base2020/src/ecs/Data.ts

export type Jsonified<T> = {
    [K in keyof T]: JsonEncoded<T[K]>;
};
export type JsonEncoded<T> =
    T extends Function ? never
    : T extends Date ? string
    : T extends (infer U)[] ? JsonEncoded<U>[]
    : T extends Record<string, any> ? Jsonified<T>
    : T
    ;

export type Store<T extends Component<T>> = Record<number, T>;
export interface Clone<T> {
    clone(): T;
}

export function copyDense<T extends Component<T>, S extends Store<T>>(storage?: S): T[] {
    if(Array.isArray(storage)) {
        return storage.map(x => x.clone());
    } else if(storage) {
        const result: T[] = [];
        for(const key in storage) {
            result[key] = storage[key].clone();
        }
        return result;
    } else {
        return [];
    }
}
export function copySparse<T extends Component<T>, S extends Store<T>>(storage?: S): Store<T> {
    if(storage) {
        const result: Store<T> = {};
        for(const key in storage) {
            result[key] = storage[key].clone();
        }
        return result;
    } else {
        return {};
    }
}

export type Id = [number, number];

export const enum Liveness {
    DEAD = 0,
    ALIVE = 1,
    INACTIVE = 2
}

export abstract class Component<T> implements Clone<Component<T>> {
    public generation: number;
    public constructor(from: Partial<Component<T>>) {
        this.generation = from.generation ?? -1;
    }
    abstract clone(): Component<T> & T;
}
export class EntityState extends Component<EntityState> {
    public alive: Liveness;
    public constructor(from: Partial<EntityState>) {
        super(from);
        this.alive = from.alive ?? Liveness.ALIVE;
    }

    clone(): EntityState {
        return new EntityState(this);
    }
}

export type StateForSchema<T> = {
    [K in keyof T]: Record<number, Component<T[K]>>;
} & {
    entity: EntityState[];
} & Clone<StateForSchema<T>>;

// Ergonomic Lookup typings
type StoreKeysOf<DATA> = {
    [K in keyof DATA]: DATA[K] extends Record<number, Component<infer T>> ? K : never;
}[keyof DATA];
type StoreTypeOf<DATA, K> = K extends keyof DATA ? DATA[K] extends Record<number, Component<infer T>> ? T : never : never;

/**
 * Create an entity in the store
 * @param data store
 * @param assign map of components to attach
 * @param state Liveness state, allows creating an inactive entity
 * @returns the new entity's ID and generation
 */
type Assigner<DATA> = {
    [K in StoreKeysOf<DATA>]?: StoreTypeOf<DATA, K>;
};
export function Create<DATA extends StateForSchema<unknown>>(data: DATA, assign: Assigner<DATA>, state = Liveness.ALIVE): Id {
    const entities = data.entity;
    // find free ID
    let freeId = -1;
    let generation = -1;
    for (let id = 0; id < entities.length; id++) {
        if (entities[id].alive == Liveness.DEAD) {
            freeId = id;
            generation = entities[id].generation + 1;
            break;
        }
    }

    if (freeId == -1) {
        freeId = entities.length;
        generation = 1;
    }

    entities[freeId] = new EntityState({
        generation,
        alive: state
    });

    for (const key in assign) {
        const store = data[key as keyof DATA] as Store<any>;
        const component = (assign[key as keyof Assigner<DATA>] as Component<unknown>).clone();
        component.generation = generation;
        store[freeId] = component;
    }

    return [freeId, generation];
}

/**
 * "Delete" an entity
 * @param data store
 * @param id entity ID
 * @param generation entity ID generation
 * @param state can be set to Liveness.INACTIVE to disable an entity without actually killing it, for later resurrection
 */
export function Remove(data: StateForSchema<unknown>, [id, generation]: Id, state = Liveness.DEAD) {
    if (data.entity[id] && data.entity[id].generation == generation) {
        data.entity[id].alive = state;
    }
}

/**
 * Look up components that may or may not exist for an entity
 * @param data store
 * @param param1 entity Id
 * @param components names of components to look for
 * @returns the cooresponding components, with unfound ones replaced by nulls
 */
type MaybeStoreTypes<DATA, Q> = {
    [I in keyof Q]: StoreTypeOf<DATA, Q[I]> | null;
};
export function Lookup<DATA extends StateForSchema<unknown>, Q extends StoreKeysOf<DATA>[]>(data: DATA, [id, generation]: Id, ...components: Q): MaybeStoreTypes<DATA, Q> {
    const entity = data.entity[id];
    // inactive entities are fine to lookup, but dead ones are not
    if (entity && entity.generation == generation && entity.alive != Liveness.DEAD) {
        return components.map(storeName => {
            const store = data[storeName as unknown as keyof DATA] as Store<any>;
            const component = store[id];
            if (component && component.generation == generation) {
                return component;
            } else {
                return null;
            }
        }) as MaybeStoreTypes<DATA, Q>;
    } else {
        return components.map(() => null) as MaybeStoreTypes<DATA, Q>;
    }
}

/**
 * Query a Data collection for all Alive entities possessing the named set of Components.
 * "id" can be used as a pseudo-component to get the Ids for a match
 * @returns an array of tuples containing the matching entity Components
 */
type ResultTypes<DATA, Q> = {
    [I in keyof Q]: Q[I] extends "id" ? Id : StoreTypeOf<DATA, Q[I]>;
};
export function Join<DATA extends StateForSchema<unknown>, Q extends (StoreKeysOf<DATA> | "id")[]>(data: DATA, ...components: Q): ResultTypes<DATA, Q>[] {
    const entities = data.entity;
    const stores = components.map(name => {
        if (name == "id") {
            return "id";
        } else {
            return data[name as unknown as keyof DATA] as Store<any>;
        };
    });

    const results: ResultTypes<DATA, Q>[] = [];
    const firstStore = stores.filter(store => store !== "id")[0] as Store<any>;
    if (Array.isArray(firstStore)) {
        for (let id = 0; id < firstStore.length; id++) {
            JoinLoop(id, entities, stores, results);
        }
    } else {
        for (const id in firstStore) {
            JoinLoop(Number(id), entities, stores, results);
        }
    }
    return results;
}
function JoinLoop<DATA extends StateForSchema<unknown>, Q extends (StoreKeysOf<DATA> | "id")[]>(id: number, entities: EntityState[], stores: (Record<number, Component<{}>> | "id")[], results: ResultTypes<DATA, Q>[]) {
    const fullId: Id = [id, -1];
    const result: (Component<{}> | Id)[] = [];

    let generation = -1;
    for (const store of stores) {
        if (store === "id") {
            result.push(fullId);
            continue;
        }
        const component = store[id];
        if (component && (component.generation == generation || generation == -1)) {
            generation = component.generation;
            result.push(component);
        } else {
            return;
        }
    }

    // only accept active entities (do this check here, where the generation is known)
    const entity = entities[id];
    if (entity.alive != Liveness.ALIVE || generation != entity.generation) return;

    // backpatch generation now that it's known
    fullId[1] = generation;

    results.push(result as ResultTypes<DATA, Q>);
}