Strings argv)
{
    {
        logger = makeJSONLogger(*logger);

        /* Ensure we don't get any SSH passphrase or host key popups. */
        unsetenv("DISPLAY");
        unsetenv("SSH_ASKPASS");

        /* If we ever use the common args framework, make sure to
           remove initPlugins below and initialize settings first.
        */
        if (argv.size() != 1)
            throw UsageError("called without required arguments");

        verbosity = (Verbosity) std::stoll(argv.front());

        FdSource source(STDIN_FILENO);

        /* Read the parent's settings. */
        while (readInt(source)) {
            auto name = readString(source);
            auto value = readString(source);
            settings.set(name, value);
        }

        auto maxBuildJobs = settings.maxBuildJobs;
        settings.maxBuildJobs.set("1"); // hack to make tests with local?root= work

        initPlugins();

        auto store = aio.blockOn(openStore());

        /* It would be more appropriate to use $XDG_RUNTIME_DIR, since
           that gets cleared on reboot, but it wouldn't work on macOS. */
        auto currentLoadName = "/current-load";
        if (auto localStore = store.try_cast_shared<LocalFSStore>())
            currentLoad = std::string { localStore->config().stateDir } + currentLoadName;
        else
            currentLoad = settings.nixStateDir + currentLoadName;

        std::shared_ptr<Store> sshStore;
        AutoCloseFD bestSlotLock;

        auto machines = getMachines();
        debug("got %d remote builders", machines.size());

        if (machines.empty()) {
            std::cerr << "# decline-permanently\n";
            return 0;
        }

        std::optional<StorePath> drvPath;
        std::string storeUri;

        while (true) {

            try {
                auto s = readString(source);
                if (s != "try") return 0;
            } catch (EndOfFile &) { return 0; }

            auto amWilling = readInt(source);
            auto neededSystem = readString(source);
            drvPath = store->parseStorePath(readString(source));
            auto requiredFeatures = readStrings<std::set<std::string>>(source);

            /* It would be possible to build locally after some builds clear out,
               so don't show the warning now: */
            bool couldBuildLocally = maxBuildJobs > 0
                 &&  (  neededSystem == settings.thisSystem
                     || settings.extraPlatforms.get().count(neededSystem) > 0)
                 &&  allSupportedLocally(*store, requiredFeatures);
            /* It's possible to build this locally right now: */
            bool canBuildLocally = amWilling && couldBuildLocally;

            /* Error ignored here, will be caught later */
            mkdir(currentLoad.c_str(), 0777);

            while (true) {
                bestSlotLock.reset();
                AutoCloseFD lock = openLockFile(currentLoad + "/main-lock", true);
                lockFile(lock.get(), ltWrite);

                bool rightType = false;

                Machine * bestMachine = nullptr;
                uint64_t bestLoad = 0;
                for (auto & m : machines) {
                    debug("considering building on remote machine '%s'", m.storeUri);

                    if (m.enabled &&
                        m.systemSupported(neededSystem) &&
                        m.allSupported(requiredFeatures) &&
                        m.mandatoryMet(requiredFeatures))
                    {
                        rightType = true;
                        AutoCloseFD free;
                        uint64_t load = 0;
                        for (uint64_t slot = 0; slot < m.maxJobs; ++slot) {
                            auto slotLock = openSlotLock(m, slot);
                            if (tryLockFile(slotLock.get(), ltWrite)) {
                                if (!free) {
                                    free = std::move(slotLock);
                                }
                            } else {
                                ++load;
                            }
                        }
                        if (!free) {
                            continue;
                        }
                        bool best = false;
                        if (!bestSlotLock) {
                            best = true;
                        } else if (load / m.speedFactor < bestLoad / bestMachine->speedFactor) {
                            best = true;
                        } else if (load / m.speedFactor == bestLoad / bestMachine->speedFactor) {
                            if (m.speedFactor > bestMachine->speedFactor) {
                                best = true;
                            } else if (m.speedFactor == bestMachine->speedFactor) {
                                if (load < bestLoad) {
                                    best = true;
                                }
                            }
                        }
                        if (best) {
                            bestLoad = load;
                            bestSlotLock = std::move(free);
                            bestMachine = &m;
                        }
                    }
                }

