'use client'

import { useState, useMemo } from 'react'
import { ChevronLeft, ChevronRight } from 'lucide-react'
import { Button } from '@/components/ui/button'
import { cn } from '@/lib/utils'

interface MiniCalendarProps {
  selectedDate: string
  onSelectDate: (date: string) => void
}

const WEEKDAYS = ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa']

function getDaysInMonth(year: number, month: number): number {
  return new Date(year, month + 1, 0).getDate()
}

function getFirstDayOfMonth(year: number, month: number): number {
  return new Date(year, month, 1).getDay()
}

function formatDate(year: number, month: number, day: number): string {
  return `${year}-${String(month + 1).padStart(2, '0')}-${String(day).padStart(2, '0')}`
}

export function MiniCalendar({ selectedDate, onSelectDate }: MiniCalendarProps) {
  const selected = selectedDate ? new Date(selectedDate) : new Date()
  const [viewYear, setViewYear] = useState(selected.getFullYear())
  const [viewMonth, setViewMonth] = useState(selected.getMonth())

  const today = new Date()
  const todayStr = formatDate(
    today.getFullYear(),
    today.getMonth(),
    today.getDate()
  )

  const selectedStr = selectedDate?.split('T')[0]?.split(' ')[0] || todayStr

  const days = useMemo(() => {
    const daysInMonth = getDaysInMonth(viewYear, viewMonth)
    const firstDay = getFirstDayOfMonth(viewYear, viewMonth)
    const result: (number | null)[] = []

    // Leading empty cells
    for (let i = 0; i < firstDay; i++) {
      result.push(null)
    }
    // Days of month
    for (let d = 1; d <= daysInMonth; d++) {
      result.push(d)
    }
    return result
  }, [viewYear, viewMonth])

  function prevMonth() {
    if (viewMonth === 0) {
      setViewYear(viewYear - 1)
      setViewMonth(11)
    } else {
      setViewMonth(viewMonth - 1)
    }
  }

  function nextMonth() {
    if (viewMonth === 11) {
      setViewYear(viewYear + 1)
      setViewMonth(0)
    } else {
      setViewMonth(viewMonth + 1)
    }
  }

  function goToToday() {
    setViewYear(today.getFullYear())
    setViewMonth(today.getMonth())
    onSelectDate(todayStr)
  }

  const monthLabel = new Date(viewYear, viewMonth).toLocaleDateString('en-US', {
    month: 'long',
    year: 'numeric',
  })

  return (
    <div className="space-y-2">
      <div className="flex items-center justify-between">
        <Button variant="ghost" size="icon" className="h-7 w-7" onClick={prevMonth}>
          <ChevronLeft className="h-4 w-4" />
        </Button>
        <button
          onClick={goToToday}
          className="text-sm font-medium hover:underline"
        >
          {monthLabel}
        </button>
        <Button variant="ghost" size="icon" className="h-7 w-7" onClick={nextMonth}>
          <ChevronRight className="h-4 w-4" />
        </Button>
      </div>

      <div className="grid grid-cols-7 gap-0">
        {WEEKDAYS.map((wd) => (
          <div
            key={wd}
            className="py-1 text-center text-[10px] font-medium text-muted-foreground"
          >
            {wd}
          </div>
        ))}
        {days.map((day, idx) => {
          if (day === null) {
            return <div key={`empty-${idx}`} className="h-7" />
          }
          const dateStr = formatDate(viewYear, viewMonth, day)
          const isToday = dateStr === todayStr
          const isSelected = dateStr === selectedStr

          return (
            <button
              key={dateStr}
              onClick={() => onSelectDate(dateStr)}
              className={cn(
                'flex h-7 w-full items-center justify-center rounded-md text-xs transition-colors hover:bg-accent',
                isToday && !isSelected && 'font-bold text-primary',
                isSelected && 'bg-primary text-primary-foreground hover:bg-primary/90'
              )}
            >
              {day}
            </button>
          )
        })}
      </div>

      <Button
        variant="outline"
        size="sm"
        className="w-full text-xs"
        onClick={goToToday}
      >
        Today
      </Button>
    </div>
  )
}