import * as React from "react";

const PREFIX = "puck:";

function load<T>(key: string, fallback: () => T): T {
  try {
    const raw = localStorage.getItem(PREFIX + key);
    if (raw == null) return fallback();
    // merge over fallback so new fields added later get their defaults
    const parsed = JSON.parse(raw);
    const base = fallback();
    return typeof base === "object" && base !== null && !Array.isArray(base)
      ? { ...base, ...(parsed as object) }
      : (parsed as T);
  } catch (e) {
    console.error(`puck: failed to load ${key}, using defaults`, e);
    return fallback();
  }
}

/** useState backed by localStorage. `fallback` runs only when nothing is stored. */
export function usePersistent<T>(key: string, fallback: () => T) {
  const [value, setValue] = React.useState<T>(() => load(key, fallback));
  React.useEffect(() => {
    try {
      localStorage.setItem(PREFIX + key, JSON.stringify(value));
    } catch (e) {
      console.error(`puck: failed to persist ${key}`, e);
    }
  }, [key, value]);
  return [value, setValue] as const;
}

/** Wipe all of Puck's persisted state (the "forget everything" escape hatch). */
export function forgetEverything() {
  for (const k of Object.keys(localStorage)) {
    if (k.startsWith(PREFIX)) localStorage.removeItem(k);
  }
}