class PhysicsSystem {
    constructor() {
        this.gravity = new Vector2(0, 0);
        this.airResistance = 0.99;
        this.collisionIterations = 3;
    }

    update(entities, deltaTime) {
        entities.forEach(entity => {
            this.updateEntity(entity, deltaTime);
        });

        for (let i = 0; i < this.collisionIterations; i++) {
            this.resolveCollisions(entities);
        }
    }

    updateEntity(entity, deltaTime) {
        if (!entity.velocity || !entity.position) return;

        entity.velocity = entity.velocity.add(this.gravity.multiply(deltaTime));
        entity.velocity = entity.velocity.multiply(this.airResistance);
        entity.position = entity.position.add(entity.velocity.multiply(deltaTime));
    }

    resolveCollisions(entities) {
        for (let i = 0; i < entities.length; i++) {
            for (let j = i + 1; j < entities.length; j++) {
                const entityA = entities[i];
                const entityB = entities[j];

                if (this.checkCollision(entityA, entityB)) {
                    this.resolveCollision(entityA, entityB);
                }
            }
        }
    }

    checkCollision(entityA, entityB) {
        if (!entityA.radius || !entityB.radius) return false;

        const distance = entityA.position.distance(entityB.position);
        return distance < (entityA.radius + entityB.radius);
    }

    resolveCollision(entityA, entityB) {
        Physics.resolveCircleCollision(entityA, entityB);
    }

    applyForce(entity, force) {
        if (!entity.velocity) return;

        const acceleration = force.divide(entity.mass || 1);
        entity.velocity = entity.velocity.add(acceleration);
    }

    setGravity(gravity) {
        this.gravity = gravity;
    }

    setAirResistance(resistance) {
        this.airResistance = Math.max(0, Math.min(1, resistance));
    }
}