import type { ModifierIR } from "./scene-ir";

function fnv1a(value: string): number {
  let hash = 0x811c9dc5;
  for (let index = 0; index < value.length; index++) {
    hash ^= value.charCodeAt(index);
    hash = Math.imul(hash, 0x01000193);
  }
  return hash >>> 0;
}

/** Hashes evaluated modifier identity/state, excluding display timestamps. */
export function modifierStackHash(stack: readonly ModifierIR[] | undefined): string {
  const canonical = (stack ?? []).map((modifier) => ({
    uuid: modifier.uuid,
    type: modifier.type,
    enabled: modifier.enabled,
    showViewport: modifier.showViewport,
    showRender: modifier.showRender,
    showEditMode: modifier.showEditMode,
    showOnCage: modifier.showOnCage,
    parameters: modifier.parameters,
    dependsOn: modifier.dependsOn,
    evaluationStatus: modifier.evaluationStatus,
  }));
  return `mod-${fnv1a(JSON.stringify(canonical)).toString(16).padStart(8, "0")}`;
}