blueshell/lib/nodes/LatchedIfElse.ts

A Behavior Tree implementation in modern Javascript

/**
 * Created by masdoorian on 06/23/21
 */
import { IfElse } from './IfElse';
import { BlueshellState, ResultCode, rc, BaseNode, Conditional } from '../models';

const LATCHED_RUNNING_CONSEQUENT = 0;
const LATCHED_RUNNING_ALTERNATIVE = 1;

/**
 * Latched If-Else Latched Composite Node.
 *
 * The conditional function is not called if the previous result was RUNNING - instead
 * the saved result of calling the conditional is used until the consequent/alternative
 * returns not RUNNING again and the state is reset
 *
 * If `conditional(state: S, event: E)` returns true,
 * control is passed to the consequent node.
 *
 * If `conditional(state: S, event: E)` returns false,
 * control is passed to the alternative node, or
 * if alternative is a result code, that is returned, or
 * if one is not provided, 'FAILURE' is returned.
 *
 * 06/23/21
 * @author Mark Asdoorian
 */
export class LatchedIfElse<S extends BlueshellState, E> extends IfElse<S, E> {
	constructor(
		name: string,
		private conditionalToLatch: Conditional<S, E>,
		consequent: BaseNode<S, E>,
		alternative?: BaseNode<S, E> | ResultCode,
	) {
		super(
			name,
			(state: S, event: E) => {
				const storage = this.getNodeStorage(state);
				let res: boolean;
				if (storage.running === undefined) {
					// we're not latched, so run the conditional and save the result
					res = this.conditionalToLatch(state, event);
					storage.running = res ? LATCHED_RUNNING_CONSEQUENT : LATCHED_RUNNING_ALTERNATIVE;
				} else {
					// we're latched, so return the saved result of the conditional
					res = storage.running === LATCHED_RUNNING_CONSEQUENT;
				}
				return res;
			},
			consequent,
			alternative,
		);
	}

	get latched() {
		return true;
	}

	protected _afterEvent(res: ResultCode, state: S, event: E): ResultCode {
		res = super._afterEvent(res, state, event);

		if (res !== rc.RUNNING) {
			const storage = this.getNodeStorage(state);
			storage.running = undefined;
		}

		return res;
	}
}