import {ref, watch, type Ref} from 'vue'
import {isValidIso} from './dateFormat'

export function useCalendarView(viewMode: Ref<'days' | 'months' | 'years'>) {
  const today = new Date()
  const currentMonth = ref(today.getMonth())
  const currentYear = ref(today.getFullYear())
  // Fenêtre de 12 ans calée pour que l'année courante tombe en 2e ligne / 2e
  // colonne d'une grille 3 colonnes (index 4) → début = année courante − 4.
  const yearPageStart = ref(today.getFullYear() - 4)

  watch(viewMode, (mode) => {
    if (mode === 'years') yearPageStart.value = currentYear.value - 4
  })

  const goToPrev = () => {
    if (viewMode.value === 'years') {
      yearPageStart.value -= 12
      return
    }
    if (viewMode.value === 'months') {
      currentYear.value -= 1
      return
    }
    if (currentMonth.value === 0) {
      currentMonth.value = 11
      currentYear.value -= 1
    } else {
      currentMonth.value -= 1
    }
  }

  const goToNext = () => {
    if (viewMode.value === 'years') {
      yearPageStart.value += 12
      return
    }
    if (viewMode.value === 'months') {
      currentYear.value += 1
      return
    }
    if (currentMonth.value === 11) {
      currentMonth.value = 0
      currentYear.value += 1
    } else {
      currentMonth.value += 1
    }
  }

  const selectMonth = (m: number) => {
    currentMonth.value = m
  }

  const selectYear = (y: number) => {
    currentYear.value = y
  }

  const syncToIso = (iso: string | null) => {
    if (iso && isValidIso(iso)) {
      currentMonth.value = Number(iso.slice(5, 7)) - 1
      currentYear.value = Number(iso.slice(0, 4))
    } else {
      const now = new Date()
      currentMonth.value = now.getMonth()
      currentYear.value = now.getFullYear()
    }
  }

  return {currentMonth, currentYear, yearPageStart, goToPrev, goToNext, selectMonth, selectYear, syncToIso}
}