                if (!bestSlotLock) {
                    if (rightType && !canBuildLocally)
                        std::cerr << "# postpone\n";
                    else
                    {
                        // add the template values.
                        std::string drvstr;
                        if (drvPath.has_value())
                            drvstr = drvPath->to_string();
                        else
                            drvstr = "<unknown>";

                        std::string machinesFormatted;

                        for (auto & m : machines) {
                            machinesFormatted += HintFmt(
                                "\n([%s], %s, [%s], [%s])",
                                concatStringsSep<StringSet>(", ", m.systemTypes),
                                m.maxJobs,
                                concatStringsSep<StringSet>(", ", m.supportedFeatures),
                                concatStringsSep<StringSet>(", ", m.mandatoryFeatures)
                            ).str();
                        }

                        auto error = HintFmt(
                            "Failed to find a machine for remote build!\n"
                            "derivation: %s\n"
                            "required (system, features): (%s, [%s])\n"
                            "%s available machines:\n"
                            "(systems, maxjobs, supportedFeatures, mandatoryFeatures)%s",
                            drvstr,
                            neededSystem,
                            concatStringsSep<StringSet>(", ", requiredFeatures),
                            machines.size(),
                            Uncolored(machinesFormatted)
                       );

                        printMsg(couldBuildLocally ? lvlChatty : lvlWarn, error.str());

                        std::cerr << "# decline\n";
                    }
                    break;
                }

#if __APPLE__
                futimes(bestSlotLock.get(), nullptr);
#else
                futimens(bestSlotLock.get(), nullptr);
#endif

                lock.reset();

                try {

                    Activity act(*logger, lvlTalkative, actUnknown, fmt("connecting to '%s'", bestMachine->storeUri));

                    sshStore = aio.blockOn(bestMachine->openStore());
                    aio.blockOn(sshStore->connect());
                    storeUri = bestMachine->storeUri;

                } catch (std::exception & e) { // NOLINT(lix-foreign-exceptions)
                    auto msg = chomp(drainFD(5, false));
                    printError("cannot build on '%s': %s%s",
                        bestMachine->storeUri, e.what(),
                        msg.empty() ? "" : ": " + msg);
                    bestMachine->enabled = false;
                    continue;
                }

                goto connected;
            }
        }

connected:
        close(5);

        assert(sshStore);

        std::cerr << "# accept\n" << storeUri << "\n";

        auto inputs = readStrings<PathSet>(source);
        auto wantedOutputs = readStrings<StringSet>(source);

        auto lockFileName = currentLoad + "/" + makeLockFilename(storeUri) + ".upload-lock";

        AutoCloseFD uploadLock = openLockFile(lockFileName, true);

        {
            Activity act(*logger, lvlTalkative, actUnknown, fmt("waiting for the upload lock to '%s'", storeUri));

            if (!unsafeLockFileSingleThreaded(uploadLock.get(), ltWrite, std::chrono::minutes(15)))
                printError("somebody is hogging the upload lock for '%s', continuing...");
        }

        auto substitute = settings.buildersUseSubstitutes ? Substitute : NoSubstitute;

        {
            Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
            aio.blockOn(copyPaths(
                *store,
                *sshStore,
                store->parseStorePathSet(inputs),
                NoRepair,
                NoCheckSigs,
                substitute
            ));
        }

        uploadLock.reset();

        auto drv = aio.blockOn(store->readDerivation(*drvPath));

        std::optional<BuildResult> optResult;

        // If we don't know whether we are trusted (e.g. `ssh://`
        // stores), we assume we are. This is necessary for backwards
        // compat.
        bool trustedOrLegacy = ({
            std::optional trusted = aio.blockOn(sshStore->isTrustedClient());
            !trusted || *trusted;
        });

