import { useEffect, useRef, useState, type CSSProperties, type FormEvent } from 'react'
import { useOverlayDismiss } from '../../hooks/useOverlayDismiss'
import type { CalendarEvent, CalendarItem, EventInput, Recurrence, WeekdayCode } from '../../api/client'
import {
  addDays, allDayISO, dateFromInput, eventDay, nthOfMonth, timedISO,
  toDateInput, toTimeInput, weekdayCodeOf, weekdayCodes,
} from './dates'
import { ColorSwatches, Toggle } from './controls'

interface Props {
  /** Fehlt er, entsteht ein neuer Termin. */
  event?: CalendarEvent
  /** Vorbelegter Start – aus dem angeklickten Tag bzw. der Stunde. */
  defaultStart: Date
  calendars: CalendarItem[]
  calendarId: string
  onSave: (input: EventInput, calendarId: string) => void
  onDelete?: () => void
  onCancel: () => void
}

type FreqChoice = 'NONE' | Recurrence['freq']
type EndChoice = 'NEVER' | 'COUNT' | 'UNTIL'

const freqLabels: Record<FreqChoice, string> = {
  NONE: 'Einmalig',
  DAILY: 'Täglich',
  WEEKLY: 'Wöchentlich',
  MONTHLY: 'Monatlich',
  YEARLY: 'Jährlich',
}

const weekdayShort = ['Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa', 'So']
const weekdayLong = ['Montag', 'Dienstag', 'Mittwoch', 'Donnerstag', 'Freitag', 'Samstag', 'Sonntag']
const monthNames = [
  'Januar', 'Februar', 'März', 'April', 'Mai', 'Juni',
  'Juli', 'August', 'September', 'Oktober', 'November', 'Dezember',
]

/** „Am 4." bzw. „Am 1. Freitag" – beide aus dem Startdatum abgeleitet, wie
 *  man es aus anderen Kalendern kennt. Bei jährlich kommt der Monat dazu. */
function monthlyModeLabels(start: Date, yearly: boolean): { day: string; weekday: string } {
  const n = nthOfMonth(start)
  const nth = n === -1 ? 'letzten' : `${n}.`
  const wd = weekdayLong[(start.getDay() + 6) % 7]
  const month = monthNames[start.getMonth()]
  return yearly
    ? { day: `Am ${start.getDate()}. ${month}`, weekday: `Am ${nth} ${wd} im ${month}` }
    : { day: `Am ${start.getDate()}.`, weekday: `Am ${nth} ${wd}` }
}

export default function EventDialog({ event, defaultStart, calendars, calendarId, onSave, onDelete, onCancel }: Props) {
  const overlay = useOverlayDismiss(onCancel)
  const titleRef = useRef<HTMLInputElement>(null)

  const allDayInit = event?.all_day ?? false
  // Bei einer Reihe bearbeitet das Formular die **Reihe**, nicht den
  // angeklickten Einzeltermin – deshalb series_start, wo vorhanden.
  const baseStartISO = event?.series_start ?? event?.start
  const baseEndISO = event?.series_end ?? event?.end
  const start = baseStartISO ? eventDay(baseStartISO, allDayInit) : defaultStart
  const startTimed = baseStartISO && !allDayInit ? new Date(baseStartISO) : defaultStart
  const end = baseEndISO
    ? eventDay(baseEndISO, allDayInit)
    : new Date(startTimed.getTime() + 60 * 60 * 1000)

  const [calId, setCalId] = useState(calendarId)
  const [summary, setSummary] = useState(event?.summary ?? '')
  const [description, setDescription] = useState(event?.description ?? '')
  const [location, setLocation] = useState(event?.location ?? '')
  const [color, setColor] = useState(event?.color ?? '')
  const [allDay, setAllDay] = useState(allDayInit)
  const [startDate, setStartDate] = useState(toDateInput(start))
  const [startTime, setStartTime] = useState(toTimeInput(startTimed))
  const [endDate, setEndDate] = useState(toDateInput(end))
  const [endTime, setEndTime] = useState(toTimeInput(end))

  const rec = event?.recurrence
  const [freq, setFreq] = useState<FreqChoice>(rec?.freq ?? 'NONE')
  const [interval, setInterval] = useState(String(rec?.interval ?? 1))
  const [endChoice, setEndChoice] = useState<EndChoice>(
    rec?.count ? 'COUNT' : rec?.until ? 'UNTIL' : 'NEVER')
  const [count, setCount] = useState(String(rec?.count ?? 10))
  const [until, setUntil] = useState(
    rec?.until ? toDateInput(eventDay(rec.until, true)) : toDateInput(addDays(start, 90)))
  const [byday, setByday] = useState<WeekdayCode[]>(rec?.byday ?? [])
  const [monthMode, setMonthMode] = useState<'DAY' | 'WEEKDAY'>(rec?.mode === 'WEEKDAY' ? 'WEEKDAY' : 'DAY')

