#include "world.hpp"
#include "idalloc.hpp"
#include "animqueue.hpp"
#include "gui.hpp"
#include "traceback.hpp"
#include "pprint.hpp"
#include "util.hpp"
#include "serializelua.hpp"

#include <iostream>

void World::store_global_pointer(lua_State *L, World *v) {
    lua_pushstring(L, "world");
    lua_pushlightuserdata(L, v);
    lua_rawset(L, LUA_REGISTRYINDEX);
}

World *World::fetch_global_pointer(lua_State *L) {
    lua_pushstring(L, "world");
    lua_rawget(L, LUA_REGISTRYINDEX);
    World *result = (World *)lua_touserdata(L, -1);
    if (result == nullptr) {
        luaL_error(L, "No world pointer stored.");
    }
    lua_pop(L, 1);
    return result;
}

World::~World() {
}

World::World(WorldType wt) {
    // Master world model by default.
    world_type_ = wt;

    // Initialize the ID allocator in master mode.
    if (is_authoritative()) {
        id_global_pool_.init_master();
    } else {
        id_global_pool_.init_synch();
    }

    // Prepare to manipulate the lua state.
    LuaVar world, globtab;
    LuaExtStack LS(state(), world, globtab);

    // Put the world pointer into the lua registry.
    World::store_global_pointer(state(), this);

    // Clear the global GUI pointer.
    Gui::store_global_pointer(state(), nullptr);

    // Clear the lthread state.
    clear_lthread_state();

    // Set the tabletype of the registry.
    LS.settabletype(LuaRegistry, LUA_TT_REGISTRY);

    // Set the tabletype of the global environment.
    LS.getglobaltable(globtab);
    LS.settabletype(globtab, LUA_TT_GLOBALENV);

    // Store the world type in the registry.
    LS.rawset(LuaRegistry, "worldtype", wt);
        
    // Create the globaldb in the registry.
    LS.rawset(LuaRegistry, "globaldb", LuaNewTable);

    // Initialize the SourceDB.
    source_db_.init(state());
    
    // Clear the clock.
    clock_ = 0;

    // Initialize global variable state.
    assign_seqno_ = 1;
}

Tangible::Tangible(World *w, int64_t id) : world_(w), anim_queue_(), id_player_pool_(&w->id_global_pool_) {
    plane_item_.set_id(id);
    plane_item_.track(&w->plane_map_);
}

void Tangible::update_plane_item() {
    AnimCoreState pos = anim_queue_.get_final_core_state();
    plane_item_.set_pos(pos.plane, pos.xyz.x, pos.xyz.y, pos.xyz.z);
}

void Tangible::serialize(StreamBuffer *sb) {
    anim_queue_.serialize(sb);
    id_player_pool_.serialize(sb);
    print_buffer_.serialize(sb);
}

void Tangible::deserialize(StreamBuffer *sb) {
    anim_queue_.deserialize(sb);
    id_player_pool_.deserialize(sb);
    print_buffer_.deserialize(sb);
    update_plane_item();
}

Tangible *World::tangible_get(int64_t id) {
    auto iter = tangibles_.find(id);
    if (iter == tangibles_.end()) {
        return nullptr;
    } else {
        return iter->second.get();
    }
}

const Tangible *World::tangible_get(int64_t id) const {
    auto iter = tangibles_.find(id);
    if (iter == tangibles_.end()) {
        return nullptr;
    } else {
        return iter->second.get();
    }
}

World::TanVector World::tangible_get_all(const IdVector &ids) const {
    TanVector result(ids.size());
    for (int i = 0; i < int(ids.size()); i++) {
        result[i] = tangible_get(ids[i]);
    }
    return result;
}

Tangible *World::tangible_get(const LuaCoreStack &LS, LuaSlot tab, bool allowdel) {
    int64_t id = LS.tanid(tab);
    if (id == 0) {
        luaL_error(LS.state(), "parameter is not a tangible");
    }
    Tangible *result = tangible_get(id);
    if (!allowdel) {
        if (result == nullptr) {
            luaL_error(LS.state(), "argument is a deleted tangible, which is not allowed here");
        }
    }
    return result;
}

Tangible *World::tangible_make(const LuaCoreStack &LS0, LuaSlot database, int64_t id) {
    assert(id != 0);
    LuaVar metatab;
    LuaExtStack LS(LS0.state(), metatab);

