import { ReactNode, useMemo, useState, useEffect } from 'react'
import { useWorkspace } from '@/context'
import {
  usePlannedDays,
  useShowWeekNumbers,
  getLastLeaveType,
  setLastLeaveType,
  useCalendarDays,
  useDayOverrides,
} from '@/hooks'
import type { PlannedLeaveDay, CalendarDayEntry } from '@/types'
import { Layout } from '@/components/layout/Layout'
import { LoadingSpinner } from '@/components/common/LoadingSpinner'
import { CalendarWeek } from '@/components/common/CalendarWeek'
import { PlannedDayModal } from '@/components/modals/PlannedDayModal'
import { getColorForType } from '@/utils/leaveTypes'
import { datesInRange } from '@/utils/dates'
import { useTranslation } from '@/i18n'
import './calendar.css'

const WEEKDAY_KEYS = [
  'calendar.weekdayMon',
  'calendar.weekdayTue',
  'calendar.weekdayWed',
  'calendar.weekdayThu',
  'calendar.weekdayFri',
  'calendar.weekdaySat',
  'calendar.weekdaySun',
] as const

export function Calendar(): ReactNode {
  const { t, locale } = useTranslation()
  const { isLoading: wsLoading, selectedChildId, workspace, personalDataUuid, parentName } = useWorkspace()
  const { data: plannedDays, isLoading: pdLoading, add, update, remove } = usePlannedDays(selectedChildId ?? undefined)
  const [showWeekNumbers] = useShowWeekNumbers()
  const [currentMonth, setCurrentMonth] = useState(new Date())
  const [selectedDates, setSelectedDates] = useState<Set<string>>(new Set())
  const [dragAnchor, setDragAnchor] = useState<string | null>(null)
  const [dragCurrent, setDragCurrent] = useState<string | null>(null)
  const [isDragging, setIsDragging] = useState(false)
  const [isModalOpen, setIsModalOpen] = useState(false)
  const [isRangeMode, setIsRangeMode] = useState(false)
  const [isSaving, setIsSaving] = useState(false)
  const [modalError, setModalError] = useState<string | null>(null)
  const [isOverrideMode, setIsOverrideMode] = useState(false)
  const [overrideError, setOverrideError] = useState<string | null>(null)

  const isLoading = wsLoading || pdLoading

  // §3.4/§3.6 — the visible grid can spill into the previous year (January's
  // leading days) or the next year (December's trailing days), so fetch
  // whichever 1-2 calendar years the current month view actually touches.
  const viewYear = currentMonth.getFullYear()
  const viewMonth = currentMonth.getMonth()
  const calendarMinYear = viewMonth === 0 ? viewYear - 1 : viewYear
  const calendarMaxYear = viewMonth === 11 ? viewYear + 1 : viewYear
  const calendarYearsSpan = calendarMaxYear - calendarMinYear + 1

  const { data: calendarWindow, refetch: refetchCalendarWindow } = useCalendarDays(
    workspace?.id ?? '',
    calendarMinYear,
    calendarYearsSpan,
  )
  const { data: dayOverrides, upsert: upsertDayOverride, remove: removeDayOverride } = useDayOverrides(
    workspace?.id ?? '',
  )

  const calendarDaysByDate = useMemo(() => {
    const map = new Map<string, CalendarDayEntry>()
    for (const day of calendarWindow?.days ?? []) {
      map.set(day.date, day)
    }
    return map
  }, [calendarWindow])

  useEffect(() => {
    const handlePointerUp = () => {
      if (isDragging && dragAnchor && dragCurrent) {
        const dates = datesInRange(dragAnchor, dragCurrent)
        setSelectedDates(new Set(dates))

        if (dates.length === 1) {
          setIsRangeMode(false)
        } else {
          setIsRangeMode(true)
        }
        setIsModalOpen(true)
      }
      setIsDragging(false)
    }

    if (isDragging) {
      window.addEventListener('pointerup', handlePointerUp)
      return () => window.removeEventListener('pointerup', handlePointerUp)
    }
  }, [isDragging, dragAnchor, dragCurrent])

