#include <map>
#include <iostream>
#include <thread>

#include <nix/config.h>
#include <nix/shared.hh>
#include <nix/store-api.hh>
#include <nix/eval.hh>
#include <nix/eval-inline.hh>
#include <nix/util.hh>
#include <nix/get-drvs.hh>
#include <nix/globals.hh>
#include <nix/common-eval-args.hh>
#include <nix/flake/flakeref.hh>
#include <nix/flake/flake.hh>
#include <nix/attr-path.hh>
#include <nix/derivations.hh>
#include <nix/local-fs-store.hh>

#include <nix/value-to-json.hh>

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/resource.h>

#include <nlohmann/json.hpp>

using namespace nix;

typedef enum { evalAuto, evalImpure, evalPure } pureEval;

struct MyArgs : MixEvalArgs, MixCommonArgs
{
    Path releaseExpr;
    Path gcRootsDir;
    bool flake = false;
    bool meta = false;
    size_t nrWorkers = 1;
    size_t maxMemorySize = 4096;
    pureEval evalMode = evalAuto;

    MyArgs() : MixCommonArgs("nix-eval-jobs")
    {
        addFlag({
            .longName = "help",
            .description = "show usage information",
            .handler = {[&]() {
                printf("USAGE: nix-eval-jobs [options] expr\n\n");
                for (const auto & [name, flag] : longFlags) {
                    if (hiddenCategories.count(flag->category)) {
                        continue;
                    }
                    printf("  --%-20s %s\n", name.c_str(), flag->description.c_str());
                }
                ::exit(0);
            }},
        });

        addFlag({
            .longName = "impure",
            .description = "set evaluation mode",
            .handler = {[&]() {
                evalMode = evalImpure;
            }},
        });

        addFlag({
            .longName = "gc-roots-dir",
            .description = "garbage collector roots directory",
            .labels = {"path"},
            .handler = {&gcRootsDir}
        });

        addFlag({
            .longName = "workers",
            .description = "number of evaluate workers",
            .labels = {"workers"},
            .handler = {[=](std::string s) {
                nrWorkers = std::stoi(s);
            }}
        });

        addFlag({
            .longName = "max-memory-size",
            .description = "maximum evaluation memory size",
            .labels = {"size"},
            .handler = {[=](std::string s) {
                maxMemorySize = std::stoi(s);
            }}
        });

        addFlag({
            .longName = "flake",
            .description = "build a flake",
            .handler = {&flake, true}
        });

        addFlag({
            .longName = "meta",
            .description = "include derivation meta field in output",
            .handler = {&meta, true}
        });

        expectArg("expr", &releaseExpr);
    }
};

static MyArgs myArgs;

static void worker(
    EvalState & state,
    Bindings & autoArgs,
    AutoCloseFD & to,
    AutoCloseFD & from,
    const Path &gcRootsDir)
{
    Value vTop;

    if (myArgs.flake) {
        using namespace flake;

        auto [flakeRef, fragment] = parseFlakeRefWithFragment(myArgs.releaseExpr, absPath("."));

        auto vFlake = state.allocValue();

        auto lockedFlake = lockFlake(state, flakeRef,
            LockFlags {
                .updateLockFile = false,
                .useRegistries = false,
                .allowMutable = false,
            });

        callFlake(state, lockedFlake, *vFlake);

        auto vOutputs = vFlake->attrs->get(state.symbols.create("outputs"))->value;
        state.forceValue(*vOutputs);
        vTop = *vOutputs;

        if (fragment.length() > 0) {
            Bindings & bindings(*state.allocBindings(0));
            auto [nTop, pos] = findAlongAttrPath(state, fragment, bindings, vTop);
            if (!nTop)
                throw Error("error: attribute '%s' missing", nTop);
            vTop = *nTop;
        }

    } else {
        state.evalFile(lookupFileArg(state, myArgs.releaseExpr), vTop);
    }

    auto vRoot = state.allocValue();
    state.autoCallFunction(autoArgs, vTop, *vRoot);

    while (true) {
        /* Wait for the master to send us a job name. */
        writeLine(to.get(), "next");

        auto s = readLine(from.get());
        if (s == "exit") break;
        if (!hasPrefix(s, "do ")) abort();
        std::string attrPath(s, 3);

        debug("worker process %d at '%s'", getpid(), attrPath);

