'use client'

import { useState } from 'react'

const DAYS   = ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa']
const MONTHS = ['January','February','March','April','May','June',
                'July','August','September','October','November','December']

interface Props {
  selected:       string          // YYYY-MM-DD or ''
  onSelect:       (date: string) => void
  minDate:        string          // YYYY-MM-DD — dates before this are disabled
  maxDate:        string          // YYYY-MM-DD — dates after this are disabled
  disabledDates?: Set<string>     // fully blocked (strikethrough, not clickable)
  busyDates?:     Set<string>     // has events but still selectable (orange dot)
}

function pad(n: number) { return String(n).padStart(2, '0') }

export default function CalendarPicker({
  selected, onSelect, minDate, maxDate, disabledDates, busyDates,
}: Props) {
  const today   = new Date().toISOString().slice(0, 10)
  const initRef = selected || minDate || today

  const [year,  setYear]  = useState(() => parseInt(initRef.slice(0, 4)))
  const [month, setMonth] = useState(() => parseInt(initRef.slice(5, 7)) - 1)

  const firstDow    = new Date(year, month, 1).getDay()
  const daysInMonth = new Date(year, month + 1, 0).getDate()

  const curMonthStr = `${year}-${pad(month + 1)}`
  const canPrev     = curMonthStr > minDate.slice(0, 7)
  const canNext     = curMonthStr < maxDate.slice(0, 7)

  const prevMonth = () => {
    if (!canPrev) return
    if (month === 0) { setYear(y => y - 1); setMonth(11) } else setMonth(m => m - 1)
  }
  const nextMonth = () => {
    if (!canNext) return
    if (month === 11) { setYear(y => y + 1); setMonth(0) } else setMonth(m => m + 1)
  }

  // Empty cells before the 1st, then day numbers
  const cells: (number | null)[] = [
    ...Array.from({ length: firstDow }, () => null),
    ...Array.from({ length: daysInMonth }, (_, i) => i + 1),
  ]

  return (
    <div style={{ userSelect: 'none', fontSize: '0.82rem' }}>

      {/* Month navigation */}
      <div style={{ display: 'flex', alignItems: 'center', justifyContent: 'space-between', marginBottom: '0.5rem' }}>
        <button
          type="button" onClick={prevMonth} disabled={!canPrev}
          style={{ background: 'none', border: 'none', padding: '2px 8px', fontSize: '1.1rem', lineHeight: 1,
            cursor: canPrev ? 'pointer' : 'default', color: canPrev ? '#11b3be' : '#ddd' }}
        >‹</button>

        <span style={{ fontWeight: 'bold' }}>{MONTHS[month]} {year}</span>

        <button
          type="button" onClick={nextMonth} disabled={!canNext}
          style={{ background: 'none', border: 'none', padding: '2px 8px', fontSize: '1.1rem', lineHeight: 1,
            cursor: canNext ? 'pointer' : 'default', color: canNext ? '#11b3be' : '#ddd' }}
        >›</button>
      </div>

      {/* Day-of-week labels */}
      <div style={{ display: 'grid', gridTemplateColumns: 'repeat(7, 1fr)', gap: '2px', marginBottom: '2px' }}>
        {DAYS.map(d => (
          <div key={d} style={{ textAlign: 'center', color: '#bbb', fontSize: '0.68rem', padding: '1px 0' }}>
            {d}
          </div>
        ))}
      </div>

      {/* Day cells */}
      <div style={{ display: 'grid', gridTemplateColumns: 'repeat(7, 1fr)', gap: '2px' }}>
        {cells.map((day, i) => {
          if (!day) return <div key={`e${i}`} />

          const date        = `${year}-${pad(month + 1)}-${pad(day)}`
          const isSelected  = date === selected
          const isToday     = date === today
          const outOfRange  = date < minDate || date > maxDate
          const hardBlocked = disabledDates?.has(date) ?? false
          const isDisabled  = outOfRange || hardBlocked
          const isBusy      = !isDisabled && (busyDates?.has(date) ?? false)

          return (
            <button
              key={date}
              type="button"
              disabled={isDisabled}
              onClick={() => onSelect(date)}
              style={{
                position:       'relative',
                padding:        '5px 2px 6px',
                borderRadius:   '6px',
                border:         isSelected
                  ? '2px solid #11b3be'
                  : isToday
                    ? '1.5px solid rgba(17,179,190,0.35)'
                    : '1px solid transparent',
                background:     isSelected ? '#11b3be' : outOfRange ? 'transparent' : hardBlocked ? '#f9f9f9' : '#fff',
                color:          isSelected ? '#fff' : isDisabled ? '#ccc' : '#333',
                cursor:         isDisabled ? 'default' : 'pointer',
                fontWeight:     isSelected ? 'bold' : 'normal',
                fontFamily:     'inherit',
                fontSize:       '0.82rem',
                textAlign:      'center',
                lineHeight:     1.3,
                textDecoration: hardBlocked ? 'line-through' : 'none',
              }}
            >
              {day}
              {isBusy && (
                <span style={{
                  position:        'absolute',
                  bottom:          '2px',
                  left:            '50%',
                  transform:       'translateX(-50%)',
                  width:           '3px',
                  height:          '3px',
                  borderRadius:    '50%',
                  background:      isSelected ? 'rgba(255,255,255,0.7)' : '#f5a623',
                  display:         'block',
                }} />
              )}
            </button>
          )
        })}
      </div>

      {/* Legend */}
      {busyDates && busyDates.size > 0 && (
        <div style={{ display: 'flex', alignItems: 'center', gap: '4px', marginTop: '0.4rem', fontSize: '0.68rem', color: '#999' }}>
          <span style={{ width: '6px', height: '6px', borderRadius: '50%', background: '#f5a623', display: 'inline-block' }} />
          May have limited availability
        </div>
      )}
    </div>
  )
}