  if (isLoading) {
    return <LoadingSpinner message={t('calendar.loading')} />
  }

  const year = currentMonth.getFullYear()
  const month = currentMonth.getMonth()

  const firstDay = new Date(year, month, 1)
  const lastDay = new Date(year, month + 1, 0)
  const daysInMonth = lastDay.getDate()
  const startOffset = (firstDay.getDay() + 6) % 7

  const weeks: string[][] = []
  let currentWeek: string[] = []

  for (let i = 0; i < startOffset; i++) {
    const prevDate = new Date(year, month, -startOffset + i + 1)
    currentWeek.push(formatDate(prevDate))
  }

  for (let day = 1; day <= daysInMonth; day++) {
    currentWeek.push(formatDate(new Date(year, month, day)))
    if (currentWeek.length === 7) {
      weeks.push(currentWeek)
      currentWeek = []
    }
  }

  const remaining = 7 - currentWeek.length
  for (let i = 0; i < remaining; i++) {
    currentWeek.push(formatDate(new Date(year, month + 1, i + 1)))
  }
  weeks.push(currentWeek)

  const handlePrevMonth = () => {
    setCurrentMonth(new Date(year, month - 1, 1))
  }

  const handleNextMonth = () => {
    setCurrentMonth(new Date(year, month + 1, 1))
  }

  const handleMonthChange = (e: React.ChangeEvent<HTMLSelectElement>) => {
    const newMonth = Number(e.target.value)
    setCurrentMonth(new Date(year, newMonth, 1))
  }

  const handleYearChange = (e: React.ChangeEvent<HTMLSelectElement>) => {
    const newYear = Number(e.target.value)
    setCurrentMonth(new Date(newYear, month, 1))
  }

  // §3.6 — an explicit mode toggle (rather than a modifier-click or context
  // menu) keeps day-override editing unambiguous and fully decoupled from
  // the pointer-drag multi-select gesture below: modifier keys don't exist
  // on touch, and a context menu needs its own a11y/keyboard path. While the
  // mode is active, pointer-drag is disabled entirely so a click always
  // means "toggle this day's override", never "start a range selection".
  const handlePointerDown = (date: string) => {
    if (isOverrideMode) return
    setDragAnchor(date)
    setDragCurrent(date)
    setIsDragging(true)
  }

  const handlePointerEnter = (date: string) => {
    if (isOverrideMode) return
    if (isDragging) {
      setDragCurrent(date)
    }
  }

  const handleOverrideToggle = async (date: string) => {
    if (!workspace?.id) return
    const info = calendarDaysByDate.get(date)
    if (!info) return

    try {
      setOverrideError(null)
      if (info.isOverride) {
        const existing = (dayOverrides ?? []).find((o) => o.date === date)
        if (existing) {
          await removeDayOverride(existing.id)
        }
      } else {
        // Toggle the effective status: a currently-free day becomes an
        // override marking it a working day, and vice versa.
        await upsertDayOverride({
          workspaceId: workspace.id,
          date,
          isWorkingDay: info.isFree,
          note: null,
        })
      }
      // The grid's shading/badges come from GET /api/calendar/days, a
      // separate fetch from the override list above — without this
      // explicit refetch the day-overrides list would be up to date but the
      // calendar cell would keep showing the pre-mutation state until a
      // full page reload.
      await refetchCalendarWindow()
    } catch (err) {
      setOverrideError(err instanceof Error ? err.message : t('calendar.overrideError'))
    }
  }

  const handleDayClick = (date: string) => {
    if (isOverrideMode) {
      void handleOverrideToggle(date)
      return
    }
    setSelectedDates(new Set([date]))
    setIsRangeMode(false)
    setIsModalOpen(true)
  }

  const getExistingDay = (date: string): PlannedLeaveDay | undefined => {
    return (plannedDays ?? []).find((pd: PlannedLeaveDay) => pd.date === date && pd.parentPersonalDataUuid === personalDataUuid)
  }

