html-tower/static/engine.js

console.log("loading engine");

const initEvent = () => {
    let subscribers = {};

    return (message, ...messageArgs) => {
        switch (message) {
        case "addSubscriber":
            let subscriberName = messageArgs[0];
            let subscriberFunc = messageArgs[1];
            subscribers[subscriberName] = subscriberFunc;
            break;
        case "raise":
            let delta = messageArgs[0];
            let eventData = messageArgs[1];
            Object.entries(subscribers).forEach(([id, subscriber]) => {
                subscriber(delta, eventData);
            });
            break;
        }
    };
};

const engine = (() => {
    let queue = [];
    let timer;
    let state;
    let time = Date.now();
    let entities = {};
    let components = {};
    let events = {};

    const engineTick = 1000 / 60;
    const tick = () => {
        let now = Date.now();
        let delta = now - time;
        time = now;
        while (queue.length > 0) {
            let eventName = queue.shift();
            events[eventName]("raise", delta);
        }
        timer = setTimeout(tick, engineTick);
    };
    const halt = () => {
        console.log("halted");
        state="halted";
        clearTimeout(timer);
    };
    return (message, ...messageArgs) => {
        switch (message) {
        case "queueEvent": {
            queue.push(messageArgs[0]);
            break;
        }
        case "events": {
            return events;
        }
        case "entities": {
            return entities;
        }
        case "components": {
            return components;
        }
        case "world": {
            return {
                entities,
                components,
                events,
            };
        }
        case "registerEntity": {
            let node = messageArgs[0];
            entities[node.id] = [];
            break;
        }
        case "removeEntity": {
            let node = messageArgs[0];
            entities[node.id].forEach(([componentType, component]) => {
                delete components[componentType].instances[component];
            });
            delete entities[node.id];
            queue.push((_) => node.remove());
            break;
        }
        case "registerComponentType": {
            let [componentType, constructor] = messageArgs;
            components[componentType] = {
                constructor,
                instances: {}
            };
            break;
        }
        case "getComponentConstructor": {
            let [componentType] = messageArgs;
            return components [componentType].constructor(engine);
        }
        case "addComponent": {
            let [entity, componentType, component] = messageArgs;
            entities[entity.id].push([componentType, component]);
            components[componentType].instances[entity.id] = component;
            break;
        }
        case "registerEvent": {
            let eventName = messageArgs[0];
            let newEvent = initEvent();
            events[eventName] = newEvent;
            break;
        }
        case "subscribeToEvent": {
            let [eventName, subscriberName, newSubscriber] = messageArgs;
            events[eventName]("addSubscriber", subscriberName, newSubscriber);
            break;
        }
        case 'start': {
            state="running";
            tick();
            break;
        }
        case 'state': {
            return state;
        }
        case 'halt': {
            halt();
            break;
        }
        };
    };
})();

initCollisionSystem (engine);
initTransformSystem(engine);
inputSystem(engine);
playerSystem(engine);
initEnvironmentSystem (engine);

engine("start");