Rocket.Chat.ReactNative/app/lib/methods/helpers/navigation/conditional.ts

// Taken from https://github.com/react-navigation/react-navigation/blob/master/packages/stack/src/utils/conditional.tsx
import { Animated } from 'react-native';

const { add, multiply } = Animated;

/**
 * Use an Animated Node based on a condition. Similar to Reanimated's `cond`.
 *
 * @param condition Animated Node representing the condition, must be 0 or 1, 1 means `true`, 0 means `false`
 * @param main Animated Node to use if the condition is `true`
 * @param fallback Animated Node to use if the condition is `false`
 */
export default function conditional(
	condition: Animated.AnimatedInterpolation,
	main: Animated.Animated,
	fallback: Animated.Animated
): Animated.AnimatedAddition {
	// To implement this behavior, we multiply the main node with the condition.
	// So if condition is 0, result will be 0, and if condition is 1, result will be main node.
	// Then we multiple reverse of the condition (0 if condition is 1) with the fallback.
	// So if condition is 0, result will be fallback node, and if condition is 1, result will be 0,
	// This way, one of them will always be 0, and other one will be the value we need.
	// In the end we add them both together, 0 + value we need = value we need
	return add(
		multiply(condition, main),
		multiply(
			condition.interpolate({
				inputRange: [0, 1],
				outputRange: [1, 0]
			}),
			fallback
		)
	);
}