        // See the very large comment in `case WorkerProto::Op::BuildDerivation:` in
        // `lix/libstore/daemon.cc` that explains the trust model here.
        //
        // This condition mirrors that: that code enforces the "rules" outlined there;
        // we do the best we can given those "rules".
        if (trustedOrLegacy || drv.type().isCA())  {
            // Hijack the inputs paths of the derivation to include all
            // the paths that come from the `inputDrvs` set. We don’t do
            // that for the derivations whose `inputDrvs` is empty
            // because:
            //
            // 1. It’s not needed
            //
            // 2. Changing the `inputSrcs` set changes the associated
            //    output ids, which break CA derivations
            if (!drv.inputDrvs.map.empty())
                drv.inputSrcs = store->parseStorePathSet(inputs);
            optResult = aio.blockOn(sshStore->buildDerivation(*drvPath, (const BasicDerivation &) drv));
            auto & result = *optResult;
            if (!result.success())
                throw Error("build of '%s' on '%s' failed: %s", store->printStorePath(*drvPath), storeUri, result.errorMsg);
        } else {
            aio.blockOn(copyClosure(
                *store, *sshStore, StorePathSet{*drvPath}, NoRepair, NoCheckSigs, substitute
            ));
            auto res = aio.blockOn(sshStore->buildPathsWithResults({
                DerivedPath::Built {
                    .drvPath = makeConstantStorePathRef(*drvPath),
                    .outputs = OutputsSpec::All {},
                }
            }));
            // One path to build should produce exactly one build result
            assert(res.size() == 1);
            optResult = std::move(res[0]);
        }


        auto outputHashes = aio.blockOn(staticOutputHashes(*store, drv));
        std::set<Realisation> missingRealisations;
        StorePathSet missingPaths;
        if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations) && !drv.type().hasKnownOutputPaths()) {
            for (auto & outputName : wantedOutputs) {
                auto thisOutputHash = outputHashes.at(outputName);
                auto thisOutputId = DrvOutput{ thisOutputHash, outputName };
                if (!aio.blockOn(store->queryRealisation(thisOutputId))) {
                    debug("missing output %s", outputName);
                    assert(optResult);
                    auto & result = *optResult;
                    auto i = result.builtOutputs.find(outputName);
                    assert(i != result.builtOutputs.end());
                    auto & newRealisation = i->second;
                    missingRealisations.insert(newRealisation);
                    missingPaths.insert(newRealisation.outPath);
                }
            }
        } else {
            auto outputPaths = drv.outputsAndOptPaths(*store);
            for (auto & [outputName, hopefullyOutputPath] : outputPaths) {
                assert(hopefullyOutputPath.second);
                if (!aio.blockOn(store->isValidPath(*hopefullyOutputPath.second)))
                    missingPaths.insert(*hopefullyOutputPath.second);
            }
        }

        if (!missingPaths.empty()) {
            Activity act(*logger, lvlTalkative, actUnknown, fmt("copying outputs from '%s'", storeUri));
            if (auto localStore = store.try_cast_shared<LocalStore>())
                for (auto & path : missingPaths)
                    localStore->locksHeld.insert(store->printStorePath(path)); /* FIXME: ugly */
            aio.blockOn(
                copyPaths(*sshStore, *store, missingPaths, NoRepair, NoCheckSigs, NoSubstitute)
            );
        }
        // XXX: Should be done as part of `copyPaths`
        for (auto & realisation : missingRealisations) {
            // Should hold, because if the feature isn't enabled the set
            // of missing realisations should be empty
            experimentalFeatureSettings.require(Xp::CaDerivations);
            aio.blockOn(store->registerDrvOutput(realisation));
        }

        return 0;
    }
}

void registerLegacyBuildRemote() {
    LegacyCommandRegistry::add("build-remote", main_build_remote);
}

}
