import {computed, type ComputedRef, type Ref} from 'vue'

export type DayCell = {
  isoDate: string
  day: number
  isCurrentMonth: boolean
  isToday: boolean
}
export type WeekRow = {
  weekNumber: number
  days: DayCell[]
}

const toIso = (d: Date): string => {
  const y = d.getFullYear()
  const m = String(d.getMonth() + 1).padStart(2, '0')
  const day = String(d.getDate()).padStart(2, '0')
  return `${y}-${m}-${day}`
}

const isoWeek = (d: Date): number => {
  const target = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()))
  const dayNum = target.getUTCDay() || 7 // dimanche = 7
  target.setUTCDate(target.getUTCDate() + 4 - dayNum) // jeudi de la semaine
  const yearStart = new Date(Date.UTC(target.getUTCFullYear(), 0, 1))
  return Math.ceil((((target.getTime() - yearStart.getTime()) / 86400000) + 1) / 7)
}

export function useMonthMatrix(
  month: Ref<number>,
  year: Ref<number>,
): {weeks: ComputedRef<WeekRow[]>} {
  const weeks = computed<WeekRow[]>(() => {
    const todayIso = toIso(new Date())
    const first = new Date(year.value, month.value, 1)
    // recule jusqu'au lundi (getDay : 0 = dimanche)
    const offset = (first.getDay() + 6) % 7
    const start = new Date(year.value, month.value, 1 - offset)

    const rows: WeekRow[] = []
    const cursor = new Date(start)
    for (let w = 0; w < 6; w++) {
      const days: DayCell[] = []
      for (let i = 0; i < 7; i++) {
        const iso = toIso(cursor)
        days.push({
          isoDate: iso,
          day: cursor.getDate(),
          isCurrentMonth: cursor.getMonth() === month.value,
          isToday: iso === todayIso,
        })
        cursor.setDate(cursor.getDate() + 1)
      }
      rows.push({weekNumber: isoWeek(new Date(`${days[0].isoDate}T00:00:00`)), days})
    }
    return rows
  })

  return {weeks}
}