  // Bezugstag für alles, was sich aus dem Start ableitet („am 1. Freitag").
  // Mittags, damit ein Sommerzeitsprung das Datum nicht kippt.
  const startDay = dateFromInput(startDate)
  const startWeekday = weekdayCodeOf(startDay)
  // Der Wochentag des Starts ist immer dabei und lässt sich nicht abwählen –
  // sonst zeigte die Reihe nicht mehr auf ihren eigenen ersten Termin.
  const activeDays: WeekdayCode[] = Array.from(new Set([...byday, startWeekday]))
  const modeLabels = monthlyModeLabels(startDay, freq === 'YEARLY')

  useEffect(() => { titleRef.current?.focus() }, [])

  useEffect(() => {
    function onKey(e: KeyboardEvent) { if (e.key === 'Escape') onCancel() }
    window.addEventListener('keydown', onKey)
    return () => window.removeEventListener('keydown', onKey)
  }, [onCancel])

  // Nur Regeln, die dieses Formular vollständig abbildet, sind bearbeitbar.
  // Alles andere ("jeden zweiten Dienstag im Monat") bliebe beim Speichern
  // auf der Strecke – der Server lehnt es deshalb auch ab.
  const readOnly = !!event?.recurring && !event?.recurrence
  const isSeries = !!event?.recurring

  function changeStartDate(v: string) {
    const shift = (+new Date(v) - +new Date(startDate)) / 86400000
    setStartDate(v)
    if (Number.isFinite(shift) && shift !== 0) {
      setEndDate(toDateInput(addDays(new Date(`${endDate}T12:00:00`), shift)))
    }
  }

  function buildRecurrence(): Recurrence | null {
    if (freq === 'NONE') return null
    const r: Recurrence = { freq, interval: Math.max(1, parseInt(interval, 10) || 1) }
    if (endChoice === 'COUNT') r.count = Math.max(1, parseInt(count, 10) || 1)
    if (endChoice === 'UNTIL') r.until = allDayISO(until)
    if (freq === 'WEEKLY') r.byday = activeDays
    if (freq === 'MONTHLY' || freq === 'YEARLY') r.mode = monthMode
    return r
  }

  function toggleDay(code: WeekdayCode) {
    if (code === startWeekday) return
    setByday(prev => prev.includes(code) ? prev.filter(c => c !== code) : [...prev, code])
  }

  function handleSubmit(e: FormEvent) {
    e.preventDefault()
    if (readOnly || !summary.trim()) return

    let startISO: string, endISO: string
    if (allDay) {
      startISO = allDayISO(startDate)
      endISO = allDayISO(endDate < startDate ? startDate : endDate)
    } else {
      startISO = timedISO(startDate, startTime)
      endISO = timedISO(endDate, endTime)
      if (endISO <= startISO) {
        endISO = new Date(+new Date(startISO) + 60 * 60 * 1000).toISOString()
      }
    }
    onSave({
      summary: summary.trim(),
      description: description.trim() || undefined,
      location: location.trim() || undefined,
      all_day: allDay,
      color: color || undefined,
      recurrence: buildRecurrence(),
      start: startISO,
      end: endISO,
    }, calId)
  }

  const inputStyle: CSSProperties = {
    width: '100%', boxSizing: 'border-box',
    background: 'var(--color-surface-2)', border: '1px solid var(--color-border)',
    borderRadius: 8, padding: '8px 10px', fontSize: 13.5, color: 'var(--color-text)',
    outline: 'none',
  }
  const labelStyle: CSSProperties = {
    fontSize: 12, color: 'var(--color-text-muted)', marginBottom: 4, display: 'block',
  }
  const noteStyle: CSSProperties = {
    background: 'var(--color-surface-2)', border: '1px solid var(--color-border)',
    borderRadius: 8, padding: '8px 10px', fontSize: 12.5,
    color: 'var(--color-text-muted)', marginBottom: 14, lineHeight: 1.45,
  }
  const calColor = calendars.find(c => c.id === calId)?.color ?? '#4285f4'

  return (
    <div style={{
      position: 'fixed', inset: 0, zIndex: 200, display: 'flex',
      alignItems: 'center', justifyContent: 'center', background: 'rgba(0,0,0,0.6)', padding: 16,
    }} {...overlay}>
      <form onSubmit={handleSubmit} style={{
        background: 'var(--color-surface)', border: '1px solid var(--color-border)',
        borderRadius: 14, padding: 24, width: 440, maxWidth: '100%', maxHeight: '90vh', overflowY: 'auto',
      }}>
        <h2 style={{ margin: '0 0 16px', fontSize: 16, fontWeight: 600, color: 'var(--color-text)' }}>
          {event ? (isSeries ? 'Terminreihe bearbeiten' : 'Termin bearbeiten') : 'Neuer Termin'}
        </h2>

