import { useEffect, useMemo, useState } from 'react'
import { Link, useParams } from 'react-router'
import { ArrowLeft, CalendarClock, ExternalLink, Lock } from 'lucide-react'
import { ApiError } from '../api/client'
import {
  fetchLearnerLiveSession,
  joinLearnerLiveSession,
  type LearnerLiveSessionDetail,
} from '../learner-live-courses'

type LoadState = 'loading' | 'ready' | 'error' | 'not-found'

function formatDateTime(value?: number, timezone?: string): string {
  if (!value) return 'TBA'
  try {
    return new Intl.DateTimeFormat(undefined, {
      month: 'short',
      day: 'numeric',
      year: 'numeric',
      hour: 'numeric',
      minute: '2-digit',
      timeZone: timezone,
    }).format(new Date(value))
  } catch {
    return new Date(value).toLocaleString()
  }
}

export function LearnerLiveSessionPage() {
  const { id = '', sessionId = '' } = useParams()
  const [detail, setDetail] = useState<LearnerLiveSessionDetail | null>(null)
  const [state, setState] = useState<LoadState>('loading')
  const [error, setError] = useState('')
  const [joinError, setJoinError] = useState('')
  const [joining, setJoining] = useState(false)

  useEffect(() => {
    let cancelled = false

    const load = async () => {
      try {
        setState('loading')
        const result = await fetchLearnerLiveSession(id, sessionId)
        if (cancelled) return
        if (!result.session.id || !result.course.id) {
          setState('not-found')
          return
        }
        setDetail(result)
        setState('ready')
      } catch (err) {
        if (cancelled) return
        if (err instanceof ApiError && err.status === 404) {
          setState('not-found')
          return
        }
        setError(err instanceof Error ? err.message : 'Unable to load live session')
        setState('error')
      }
    }

    void load()
    return () => { cancelled = true }
  }, [id, sessionId])

  const canJoin = useMemo(() => Boolean(detail?.access.allowed), [detail])

  const handleJoin = async () => {
    if (!detail) return
    setJoinError('')
    setJoining(true)
    try {
      const result = await joinLearnerLiveSession(detail.course.id, detail.session.id)
      if (!result.joinUrl) {
        throw new Error('Join URL is not available yet')
      }
      window.open(result.joinUrl, '_blank', 'noopener,noreferrer')
    } catch (err) {
      setJoinError(err instanceof Error ? err.message : 'Failed to join session')
    } finally {
      setJoining(false)
    }
  }

  if (state === 'loading') {
    return <p className="text-sm text-slate-600">Loading session details...</p>
  }

  if (state === 'not-found') {
    return (
      <div>
        <h1 className="text-3xl font-semibold text-slate-900">Session not found</h1>
        <p className="mt-2 text-sm text-slate-600">This session may not be available for your learner account.</p>
        <Link to="/learn/live" className="mt-5 inline-flex items-center gap-2 text-sm font-semibold text-sky-700">
          <ArrowLeft size={16} />
          Back to live sessions
        </Link>
      </div>
    )
  }

  if (state === 'error') {
    return <p className="text-sm text-red-600">{error}</p>
  }

  return (
    <article data-testid="learner-live-session-detail-page">
      <Link data-testid="learner-live-session-back" to="/learn/live" className="mb-6 inline-flex items-center gap-2 text-sm font-semibold text-slate-600 hover:text-slate-900">
        <ArrowLeft size={16} />
        Learner live sessions
      </Link>

      <header className="rounded-3xl border border-slate-200 bg-slate-50 p-6 md:p-8">
        <p className="text-xs font-semibold uppercase tracking-[0.12em] text-slate-500">{detail?.course.title}</p>
        <h1 className="mt-2 text-3xl font-semibold leading-tight tracking-tight text-slate-900 md:text-5xl">{detail?.session.title}</h1>
        <p className="mt-4 inline-flex items-center gap-2 text-sm text-slate-600">
          <CalendarClock size={15} />
          {formatDateTime(detail?.session.startsAt, detail?.session.timezone || detail?.cohort.timezone)}
        </p>
      </header>

      {!canJoin && (
        <section className="mt-6 rounded-2xl border border-amber-200 bg-amber-50 p-4">
          <p className="inline-flex items-center gap-2 text-sm font-semibold text-amber-900">
            <Lock size={16} />
            Session Locked
          </p>
          <p className="mt-2 text-sm text-amber-800">{detail?.access.message || 'Access to this session is currently restricted.'}</p>
        </section>
      )}

      <section className="mt-6 rounded-2xl border border-slate-200 bg-slate-50 p-6">
        <p className="text-sm text-slate-600">Cohort: <span className="font-semibold text-slate-800">{detail?.cohort.title}</span></p>

        {canJoin ? (
          <button
            data-testid="learner-live-session-join"
            type="button"
            onClick={() => { void handleJoin() }}
            disabled={joining}
            className="mt-4 inline-flex items-center gap-2 rounded-lg border border-emerald-300 bg-emerald-50 px-4 py-2 text-sm font-semibold text-emerald-800 hover:border-emerald-500 hover:bg-emerald-100 disabled:cursor-not-allowed disabled:opacity-60"
          >
            <ExternalLink size={16} />
            {joining ? 'Joining...' : 'Join Session'}
          </button>
        ) : (
          <p className="mt-4 text-sm text-slate-500">Join is enabled when enrollment and entitlement checks pass.</p>
        )}

        {joinError && <p className="mt-3 text-sm text-red-600">{joinError}</p>}
      </section>
    </article>
  )
}