/**
 * Pure cursor logic for vim-style list navigation in the TUI.
 *
 * The two list panels (FeedList, ArticleList) share the same `j/k/g/G` shape
 * but used to hand-roll it twice with subtly different scroll-echo guards.
 * This Module owns the math; `useListCursor` and `useScrollEchoGuard` are
 * thin React adapters over it.
 */

export type NavKey = 'down' | 'up' | 'home' | 'end';

/**
 * Translate a raw keyboard event into a navigation intent. Returns `null`
 * when the keystroke isn't one of `j/k/g/G/ArrowUp/ArrowDown` — the caller
 * should let other handlers see those keys.
 */
export function navKeyFromInput(name: string, shift: boolean): NavKey | null {
  if (name === 'j' || name === 'down') return 'down';
  if (name === 'k' || name === 'up') return 'up';
  if (name === 'g') return shift ? 'end' : 'home';
  return null;
}

/** New cursor position after applying `key`, clamped to `[0, length-1]`. */
export function nextCursor(prev: number, key: NavKey, length: number): number {
  if (length <= 0) return 0;
  switch (key) {
    case 'down':
      return Math.min(prev + 1, length - 1);
    case 'up':
      return Math.max(prev - 1, 0);
    case 'home':
      return 0;
    case 'end':
      return length - 1;
  }
}

/**
 * Some terminals fire a phantom arrow key shortly after a mouse-wheel scroll.
 * `armEcho` records the scroll direction + an expiry; `shouldSwallowEcho`
 * suppresses *only* the next matching-direction key, leaving real keypresses
 * (including opposite-direction ones) to pass through.
 */
export interface ScrollEcho {
  direction: 'up' | 'down';
  expiresAt: number;
}

export function shouldSwallowEcho(echo: ScrollEcho | null, key: 'up' | 'down', now: number): boolean {
  if (!echo) return false;
  if (now > echo.expiresAt) return false;
  return echo.direction === key;
}