  const handleSavePlannedDay = async (payload: {
    dayType: 'sjukpenning' | 'lagsta' | 'vacation'
    parentId: string
    isDubbeldag: boolean
  }) => {
    if (selectedDates.size === 0 || !selectedChildId || !workspace?.id || !personalDataUuid) return

    try {
      setIsSaving(true)
      setModalError(null)

      setLastLeaveType(payload.dayType)

      for (const date of selectedDates) {
        const existingDay = (plannedDays ?? []).find(
          (pd: PlannedLeaveDay) => pd.date === date && pd.parentPersonalDataUuid === personalDataUuid
        )

        if (existingDay) {
          await update(existingDay.id, {
            day_type: payload.dayType,
            is_dubbeldag: payload.isDubbeldag,
          })
        } else {
          await add({
            workspace_id: workspace.id,
            child_id: selectedChildId,
            parent_personal_data_uuid: personalDataUuid,
            date,
            day_type: payload.dayType,
            is_dubbeldag: payload.isDubbeldag,
          })
        }
      }

      setIsModalOpen(false)
      setSelectedDates(new Set())
    } catch (err) {
      setModalError(err instanceof Error ? err.message : t('calendar.saveError'))
    } finally {
      setIsSaving(false)
    }
  }

  const handleDeletePlannedDay = async () => {
    if (selectedDates.size !== 1) return

    try {
      setIsSaving(true)
      setModalError(null)

      const dates = Array.from(selectedDates)
      const date = dates[0]
      if (!date) return

      const existingDay = getExistingDay(date)
      if (existingDay) {
        await remove(existingDay.id)
      }

      setIsModalOpen(false)
      setSelectedDates(new Set())
    } catch (err) {
      setModalError(err instanceof Error ? err.message : t('calendar.deleteError'))
    } finally {
      setIsSaving(false)
    }
  }

  const defaultLeaveType = getLastLeaveType() ?? 'vacation'
  const firstSelectedDate = Array.from(selectedDates).sort()[0]

  // Dates to highlight in the grid. While dragging, show a live preview of the
  // range under the cursor; otherwise show the committed selection.
  const highlightedDates =
    isDragging && dragAnchor && dragCurrent
      ? new Set(datesInRange(dragAnchor, dragCurrent))
      : selectedDates

  return (
    <Layout>
      <div data-testid="calendar" className="calendar">
        <div className="calendar__header">
          <button onClick={handlePrevMonth} aria-label={t('calendar.prevMonthAria')}>
            ←
          </button>
          <h2 className="calendar__title">
            <select
              value={month}
              onChange={handleMonthChange}
              className="calendar__month-select"
              aria-label={t('calendar.selectMonthAria')}
            >
              {[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11].map((m) => {
                const date = new Date(year, m, 1)
                const monthName = date.toLocaleDateString(locale === 'sv' ? 'sv-SE' : 'en-US', { month: 'long' })
                return (
                  <option key={m} value={m}>
                    {monthName}
                  </option>
                )
              })}
            </select>
            <select
              value={year}
              onChange={handleYearChange}
              className="calendar__year-select"
              aria-label={t('calendar.selectYearAria')}
            >
              {Array.from({ length: 2055 - 2026 + 1 }, (_, i) => 2026 + i).map((y) => (
                <option key={y} value={y}>
                  {y}
                </option>
              ))}
            </select>
          </h2>
          <button onClick={handleNextMonth} aria-label={t('calendar.nextMonthAria')}>
            →
          </button>
        </div>

        <div className="calendar__toolbar">
          <button
            type="button"
            onClick={() => setIsOverrideMode((prev) => !prev)}
            aria-pressed={isOverrideMode}
            className={`calendar__override-toggle${isOverrideMode ? ' calendar__override-toggle--active' : ''}`}
            data-testid="calendar-override-toggle"
          >
            {isOverrideMode ? t('calendar.overrideModeActiveLabel') : t('calendar.overrideModeLabel')}
          </button>
          {isOverrideMode && (
            <p className="calendar__toolbar-hint" data-testid="calendar-override-hint">
              {t('calendar.overrideModeHint')}
            </p>
          )}
          {overrideError && (
            <p className="calendar__toolbar-error" role="alert" data-testid="calendar-override-error">
              {overrideError}
            </p>
          )}
        </div>