    // Create the C++ part of the structure.
    UniqueTangible &t = tangibles_[id];
    assert (t == nullptr);
    t.reset(new Tangible(this, id));

    // AnimQueue initializes itself to a valid default state.
    AnimState state;
    state.add_defaults(nullptr);
    t->anim_queue_.clear(state);
    t->update_plane_item();
    
    // Fetch the tangible's Lua database and metatable.
    LS.maketan(database, id);
    LS.getmetatable(metatab, database);

    // Set up the inventory and thread table.
    LS.rawset(database, "inventory", LuaNewTable);
    LS.rawset(metatab, "threads", LuaNewTable);

    return t.get();
}

Tangible *World::tangible_make(int64_t id) {
    LuaVar database;
    LuaExtStack LS(state(), database);
    return tangible_make(LS, database, id);
}

void World::tangible_delete(int64_t id) {
    lua_State *L = state();
    LuaVar tangibles, database, metatab;
    LuaExtStack LS(L, tangibles, database, metatab);

    // Fetch the C++ side of the tangible.
    auto iter = tangibles_.find(id);
    if (iter == tangibles_.end()) {
        return; // Nothing to delete.
    }

    // Fetch the lua side of the tangible.
    LS.maketan(database, id);
    assert(LS.istable(database));
    LS.getmetatable(metatab, database);

    // Clear out the database and the metatable.
    LS.cleartable(database, false);
    LS.cleartable(metatab, true);

    // Now put the bare minimum info back into the metatable.
    LS.rawset(metatab, "id", id);
    LS.rawset(metatab, "__metatable", false);

    // Remove the C++ portion from the tangibles table.
    tangibles_.erase(iter);
}

void World::get_near(PlaneScan &scan, util::IdVector *into) const {
    into->clear();
    // If 'near' is set, update the plane and center.
    int64_t actor_id = scan.near();
    if (actor_id != 0) {
        const Tangible *player = tangible_get(actor_id);
        if (player == nullptr) {
            return;
        }
        const PlaneItem &pi = player->plane_item_;
        scan.set_plane(pi.plane());
        scan.set_center(util::XYZ(pi.x(), pi.y(), pi.z()));
    }
    plane_map_.scan(scan, into);
}

void World::get_near(int64_t player_id, float radius, bool exclude_nowhere, bool omit_player, bool sorted, util::IdVector *into) const {
    PlaneScan scan;
    scan.set_radius(radius);
    scan.set_shape(PlaneScan::SPHERE);
    scan.set_sorted(sorted);
    scan.set_omit_nowhere(exclude_nowhere);
    scan.set_near(player_id, !omit_player);
    get_near(scan, into);
}

void World::get_encoded_animation_queues(uint32_t count, const int64_t *ids, util::SharedStdStringVec &into) {
    util::SharedStdString empty = std::make_shared<std::string>("");
    into.resize(count);
    for (int i = 0; i < int(count); i++) {
        Tangible *tan = tangible_get(ids[i]);
        if (tan == nullptr) {
            into[i] = empty;
        } else {
            into[i] = tan->anim_queue_.get_encoded_queue();
        }
    }
}

World::Redirects World::fetch_redirects() {
    World::Redirects result = std::move(redirects_);
    redirects_.clear();
    return result;
}

int64_t World::create_login_actor() {
    assert(stack_is_clear());
    int64_t id = id_global_pool_.get_one();
    LuaVar database, classtab, mt;
    LuaExtStack LS(state(), database, classtab, mt);
    Tangible *tan = tangible_make(LS, database, id);
    LS.makeclass(classtab, "login");
    LS.getmetatable(mt, database);
    LS.rawset(mt, "__index", classtab);
    tan->configure_id_pool_for_actor();
    tan->print_buffer_.clear();
    return tan->id();
}

eng::string World::probe_lua(int64_t actor_id, const eng::string &lua) {
    assert(stack_is_clear());
    lua_State *L = state();

    Tangible *actor = tangible_get(actor_id);
    if (actor == nullptr) {
        return "";
    }

    LuaVar closure;
    LuaExtStack LS(L, closure);

    // create the compiled closure.
    int status = luaL_loadbuffer(L, lua.c_str(), lua.size(), "=probe");
    lua_replace(L, closure.index());
    if (status != LUA_OK) {
        // The closure is actually an error message. Do nothing.
        // This should normally not happen: LuaConsole should filter
        // out syntax errors.
        return "";
    }

