import { SvelteMap } from 'svelte/reactivity';

export interface Entity {
    id: string;
}

/**
 * Svelte 5 Entity Store
 * Uses SvelteMap for O(1) lookups and granular reactivity.
 */
export class EntityStore<T extends Entity> {
    // SvelteMap is a reactive version of the native Map
    #entities = new SvelteMap<string, T>();

    constructor(initialEntities: T[] = []) {
        this.setAll(initialEntities);
    }

    // --- Selectors (Equivalent to Selectors) ---

    /** Get all entities as an array */
    get all() {
        return Array.from(this.#entities.values());
    }

    /** Select a single entity by ID */
    getById(id: string) {
        return this.#entities.get(id);
    }

    /** Select multiple entities by IDs */
    getByIds(ids: string[]) {
        return ids.map(id => this.#entities.get(id)).filter((e): e is T => !!e);
    }

    // --- Actions (CRUD) ---

    addOne(entity: T) {
        this.#entities.set(entity.id, entity);
    }

    addMany(entities: T[]) {
        entities.forEach(e => this.addOne(e));
    }

    updateOne(id: string, changes: Partial<T>) {
        const entity = this.#entities.get(id);
        if (entity) {
            this.#entities.set(id, { ...entity, ...changes });
        }
    }

    removeOne(id: string) {
        this.#entities.delete(id);
    }

    removeMany(ids: string[]) {
        ids.forEach(id => this.#entities.delete(id));
    }

    setAll(entities: T[]) {
        this.#entities.clear();
        this.addMany(entities);
    }

    has(id: string) {
        return this.#entities.has(id);
    }

    clear() {
        this.#entities.clear();
    }
}

/**
 * Creates a new EntityStore instance with the given initial entities.
 * @param initialEntities The initial entities to populate the store with.
 * @returns - A new EntityStore instance.
 */
export function createEntityStore<T extends Entity>(initialEntities: T[] = []) {
    return new EntityStore<T>(initialEntities);
}