import { useEffect, useState, type FormEvent } from 'react'
import { useAuth } from '../../contexts/AuthContext'
import api from '../../services/api'
import { Button } from '@/components/ui/button'
import { Input } from '@/components/ui/input'
import { Label } from '@/components/ui/label'
import { Alert, AlertDescription } from '@/components/ui/alert'

interface OidcConfig {
  enabled: boolean
  label: string
  login_url: string
}

interface AuthConfig {
  oidc: OidcConfig | null
}

export function LoginPage() {
  const { login } = useAuth()
  const [username, setUsername] = useState('')
  const [password, setPassword] = useState('')
  const [error, setError] = useState<string | null>(null)
  const [loading, setLoading] = useState(false)
  const [oidc, setOidc] = useState<OidcConfig | null>(null)
  // While the OIDC config loads we may auto-bounce to the IdP. Hide
  // the form until we know we're staying so the user doesn't see a
  // flash of password fields right before the redirect kicks in.
  const [autoRedirecting, setAutoRedirecting] = useState(true)

  // Ask the backend which login methods to show. If OIDC is enabled
  // and the user already has an SSO session at the IdP, the natural
  // flow is for them to land here, get bounced through Authentik, and
  // come straight back signed in — without ever clicking a button.
  // Two escape hatches: `?password=1` in the URL for explicit password
  // login, and a `skipAutoSso` sessionStorage flag set by logout and
  // by the OIDC callback's error branch so users don't get trapped in
  // a redirect loop.
  useEffect(() => {
    let cancelled = false
    ;(async () => {
      try {
        const res = await api.get<AuthConfig>('/auth/config')
        if (cancelled) return
        const cfg = res.data.oidc
        setOidc(cfg)
        if (!cfg?.enabled) {
          setAutoRedirecting(false)
          return
        }
        const params = new URLSearchParams(window.location.search)
        if (
          params.has('password') ||
          sessionStorage.getItem('skipAutoSso') === '1'
        ) {
          sessionStorage.removeItem('skipAutoSso')
          setAutoRedirecting(false)
          return
        }
        window.location.href = cfg.login_url
      } catch {
        if (!cancelled) setAutoRedirecting(false)
      }
    })()
    return () => {
      cancelled = true
    }
  }, [])

  const handleSubmit = async (e: FormEvent) => {
    e.preventDefault()
    setError(null)
    setLoading(true)
    try {
      await login(username, password)
    } catch (err: any) {
      setError(
        err.response?.data?.detail ?? 'Unable to sign in. Check your credentials.',
      )
    } finally {
      setLoading(false)
    }
  }

  if (autoRedirecting) {
    return (
      <div className="flex min-h-screen items-center justify-center bg-bg px-4">
        <div className="w-full max-w-sm space-y-3 rounded-lg border border-border bg-surface p-8 text-center shadow-xl">
          <div className="text-text-muted">
            Signing in with {oidc?.label ?? 'identity provider'}&hellip;
          </div>
          <a
            href="?password=1"
            className="inline-block text-xs text-text-muted underline hover:text-text"
            onClick={() => setAutoRedirecting(false)}
          >
            Use password instead
          </a>
        </div>
      </div>
    )
  }

  return (
    <div className="flex min-h-screen items-center justify-center bg-bg px-4">
      <div className="w-full max-w-sm space-y-5 rounded-lg border border-border bg-surface p-8 shadow-xl">
        <h1 className="text-center text-xl font-semibold text-text">
          Sign in to Mulita
        </h1>

        {error && (
          <Alert variant="destructive">
            <AlertDescription>{error}</AlertDescription>
          </Alert>
        )}

        {oidc?.enabled && (
          <>
            {/* Full-page navigation (not a fetch) — Authlib sets a
             *  signed session cookie in the /oidc/login response, so
             *  the browser needs to follow the redirect chain itself. */}
            <Button asChild variant="outline" className="w-full">
              <a href={oidc.login_url}>Sign in with {oidc.label}</a>
            </Button>
            <div className="flex items-center gap-3 text-[11px] uppercase tracking-wide text-text-muted">
              <span className="h-px flex-1 bg-border" />
              or continue with password
              <span className="h-px flex-1 bg-border" />
            </div>
          </>
        )}

        <form onSubmit={handleSubmit} className="space-y-5">
          <div className="space-y-1.5">
            <Label htmlFor="login-user">Username</Label>
            <Input
              id="login-user"
              type="text"
              value={username}
              onChange={(e) => setUsername(e.target.value)}
              required
              autoFocus
            />
          </div>

          <div className="space-y-1.5">
            <Label htmlFor="login-pass">Password</Label>
            <Input
              id="login-pass"
              type="password"
              value={password}
              onChange={(e) => setPassword(e.target.value)}
              required
            />
          </div>

          <Button type="submit" disabled={loading} className="w-full">
            {loading ? 'Signing in…' : 'Sign In'}
          </Button>
        </form>
      </div>
    </div>
  )
}
