export const LOCAL_DRAFT_SCHEMA_VERSION = 1;

export interface LocalDraftEnvelope<Draft> {
  schemaVersion: typeof LOCAL_DRAFT_SCHEMA_VERSION;
  serverVersion: number;
  updatedAt: string;
  draft: Draft;
}

export function adminDraftKey(guideId: string, section: string): string {
  return `buzz-sheet:admin-draft:${guideId}:${section}`;
}

export function serializeLocalDraft<Draft>(draft: Draft, serverVersion: number): string {
  return JSON.stringify({
    schemaVersion: LOCAL_DRAFT_SCHEMA_VERSION,
    serverVersion,
    updatedAt: new Date().toISOString(),
    draft,
  } satisfies LocalDraftEnvelope<Draft>);
}

export function parseLocalDraft<Draft>(serialized: string, parseDraft: (value: unknown) => Draft | null): LocalDraftEnvelope<Draft> | null {
  try {
    const value: unknown = JSON.parse(serialized);
    if (!value || typeof value !== "object") return null;
    const envelope = value as Record<string, unknown>;
    if (envelope.schemaVersion !== LOCAL_DRAFT_SCHEMA_VERSION || typeof envelope.serverVersion !== "number" || typeof envelope.updatedAt !== "string") return null;
    const draft = parseDraft(envelope.draft);
    return draft === null ? null : {
      schemaVersion: LOCAL_DRAFT_SCHEMA_VERSION,
      serverVersion: envelope.serverVersion,
      updatedAt: envelope.updatedAt,
      draft,
    };
  } catch {
    return null;
  }
}