/**
 * Describes change of a numeric value over time.
 * Values are stored in {@link Keyframe}s, interpolation is defined by tangents on {@link Keyframe}s.
 * The curve is a cubic Hermite spline.
 *
 * @example
 *  const jump_curve = AnimationCurve.from([
 *      Keyframe.from(0, 0), // start at height 0
 *      Keyframe.from(0.3, 2), // at time 0.3, jump height will be 2 meters
 *      Keyframe.from(1, 0) // at time 1.0, land back on the ground
 *  ]);
 *
 *  jump_curve.evaluate(0.1); // what is the height at time 0.1?
 *
 * @example
 *  const curve = AnimationCurve.easeInOut();
 *
 *  sprite.transparency = curve.evaluate(time); // smoothly animate transparency of the sprite
 *
 * @implements Iterable<Keyframe>
 *
 * @see https://en.wikipedia.org/wiki/Cubic_Hermite_spline.
 * @author Alex Goldring
 * @copyright Company Named Limited (c) 2026
 */
export class AnimationCurve implements Iterable<Keyframe> {
    /**
     * Utility constructor
     * @param {Keyframe[]} keys
     * @returns {AnimationCurve}
     */
    static from(keys: Keyframe[]): AnimationCurve;
    /**
     * S-shaped curve that starts slowly, ramps up and flattens out again.
     * Useful for pleasing transitions where exit and entry should not be abrupt.
     *
     * @param {number} [timeStart]
     * @param {number} [valueStart]
     * @param {number} [timeEnd]
     * @param {number} [valueEnd]
     * @return {AnimationCurve}
     */
    static easeInOut(timeStart?: number, valueStart?: number, timeEnd?: number, valueEnd?: number): AnimationCurve;
    /**
     * A flat-line curve with a specific start and end time
     * @param {number} [timeStart]
     * @param {number} [timeEnd]
     * @param {number} [value]
     * @return {AnimationCurve}
     */
    static constant(timeStart?: number, timeEnd?: number, value?: number): AnimationCurve;
    /**
     * Curve with two keyframes connected by a straight line
     * @param {number} [timeStart]
     * @param {number} [valueStart]
     * @param {number} [timeEnd]
     * @param {number} [valueEnd]
     * @return {AnimationCurve}
     */
    static linear(timeStart?: number, valueStart?: number, timeEnd?: number, valueEnd?: number): AnimationCurve;
    /**
     * Keyframes defining the curve, in chronological order.
     * The curve manages the contents of this array, do not modify it directly.
     * @readonly
     * @type {Keyframe[]}
     */
    readonly keys: Keyframe[];
    /**
     * Add a new keyframe into the animation.
     * Keyframes can be added out of order, they will be inserted into the correct chronological position.
     * @param {Keyframe} key
     * @returns {number} key index where it was inserted at
     */
    add(key: Keyframe): number;
    /**
     * Insert multiple keyframes. Input doesn't need to be sorted.
     * @param {Keyframe[]} keys
     */
    addMany(keys: Keyframe[]): void;
    /**
     *
     * @param {Keyframe} key
     * @returns {boolean} true if the key was removed, false if the key was not found
     */
    remove(key: Keyframe): boolean;
    /**
     * Remove all keys, making the curve empty.
     */
    clear(): void;
    /**
     * Does this curve have any keyframes?
     * @return {boolean} true iff keyframe count == 0, false otherwise
     */
    isEmpty(): boolean;
    /**
     * Number of keyframes in the curve.
     * @returns {number}
     */
    get length(): number;
    /**
     * Timestamp of the first keyframe.
     * Returns 0 if there are no keyframes.
     * @returns {number}
     */
    get start_time(): number;
    /**
     * Time of the last chronological key in the curve.
     * Returns 0 if there are no keyframes.
     * @return {number}
     */
    get end_time(): number;
    /**
     * Time difference between the first and the last keyframe.
     * Returns 0 if there are no keyframes.
     * @returns {number}
     */
    get duration(): number;
    /**
     * Returns index of a key that is just before or at the time specified.
     * Useful for insertion and evaluation logic.
     * Note: if time is past the end of last key - index of the last key will be returned instead
     * @param {number} time
     * @returns {number} index of the key
     */
    getKeyIndexLow(time: number): number;
    /**
     * Evaluate interpolated value across the curve at a given time.
     * @param {number} time time in seconds
     * @return {number} value at the specified time
     */
    evaluate(time: number): number;
    /**
     * Set tangents of a key to match surrounding keys
     * Produces a smoother looking curve
     * @param {number} index index of keyframe
     */
    alignTangents(index: number): void;
    /**
     * @deprecated
     * @param {number} index Index of keyframe to be affected
     * @param {number} weight How much smoothing to apply, 1 will be fully smoothed out and 0 will have no effect at all. Value between 0 and 1
     */
    smoothTangents(index: number, weight: number): void;
    /**
     * Smooth out the curve
     */
    alignAllTangents(): void;
    /**
     * The copy is deep
     * @param {AnimationCurve} other
     */
    copy(other: AnimationCurve): void;
    /**
     *
     * @return {AnimationCurve}
     */
    clone(): AnimationCurve;
    /**
     *
     * @param {AnimationCurve} other
     * @return {boolean}
     */
    equals(other: AnimationCurve): boolean;
    /**
     *
     * @return {number}
     */
    hash(): number;
    toJSON(): {
        keys: any[];
    };
    fromJSON({ keys }: {
        keys?: any[];
    }): void;
    /**
     * Useful for fast type checks
     * @readonly
     * @type {boolean}
     */
    readonly isAnimationCurve: boolean;
    /**
     * Smooths out the curve.
     * Alias to {@link alignAllTangents}.
     */
    smooth: () => void;
    [Symbol.iterator](): Generator<Keyframe, void, unknown>;
}
import { Keyframe } from "./Keyframe.js";
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