thi-ng/umbrella

import type { ICopy, IReset } from "@thi.ng/api";
import { AGen } from "./agen.js";

/**
 * Returns new multiply gen, producing `y(t) = factor * y(t-1)`, using
 * given `factor` and `start` values.
 *
 * Also see {@link curve}.
 *
 * @param factor -
 * @param start -
 * @param clamp -
 */
export const mul = (factor?: number, start?: number, clamp?: number) =>
    new Mul(factor, start, clamp);

export class Mul extends AGen<number> implements ICopy<Mul>, IReset {
    constructor(
        protected _factor = 1,
        protected _start = 1,
        protected _clamp?: number
    ) {
        super(0);
        this.reset();
    }

    copy() {
        return new Mul(this._factor, this._start, this._clamp);
    }

    reset() {
        this._val = this._start / this._factor;
        return this;
    }

    next() {
        let v = this._val * this._factor;
        return (this._val =
            this._clamp !== undefined
                ? this._start < this._clamp
                    ? Math.min(v, this._clamp)
                    : Math.max(v, this._clamp)
                : v);
    }
}