        /* Evaluate it and send info back to the master. */
        nlohmann::json reply;
        reply["attr"] = attrPath;

        try {
            auto vTmp = findAlongAttrPath(state, attrPath, autoArgs, *vRoot).first;

            auto v = state.allocValue();
            state.autoCallFunction(autoArgs, *vTmp, *v);

            if (auto drv = getDerivation(state, *v, false)) {

                if (drv->querySystem() == "unknown")
                    throw EvalError("derivation must have a 'system' attribute");

                auto drvPath = drv->queryDrvPath();
                auto localStore = state.store.dynamic_pointer_cast<LocalFSStore>();
                auto storePath = localStore->parseStorePath(drvPath);
                auto outputs = drv->queryOutputs(false);

                reply["name"] = drv->queryName();
                reply["system"] = drv->querySystem();
                reply["drvPath"] = drvPath;
                for (auto out : outputs){
                    reply["outputs"][out.first] = out.second;
                }

                if (myArgs.meta) {
                    nlohmann::json meta;
                    for (auto & name : drv->queryMetaNames()) {
                      PathSet context;
                      std::stringstream ss;

                      auto metaValue = drv->queryMeta(name);
                      // Skip non-serialisable types
                      // TODO: Fix serialisation of derivations to store paths
                      if (metaValue == 0) {
                        continue;
                      }

                      printValueAsJSON(state, true, *metaValue, noPos, ss, context);
                      nlohmann::json field = nlohmann::json::parse(ss.str());
                      meta[name] = field;
                    }
                    reply["meta"] = meta;
                }

                /* Register the derivation as a GC root.  !!! This
                   registers roots for jobs that we may have already
                   done. */
                if (gcRootsDir != "") {
                    Path root = gcRootsDir + "/" + std::string(baseNameOf(drvPath));
                    if (!pathExists(root))
                        localStore->addPermRoot(storePath, root);
                }

            }

            else if (v->type() == nAttrs)
              {
                auto attrs = nlohmann::json::array();
                StringSet ss;
                for (auto & i : v->attrs->lexicographicOrder()) {
                    std::string name(i->name);
                    if (name.find('.') != std::string::npos || name.find(' ') != std::string::npos) {
                        printError("skipping job with illegal name '%s'", name);
                        continue;
                    }
                    attrs.push_back(name);
                }
                reply["attrs"] = std::move(attrs);
            }

            else if (v->type() == nNull)
                ;

            else throw TypeError("attribute '%s' is %s, which is not supported", attrPath, showType(*v));

        } catch (EvalError & e) {
            auto msg = e.msg();
            // Transmits the error we got from the previous evaluation
            // in the JSON output.
            reply["error"] = filterANSIEscapes(msg, true);
            // Don't forget to print it into the STDERR log, this is
            // what's shown in the Hydra UI.
            printError(msg);
        }

        writeLine(to.get(), reply.dump());

        /* If our RSS exceeds the maximum, exit. The master will
           start a new process. */
        struct rusage r;
        getrusage(RUSAGE_SELF, &r);
        if ((size_t) r.ru_maxrss > myArgs.maxMemorySize * 1024) break;
    }

    writeLine(to.get(), "restart");
}

int main(int argc, char * * argv)
{
    /* Prevent undeclared dependencies in the evaluation via
       $NIX_PATH. */
    unsetenv("NIX_PATH");

    return handleExceptions(argv[0], [&]() {
        initNix();
        initGC();

        myArgs.parseCmdline(argvToStrings(argc, argv));

        /* FIXME: The build hook in conjunction with import-from-derivation is causing "unexpected EOF" during eval */
        settings.builders = "";

        /* Prevent access to paths outside of the Nix search path and
           to the environment. */
        evalSettings.restrictEval = false;

