import { useEffect, useRef } from 'react';

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

type Handler = (e: KeyboardEvent) => void;

/**
 * Fires when the given key is pressed outside any text field.
 * Pass modifiers as part of the key spec, e.g. `mod+k` for Ctrl/Meta+K.
 * Single-char keys ignore shift unless explicitly `shift+x`.
 */
export function useShortcut(spec: string | string[], handler: Handler, deps: unknown[] = []) {
  const handlerRef = useRef(handler);
  handlerRef.current = handler;

  useEffect(() => {
    const specs = (Array.isArray(spec) ? spec : [spec]).map(parseSpec);
    const onKey = (e: KeyboardEvent) => {
      if (isTextField(e.target)) {
        // Allow mod+key even inside text fields (e.g. ⌘K)
        if (!specs.some((s) => s.mod && matches(s, e))) return;
      }
      for (const s of specs) {
        if (matches(s, e)) {
          handlerRef.current(e);
          return;
        }
      }
    };
    window.addEventListener('keydown', onKey);
    return () => window.removeEventListener('keydown', onKey);
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, deps);
}

interface ParsedSpec {
  key: string;
  mod: boolean;
  shift: boolean;
}

function parseSpec(s: string): ParsedSpec {
  const parts = s.toLowerCase().split('+');
  const key = parts[parts.length - 1];
  return {
    key,
    mod: parts.includes('mod'),
    shift: parts.includes('shift'),
  };
}

function matches(s: ParsedSpec, e: KeyboardEvent): boolean {
  if (e.key.toLowerCase() !== s.key) return false;
  if (s.mod !== (e.metaKey || e.ctrlKey)) return false;
  if (s.shift && !e.shiftKey) return false;
  return true;
}

/**
 * Tracks a two-key "g" prefix and fires the matching handler when the second
 * key is pressed within the timeout window. Any other key cancels.
 */
export function useLeaderShortcut(
  leader: string,
  mapping: Record<string, () => void>,
  timeoutMs = 1000,
) {
  const state = useRef<{ armed: boolean; timer: number | null }>({ armed: false, timer: null });

  useEffect(() => {
    const onKey = (e: KeyboardEvent) => {
      if (isTextField(e.target)) return;
      if (e.metaKey || e.ctrlKey || e.altKey) {
        state.current.armed = false;
        return;
      }
      const key = e.key.toLowerCase();
      if (!state.current.armed) {
        if (key === leader) {
          state.current.armed = true;
          if (state.current.timer) window.clearTimeout(state.current.timer);
          state.current.timer = window.setTimeout(() => {
            state.current.armed = false;
          }, timeoutMs);
          e.preventDefault();
        }
        return;
      }
      // armed: expect second key
      state.current.armed = false;
      if (state.current.timer) {
        window.clearTimeout(state.current.timer);
        state.current.timer = null;
      }
      const fn = mapping[key];
      if (fn) {
        e.preventDefault();
        fn();
      }
    };
    window.addEventListener('keydown', onKey);
    return () => window.removeEventListener('keydown', onKey);
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [leader, timeoutMs, JSON.stringify(Object.keys(mapping))]);
}