/**
 * FEAT-2: Becken-Detailseite — Stammdaten, BELEGUNG (welche Tiere wohnen
 * aktuell hier, mit Farbschlag + Link zur Rennmaus), Löschen mit
 * Bestätigung; Konflikt (Becken nicht leer) wird deutsch gemeldet.
 */
import { useMemo, useState } from 'react'
import { Link, useNavigate, useParams } from 'react-router-dom'
import { de } from '../strings/de'
import { ApiError } from '../api/client'
import { deleteEnclosure, getEnclosure } from '../api/enclosures'
import { listGerbils } from '../api/gerbils'
import { listColorVarieties } from '../api/lookups'
import { condition } from '../api/gridify'
import { useApi, useMutation } from '../hooks/useApi'

export default function BeckenDetailPage() {
  const t = de.pages.becken
  const { id = '' } = useParams()
  const navigate = useNavigate()
  const [deleteError, setDeleteError] = useState<string | null>(null)

  const enclosure = useApi(() => getEnclosure(id), [id])
  // Belegung: alle Tiere, deren aktuelles Becken dieses ist.
  const occupants = useApi(
    () =>
      listGerbils({
        filter: condition({ field: 'enclosureId', op: '==', value: id }),
        orderBy: 'name',
        page: 1,
        pageSize: 500,
      }),
    [id],
  )
  const colorVarieties = useApi(() => listColorVarieties(), [])
  const colorNameById = useMemo(
    () => new Map((colorVarieties.data ?? []).map((c) => [c.id, c.name])),
    [colorVarieties.data],
  )

  const removal = useMutation(() => deleteEnclosure(id))

  async function onDelete() {
    if (!window.confirm(t.delete.confirmMessage)) return
    setDeleteError(null)
    const result = await removal.run()
    if (result.ok) {
      navigate('/gehege')
    } else if (result.cause instanceof ApiError && result.cause.status === 409) {
      // Backend meldet Konflikt, wenn noch Tiere im Becken wohnen.
      setDeleteError(t.delete.conflict)
    } else {
      setDeleteError(result.error)
    }
  }

  if (enclosure.loading) return <p className="muted">{de.common.loading}</p>
  if (enclosure.error || !enclosure.data) {
    return (
      <section className="page">
        <p className="muted">{enclosure.error ?? t.detail.notFound}</p>
        <Link to="/gehege" className="btn">
          {t.detail.back}
        </Link>
      </section>
    )
  }

  const e = enclosure.data
  const animals = occupants.data?.items ?? []
  const count = occupants.data?.totalCount ?? 0

  return (
    <section className="page">
      <header className="page-head">
        <div>
          <h2>{e.name}</h2>
          {occupants.data && (
            <p className="muted">
              {count} {count === 1 ? t.occupancy.countOne : t.occupancy.countMany}
            </p>
          )}
        </div>
        <div className="head-actions">
          <Link to={`/gehege/${e.id}/bearbeiten`} className="btn btn--primary">
            {t.detail.edit}
          </Link>
          <button
            type="button"
            className="btn btn--danger"
            onClick={onDelete}
            disabled={removal.pending}
          >
            {t.delete.action}
          </button>
          <Link to="/gehege" className="btn">
            {t.detail.back}
          </Link>
        </div>
      </header>

      {deleteError && <div className="alert alert--error">{deleteError}</div>}

      {e.notes && (
        <dl className="def-list">
          <div className="def-row">
            <dt>{t.fields.notes}</dt>
            <dd>{e.notes}</dd>
          </div>
        </dl>
      )}

      <h3>{t.occupancy.title}</h3>
      {occupants.loading && <p className="muted">{de.common.loading}</p>}
      {occupants.error && (
        <div className="alert alert--error">
          <span>{occupants.error}</span>
          <button type="button" className="btn" onClick={occupants.reload}>
            {de.common.retry}
          </button>
        </div>
      )}
      {!occupants.loading && !occupants.error && animals.length === 0 && (
        <p className="muted">{t.occupancy.empty}</p>
      )}
      {animals.length > 0 && (
        <ul className="card-list">
          {animals.map((g) => (
            <li key={g.id}>
              <Link to={`/rennmaeuse/${g.id}`} className="gerbil-card">
                <span className="gerbil-card__name">{g.name}</span>
                <span className="gerbil-card__meta">
                  {g.colorVarietyId ? (colorNameById.get(g.colorVarietyId) ?? '—') : '—'}
                </span>
              </Link>
            </li>
          ))}
        </ul>
      )}
    </section>
  )
}