import { EventDispatcher, MathUtils, type Camera } from 'three';
import type Context from '../core/Context';
import type Disposable from '../core/Disposable';
import type Instance from '../core/Instance';

/* eslint no-unused-vars: 0 */
/* eslint class-methods-use-this: 0 */

export interface EntityEventMap {
    initialized: unknown;
    'frozen-property-changed': { frozen: boolean };
}

export type EntityUserData = Record<string, unknown>;

export type EntityPreprocessOptions = {
    instance: Instance;
};

/**
 * Abstract base class for all entities in Giro3D.
 * The Entity is the core component of Giro3D and represent an updatable
 * object that is added to an {@link core.Instance | Instance}.
 *
 * The class inherits three.js' [`EventDispatcher`](https://threejs.org/docs/index.html?q=even#api/en/core/EventDispatcher).
 *
 * ### The `userData` property
 *
 * The `userData` property can be used to attach custom data to the entity, in a type safe manner.
 * It is recommended to use this property instead of attaching arbitrary properties to the object:
 *
 * ```ts
 * type MyCustomUserData = {
 *   creationDate: Date;
 *   owner: string;
 * };
 * const entity: Entity<MyCustomUserData> = ...;
 *
 * entity.userData.creationDate = Date.now();
 * entity.userData.owner = 'John Doe';
 * ```
 *
 * ### Lifetime
 *
 * The lifetime of an entity follows this pattern: when the entity is added to an instance, its
 * {@link preprocess} method is called. When the promise
 * returned by this method resolves, the entity can be used in the main loop, where the update
 * methods (see below) will be used to update the entity over time. Finally, when the entity is
 * removed from the instance, its {@link dispose} method
 * is called to cleanup memory.
 *
 * ### The update methods
 *
 * This class exposes three methods to update the object:
 * - {@link Entity.preUpdate}
 * to determine which _parts_ of the object should actually be updated.
 * - {@link Entity.update} called for each part returned
 * by `preUpdate()`
 * - {@link Entity.postUpdate} to finalize
 * the update step.
 *
 * ### A note on "parts"
 *
 * The notion of "part to be updated" is entity-specific. For example, if the entity is a tiled map,
 * the parts may be map tiles. If the entity is a point cloud, it may be point clusters, and so on.
 * On the other hand, if the entity is not made of distinct objects, the "part to update" may be the
 * entity itself, or a dummy object.
 *
 * ```js
 * const instance = new Instance(...);
 * const entity = new Entity('exampleEntity');
 * instance.add(entity);
 * ```
 * @typeParam TEventMap - The event map of the entity.
 * @typeParam TUserData - The type of the `userData` property.
 */
abstract class Entity<TEventMap extends EntityEventMap = EntityEventMap, TUserData = EntityUserData>
    extends EventDispatcher<TEventMap & EntityEventMap>
    implements Disposable
{
    /**
     * The unique identifier of this entity.
     */
    readonly id: string;
    private _frozen: boolean;
    private _ready = false;
    private _instance?: Instance;

    /**
     * Determine if this entity is ready to use.
     */
    get ready() {
        return this._ready;
    }

    get instance(): Instance {
        if (!this._instance) {
            throw new Error(
                'This entity has not been added to an instance or its initialization is not finished.\n' +
                    'To check if the entity is ready, use the .ready property',
            );
        }
        return this._instance;
    }

    /**
     * The name of this entity.
     */
    name: string | undefined;

    /**
     * An object that can be used to store custom data about the {@link Entity}.
     */
    readonly userData: TUserData;

    /**
     * Read-only flag to check if a given object is of type Entity.
     */
    readonly isEntity: boolean = true as const;
    /**
     * The name of the type of this object.
     */
    type: string;

    /**
     * Creates an entity with the specified unique identifier.
     */
    constructor() {
        super();

        this.id = MathUtils.generateUUID();
        this.type = 'Entity';
        this._frozen = false;
        // @ts-expect-error {} cannot be assigned to TUserData, but it's better than null/undefined.
        this.userData = {};
    }

    /**
     * Gets or sets the frozen status of this entity. A frozen entity is still visible
     * but will not be updated automatically.
     *
     * Useful for debugging purposes.
     */
    get frozen() {
        return this._frozen;
    }

    set frozen(v) {
        if (this._frozen !== v) {
            this._frozen = v;
            this.dispatchEvent({ type: 'frozen-property-changed', frozen: v });
        }
    }

    /**
     * Gets whether this entity is currently loading data.
     */
    get loading() {
        // Implement this in derived classes.
        return false;
    }

    /**
     * Gets the current loading progress (between 0 and 1).
     * Note: This property is only meaningful if {@link loading} is `true`.
     */
    get progress() {
        // Implement this in derived classes.
        return 1;
    }

    /**
     * Asynchronously preprocess the entity. This method may be overriden to perform
     * any operation that must be done before the entity can be used in the scene, such
     * as fetching metadata about a dataset, etc.
     *
     * @param opts - The preprocess options.
     *
     * @returns A promise that resolves when the entity is ready to be used.
     */
    protected preprocess(_opts: EntityPreprocessOptions): Promise<void> {
        return Promise.resolve();
    }

