import { useEffect, useId, useLayoutEffect, useMemo, useRef, useState } from 'react'
import { createPortal } from 'react-dom'
import { CalendarDays, ChevronLeft } from 'lucide-react'
import styles from './StepDatePicker.module.css'

type Step = 'year' | 'month' | 'day'

interface StepDatePickerProps {
  id?: string
  value: string
  onChange: (isoDate: string) => void
  disabled?: boolean
  placeholder?: string
}

const PANEL_WIDTH = 300

const MONTHS = [
  'Jan',
  'Feb',
  'Mar',
  'Apr',
  'May',
  'Jun',
  'Jul',
  'Aug',
  'Sep',
  'Oct',
  'Nov',
  'Dec',
] as const

function parseIsoDate(value: string | null | undefined): {
  year: number
  month: number
  day: number
} | null {
  if (!value?.trim()) return null
  const match = value.trim().match(/^(\d{4})-(\d{2})-(\d{2})/)
  if (!match) return null
  const year = Number(match[1])
  const month = Number(match[2])
  const day = Number(match[3])
  if (!year || month < 1 || month > 12 || day < 1 || day > 31) return null
  const probe = new Date(year, month - 1, day)
  if (
    probe.getFullYear() !== year ||
    probe.getMonth() !== month - 1 ||
    probe.getDate() !== day
  ) {
    return null
  }
  return { year, month, day }
}

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

function formatDisplayDate(iso: string): string {
  const parsed = parseIsoDate(iso)
  if (!parsed) return ''
  return new Date(parsed.year, parsed.month - 1, parsed.day).toLocaleDateString(
    'en-US',
    { month: 'short', day: 'numeric', year: 'numeric' },
  )
}

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

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

export function StepDatePicker({
  id,
  value,
  onChange,
  disabled = false,
  placeholder = 'Select date',
}: StepDatePickerProps) {
  const autoId = useId()
  const fieldId = id ?? autoId
  const rootRef = useRef<HTMLDivElement>(null)
  const panelRef = useRef<HTMLDivElement>(null)
  const [open, setOpen] = useState(false)
  const [step, setStep] = useState<Step>('year')
  const [panelPos, setPanelPos] = useState<{ top: number; left: number } | null>(
    null,
  )

  const today = useMemo(() => {
    const now = new Date()
    return {
      year: now.getFullYear(),
      month: now.getMonth() + 1,
      day: now.getDate(),
    }
  }, [])

  const selected = parseIsoDate(value)
  const [draftYear, setDraftYear] = useState(selected?.year ?? today.year)
  const [draftMonth, setDraftMonth] = useState(selected?.month ?? today.month)

  const years = useMemo(() => {
    const start = today.year - 8
    const end = today.year + 12
    return Array.from({ length: end - start + 1 }, (_, i) => start + i)
  }, [today.year])

  function updatePanelPosition() {
    const trigger = rootRef.current
    if (!trigger) return
    const rect = trigger.getBoundingClientRect()
    const width = Math.min(PANEL_WIDTH, window.innerWidth - 24)
    let left = rect.right - width
    if (left < 12) left = 12
    if (left + width > window.innerWidth - 12) {
      left = Math.max(12, window.innerWidth - 12 - width)
    }
    setPanelPos({ top: rect.bottom + 4, left })
  }

  useLayoutEffect(() => {
    if (!open) {
      setPanelPos(null)
      return
    }
    updatePanelPosition()
    const onReposition = () => updatePanelPosition()
    window.addEventListener('resize', onReposition)
    window.addEventListener('scroll', onReposition, true)
    return () => {
      window.removeEventListener('resize', onReposition)
      window.removeEventListener('scroll', onReposition, true)
    }
  }, [open])

  useEffect(() => {
    if (!open) return
    const onPointerDown = (event: MouseEvent) => {
      const target = event.target as Node
      if (rootRef.current?.contains(target)) return
      if (panelRef.current?.contains(target)) return
      setOpen(false)
    }
    const onKeyDown = (event: KeyboardEvent) => {
      if (event.key === 'Escape') setOpen(false)
    }
    document.addEventListener('mousedown', onPointerDown)
    document.addEventListener('keydown', onKeyDown)
    return () => {
      document.removeEventListener('mousedown', onPointerDown)
      document.removeEventListener('keydown', onKeyDown)
    }
  }, [open])

  function openPicker() {
    if (disabled) return
    const initial = selected ?? today
    setDraftYear(initial.year)
    setDraftMonth(initial.month)
    setStep('year')
    setOpen(true)
  }

  function pickYear(year: number) {
    setDraftYear(year)
    setStep('month')
  }

  function pickMonth(month: number) {
    setDraftMonth(month)
    setStep('day')
  }