    // Call the closure.
    int top = lua_gettop(L);
    lua_pushvalue(L, closure.index());
    open_lthread_state(actor_id, actor_id, 0, false, true);
    eng::string msg = traceback_pcall(L, 0, LUA_MULTRET);
    
    // If there's an error message, print it.
    // Otherwise, pretty-print the results.
    std::ostream *ostream = lthread_print_stream();
    if (msg.empty()) {
        for (int i = top + 1; i <= lua_gettop(L); i++) {
            LuaSpecial root(i);
            pprint(LS, root, PrettyPrintOptions(), ostream);
            // TODO: this endl is unnecessary if we just printed a newline.
            (*ostream) << std::endl;
        }
    } else {
        (*ostream) << msg << std::endl;
    }

    // Collect the lthread_prints (and also make sure they
    // don't go into the printbuffer).
    eng::string result = lthread_prints_->str();
    lthread_prints_.reset();

    close_lthread_state();
    return result;
}

void World::update_gui(int64_t actor_id, int64_t place_id, Gui *gui) {
    assert(stack_is_clear());
    gui->clear(place_id);
    lua_State *L = state();

    LuaVar actor, place, ugui, func, tangibles, mt, index;
    LuaExtStack LS(L, actor, place, ugui, func, tangibles, mt, index);

    // Get the actor and place.
    LS.rawget(tangibles, LuaRegistry, "tangibles");
    LS.rawget(actor, tangibles, actor_id);
    LS.rawget(place, tangibles, place_id);
    if (!LS.istable(actor) || !LS.istable(place)) {
        return;
    }

    // Get the interface closure.
    LS.getmetatable(mt, place);
    if (!LS.istable(mt)) {
        return;
    }
    LS.rawget(index, mt, "__index");
    if (!LS.istable(index)) {
        return;
    }
    LS.rawget(func, index, "interface");
    if (!LS.isfunction(func)) {
        return;
    }

    // Call the interface function.
    lua_pushvalue(L, func.index());
    lua_pushvalue(L, actor.index());
    lua_pushvalue(L, place.index());
    Gui::store_global_pointer(L, gui);
    open_lthread_state(actor_id, place_id, 0, false, false);
    eng::string msg = traceback_pcall(L, 2, 0);
    close_lthread_state();
    Gui::store_global_pointer(L, nullptr);
    if (!msg.empty()) {
        gui->clear(0);
        util::dprint(msg);
        return;
    }
}

void World::update_source(const util::LuaSourcePtr &source) {
    if (source != nullptr) {
        update_source(*source);
    }
}

// This is called from World::update_source, and also
// from World::patch_source in the difference transmitter.
//
// For the moment, errors are channeled to util::dprint,
// and 'print' statements just go to std::cerr.  Neither
// of these is ideal.  We need to get serious about setting
// up error handling.
//
// We also need to figure out a solution for what happens if
// some lua source file tries to modify, say, tangible state
// in top-level code.
//
void World::rebuild_sourcedb() {
    for (const eng::string &mod: source_db_.modules()) {
        open_lthread_state(0, 0, 0, false, true);
        eng::string err = source_db_.rebuild_module(mod);
        eng::string prints = lthread_prints_->str();
        lthread_prints_.reset();
        close_lthread_state();
        if (!err.empty() || !prints.empty()) {
            util::dprint("Loading Module ", mod);
            if (!err.empty()) util::dprint(err);
            if (!prints.empty()) util::dprint(prints);
        }
    }
}

void World::update_source(const util::LuaSourceVec &source) {
    assert(stack_is_clear());
    source_db_.update(source);
    rebuild_sourcedb();
    assert(stack_is_clear());
}

void World::http_response(const HttpParser &response) {
    // Find the request.
    auto iter = http_requests_.find(response.request_id());
    if (iter == http_requests_.end()) {
        return;
    }
    HttpClientRequest request = iter->second;
    http_requests_.erase(iter);

    lua_State *CO;
    {
        // Get the place and thread as lua objects.
        LuaVar tangibles, place, mt, threads, thinfo, thread;
        LuaExtStack LS(state(), tangibles, place, mt, threads, thinfo, thread);
        LS.rawget(tangibles, LuaRegistry, "tangibles");
        LS.rawget(place, tangibles, request.place_id());
        if (!LS.istable(place)) {
            return;
        }
        LS.getmetatable(mt, place);
        if (!LS.istable(mt)) {
            return;
        }
        LS.rawget(threads, mt, "threads");
        if (!LS.istable(threads)) {
            return;
        }
        LS.rawget(thinfo, threads, request.thread_id());
        if (!LS.istable(thinfo)) {
            return;
        }
        LS.rawget(thread, thinfo, "thread");
        if (!LS.isthread(thread)) {
            return;
        }
        CO = LS.ckthread(thread);
    }

