Tone.js/Tone/event/PatternGenerator.ts

import { assert } from "../core/util/Debug";

/**
 * The name of the patterns
 */
export type PatternName = "up" | "down" | "upDown" | "downUp" | "alternateUp" | "alternateDown" | "random" | "randomOnce";

/**
 * Start at the first value and go up to the last
 */
function* upPatternGen<T>(values: T[]): IterableIterator<T> {
	let index = 0;
	while (index < values.length) {
		index = clamp(index, values);
		yield values[index];
		index++;
	}
}

/**
 * Start at the last value and go down to 0
 */
function* downPatternGen<T>(values: T[]): IterableIterator<T> {
	let index = values.length - 1;
	while (index >= 0) {
		index = clamp(index, values);
		yield values[index];
		index--;
	}
}

/**
 * Infinitely yield the generator
 */
function* infiniteGen<T>(values: T[], gen: typeof upPatternGen): IterableIterator<T> {
	while (true) {
		yield* gen(values);
	}
}

/**
 * Make sure that the index is in the given range
 */
function clamp(index: number, values: any[]): number {
	return Math.max(Math.min(index, values.length - 1), 0);
}

/**
 * Alternate between two generators
 */
function* alternatingGenerator<T>(values: T[], directionUp: boolean): IterableIterator<T> {
	let index = directionUp ? 0 : values.length - 1;
	while (true) {
		index = clamp(index, values);
		yield values[index];
		if (directionUp) {
			index++;
			if (index >= values.length - 1) {
				directionUp = false;
			}
		} else {
			index--;
			if (index <= 0) {
				directionUp = true;
			}
		}
	}
}

/**
 * Starting from the bottom move up 2, down 1
 */
function* jumpUp<T>(values: T[]): IterableIterator<T> {
	let index = 0;
	let stepIndex = 0;
	while (index < values.length) {
		index = clamp(index, values);
		yield values[index];
		stepIndex++;
		index += (stepIndex % 2 ? 2 : -1);
	}
}

/**
 * Starting from the top move down 2, up 1
 */
function* jumpDown<T>(values: T[]): IterableIterator<T> {
	let index = values.length - 1;
	let stepIndex = 0;
	while (index >= 0) {
		index = clamp(index, values);
		yield values[index];
		stepIndex++;
		index += (stepIndex % 2 ? -2 : 1);
	}
}

/**
 * Choose a random index each time
 */
function* randomGen<T>(values: T[]): IterableIterator<T> {
	while (true) {
		const randomIndex = Math.floor(Math.random() * values.length);
		yield values[randomIndex];
	}
}

/**
 * Randomly go through all of the values once before choosing a new random order
 */
function* randomOnce<T>(values: T[]): IterableIterator<T> {
	// create an array of indices
	const copy: number[] = [];
	for (let i = 0; i < values.length; i++) {
		copy.push(i);
	}
	while (copy.length > 0) {
		// random choose an index, and then remove it so it's not chosen again
		const randVal = copy.splice(Math.floor(copy.length * Math.random()), 1);
		const index = clamp(randVal[0], values);
		yield values[index];
	}
}

/**
 * PatternGenerator returns a generator which will iterate over the given array
 * of values and yield the items according to the passed in pattern
 * @param values An array of values to iterate over
 * @param pattern The name of the pattern use when iterating over
 * @param index Where to start in the offset of the values array
 */
export function* PatternGenerator<T>(values: T[], pattern: PatternName = "up", index: number = 0): Iterator<T> {
	// safeguards
	assert(values.length > 0, "The array must have more than one value in it");
	switch (pattern) {
		case "up" :
			yield* infiniteGen(values, upPatternGen);
		case "down" :
			yield* infiniteGen(values, downPatternGen);
		case "upDown" :
			yield* alternatingGenerator(values, true);
		case "downUp" :
			yield* alternatingGenerator(values, false);
		case "alternateUp":
			yield* infiniteGen(values, jumpUp);
		case "alternateDown":
			yield* infiniteGen(values, jumpDown);
		case "random":
			yield* randomGen(values);
		case "randomOnce":
			yield* infiniteGen(values, randomOnce);
	}
}