  function pickDay(day: number) {
    onChange(toIsoDate(draftYear, draftMonth, day))
    setOpen(false)
  }

  const display = value ? formatDisplayDate(value) : ''
  const dayCount = daysInMonth(draftYear, draftMonth)
  const padStart = startWeekday(draftYear, draftMonth)
  const highlightDay =
    selected && selected.year === draftYear && selected.month === draftMonth
      ? selected.day
      : draftYear === today.year && draftMonth === today.month
        ? today.day
        : null

  const panel =
    open && panelPos
      ? createPortal(
          <div
            ref={panelRef}
            className={styles.panel}
            role="dialog"
            aria-label="Choose date"
            style={{ top: panelPos.top, left: panelPos.left }}
          >
            <div className={styles.panelHeader}>
              {step !== 'year' ? (
                <button
                  type="button"
                  className={styles.backBtn}
                  onClick={() => setStep(step === 'day' ? 'month' : 'year')}
                  aria-label="Back"
                >
                  <ChevronLeft size={16} />
                </button>
              ) : (
                <span className={styles.backSpacer} />
              )}
              <div className={styles.steps}>
                <button
                  type="button"
                  className={`${styles.stepChip} ${step === 'year' ? styles.stepActive : ''}`}
                  onClick={() => setStep('year')}
                >
                  {draftYear}
                </button>
                <button
                  type="button"
                  className={`${styles.stepChip} ${step === 'month' ? styles.stepActive : ''}`}
                  onClick={() => setStep('month')}
                >
                  {MONTHS[draftMonth - 1]}
                </button>
                <span
                  className={`${styles.stepChip} ${step === 'day' ? styles.stepActive : ''} ${styles.stepStatic}`}
                >
                  Day
                </span>
              </div>
            </div>

            {step === 'year' ? (
              <div className={styles.yearList}>
                {years.map((year) => (
                  <button
                    key={year}
                    type="button"
                    className={`${styles.optionBtn} ${
                      year === draftYear ? styles.optionSelected : ''
                    } ${year === today.year ? styles.optionToday : ''}`}
                    onClick={() => pickYear(year)}
                  >
                    {year}
                  </button>
                ))}
              </div>
            ) : null}

            {step === 'month' ? (
              <div className={styles.monthGrid}>
                {MONTHS.map((label, index) => {
                  const month = index + 1
                  return (
                    <button
                      key={label}
                      type="button"
                      className={`${styles.optionBtn} ${
                        month === draftMonth ? styles.optionSelected : ''
                      } ${
                        draftYear === today.year && month === today.month
                          ? styles.optionToday
                          : ''
                      }`}
                      onClick={() => pickMonth(month)}
                    >
                      {label}
                    </button>
                  )
                })}
              </div>
            ) : null}

            {step === 'day' ? (
              <div className={styles.dayPanel}>
                <div className={styles.weekdayRow}>
                  {['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa'].map((d) => (
                    <span key={d} className={styles.weekday}>
                      {d}
                    </span>
                  ))}
                </div>
                <div className={styles.dayGrid}>
                  {Array.from({ length: padStart }, (_, i) => (
                    <span key={`pad-${i}`} className={styles.dayEmpty} />
                  ))}
                  {Array.from({ length: dayCount }, (_, i) => {
                    const day = i + 1
                    const isSelected =
                      selected?.year === draftYear &&
                      selected?.month === draftMonth &&
                      selected?.day === day
                    const isToday =
                      draftYear === today.year &&
                      draftMonth === today.month &&
                      day === today.day
                    return (
                      <button
                        key={day}
                        type="button"
                        className={`${styles.dayBtn} ${
                          isSelected ? styles.daySelected : ''
                        } ${isToday && !isSelected ? styles.dayToday : ''} ${
                          highlightDay === day && !isSelected ? styles.dayPrefill : ''
                        }`}
                        onClick={() => pickDay(day)}
                      >
                        {day}
                      </button>
                    )
                  })}
                </div>
              </div>
            ) : null}
          </div>,
          document.body,
        )
      : null

  return (
    <div className={styles.root} ref={rootRef}>
      <button
        id={fieldId}
        type="button"
        className={`${styles.trigger} ${open ? styles.triggerOpen : ''} ${
          !display ? styles.triggerPlaceholder : ''
        }`}
        onClick={() => (open ? setOpen(false) : openPicker())}
        disabled={disabled}
        aria-haspopup="dialog"
        aria-expanded={open}
      >
        <span className={styles.triggerText}>{display || placeholder}</span>
        <CalendarDays size={16} className={styles.icon} aria-hidden="true" />
      </button>
      {panel}
    </div>
  )
}