    // Push the response onto the awakening thread.
    lua_pushnil(CO);
    LuaSpecial responsetable(lua_gettop(CO));
    LuaCoreStack LSCO(CO);
    response.store(LSCO, responsetable);

    // Awaken the thread, with its new return value.
    schedule(0, request.thread_id(), request.place_id());
    run_scheduled_threads();
}

void World::http_responses(const HttpParserVec &responses) {
    for (const HttpParser &response : responses) {
        http_response(response);
    }
}

void World::abort_all_http_requests(int status_code, std::string_view error) {
    HttpParser abortresponse;
    abortresponse.fail(status_code, error);
    while (!http_requests_.empty()) {
        abortresponse.set_request_id(http_requests_.begin()->first);
        http_response(abortresponse);
    }
}

HttpServerResponse World::http_serve(const HttpParser &request) {
    assert(stack_is_clear());
    HttpServerResponse response;

    // We're only supposed to be passed complete requests.
    assert(request.complete());

    // If the request is HTTP/1.1, then the response should be HTTP/1.1
    response.set_http11(request.http11());

    // If the incoming request has already been detected to be
    // invalid by the HTTP parser, then just send the error 
    // message back to the client without involving lua at all.
    if (request.errstatus()) {
        response.fail(request.status(), request.error());
        return response;
    }

    lua_State *L = state();
    LuaVar www, func, reqtab;
    LuaExtStack LS(L, www, func, reqtab);
    
    // Get the www class.  If there's no such class,
    // return a 503 Service Unavailable to the client.
    eng::string err = LS.getclass(www, "www");
    if (!err.empty()) {
        response.fail(503, "class www doesn't exist");
        return response;
    }

    // Get the name of the desired function.
    std::string_view orig_fn = request.first_path_component("index");
    eng::string lua_fn = HttpParser::to_lua_identifier(orig_fn);
    if (lua_fn.empty()) {
        response.fail(404, util::ss("cannot convert to lua function name: ", orig_fn));
        return response;
    }

    // Get the closure.  If there's no such closure,
    // return a 404 Not Found to the client.
    LS.rawget(func, www, lua_fn);
    if (!LS.isfunction(func)) {
        response.fail(404, util::ss("no such lua function: www.", lua_fn));
        return response;
    }

    // Store the request into a lua table.
    request.store(LS, reqtab);

    // Call the function.
    int oldtop = lua_gettop(L);
    lua_pushvalue(L, func.index());
    lua_pushvalue(L, reqtab.index());
    Gui::store_global_pointer(L, nullptr);
    open_lthread_state(0, 0, 0, false, false);
    eng::string msg = traceback_pcall(L, 1, LUA_MULTRET);
    close_lthread_state();

    // If the call threw an error, return
    // a 500 Internal Server Error to the client.
    if (!msg.empty()) {
        response.fail(500, msg);
        return response;
    }

    // If the call didn't return a single table, return
    // a 500 Internal Server Error to the client.
    int newtop = lua_gettop(L);
    if ((newtop != oldtop + 1) || (!lua_istable(L, newtop))) {
        response.fail(500, util::ss("lua function www.", lua_fn, " didn't return a table"));
        return response;
    }

    // Try to convert the table into a response.
    LuaKeywordParser kp(LS, LuaSpecial(newtop));
    response.configure(kp);
    response.set_defaults();
    eng::string kperr = kp.final_check();
    if (!kperr.empty()) {
        response.fail(500, kperr);
    }
    return response;
}

void World::run_unittests() {
    assert(stack_is_clear());
    source_db_.run_unittests();
    assert(stack_is_clear());
}

