import type { UIMessage } from "ai";

export function chatStorageKey(userName: string, scope: string): string {
  return `chat:${userName}:${scope}`;
}

export function loadMessages(userName: string, scope: string): UIMessage[] | undefined {
  try {
    const raw = localStorage.getItem(chatStorageKey(userName, scope));
    if (!raw) return undefined;
    const parsed = JSON.parse(raw);
    if (!Array.isArray(parsed) || parsed.length === 0) return undefined;
    return parsed.map((m: any) => ({
      ...m,
      createdAt: m.createdAt ? new Date(m.createdAt) : undefined,
    }));
  } catch {
    return undefined;
  }
}

export function saveMessages(userName: string, scope: string, messages: UIMessage[]): void {
  try {
    if (messages.length === 0) {
      localStorage.removeItem(chatStorageKey(userName, scope));
    } else {
      const serializable = messages.map((m) => {
        const anyMsg = m as any;
        return {
          id: m.id,
          role: m.role,
          content: anyMsg.content ?? "",
          parts: m.parts,
          createdAt: anyMsg.createdAt?.toISOString?.() ?? anyMsg.createdAt,
        };
      });
      localStorage.setItem(chatStorageKey(userName, scope), JSON.stringify(serializable));
    }
  } catch (e) {
    console.warn("[chat-persist] save failed:", e);
  }
}

export function getStableAnonId(): string {
  const key = "collab-editor:anon-id";
  const stored = localStorage.getItem(key);
  if (stored) return stored;
  const id = `anon-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
  localStorage.setItem(key, id);
  return id;
}