    /**
     * @internal
     */
    async initialize(opts: EntityPreprocessOptions): Promise<void> {
        this._instance = opts.instance;

        await this.preprocess(opts);

        this._ready = true;
        this.dispatchEvent({ type: 'initialized' });
    }

    /**
     * This method is called before `update` to check if the MainLoop
     * should try to update this entity or not. For better performances,
     * it should return `false` if the entity has no impact on the
     * rendering (e.g. the element is not visible).
     *
     * The inherited child _can_ completely ignore this value if it makes sense.
     *
     * @returns `true` if should check for update
     */
    shouldCheckForUpdate(): boolean {
        return this._ready;
    }

    /**
     * This method is called at the beginning of the `update` step to determine
     * if we should do a full render of the object. This should be the case if, for
     * instance, the source is the camera.
     *
     * You can override this depending on your needs. The inherited child should
     * not ignore this value, it should do a boolean OR, e.g.:
     * `return super.shouldFullUpdate(updateSource) || this.contains(updateSource);`
     *
     * @param updateSource - Source of change
     * @returns `true` if requires a full update of this object
     */
    shouldFullUpdate(updateSource: unknown): boolean {
        return updateSource === this || (updateSource as Camera).isCamera;
    }

    /**
     * This method is called at the beginning of the `update` step to determine
     * if we should re-render `updateSource`.
     * Not used when `shouldFullUpdate` returns `true`.
     *
     * You can override this depending on your needs.  The inherited child should
     * not ignore this value, it should do a boolean OR, e.g.:
     * `return super.shouldUpdate(updateSource) || this.contains(updateSource);`
     *
     * @param updateSource - Source of change
     * @returns `true` if requires an update of `updateSource`
     */
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    shouldUpdate(updateSource: unknown): boolean {
        return false;
    }

    /**
     * Filters what objects need to be updated, based on `updatedSources`.
     * The returned objects are then passed to {@link preUpdate} and {@link postUpdate}.
     *
     * Inherited classes should override {@link shouldFullUpdate} and {@link shouldUpdate}
     * if they need to change this behavior.
     *
     * @param updateSources - Sources that triggered an update
     * @returns Set of objects to update
     */
    filterChangeSources(updateSources: Set<unknown>): Set<unknown> {
        let fullUpdate = false;
        const filtered = new Set<unknown>();
        updateSources.forEach(src => {
            fullUpdate = fullUpdate || this.shouldFullUpdate(src);
            if (this.shouldUpdate(src)) {
                filtered.add(src);
            }
        });
        return fullUpdate ? new Set([this]) : filtered;
    }

    /**
     * This method is called just before `update()` to filter and select
     * which _elements_ should be actually updated. For example, in the
     * case of complex entities made of a hierarchy of elements, the entire
     * hierarchy may not need to be updated.
     *
     * Use this method to optimize the update step by reducing the number
     * of elements to process.
     *
     * Note: if this functions returns nothing, `update()` will not be called.
     *
     * @param context - the update context.
     * @param changeSources - the objects that triggered an update step.
     * This is useful to filter out unnecessary updates if no sources are
     * relevant to this entity. For example, if one of the sources is a
     * camera that moved during the previous frame, any entity that depends
     * on the camera's field of view should be updated.
     * @returns the _elements_ to update during `update()`.
     */
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    preUpdate(context: Context, changeSources: Set<unknown>): unknown[] | null {
        return null;
    }

    /**
     * Performs an update on an _element_ of the entity.
     *
     * Note: this method will be called for each element returned by `preUpdate()`.
     *
     * @param context - the update context.
     * This is the same object that the entity whose `update()` is being called.
     * @param element - the element to update.
     * This is one of the elements returned by {@link preUpdate}.
     * @returns New elements to update
     */
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    update(context: Context, element: unknown): unknown[] | undefined | null {
        return undefined;
    }

    /**
     * Method called after {@link Entity.update}.
     *
     * @param context - the update context.
     * @param changeSources - the objects that triggered an update step.
     * This is useful to filter out unnecessary updates if no sources are
     * relevant to this entity. For example, if one of the sources is a
     * camera that moved during the previous frame, any entity that depends
     * on the camera's field of view should be updated.
     */
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    postUpdate(context: Context, changeSources: Set<unknown>) {
        /** do nothing */
    }

    /**
     * Disposes this entity and all resources associated with it.
     *
     * The default implementation of this method does nothing.
     * You should implement it in your custom entities to handle any special logic of disposal.
     *
     * For example: disposing materials, geometries, stopping HTTP requests, etc.
     *
     */
    dispose() {
        /** do nothing */
    }

    /**
     * Notifies the parent instance that a change occured in the scene.
     */
    protected notifyChange(source?: unknown | unknown[]): void {
        this._instance?.notifyChange(source);
    }
}

export function isEntity(o: unknown): o is Entity {
    return (o as Entity)?.isEntity;
}

export default Entity;