/** Velocity-based kinematic motion. Rapier remains the collision authority. */
export class CharacterMotor {
  velocity = { x: 0, y: 0, z: 0 };
  actualVelocity = { x: 0, y: 0, z: 0 };
  grounded = false;
  gravityScale = 1;
  contacts: { handle: number; normal: number[] }[] = [];
  constructor(public body: any, public collider: any, public controller: any,
    public config: any, private rapier: any) {}
  set(value: any) {
    for (const axis of ["x", "y", "z"] as const)
      if (value[axis] !== undefined) {
        if (!Number.isFinite(value[axis])) throw Error("Invalid character velocity");
        this.velocity[axis] = Math.max(-100, Math.min(100, value[axis]));
      }
    if (value.gravityScale !== undefined) {
      if (!Number.isFinite(value.gravityScale)) throw Error("Invalid gravity scale");
      this.gravityScale = Math.max(0, Math.min(5, value.gravityScale));
    }
  }
  teleport(position: number[]) {
    if (position.length !== 3 || !position.every(Number.isFinite)) throw Error("Invalid teleport");
    const p = { x: position[0], y: position[1], z: position[2] };
    this.body.setTranslation(p, true);
    this.body.setNextKinematicTranslation(p);
    this.velocity = { x: 0, y: 0, z: 0 };
    this.actualVelocity = { x: 0, y: 0, z: 0 };
    this.gravityScale = 1;
    this.grounded = false;
    this.contacts = [];
  }
  step(dt: number, extra = [0, 0, 0]) {
    this.velocity.y = Math.max(-45, this.velocity.y - (this.config.gravity ?? 24) * this.gravityScale * dt);
    // Fixed-step gravity already maintains ground contact. Rapier 0.20 snap-down
    // plus small vertical gravity steps can accumulate penetration on flat floors.
    this.controller.disableSnapToGround();
    this.controller.computeColliderMovement(this.collider, {
      x: this.velocity.x * dt + extra[0],
      y: this.velocity.y * dt + extra[1],
      z: this.velocity.z * dt + extra[2],
    }, this.rapier.QueryFilterFlags.EXCLUDE_SENSORS);
    const movement = this.controller.computedMovement(), p = this.body.translation();
    this.actualVelocity = { x: movement.x / dt, y: movement.y / dt, z: movement.z / dt };
    this.body.setNextKinematicTranslation({ x: p.x + movement.x, y: p.y + movement.y, z: p.z + movement.z });
    this.grounded = this.controller.computedGrounded();
    this.contacts = [];
    for (let i = 0; i < this.controller.numComputedCollisions(); i++) {
      const hit = this.controller.computedCollision(i);
      if (hit?.collider) this.contacts.push({ handle: hit.collider.handle, normal: [hit.normal1.x, hit.normal1.y, hit.normal1.z] });
    }
    if (this.grounded && this.velocity.y < 0) this.velocity.y = 0;
    if (this.velocity.y > 0 && this.contacts.some(c => c.normal[1] < -0.6)) this.velocity.y = 0;
  }
}