import { useEffect, useState, type FormEvent } from 'react'
import { Link, useNavigate, useParams } from 'react-router'
import { api, ApiError, errorMessage, type Book } from '../api'
import { card, inputClass, labelText, primaryButton, secondaryButton } from '../ui'
import { useGenres } from './useGenres'

type Fields = { title: string; author: string; genre_id: string; total_pages: string; current_page: string }
type FormError = { message: string; field?: string }

const EMPTY: Fields = { title: '', author: '', genre_id: '', total_pages: '', current_page: '0' }

export function BookForm() {
  const { id } = useParams()
  const editing = id !== undefined
  const navigate = useNavigate()
  const { genres, error: genresError } = useGenres()
  const [fields, setFields] = useState<Fields>(EMPTY)
  const [loading, setLoading] = useState(editing)
  const [loadError, setLoadError] = useState<string | null>(null)
  const [error, setError] = useState<FormError | null>(null)
  const [busy, setBusy] = useState(false)
  const [attempt, setAttempt] = useState(0)

  useEffect(() => {
    if (!editing) return
    let cancelled = false
    setLoadError(null)
    setLoading(true)
    api<Book>('GET', `/books/${id}`).then(
      (book) => {
        if (cancelled) return
        setFields({
          title: book.title,
          author: book.author,
          genre_id: String(book.genre.id),
          total_pages: String(book.total_pages),
          current_page: String(book.current_page),
        })
        setLoading(false)
      },
      (err) => {
        if (cancelled) return
        setLoadError(errorMessage(err))
        setLoading(false)
      },
    )
    return () => {
      cancelled = true
    }
  }, [editing, id, attempt])

  function set(name: keyof Fields) {
    return (event: { target: { value: string } }) => setFields((prev) => ({ ...prev, [name]: event.target.value }))
  }

  function invalid(name: keyof Fields) {
    return error?.field === name ? { 'aria-invalid': true, 'aria-describedby': 'form-error' } : {}
  }

  async function submit(event: FormEvent) {
    event.preventDefault()
    setError(null)
    setBusy(true)
    const payload = {
      title: fields.title,
      author: fields.author,
      genre_id: Number(fields.genre_id),
      total_pages: Number(fields.total_pages),
      current_page: Number(fields.current_page),
    }
    try {
      const saved = editing
        ? await api<Book>('PATCH', `/books/${id}`, payload)
        : await api<Book>('POST', '/books', payload)
      navigate(`/books/${saved.id}`)
    } catch (err) {
      setError({ message: errorMessage(err), field: err instanceof ApiError ? err.field : undefined })
      setBusy(false)
    }
  }

  if (loadError) {
    return (
      <div role="alert" className={card}>
        <p className="text-red-700">{loadError}</p>
        <div className="mt-2 flex items-center gap-3">
          <button type="button" className={secondaryButton} onClick={() => setAttempt((n) => n + 1)}>
            Retry
          </button>
          <Link to="/books" className="text-indigo-700 underline">
            ← Back to library
          </Link>
        </div>
      </div>
    )
  }
  if (loading) return <p className="text-slate-500">Loading…</p>

  return (
    <form onSubmit={submit} className={`space-y-4 ${card}`}>
      <h1 className="text-2xl font-semibold">{editing ? 'Edit book' : 'Add a book'}</h1>
      <label className="block">
        <span className={labelText}>Title</span>
        <input className={inputClass} value={fields.title} onChange={set('title')} maxLength={500} required {...invalid('title')} />
      </label>
      <label className="block">
        <span className={labelText}>Author</span>
        <input className={inputClass} value={fields.author} onChange={set('author')} maxLength={500} required {...invalid('author')} />
      </label>
      <label className="block">
        <span className={labelText}>Genre</span>
        <select className={inputClass} value={fields.genre_id} onChange={set('genre_id')} required {...invalid('genre_id')}>
          <option value="">Choose a genre</option>
          {genres.map((g) => (
            <option key={g.id} value={String(g.id)}>
              {g.name}
            </option>
          ))}
        </select>
      </label>
      {genresError && <p role="alert" className="text-sm text-red-700">{`Could not load genres: ${genresError}`}</p>}
      <div className="flex gap-4">
        <label className="block">
          <span className={labelText}>Total pages</span>
          <input
            type="number"
            className={inputClass}
            min={1}
            max={100000}
            value={fields.total_pages}
            onChange={set('total_pages')}
            required
            {...invalid('total_pages')}
          />
        </label>
        <label className="block">
          <span className={labelText}>Current page</span>
          <input
            type="number"
            className={inputClass}
            min={0}
            max={fields.total_pages || undefined}
            value={fields.current_page}
            onChange={set('current_page')}
            required
            {...invalid('current_page')}
          />
        </label>
      </div>
      {error && (
        <p id="form-error" role="alert" className="text-sm text-red-700">
          {error.message}
        </p>
      )}
      <div className="flex gap-2">
        <button type="submit" disabled={busy} className={primaryButton}>
          {editing ? 'Save changes' : 'Add book'}
        </button>
        <Link to={editing ? `/books/${id}` : '/books'} className={secondaryButton}>
          Cancel
        </Link>
      </div>
    </form>
  )
}