import { useEffect, useRef, useState } from 'react'
import api from '../api/client'
import './ArticleSaveButton.css'

/**
 * Keep this article.
 *
 * A library holds both articles and questions, because putting one of each
 * aside is the same act to whoever is doing it. The article goes in as itself
 * rather than standing in for the questions written against it — a topic with
 * no questions is still worth keeping, and a reader who saved the reading did
 * not ask for a session.
 *
 * Which libraries already hold it is asked of the server, as one question. It
 * was kept on the device for a while, because the API could not answer; that
 * was wrong on the second machine and silently so.
 */
//: What the panel is wide enough to want. Matches `width` in the stylesheet.
const PANEL = 280

export default function ArticleSaveButton({ articleId }) {
  const [open, setOpen] = useState(false)
  // Which edge the panel hangs from. It hung from the right always, which is
  // right for a star at the right of a toolbar and wrong for this one, which
  // is the first thing in the article's bar: on a phone 200px of the panel sat
  // off the left of the screen, over the title, unreadable.
  const [side, setSide] = useState('right')
  const [libraries, setLibraries] = useState([])
  const [query, setQuery] = useState('')
  const [busy, setBusy] = useState(false)
  const [saved, setSaved] = useState([])
  const wrap = useRef(null)
  const anchor = useRef(null)

  // Asked once per article rather than per library: fetching each library's
  // contents to find out would also stamp every one of them as used and
  // reorder the reader's own list.
  useEffect(() => {
    if (!articleId) return undefined
    let live = true
    api.get(`/collections/for-article/${articleId}`)
      .then(res => { if (live) setSaved(res.data?.collection_ids || []) })
      .catch(() => { if (live) setSaved([]) })
    return () => { live = false }
  }, [articleId])

  useEffect(() => {
    if (!open) return
    api.get('/collections/').then(res => setLibraries(Array.isArray(res.data) ? res.data : []))
      .catch(() => setLibraries([]))
  }, [open])

  // A popover that outlives the click that dismissed it is a popover you have
  // to close twice.
  useEffect(() => {
    if (!open) return undefined
    const away = (event) => { if (!wrap.current?.contains(event.target)) setOpen(false) }
    document.addEventListener('mousedown', away)
    return () => document.removeEventListener('mousedown', away)
  }, [open])

  const saveInto = async (collectionId) => {
    setBusy(true)
    try {
      await api.put(`/collections/${collectionId}/articles/${articleId}`)
      setSaved(prev => (prev.includes(collectionId) ? prev : [...prev, collectionId]))
      setQuery('')
    } catch { /* nothing is marked, which is the honest signal */ }
    finally { setBusy(false) }
  }

  // Putting it back is the same control, so the star is a toggle per library
  // rather than a one-way door with the undo somewhere else.
  const removeFrom = async (collectionId) => {
    setBusy(true)
    try {
      await api.delete(`/collections/${collectionId}/articles/${articleId}`)
      setSaved(prev => prev.filter(id => id !== collectionId))
    } catch { /* it stays marked, which is what the server still believes */ }
    finally { setBusy(false) }
  }

  const createAndSave = async (title) => {
    const name = title.trim()
    if (!name) return
    setBusy(true)
    try {
      const made = await api.post('/collections/', { title: name })
      setLibraries(list => [...list, made.data])
      setBusy(false)
      await saveInto(made.data.id)
    } catch { setBusy(false) }
  }

  const needle = query.trim().toLowerCase()
  const found = libraries.filter(row => row.title.toLowerCase().includes(needle))
  // Offered only when nothing you already have is called this — two libraries
  // of the same name is a filing system nobody can use.
  const canCreate = !!needle && !libraries.some(row => row.title.trim().toLowerCase() === needle)
  const isSaved = saved.length > 0

  return (
    <span className="asave" ref={wrap}>
      <button type="button" ref={anchor} className={`article-tool${isSaved ? ' is-on' : ''}`}
        aria-expanded={open} aria-haspopup="dialog"
        aria-label={isSaved ? `Saved to ${saved.length} librar${saved.length === 1 ? 'y' : 'ies'}` : 'Save this article to a library'}
        onClick={() => {
          // Measured when it opens rather than guessed: the same star sits at
          // the left of the reading bar and could sit anywhere else later.
          const box = anchor.current?.getBoundingClientRect?.()
          if (box) setSide(box.right - PANEL < 8 ? 'left' : 'right')
          setOpen(v => !v)
        }}>
        <span aria-hidden="true">{isSaved ? '★' : '☆'}</span>
      </button>
      {open && (
        <div className={`asave-pop is-${side}`} role="dialog" aria-label="Save this article to a library">
          <p className="asave-title">Save this article</p>
          {/* One box for both. Searching what you have and naming what you do
              not are the same act — you type the name of the library you want
              and it either exists or it doesn't. */}
          <input className="asave-find" value={query} disabled={busy}
            placeholder="Create or find a library" aria-label="Create or find a library"
            onChange={event => setQuery(event.target.value)}
            onKeyDown={event => {
              if (event.key === 'Enter' && canCreate) { event.preventDefault(); createAndSave(query) }
            }} />
          {canCreate && (
            <button type="button" className="asave-new" disabled={busy} onClick={() => createAndSave(query)}>
              <span>{query.trim()}</span><span aria-hidden="true">+</span>
            </button>
          )}
          {found.length > 0 && (
            <ul className="asave-list">
              {found.map(row => {
                const inIt = saved.includes(row.id)
                return (
                  <li key={row.id}>
                    <button type="button" className={inIt ? 'is-in' : ''} disabled={busy}
                      aria-pressed={inIt}
                      onClick={() => (inIt ? removeFrom(row.id) : saveInto(row.id))}>
                      {inIt ? '✓ ' : '+ '}{row.title}
                    </button>
                  </li>
                )
              })}
            </ul>
          )}
          {!found.length && !canCreate && (
            <p className="asave-empty">{libraries.length ? 'No library by that name.' : 'Type a name to make your first library.'}</p>
          )}
        </div>
      )}
    </span>
  )
}