import { Object3D } from "../core/Object3D.js";
import { ColorRepresentation } from "../math/Color.js";
import { Vector3 } from "../math/Vector3.js";
import { DirectionalLightShadow } from "./DirectionalLightShadow.js";
import { Light } from "./Light.js";

/**
 * A light that gets emitted in a specific direction
 * @remarks
 * This light will behave as though it is infinitely far away and the rays produced from it are all parallel
 * The common use case for this is to simulate daylight; the sun is far enough away that its position can be considered to be infinite, and all light rays coming from it are parallel.
 * A common point of confusion for directional lights is that setting the rotation has no effect
 * @remarks
 * This is because three.js's {@link DirectionalLight} is the equivalent to what is often called a 'Target Direct Light' in other applications.
 * This means that its direction is calculated as pointing from the light's {@link THREE.Object3D.position | position} to the {@link THREE.DirectionalLight.target | target}'s
 * position (as opposed to a 'Free Direct Light' that just has a rotation component).
 * See the {@link THREE.DirectionalLight.target | target} property below for details on updating the target.
 * @example
 * ```typescript
 * // White directional light at half intensity shining from the top.
 * const {@link DirectionalLight} = new THREE.DirectionalLight(0xffffff, 0.5);
 * scene.add(directionalLight);
 * ```
 * @see Example: {@link https://threejs.org/examples/#misc_controls_fly | controls / fly }
 * @see Example: {@link https://threejs.org/examples/#webgl_effects_parallaxbarrier | effects / parallaxbarrier }
 * @see Example: {@link https://threejs.org/examples/#webgl_effects_stereo | effects / stereo }
 * @see Example: {@link https://threejs.org/examples/#webgl_geometry_extrude_splines | geometry / extrude / splines }
 * @see Example: {@link https://threejs.org/examples/#webgl_materials_bumpmap | materials / bumpmap }
 * @see {@link https://threejs.org/docs/index.html#api/en/lights/DirectionalLight | Official Documentation}
 * @see {@link https://github.com/mrdoob/three.js/blob/master/src/lights/DirectionalLight.js | Source}
 */
export class DirectionalLight extends Light<DirectionalLightShadow> {
    /**
     * Creates a new {@link DirectionalLight}.
     * @param color Hexadecimal color of the light. Default `0xffffff` _(white)_.
     * @param intensity Numeric value of the light's strength/intensity. Expects a `Float`. Default `1`
     */
    constructor(color?: ColorRepresentation, intensity?: number);

    /**
     * Read-only flag to check if a given object is of type {@link DirectionalLight}.
     * @remarks This is a _constant_ value
     * @defaultValue `true`
     */
    readonly isDirectionalLight: true;

    /**
     * A Read-only _string_ to check if `this` object type.
     * @remarks Sub-classes will update this value.
     * @defaultValue `DirectionalLight`
     */
    override readonly type: string | "DirectionalLight";

    /**
     * Whether the object gets rendered into shadow map.
     * @remarks
     * If set to `true` light will cast dynamic shadows.
     * **Warning**: This is expensive and requires tweaking to get shadows looking right.
     * @see {@link THREE.DirectionalLightShadow | DirectionalLightShadow} for details.
     * @defaultValue `false`
     */
    override castShadow: boolean;

    /**
     * This is set equal to {@link THREE.Object3D.DEFAULT_UP}, so that the light shines from the top down.
     * @defaultValue {@link Object3D.DEFAULT_UP} _(0, 1, 0)_
     */
    override readonly position: Vector3;

    /**
     * A {@link THREE.DirectionalLightShadow | DirectionalLightShadow} used to calculate shadows for this light.
     * @defaultValue `new THREE.DirectionalLightShadow()`
     */
    shadow: DirectionalLightShadow;

    /**
     * The {@link DirectionalLight} points from its {@link DirectionalLight.position | position} to target.position.
     * @remarks **Note**: For the target's position to be changed to anything other than the default,
     * it must be added to the {@link THREE.Scene | scene} using
     * ```typescript
     * Scene.add( light.target );
     * ```
     * This is so that the target's {@link THREE.Object3D.matrixWorld | matrixWorld} gets automatically updated each frame.
     *
     * It is also possible to set the target to be another object in the scene (anything with a {@link THREE.Object3D.position | position} property),
     * like so:
     * ```typescript
     * const targetObject = new THREE.Object3D();
     * scene.add(targetObject);
     * light.target = targetObject;
     * ```
     * The {@link DirectionalLight} will now track the target object.
     * @defaultValue `new THREE.Object3D()` at _(0, 0, 0)_
     */
    target: Object3D;

    /**
     * Frees the GPU-related resources allocated by this instance
     * @remarks
     * Call this method whenever this instance is no longer used in your app.
     */
    dispose(): void;
}