@woosh/meep-engine/src/engine/intelligence/behavior/util/BranchBehavior.js

Pure JavaScript game engine. Fully featured and production ready.

import { assert } from "../../../../core/assert.js";
import { Behavior } from "../Behavior.js";
import { BehaviorStatus } from "../BehaviorStatus.js";
import { SucceedingBehavior } from "../primitive/SucceedingBehavior.js";


/**
 * Utility behavior that works just like an IF/ELSE statement
 * If you are not sure if this is the right behavior for your use-case, consider using a selector behavior instead,
 * as selector is a more commonly applicable behavior type
 * @author Alex Goldring
 * @copyright Company Named Limited (c) 2025
 */
export class BranchBehavior extends Behavior {
    #branch_success = SucceedingBehavior.INSTANCE
    #branch_failure = SucceedingBehavior.INSTANCE
    #condition = SucceedingBehavior.INSTANCE

    /**
     *
     * @type {Behavior|null}
     */
    #current = null;

    /**
     *
     * @param {Behavior} condition
     * @param {Behavior} [branch_success]
     * @param {Behavior} [branch_failure]
     */
    static from(
        condition,
        branch_success = SucceedingBehavior.INSTANCE,
        branch_failure = SucceedingBehavior.INSTANCE
    ) {
        assert.defined(condition, 'condition');
        assert.notNull(condition, 'condition');
        assert.equal(condition.isBehavior, true, 'condition.isBehavior !== true');

        assert.defined(branch_success, 'branch_success');
        assert.notNull(branch_success, 'branch_success');
        assert.equal(branch_success.isBehavior, true, 'branch_success.isBehavior !== true');

        assert.defined(branch_failure, 'branch_failure');
        assert.notNull(branch_failure, 'branch_failure');
        assert.equal(branch_failure.isBehavior, true, 'branch_failure.isBehavior !== true');


        const r = new BranchBehavior();

        r.#condition = condition;
        r.#branch_success = branch_success;
        r.#branch_failure = branch_failure;

        return r;
    }


    initialize(context) {
        super.initialize(context);

        this.#current = this.#condition;
        this.#current.initialize(context);
    }

    tick(timeDelta) {
        const s = this.#current.tick(timeDelta);

        if (s !== BehaviorStatus.Succeeded && s !== BehaviorStatus.Failed) {

            // current behavior was not resolved, continue
            return s;

        }

        if (this.#current !== this.#condition) {
            // underlying branch was resolved
            return s;
        }

        // condition was resolved, move onto a branch
        this.#current.finalize();

        if (s === BehaviorStatus.Succeeded) {
            this.#current = this.#branch_success;
        } else {
            this.#current = this.#branch_failure;
        }

        this.#current.initialize(this.context);

        return this.#current.tick(timeDelta);
    }

    finalize() {
        super.finalize();

        if (this.#current !== null) {
            this.#current.finalize()
        }
    }

}