        <div className={`calendar__grid${showWeekNumbers ? ' calendar__grid--with-week-numbers' : ''}`}>
          {showWeekNumbers && <div className="calendar__week-number-header" />}
          {WEEKDAY_KEYS.map((key) => (
            <div key={key} className="calendar__weekday">
              {t(key)}
            </div>
          ))}

          {weeks.map((week, weekIdx) => {
            const firstDate = week[0]
            const weekMonth = firstDate ? new Date(firstDate + 'T00:00:00Z').getMonth() : month
            return (
              <CalendarWeek
                key={weekIdx}
                weekDates={week}
                plannedDays={plannedDays ?? []}
                selectedDates={highlightedDates}
                parentName={parentName ?? t('calendar.you')}
                personalDataUuid={personalDataUuid ?? ''}
                isCurrentMonth={weekMonth === month}
                showWeekNumbers={showWeekNumbers}
                onDayClick={handleDayClick}
                onPointerDown={handlePointerDown}
                onPointerEnter={handlePointerEnter}
                calendarDaysByDate={calendarDaysByDate}
              />
            )
          })}
        </div>

        <div className="calendar__legend">
          <h3>{t('calendar.legendTitle')}</h3>
          <div className="calendar__legend-items">
            <div className="calendar__legend-item">
              <span className="calendar__legend-swatch" style={{ backgroundColor: getColorForType('vacation') }} />
              <span>{t('calendar.legendVacation')}</span>
            </div>
            <div className="calendar__legend-item">
              <span className="calendar__legend-swatch" style={{ backgroundColor: getColorForType('sjukpenning') }} />
              <span>{t('calendar.legendIncomeBased')}</span>
            </div>
            <div className="calendar__legend-item">
              <span className="calendar__legend-swatch" style={{ backgroundColor: getColorForType('lagsta') }} />
              <span>{t('calendar.legendMinimumRate')}</span>
            </div>
            <div className="calendar__legend-item">
              <span className="calendar__legend-swatch calendar__legend-swatch--red-day" />
              <span>{t('calendar.legendRedDay')}</span>
            </div>
            <div className="calendar__legend-item">
              <span className="calendar__legend-swatch calendar__legend-swatch--klamdag" />
              <span>{t('calendar.legendKlamdag')}</span>
            </div>
            <div className="calendar__legend-item">
              <span className="calendar__legend-swatch calendar__legend-swatch--override" />
              <span>{t('calendar.legendOverride')}</span>
            </div>
            <div className="calendar__legend-item">
              <span className="calendar__legend-swatch calendar__legend-swatch--dubbeldag">2×</span>
              <span>{t('calendar.legendDoubleDay')}</span>
            </div>
          </div>
        </div>

        {firstSelectedDate && (
          <PlannedDayModal
            date={firstSelectedDate}
            isOpen={isModalOpen}
            existingDay={isRangeMode ? null : getExistingDay(firstSelectedDate) ?? null}
            parents={[{ id: personalDataUuid ?? '', name: parentName ?? t('calendar.you') }]}
            selectedParentId={personalDataUuid ?? ''}
            onSave={handleSavePlannedDay}
            onDelete={!isRangeMode && getExistingDay(firstSelectedDate) ? handleDeletePlannedDay : undefined}
            onClose={() => {
              setIsModalOpen(false)
              setSelectedDates(new Set())
            }}
            isSaving={isSaving}
            error={modalError}
            isRangeMode={isRangeMode}
            dayCount={selectedDates.size}
            defaultDayType={defaultLeaveType}
          />
        )}
      </div>
    </Layout>
  )
}

function formatDate(date: Date): string {
  const year = date.getFullYear()
  const month = String(date.getMonth() + 1).padStart(2, '0')
  const day = String(date.getDate()).padStart(2, '0')
  return `${year}-${month}-${day}`
}