export const CHECKLIST_KEY_V1 = 'magikarp-checklist-v1';
export const CHECKLIST_KEY_V2 = 'magikarp-checklist-v2';

export type VariantKey = 'base' | 'holofoil' | 'reverseHolofoil';
export type VariantState = Partial<Record<VariantKey, boolean>>;
export type ChecklistV2 = Record<string, VariantState>; // cardId -> variant flags

// Legacy loader (v1)
export function loadChecklistV1(): Set<string> {
  if (typeof window === 'undefined') return new Set();
  try {
    const raw = localStorage.getItem(CHECKLIST_KEY_V1);
    if (!raw) return new Set();
    const arr = JSON.parse(raw) as string[];
    return new Set(arr);
  } catch {
    return new Set();
  }
}

// Local-only helpers (kept for migration / fallback)
export function loadChecklistLocal(): ChecklistV2 {
  if (typeof window === 'undefined') return {};
  try {
    const v2 = localStorage.getItem(CHECKLIST_KEY_V2);
    if (v2) return JSON.parse(v2) as ChecklistV2;
    const v1 = loadChecklistV1();
    if (v1.size === 0) return {};
    const migrated: ChecklistV2 = {};
    v1.forEach((id) => { migrated[id] = { base: true }; });
    return migrated;
  } catch {
    return {};
  }
}

export function saveChecklistLocal(state: ChecklistV2) {
  if (typeof window === 'undefined') return;
  try {
    localStorage.setItem(CHECKLIST_KEY_V2, JSON.stringify(state));
  } catch {
    // ignore
  }
}

// Server-backed persistence
export async function loadChecklistServer(): Promise<ChecklistV2> {
  try {
    const res = await fetch('/api/checklist', { cache: 'no-store' });
    if (!res.ok) throw new Error('failed');
    const json = await res.json();
    const serverData = (json?.data || {}) as ChecklistV2;
    // If server is empty, try migrate from local and push
    const hasServerData = serverData && Object.keys(serverData).length > 0;
    if (!hasServerData && typeof window !== 'undefined') {
      const local = loadChecklistLocal();
      const hasLocal = Object.keys(local).length > 0;
      if (hasLocal) {
        await saveChecklistServer(local);
        // Clear legacy keys after successful push
        try { localStorage.removeItem(CHECKLIST_KEY_V2); } catch {}
        try { localStorage.removeItem(CHECKLIST_KEY_V1); } catch {}
        return local;
      }
    }
    return serverData || {};
  } catch {
    // As a fallback (e.g., during dev with API not ready), use local
    return loadChecklistLocal();
  }
}

export async function saveChecklistServer(state: ChecklistV2): Promise<void> {
  try {
    await fetch('/api/checklist', {
      method: 'PUT',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify(state),
    });
  } catch {
    // best-effort: persist locally so user doesn't lose progress offline
    saveChecklistLocal(state);
  }
}