nexus/frontend/src/composables/useTimer.ts

import { ref, onMounted, onUnmounted } from 'vue'

export function useTimer() {
  const elapsed = ref(0)
  let interval: ReturnType<typeof setInterval> | null = null

  function start() {
    if (interval !== null) return
    const startTime = Date.now()
    elapsed.value = 0
    interval = setInterval(() => {
      elapsed.value = Math.floor((Date.now() - startTime) / 1000)
    }, 1000)
  }

  function stop() {
    if (interval !== null) {
      clearInterval(interval)
      interval = null
    }
  }

  function format(minutes: number, seconds: number): string {
    return `${String(minutes).padStart(2, '0')}:${String(seconds).padStart(2, '0')}`
  }

  const formatted = (): string => {
    const m = Math.floor(elapsed.value / 60)
    const s = elapsed.value % 60
    return format(m, s)
  }

  onMounted(start)
  onUnmounted(stop)

  return { elapsed, formatted, start, stop }
}