import { useEffect, useRef, useState } from 'react'
import { getPosts, fileDownloadUrl, type ChannelKindKey, type FileRef, type Org, type PostView } from '../api/client'

const POLL_INTERVAL_MS = 3000

const timeFormatter = new Intl.DateTimeFormat('ko-KR', { hour: '2-digit', minute: '2-digit' })

function humanizeSize(bytes: number): string {
  if (bytes < 1024) {
    return `${bytes} B`
  }
  const kb = bytes / 1024
  if (kb < 1024) {
    return `${kb.toFixed(1)} KB`
  }
  return `${(kb / 1024).toFixed(1)} MB`
}

function AttachmentChip({ file }: { file: FileRef }) {
  return (
    <a
      href={fileDownloadUrl(file.id)}
      className="inline-flex items-center gap-1 rounded-md border border-gray-200 bg-gray-50 px-2 py-1 text-xs text-gray-600 hover:bg-gray-100"
    >
      <span className="font-medium text-gray-700">{file.name}</span>
      <span className="text-gray-400">({humanizeSize(file.size)})</span>
    </a>
  )
}

// 이름에서 결정되는 아바타 색 — 같은 사람은 항상 같은 색이 나온다 (Mattermost 이니셜 아바타 방식)
const AVATAR_COLORS = [
  'bg-rose-500',
  'bg-orange-500',
  'bg-amber-500',
  'bg-emerald-500',
  'bg-teal-500',
  'bg-sky-500',
  'bg-indigo-500',
  'bg-violet-500',
  'bg-fuchsia-500',
]

function avatarColor(name: string): string {
  let hash = 0
  for (const ch of name) {
    hash = (hash + ch.codePointAt(0)!) % AVATAR_COLORS.length
  }
  return AVATAR_COLORS[hash]
}

function Avatar({ name }: { name: string }) {
  return (
    <span
      aria-hidden="true"
      className={`flex h-9 w-9 shrink-0 items-center justify-center rounded-full text-sm font-semibold text-white ${avatarColor(name)}`}
    >
      {[...name][0] ?? '?'}
    </span>
  )
}

/** 같은 사람이 5분 안에 연달아 쓴 메시지는 아바타·이름 없이 이어 붙인다 (Mattermost와 동일) */
const GROUP_WINDOW_MS = 5 * 60 * 1000

function PostRow({ post, prev }: { post: PostView; prev: PostView | null }) {
  if (post.system) {
    return <p className="py-2 text-center text-xs text-gray-400">{post.message}</p>
  }

  const continued =
    prev !== null &&
    !prev.system &&
    prev.user === post.user &&
    post.createAt - prev.createAt < GROUP_WINDOW_MS

  return (
    <div className={`flex gap-3 ${continued ? 'mt-0.5' : 'mt-4 first:mt-0'}`}>
      {continued ? <span className="w-9 shrink-0" /> : <Avatar name={post.user} />}

      <div className="min-w-0 flex-1">
        {!continued && (
          <div className="flex items-baseline gap-2">
            <span className="text-sm font-semibold text-gray-900">{post.user}</span>
            <span className="text-xs text-gray-400">
              {timeFormatter.format(new Date(post.createAt))}
            </span>
          </div>
        )}
        {post.message && (
          <p className="whitespace-pre-wrap text-sm leading-relaxed text-gray-800">
            {post.message}
          </p>
        )}
        {post.files.length > 0 && (
          <div className="mt-1.5 flex flex-wrap gap-1.5">
            {post.files.map((f) => (
              <AttachmentChip key={f.id} file={f} />
            ))}
          </div>
        )}
      </div>
    </div>
  )
}

/** 기관관리 상세의 게시물 탭. 선택한 채널의 최근 게시글을 3초 간격으로 폴링해서 보여준다. */
export default function ChannelPosts({ org }: { org: Org }) {
  const bothMissing = !org.channelIdMj && !org.channelIdLaw
  const [channel, setChannel] = useState<ChannelKindKey>(org.channelIdMj ? 'mj' : 'law')
  const [posts, setPosts] = useState<PostView[]>([])
  const [error, setError] = useState<string | null>(null)

  const containerRef = useRef<HTMLDivElement>(null)
  const prevCountRef = useRef(0)

  useEffect(() => {
    if (bothMissing) {
      return
    }

    let cancelled = false

    async function load() {
      try {
        const data = await getPosts(org.id, channel)
        if (!cancelled) {
          setPosts(data)
          setError(null)
        }
      } catch {
        if (!cancelled) {
          setError('연결이 원활하지 않습니다. 재시도 중…')
        }
      }
    }

    void load()
    const timer = setInterval(() => void load(), POLL_INTERVAL_MS)
    return () => {
      cancelled = true
      clearInterval(timer)
    }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [channel, org.id])

  useEffect(() => {
    if (posts.length > prevCountRef.current && containerRef.current) {
      containerRef.current.scrollTop = containerRef.current.scrollHeight
    }
    prevCountRef.current = posts.length
  }, [posts.length])

  return (
    <div className="p-4">
      <div className="flex gap-2">
        <button
          type="button"
          disabled={!org.channelIdMj}
          title={org.channelIdMj ? undefined : '채널 미생성'}
          onClick={() => setChannel('mj')}
          className={`rounded-full border px-3 py-1 text-xs ${
            channel === 'mj'
              ? 'border-blue-600 bg-blue-50 font-semibold text-blue-700'
              : 'border-gray-200 text-gray-500'
          } disabled:cursor-not-allowed disabled:opacity-40`}
        >
          문정원
        </button>
        <button
          type="button"
          disabled={!org.channelIdLaw}
          title={org.channelIdLaw ? undefined : '채널 미생성'}
          onClick={() => setChannel('law')}
          className={`rounded-full border px-3 py-1 text-xs ${
            channel === 'law'
              ? 'border-blue-600 bg-blue-50 font-semibold text-blue-700'
              : 'border-gray-200 text-gray-500'
          } disabled:cursor-not-allowed disabled:opacity-40`}
        >
          법률검토
        </button>
      </div>

      {bothMissing ? (
        <p className="mt-6 text-center text-sm text-gray-400">채널이 아직 생성되지 않았습니다.</p>
      ) : (
        <>
          {error && (
            <p className="mt-3 rounded-md bg-amber-50 px-3 py-1.5 text-xs text-amber-700">{error}</p>
          )}
          <div
            ref={containerRef}
            className="mt-3 h-96 overflow-y-auto rounded-lg border border-gray-200 bg-white p-4"
          >
            {posts.length === 0 ? (
              <p className="py-6 text-center text-sm text-gray-400">
                아직 게시글이 없습니다. Mattermost에서 메시지를 보내면 여기 나타납니다.
              </p>
            ) : (
              posts.map((post, i) => (
                <PostRow key={post.id} post={post} prev={i > 0 ? posts[i - 1] : null} />
              ))
            )}
          </div>
        </>
      )}
    </div>
  )
}