void World::invoke(const Invocation &inv) {
    switch (inv.kind()) {
    case Invocation::KIND_PLAN:
        invoke_plan(inv.actor(), inv.place(), inv.action(), inv.data());
        break;
    case Invocation::KIND_LUA:
        invoke_lua(inv.actor(), inv.place(), inv.action(), inv.data());
        break;
    case Invocation::KIND_FLUSH_PRINTS:
        invoke_flush_prints(inv.actor(), inv.place(), inv.action(), inv.data());
        break;
    case Invocation::KIND_TICK:
        invoke_tick(inv.actor(), inv.place(), inv.action(), inv.data());
        break;
    case Invocation::KIND_LUA_SOURCE:
        invoke_lua_source(inv.actor(), inv.place(), inv.action(), inv.data());
        break;
    default:
        // Do nothing.  Standard behavior for any invalid command is to
        // simply do nothing at all.  Perhaps eventually we may add a flag
        // to the world model to indicate that we've detected an invalid
        // command, to allow us to close the connection to a client that
        // is misbehaving.
        break;
    }
}

void World::invoke_flush_prints(int64_t actor_id, int64_t place_id, const eng::string &action, const InvocationData &data) {
    assert(stack_is_clear());
    // Check argument sanity.
    if (actor_id != place_id) {
        return;
    }
    int64_t line = sv::to_int64(action, -1);
    if ((line < 0)||(line > INT_MAX)) {
        return;
    }
    Tangible *tactor = tangible_get(actor_id);
    if (tactor == nullptr) {
        return;
    }
    tactor->print_buffer_.discard_upto(line);
    assert(stack_is_clear());
}



void World::invoke_lua(int64_t actor_id, int64_t place_id, const eng::string &action, const InvocationData &data) {
    assert(stack_is_clear());

    // Make sure that actor and place exist and are not stubs.
    Tangible *tactor = tangible_get(actor_id);
    Tangible *tplace = tangible_get(place_id);
    if ((tactor == nullptr) || (tplace == nullptr)) {
        return;
    }

    // Get a thread ID for the new thread.
    int64_t tid = tplace->id_player_pool_.get_one();

    // Set up for lua manipulation.
    {
        lua_State *L = state();
        LuaVar func, tangibles, place, mt, thread, thinfo, threads;
        LuaExtStack LS(L, func, tangibles, place, mt, thread, thinfo, threads);

        // create the compiled closure.
        int status = luaL_loadbuffer(L, action.c_str(), action.size(), "=invoke");
        lua_replace(L, func.index());
        if (status != LUA_OK) {
            // The closure is actually an error message. Do nothing.
            // This should normally not happen: LuaConsole should filter
            // out syntax errors.
            return;
        }

        // Get the place.
        LS.rawget(tangibles, LuaRegistry, "tangibles");
        LS.rawget(place, tangibles, place_id);
        if (!LS.istable(place)) {
            return;
        }

        // Get the place's metatable.
        LS.getmetatable(mt, place);
        if (!LS.istable(mt)) {
            return;
        }

        // Create a new thread, set up function and parameters.
        lua_State *CO = LS.newthread(thread);
        lua_pushvalue(L, func.index());
        lua_xmove(L, CO, 1);

        // Create the thread info table.
        LS.newtable(thinfo);
        LS.rawset(thinfo, "thread", thread);
        LS.rawset(thinfo, "actorid", actor_id);
        LS.rawset(thinfo, "isnew", true);
        LS.rawset(thinfo, "useppool", true);
        LS.rawset(thinfo, "print", true);
        
        // Store the thread into place's thread table.
        LS.rawget(threads, mt, "threads");
        if (!LS.istable(threads)) {
            return;
        }
        LS.rawset(threads, tid, thinfo);
    }

    schedule(0, tid, place_id);
    run_scheduled_threads();
    assert(stack_is_clear());
}

void World::invoke_plan(int64_t actor_id, int64_t place_id, const eng::string &action, const InvocationData &data) {
    assert(stack_is_clear());

    // Validate that the action is legal.
    Gui validation_gui;
    update_gui(actor_id, place_id, &validation_gui);
    if (!validation_gui.has_action(action)) {
        return;
    }

    // Make sure the action starts with "cb_"
    if (!sv::has_prefix(action, "cb_")) {
        return;
    }

    // Get the actor and place.  Make sure both exist.
    Tangible *tactor = tangible_get(actor_id);
    Tangible *tplace = tangible_get(place_id);
    if ((tactor == nullptr) || (tplace == nullptr)) {
        return;
    }

    // Get an ID for the thread.  We always use the player
    // pool in this case.
    int64_t tid = tactor->id_player_pool_.get_one();

