import { useEffect, useRef } from "react";

// Keyboard shortcuts (SPEC §9.4; the list users see is lib/shortcuts.ts).
// Ignores keystrokes while typing in inputs, except Escape. "g" starts a
// two-key sequence (g i = Inbox). With `enabled` false only Escape works.
export interface Shortcuts {
  enabled?: boolean;
  onSearch?: () => void;
  onCompose?: () => void;
  onReply?: () => void;
  onReplyAll?: () => void;
  onForward?: () => void;
  onArchive?: () => void;
  onTrash?: () => void;
  onTogglePin?: () => void;
  onSnooze?: () => void;
  onMarkRead?: () => void;
  onMarkUnread?: () => void;
  onBack?: () => void;
  onGoInbox?: () => void;
  onGoSnoozed?: () => void;
  onGoDrafts?: () => void;
  onGoSent?: () => void;
  onGoSubscriptions?: () => void;
  onHelp?: () => void;
  onEscape?: () => void;
  onNext?: () => void;
  onPrev?: () => void;
}

function isTyping(el: EventTarget | null): boolean {
  if (!(el instanceof HTMLElement)) return false;
  const tag = el.tagName;
  return tag === "INPUT" || tag === "TEXTAREA" || tag === "SELECT" || el.isContentEditable;
}

export function useKeyboardShortcuts(shortcuts: Shortcuts): void {
  const ref = useRef(shortcuts);
  ref.current = shortcuts;
  const pendingG = useRef(false);

  useEffect(() => {
    const handler = (e: KeyboardEvent) => {
      const s = ref.current;
      if (e.key === "Escape") {
        s.onEscape?.();
        return;
      }
      if (s.enabled === false || isTyping(e.target)) return;
      if (e.metaKey || e.ctrlKey || e.altKey) return;

      const run = (fn: (() => void) | undefined) => {
        if (!fn) return;
        e.preventDefault();
        fn();
      };

      if (pendingG.current) {
        pendingG.current = false;
        const go: Record<string, (() => void) | undefined> = {
          i: s.onGoInbox,
          z: s.onGoSnoozed,
          d: s.onGoDrafts,
          t: s.onGoSent,
          b: s.onGoSubscriptions,
        };
        if (e.key in go) {
          run(go[e.key]);
          return;
        }
      }

      // Shift+letter arrives as the capital letter.
      const actions: Record<string, (() => void) | undefined> = {
        "/": s.onSearch,
        "?": s.onHelp,
        c: s.onCompose,
        r: s.onReply,
        a: s.onReplyAll,
        f: s.onForward,
        e: s.onArchive,
        "#": s.onTrash,
        s: s.onTogglePin,
        b: s.onSnooze,
        I: s.onMarkRead,
        U: s.onMarkUnread,
        u: s.onBack,
        j: s.onNext,
        k: s.onPrev,
      };
      if (e.key === "g") {
        pendingG.current = true;
        window.setTimeout(() => (pendingG.current = false), 1000);
        return;
      }
      if (e.key in actions) run(actions[e.key]);
    };
    window.addEventListener("keydown", handler);
    return () => window.removeEventListener("keydown", handler);
  }, []);
}