        {readOnly && (
          <div style={noteStyle}>
            Diese Wiederholungsregel kann dieses Formular nicht vollständig
            abbilden – zum Ändern einen CalDAV-Client verwenden (z. B. DAVx5).
            Der Termin bleibt unverändert erhalten.
          </div>
        )}
        {isSeries && !readOnly && (
          <div style={noteStyle}>
            Terminreihe: Änderungen gelten für <strong>alle</strong> Termine der
            Reihe. Angezeigt wird deshalb ihr Beginn, nicht der angeklickte Tag.
          </div>
        )}

        <div style={{ marginBottom: 12 }}>
          <label style={labelStyle}>Titel</label>
          <input ref={titleRef} type="text" value={summary} disabled={readOnly}
                 onChange={e => setSummary(e.target.value)} style={inputStyle} required />
        </div>

        {calendars.length > 1 && (
          <div style={{ marginBottom: 12 }}>
            <label style={labelStyle}>Kalender</label>
            {/* Beim Bearbeiten fest: Ein Umhängen wäre Löschen und Neuanlegen
                unter neuer Kennung – das gehört nicht versteckt in ein
                Auswahlfeld. */}
            <select value={calId} disabled={!!event} onChange={e => setCalId(e.target.value)} style={inputStyle}>
              {calendars.map(c => <option key={c.id} value={c.id}>{c.name}</option>)}
            </select>
          </div>
        )}

        <div style={{ marginBottom: 14 }}>
          <Toggle checked={allDay} onChange={setAllDay} disabled={readOnly} label="Ganztägig" />
        </div>

        <div style={{ display: 'flex', gap: 8, marginBottom: 12 }}>
          <div style={{ flex: 1 }}>
            <label style={labelStyle}>Start</label>
            <input type="date" value={startDate} disabled={readOnly}
                   onChange={e => changeStartDate(e.target.value)} style={inputStyle} />
          </div>
          {!allDay && (
            <div style={{ width: 116 }}>
              <label style={labelStyle}>Uhrzeit</label>
              <input type="time" value={startTime} disabled={readOnly} onChange={e => setStartTime(e.target.value)} style={inputStyle} />
            </div>
          )}
        </div>

        <div style={{ display: 'flex', gap: 8, marginBottom: 14 }}>
          <div style={{ flex: 1 }}>
            <label style={labelStyle}>Ende</label>
            <input type="date" value={endDate} min={startDate} disabled={readOnly}
                   onChange={e => setEndDate(e.target.value)} style={inputStyle} />
          </div>
          {!allDay && (
            <div style={{ width: 116 }}>
              <label style={labelStyle}>Uhrzeit</label>
              <input type="time" value={endTime} disabled={readOnly} onChange={e => setEndTime(e.target.value)} style={inputStyle} />
            </div>
          )}
        </div>

        {/* ── Wiederholung ───────────────────────────────────────────── */}
        <div style={{ marginBottom: 14 }}>
          <label style={labelStyle}>Wiederholung</label>
          <div style={{ display: 'flex', gap: 8 }}>
            <select value={freq} disabled={readOnly}
                    onChange={e => setFreq(e.target.value as FreqChoice)}
                    style={{ ...inputStyle, flex: 1 }}>
              {(Object.keys(freqLabels) as FreqChoice[]).map(f => (
                <option key={f} value={f}>{freqLabels[f]}</option>
              ))}
            </select>
            {freq !== 'NONE' && (
              <div style={{ display: 'flex', alignItems: 'center', gap: 6, flexShrink: 0 }}>
                <span style={{ fontSize: 12.5, color: 'var(--color-text-muted)' }}>alle</span>
                <input type="number" min={1} max={99} value={interval} disabled={readOnly}
                       onChange={e => setInterval(e.target.value)}
                       style={{ ...inputStyle, width: 60 }} />
              </div>
            )}
          </div>
        </div>

