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;
}

export type ModifierParameterMetadata = {
  key: string;
  value: unknown;
  kind: "boolean" | "number" | "string" | "enum" | "object";
  options?: string[];
};

/** Derives editable fields from the metadata carried by the authoritative modifier IR. */
export function modifierParameterMetadata(modifier: ModifierIR): ModifierParameterMetadata[] {
  return Object.entries(modifier.parameters ?? {}).map(([key, rawValue]) => {
    // Main may carry a descriptor when RNA exposes enum choices alongside the
    // current value. Keep the descriptor opaque to callers while deriving the
    // editable value and choices from it.
    const descriptor = rawValue && typeof rawValue === "object" && !Array.isArray(rawValue) &&
      "value" in rawValue && ("kind" in rawValue || "options" in rawValue)
      ? rawValue as { value: unknown; kind?: ModifierParameterMetadata["kind"]; options?: unknown[] }
      : undefined;
    const rawOptions = descriptor?.options ?? (Array.isArray(rawValue) && rawValue.every((entry) => typeof entry === "string") ? rawValue : undefined);
    const options = rawOptions?.map(String);
    const value = descriptor?.value ?? (options ? options[0] : rawValue);
    const kind = descriptor?.kind ?? (
      typeof value === "boolean" ? "boolean" :
      typeof value === "number" ? "number" :
      typeof value === "string" ? (options ? "enum" : "string") :
      "object"
    );
    return { key, value, kind, options: options ?? undefined };
  });
}

/** 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")}`;
}