import { useEffect, useRef } from "react"

/**
 * Window-level keyboard shortcuts.
 *
 * A chord reads as `mod+shift+z`, where `mod` is ⌘ on a Mac and Ctrl
 * everywhere else. Bindings are plain data, so a view declares the whole set
 * it answers to in one place.
 */
export type Shortcuts = Record<string, (event: KeyboardEvent) => void>

/** Text fields and the code editor keep their own bindings and their own undo. */
export function isTextEntry(target: EventTarget | null): boolean {
  return Boolean(
    (target as Element | null)?.closest?.(
      "input, textarea, [contenteditable='true'], .monaco-editor",
    ),
  )
}

/** Focus is inside the embedded code editor. */
export function inCodeEditor(target: EventTarget | null): boolean {
  return Boolean((target as Element | null)?.closest?.(".monaco-editor"))
}

function chordOf(event: KeyboardEvent): string {
  const parts: string[] = []
  if (event.metaKey || event.ctrlKey) parts.push("mod")
  if (event.altKey) parts.push("alt")
  if (event.shiftKey) parts.push("shift")
  // Shift makes it a capital Z, so compare on the letter alone.
  parts.push(event.key.toLowerCase())
  return parts.join("+")
}

/**
 * Bind chords for as long as the component is mounted.
 *
 * A chord listed in `inTextEntry` fires even while a field or the code editor
 * has focus; every other one steps aside, because typing there means typing.
 */
export function useShortcuts(bindings: Shortcuts, inTextEntry: string[] = []) {
  // Read through a ref, so a fresh handler on every render never re-binds.
  const latest = useRef({ bindings, inTextEntry })
  latest.current = { bindings, inTextEntry }

  useEffect(() => {
    const onKeyDown = (event: KeyboardEvent) => {
      const chord = chordOf(event)
      const run = latest.current.bindings[chord]
      if (!run) return
      if (
        isTextEntry(event.target) &&
        !latest.current.inTextEntry.includes(chord)
      ) {
        return
      }
      event.preventDefault()
      run(event)
    }
    window.addEventListener("keydown", onKeyDown)
    return () => window.removeEventListener("keydown", onKeyDown)
  }, [])
}