    {
        // Set up for Lua manipulation.
        lua_State *L = state();
        LuaVar actor, place, func, tangibles, mt, index, thread, threads, thinfo, message, invdata;
        LuaExtStack LS(L, actor, place, func, tangibles, mt, index, thread, threads, thinfo, message, invdata);

        // Get the actor and place.
        LS.rawget(tangibles, LuaRegistry, "tangibles");
        LS.rawget(actor, tangibles, actor_id);
        LS.rawget(place, tangibles, place_id);
        if (!LS.istable(actor) || !LS.istable(place)) {
            return;
        }

        // Get the action closure.
        LS.getmetatable(mt, place);
        if (!LS.istable(mt)) {
            return;
        }
        LS.rawget(index, mt, "__index");
        if (!LS.istable(index)) {
            return;
        }
        LS.rawget(func, index, action);
        if (!LS.isfunction(func)) {
            return;
        }

        // Convert the InvocationData into a lua table.
        LS.newtable(invdata);
        for (const auto &p : data) {
            LS.rawset(invdata, p.first, p.second);
        }

        // Create a new thread, set up function and parameters.
        lua_State *CO = LS.newthread(thread);
        lua_pushvalue(L, func.index());
        lua_pushvalue(L, actor.index());
        lua_pushvalue(L, place.index());
        lua_pushvalue(L, invdata.index());
        lua_xmove(L, CO, 4);

        // Create the thread info table.
        LS.newtable(thinfo);
        LS.rawset(thinfo, "thread", thread);
        LS.rawset(thinfo, "actorid", actor_id);
        LS.rawset(thinfo, "isnew", true);
        LS.rawset(thinfo, "useppool", true);
        LS.rawset(thinfo, "print", false);
        
        // Store the thread into place's thread table.
        LS.rawget(threads, mt, "threads");
        if (!LS.istable(threads)) {
            return;
        }
        LS.rawset(threads, tid, thinfo);
    }
    
    // Push the thread's ID into the runnable thread queue,
    // then run the thread queue.
    schedule(0, tid, place_id);
    run_scheduled_threads();
    assert(stack_is_clear());
}

void World::invoke_tick(int64_t actor_id, int64_t place_id, const eng::string &action, const InvocationData &data) {
    if (!is_authoritative()) {
        return;
    }
    clock_ += 1;
    run_scheduled_threads();
}

void World::invoke_lua_source(int64_t actor_id, int64_t place_id, const eng::string &action, const InvocationData &data) {
    if (!is_authoritative()) {
        return;
    }
    // We need some kind of authentication here.
    try {
        StreamBuffer sb(action);
        util::LuaSourceVec sv;
        SourceDB::deserialize_source(&sv, &sb);
        update_source(sv);
    } catch (const StreamException &ex) {
        return;
    }
}

void World::guard_blockable(lua_State *L, const char *fn) {
    if (lthread_thread_id_ == 0) {
        // in a probe, blocking functions like http.get throw an error.
        luaL_error(L, "cannot %s in a probe", fn);
        assert(false);
    }
    if (!is_authoritative()) {
        // in a nonauth model, blocking functions like http.get are converted to nopredict.
        lua_yield(L, 0);
        luaL_error(L, "unexplained nopredict failure in %s", fn);
        assert(false);
    }
}

void World::guard_nopredict(lua_State *L, const char *fn) {
    // Caution: this code must be equivalent to the
    // code in LuaCoreStack::guard_nopredict.
    if (lthread_thread_id_ == 0) {
        return;
    }
    if (!is_authoritative()) {
        lua_yield(L, 0);
        luaL_error(L, "unexplained nopredict failure in %s", fn);
    }
}

void World::schedule(int64_t clk, int64_t thid, int64_t plid) {
    if (clk > 0) {
        assert(is_authoritative());
    }
    thread_sched_.add(clk, thid, plid);
}

void World::run_scheduled_threads() {
    assert(stack_is_clear());
    lua_State *L = state();
    LuaVar tangibles, place, mt, threads, thinfo, actorid, isnew, useppool, thread, print;
    LuaExtStack LS(L, tangibles, place, mt, threads, thinfo, actorid, isnew, useppool, thread, print);

