// A small keyed cache behind the panel: the conversation index and the
// last threads land here so the next open paints before the network
// answers. localStorage when it exists, memory otherwise.
export interface PanelCache {
  get: <T>(key: string) => T | null;
  set: (key: string, value: unknown) => void;
}

const memory = new Map<string, string>();

function storage(): Pick<Storage, "getItem" | "setItem" | "removeItem"> {
  try {
    if (typeof localStorage !== "undefined") {
      return localStorage;
    }
  } catch {
    /* sandboxed */
  }
  return {
    getItem: (key) => memory.get(key) ?? null,
    removeItem: (key) => {
      memory.delete(key);
    },
    setItem: (key, value) => {
      memory.set(key, value);
    },
  };
}

export function panelCache(prefix: string): PanelCache {
  const store = storage();
  return {
    get<T>(key: string): T | null {
      try {
        const raw = store.getItem(`${prefix}:${key}`);
        return raw ? (JSON.parse(raw) as T) : null;
      } catch {
        return null;
      }
    },
    set(key: string, value: unknown): void {
      try {
        store.setItem(`${prefix}:${key}`, JSON.stringify(value));
      } catch {
        store.removeItem(`${prefix}:${key}`);
      }
    },
  };
}