        {/* Wöchentlich: an welchen Tagen. Der Starttag ist fest an –
            eine Reihe, die ihren eigenen ersten Termin auslässt, ist keine. */}
        {freq === 'WEEKLY' && (
          <div style={{ marginBottom: 14 }}>
            <label style={labelStyle}>An diesen Tagen</label>
            <div style={{ display: 'flex', gap: 5 }}>
              {weekdayCodes.map((code, i) => {
                const on = activeDays.includes(code)
                const fixed = code === startWeekday
                return (
                  <button
                    key={code} type="button" disabled={readOnly || fixed}
                    onClick={() => toggleDay(code)}
                    title={fixed ? `${weekdayLong[i]} – Tag des Starts` : weekdayLong[i]}
                    style={{
                      flex: 1, padding: '6px 0', borderRadius: 7, fontSize: 12,
                      border: '1px solid var(--color-border)',
                      background: on ? 'var(--color-primary)' : 'transparent',
                      color: on ? '#fff' : 'var(--color-text-muted)',
                      cursor: readOnly || fixed ? 'default' : 'pointer',
                      opacity: fixed && !readOnly ? 0.85 : 1,
                      transition: 'background 0.12s, color 0.12s',
                    }}
                  >
                    {weekdayShort[i]}
                  </button>
                )
              })}
            </div>
          </div>
        )}

        {/* Monatlich/jährlich: am festen Tag oder am n-ten Wochentag. */}
        {(freq === 'MONTHLY' || freq === 'YEARLY') && (
          <div style={{ marginBottom: 14 }}>
            <label style={labelStyle}>Wiederholt sich</label>
            <select value={monthMode} disabled={readOnly}
                    onChange={e => setMonthMode(e.target.value as 'DAY' | 'WEEKDAY')}
                    style={inputStyle}>
              <option value="DAY">{modeLabels.day}</option>
              <option value="WEEKDAY">{modeLabels.weekday}</option>
            </select>
          </div>
        )}

        {freq !== 'NONE' && (
          <div style={{ marginBottom: 14 }}>
            <label style={labelStyle}>Endet</label>
            <div style={{ display: 'flex', gap: 8 }}>
              <select value={endChoice} disabled={readOnly}
                      onChange={e => setEndChoice(e.target.value as EndChoice)}
                      style={{ ...inputStyle, flex: 1 }}>
                <option value="NEVER">Nie</option>
                <option value="COUNT">Nach Anzahl</option>
                <option value="UNTIL">An einem Datum</option>
              </select>
              {endChoice === 'COUNT' && (
                <div style={{ display: 'flex', alignItems: 'center', gap: 6, flexShrink: 0 }}>
                  <input type="number" min={1} max={999} value={count} disabled={readOnly}
                         onChange={e => setCount(e.target.value)} style={{ ...inputStyle, width: 70 }} />
                  <span style={{ fontSize: 12.5, color: 'var(--color-text-muted)' }}>Mal</span>
                </div>
              )}
              {endChoice === 'UNTIL' && (
                <input type="date" value={until} min={startDate} disabled={readOnly}
                       onChange={e => setUntil(e.target.value)} style={{ ...inputStyle, width: 160 }} />
              )}
            </div>
          </div>
        )}

        {/* ── Farbe ──────────────────────────────────────────────────── */}
        <div style={{ marginBottom: 14 }}>
          <label style={labelStyle}>Farbe</label>
          <ColorSwatches value={color} onChange={setColor} inherit={calColor} disabled={readOnly} />
        </div>

        <div style={{ marginBottom: 12 }}>
          <label style={labelStyle}>Ort</label>
          <input type="text" value={location} disabled={readOnly} onChange={e => setLocation(e.target.value)} style={inputStyle} />
        </div>

        <div style={{ marginBottom: 20 }}>
          <label style={labelStyle}>Beschreibung</label>
          <textarea value={description} disabled={readOnly} onChange={e => setDescription(e.target.value)}
                    rows={3} style={{ ...inputStyle, resize: 'vertical' }} />
        </div>

        <div style={{ display: 'flex', justifyContent: 'space-between', gap: 8 }}>
          {onDelete ? (
            <button type="button" onClick={onDelete} style={{
              padding: '8px 14px', borderRadius: 8, border: 'none',
              background: 'var(--color-danger)', color: '#fff', fontSize: 13, cursor: 'pointer',
            }}>
              {isSeries ? 'Reihe löschen' : 'Löschen'}
            </button>
          ) : <span />}
          <div style={{ display: 'flex', gap: 8 }}>
            <button type="button" onClick={onCancel} style={{
              padding: '8px 16px', borderRadius: 8, border: '1px solid var(--color-border)',
              background: 'transparent', color: 'var(--color-text-muted)', fontSize: 13, cursor: 'pointer',
            }}>
              {readOnly ? 'Schließen' : 'Abbrechen'}
            </button>
            {!readOnly && (
              <button type="submit" style={{
                padding: '8px 16px', borderRadius: 8, border: 'none',
                background: 'var(--color-primary)', color: '#fff', fontSize: 13, fontWeight: 600, cursor: 'pointer',
              }}>
                Speichern
              </button>
            )}
          </div>
        </div>
      </form>
    </div>
  )
}