    LS.rawget(tangibles, LuaRegistry, "tangibles");
    while (thread_sched_.ready(clock_)) {
        SchedEntry sched = thread_sched_.pop();
        LS.rawget(place, tangibles, sched.place_id());
        if (!LS.istable(place)) {
            continue;
        }
        LS.getmetatable(mt, place);
        if (!LS.istable(mt)) {
            continue;
        }
        LS.rawget(threads, mt, "threads");
        if (!LS.istable(threads)) {
            continue;
        }
        LS.rawget(thinfo, threads, sched.thread_id());
        if (!LS.istable(thinfo)) {
            continue;
        }
        LS.rawget(actorid, thinfo, "actorid");
        if (!LS.isnumber(actorid)) {
            continue;
        }
        LS.rawget(isnew, thinfo, "isnew");
        if (!LS.isboolean(isnew)) {
            continue;
        }
        LS.rawget(useppool, thinfo, "useppool");
        if (!LS.isboolean(useppool)) {
            continue;
        }
        LS.rawget(thread, thinfo, "thread");
        if (!LS.isthread(thread)) {
            continue;
        }

        // Resume the coroutine.
        lua_State *CO = LS.ckthread(thread);
        open_lthread_state(LS.ckinteger(actorid), sched.place_id(), sched.thread_id(), LS.ckboolean(useppool), true);
        int nargs = LS.ckboolean(isnew) ? (lua_gettop(CO) - 1) : lua_gettop(CO);
        int status = lua_resume(CO, nullptr, nargs);
        std::ostream *ostream = lthread_print_stream();

        if (status == LUA_OK) {
            // Successfully ran to completion.  Print any return values.
            // Remove from thread table.
            LS.rawget(print, thinfo, "print");
            LS.rawset(threads, sched.thread_id(), LuaNil);
            LuaCoreStack LSCO(CO);
            if (LS.ckboolean(print)) {
                for (int i = 1; i <= lua_gettop(CO); i++) {
                    pprint(LSCO, LuaSpecial(i), PrettyPrintOptions(), ostream);
                    (*ostream) << std::endl;
                }
            }
        } else if (status == LUA_YIELD) {
            if (is_authoritative()) {
                LS.rawset(thinfo, "isnew", false);
                LS.rawset(thinfo, "useppool", false);
            } else {
                // When a nonauthoritative model yields, for any reason,
                // the thread is discarded.  This is also used as a way to implement
                // nopredict: the thread that wants to 'nopredict' just yields,
                // knowing that this will cause it to be killed.
                LS.rawset(threads, sched.thread_id(), LuaNil);
            }
        } else {
            // Generated an error.  Add a traceback, print, and kill the coroutine.
            // Currently, the error is sent to the actor.  That seems... not right in the long run.
            if (is_authoritative()) {
                traceback_coroutine(CO);
                (*ostream) << lua_tostring(CO, -1);
            }
            LS.rawset(threads, sched.thread_id(), LuaNil);
        }
        close_lthread_state();
    }
}

int64_t World::alloc_id_predictable() {
    if (!lthread_use_ppool_) {
        return id_global_pool_.get_one();
    }
    Tangible *t = tangible_get(lthread_actor_id_);
    if (t == nullptr) {
        return id_global_pool_.get_one();
    }
    return t->id_player_pool_.get_one();
}

const PrintBuffer *World::get_printbuffer(int64_t actor_id) {
    Tangible *actor = tangible_get(actor_id);
    if (actor != nullptr) {
        return &actor->print_buffer_;
    }
    return nullptr;
}

void World::clear_lthread_state() {
    lthread_prints_.reset();
    lthread_actor_id_ = 0;
    lthread_place_id_ = 0;
    lthread_thread_id_ = 0;
    lthread_use_ppool_ = false;
}

void World::open_lthread_state(int64_t actor, int64_t place, int64_t thread, bool ppool, bool prints) {
    lthread_actor_id_ = actor;
    lthread_place_id_ = place;
    lthread_thread_id_ = thread;
    lthread_use_ppool_ = ppool;
    if (prints) {
        lthread_prints_.reset(new eng::ostringstream);
    } else {
        lthread_prints_.reset();
    }
}

void World::close_lthread_state() {
    // Copy prints from lthread_prints_ stringstream into
    // the appropriate actor's PrintBuffer.  If for some reason
    // there isn't an actor, or if the actor doesn't have a PrintBuffer,
    // send the output to std::cerr.
    if (lthread_prints_ != nullptr) {
        const eng::string &output = lthread_prints_->str();
        Tangible *actor = tangible_get(lthread_actor_id_);
        if (actor != nullptr) {
            actor->print_buffer_.add_string(output, is_authoritative());
        }
    }
    // Now clean up everything.
    clear_lthread_state();
}

std::ostream *World::lthread_print_stream() const {
    if (lthread_prints_ != nullptr) {
        return lthread_prints_.get();
    } else {
        return &std::cerr;
    }
}

void World::set_global(LuaCoreStack &LS0, const eng::string &gvar, LuaSlot value) {
    lua_State *L = LS0.state();
    LuaVar globaldb, copy;
    LuaExtStack LS(L, globaldb, copy);