        /* When building a flake, use pure evaluation (no access to
           'getEnv', 'currentSystem' etc. */
        evalSettings.pureEval = myArgs.evalMode == evalAuto ? myArgs.flake : myArgs.evalMode == evalPure;

        if (myArgs.releaseExpr == "") throw UsageError("no expression specified");

        if (myArgs.gcRootsDir == "") printMsg(lvlError, "warning: `--gc-roots-dir' not specified");

        struct State
        {
            std::set<std::string> todo{""};
            std::set<std::string> active;
            std::exception_ptr exc;
        };

        std::condition_variable wakeup;

        Sync<State> state_;

        /* Start a handler thread per worker process. */
        auto handler = [&]()
        {
            try {
                pid_t pid = -1;
                AutoCloseFD from, to;

                while (true) {

                    /* Start a new worker process if necessary. */
                    if (pid == -1) {
                        Pipe toPipe, fromPipe;
                        toPipe.create();
                        fromPipe.create();
                        pid = startProcess(
                            [&,
                             to{std::make_shared<AutoCloseFD>(std::move(fromPipe.writeSide))},
                             from{std::make_shared<AutoCloseFD>(std::move(toPipe.readSide))}
                            ]()
                            {
                                try {
                                    EvalState state(myArgs.searchPath, openStore());
                                    Bindings & autoArgs = *myArgs.getAutoArgs(state);
                                    worker(state, autoArgs, *to, *from, myArgs.gcRootsDir);
                                } catch (Error & e) {
                                    nlohmann::json err;
                                    auto msg = e.msg();
                                    err["error"] = filterANSIEscapes(msg, true);
                                    printError(msg);
                                    writeLine(to->get(), err.dump());
                                    // Don't forget to print it into the STDERR log, this is
                                    // what's shown in the Hydra UI.
                                    writeLine(to->get(), "restart");
                                }
                            },
                            ProcessOptions { .allowVfork = false });
                        from = std::move(fromPipe.readSide);
                        to = std::move(toPipe.writeSide);
                        debug("created worker process %d", pid);
                    }

                    /* Check whether the existing worker process is still there. */
                    auto s = readLine(from.get());
                    if (s == "restart") {
                        pid = -1;
                        continue;
                    } else if (s != "next") {
                        auto json = nlohmann::json::parse(s);
                        throw Error("worker error: %s", (std::string) json["error"]);
                    }

                    /* Wait for a job name to become available. */
                    std::string attrPath;

                    while (true) {
                        checkInterrupt();
                        auto state(state_.lock());
                        if ((state->todo.empty() && state->active.empty()) || state->exc) {
                            writeLine(to.get(), "exit");
                            return;
                        }
                        if (!state->todo.empty()) {
                            attrPath = *state->todo.begin();
                            state->todo.erase(state->todo.begin());
                            state->active.insert(attrPath);
                            break;
                        } else
                            state.wait(wakeup);
                    }

                    /* Tell the worker to evaluate it. */
                    writeLine(to.get(), "do " + attrPath);

                    /* Wait for the response. */
                    auto respString = readLine(from.get());
                    auto response = nlohmann::json::parse(respString);

                    /* Handle the response. */
                    StringSet newAttrs;
                    if (response.find("attrs") != response.end()) {
                        for (auto & i : response["attrs"]) {
                            auto s = (attrPath.empty() ? "" : attrPath + ".") + (std::string) i;
                            newAttrs.insert(s);
                        }
                    } else {
                        auto state(state_.lock());
                        std::cout << respString << "\n";
                    }

                    /* Add newly discovered job names to the queue. */
                    {
                        auto state(state_.lock());
                        state->active.erase(attrPath);
                        for (auto & s : newAttrs)
                            state->todo.insert(s);
                        wakeup.notify_all();
                    }
                }
            } catch (...) {
                auto state(state_.lock());
                state->exc = std::current_exception();
                wakeup.notify_all();
            }
        };

        std::vector<std::thread> threads;
        for (size_t i = 0; i < myArgs.nrWorkers; i++)
            threads.emplace_back(std::thread(handler));

        for (auto & thread : threads)
            thread.join();

        auto state(state_.lock());

        if (state->exc)
            std::rethrow_exception(state->exc);

    });
}