import type { ToastAction, ToastItem } from './types';

/**
 * Reducer for managing toast state
 *
 * Removal is a two-phase flow so web can play its CSS exit transition
 * before the DOM node is unmounted:
 *   `MARK_CLOSED` → flips `pendingRemoval: true` (node stays mounted).
 *   `REMOVE`      → filters the toast out of the array (node unmounts).
 *
 * Native dispatches `REMOVE` directly since Reanimated's `exiting`
 * layout animation plays before unmount without a lingering state.
 */
export function toastReducer(state: ToastItem[], action: ToastAction): ToastItem[] {
  switch (action.type) {
    case 'SHOW': {
      const filtered = state.filter((toast) => toast.id !== action.payload.id);
      return [...filtered, action.payload];
    }

    case 'MARK_CLOSED': {
      const idsSet = new Set(action.payload.ids);
      // Early out preserves the array reference when nothing would change,
      // which keeps `useMemo(..., [toasts])` consumers stable.
      const hasChange = state.some((toast) => idsSet.has(toast.id) && !toast.pendingRemoval);
      if (!hasChange) return state;
      return state.map((toast) =>
        idsSet.has(toast.id) && !toast.pendingRemoval ? { ...toast, pendingRemoval: true } : toast,
      );
    }

    case 'REMOVE': {
      const idsSet = new Set(action.payload.ids);
      return state.filter((toast) => !idsSet.has(toast.id));
    }

    default:
      return state;
  }
}