export const POINTER_CONTRACT_SCHEMA_VERSION = 1 as const;
export type PointerKind = "mouse" | "touch" | "pen";

export interface PointerObservation {
  schemaVersion: typeof POINTER_CONTRACT_SCHEMA_VERSION;
  pointerType: PointerKind;
  pointerId: number;
  pressure: number;
  tiltX: number;
  tiltY: number;
  button: number;
  buttons: number;
  cancelled: boolean;
}

function bounded(value: number, min: number, max: number, fallback: number): number {
  return Number.isFinite(value) ? Math.max(min, Math.min(max, value)) : fallback;
}

export function observePointerEvent(event: { pointerType?: string; pointerId?: number; pressure?: number; tiltX?: number; tiltY?: number; button?: number; buttons?: number; type?: string }): PointerObservation {
  const pointerType = event.pointerType === "touch" || event.pointerType === "pen" || event.pointerType === "mouse" ? event.pointerType : null;
  if (!pointerType) throw new Error("POINTER_TYPE_UNSUPPORTED");
  if (!Number.isSafeInteger(event.pointerId) || event.pointerId! < 0) throw new Error("POINTER_ID_INVALID");
  return {
    schemaVersion: POINTER_CONTRACT_SCHEMA_VERSION,
    pointerType,
    pointerId: event.pointerId!,
    pressure: bounded(event.pressure ?? (pointerType === "mouse" ? 0 : 0.5), 0, 1, 0),
    tiltX: bounded(event.tiltX ?? 0, -90, 90, 0),
    tiltY: bounded(event.tiltY ?? 0, -90, 90, 0),
    button: Number.isInteger(event.button) ? event.button! : -1,
    buttons: Number.isInteger(event.buttons) && event.buttons! >= 0 ? event.buttons! : 0,
    cancelled: event.type === "pointercancel",
  };
}