    // Serialize then deserialize the data, to produce a copy.
    StreamBuffer sb;
    eng::string error = serialize_lua(LS, value, &sb);
    if (!error.empty()) {
        luaL_error(L, "%s", error.c_str());
        return;
    }
    eng::string serialized(sb.view());
    error = deserialize_lua(LS, copy, &sb);
    if (!error.empty()) {
        luaL_error(L, "%s", error.c_str());
        return;
    }

    // Store the copy in the globalDB.
    LS.rawget(globaldb, LuaRegistry, "globaldb");
    LS.rawset(globaldb, gvar, copy);

    // Store the serialized blob.
    gvname_to_serial_[gvar] = serialized;

    // Implement the tracking so that we can rapidly determine which global
    // variables need to be difference transmitted.
    //
    // In the master model, we generate a sequence number for the assignment.
    // We store the mapping from global variable name to that sequence number
    // and vice versa.
    //
    // On the client side, we just record the global variable in a list
    // of recently modified globals.
    // 
    if (is_authoritative()) {
        int64_t &seqno = gvname_to_seqno_[gvar];
        seqno_to_gvname_.erase(seqno);
        seqno = assign_seqno_++;
        seqno_to_gvname_[seqno] = gvar;
    } else {
        gvname_modified_.insert(gvar);
    }
}


void World::serialize(StreamBuffer *sb) {
    assert(stack_is_clear());
    assert(redirects_.empty());
    // int64_t wc0 = sb->total_writes();
    lua_snap_.serialize(sb);
    id_global_pool_.serialize(sb);
    sb->write_int64(clock_);
    thread_sched_.serialize(sb);
    http_requests_.serialize(sb);
    sb->write_uint32(tangibles_.size());
    for (const auto &p : tangibles_) {
        sb->write_int64(p.first);
        p.second->serialize(sb);
    }
    assert(stack_is_clear());
}

void World::deserialize(StreamBuffer *sb) {
    assert(stack_is_clear());
    redirects_.clear();
    lua_snap_.deserialize(sb);
    id_global_pool_.deserialize(sb);
    clock_ = sb->read_int64();
    thread_sched_.deserialize(sb);
    http_requests_.deserialize(sb);
    // Mark all tangibles for deletion by setting ID to zero.
    for (const auto &p : tangibles_) {
        p.second->plane_item_.set_id(0);
    }
    // Deserialize tangibles.
    size_t ntan = sb->read_uint32();
    for (size_t i = 0; i < ntan; i++) {
        int64_t id = sb->read_int64();
        UniqueTangible &t = tangibles_[id];
        if (t == nullptr) {
            t.reset(new Tangible(this, id));
        } else {
            t->plane_item_.set_id(id);
        }
        t->deserialize(sb);
    }
    // Delete tangibles that didn't get deserialized.
    for (auto iter = tangibles_.begin(); iter != tangibles_.end(); ) {
        if (iter->second->plane_item_.id() == 0) {
            tangibles_.erase(iter++);
        } else {
            ++iter;
        }
    }
    // After a save and load, http requests no longer should exist
    abort_all_http_requests(425, "http requests aborted by loading a save game");
    assert(stack_is_clear());
}

void World::snapshot() {
    assert(snapshot_.empty());
    serialize(&snapshot_);
    assert(!snapshot_.empty());
}

void World::rollback() {
    assert(!snapshot_.empty());
    deserialize(&snapshot_);
    assert(snapshot_.empty());
}

// This is the main routine for the DLL.   We have to use a registration device
// to register this main routine with DrivenEngine. DrivenEngine will then call
// it exactly once the first time that the driver initializes an EngineWrapper.
// 
void engine_initialization() {
    SourceDB::register_lua_builtins();
}

static DrivenEngineInitializerReg eireg(engine_initialization);