import { useEffect, useRef, useState } from 'preact/hooks';
import { apiFetch, ApiError, jsonBody, toApiError } from '../lib/api';
import { setAuthed } from '../lib/auth';
import { currentSearch, didClientNavigate, getQueryParam, navigate, sanitizeNext } from '../router';
import { Spinner } from '../components/Spinner';
import type { User } from '../types';

type Probe = 'checking' | 'connected' | 'unreachable';

interface FieldError {
  email?: string;
  password?: string;
  username?: string;
}

const EMAIL_RE = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;

export function Login() {
  const [register, setRegister] = useState(() => getQueryParam(currentSearch.value, 'mode') === 'register');
  const [email, setEmail] = useState('');
  const [username, setUsername] = useState('');
  const [password, setPassword] = useState('');
  const [submitting, setSubmitting] = useState(false);
  const [fieldErrors, setFieldErrors] = useState<FieldError>({});
  const [serverError, setServerError] = useState<string | null>(null);
  const [probe, setProbe] = useState<Probe>('checking');
  const emailRef = useRef<HTMLInputElement>(null);

  const next = sanitizeNext(getQueryParam(currentSearch.value, 'next'));

  useEffect(() => {
    probeServer();
    // autofocus Email only on client-side navigation, never cold page load
    if (didClientNavigate) emailRef.current?.focus();
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  const probeServer = async () => {
    setProbe('checking');
    try {
      await apiFetch('/web/auth/me', { refreshOn401: false });
      setProbe('connected');
    } catch {
      setProbe('unreachable');
    }
  };

  const toggleMode = () => {
    const newMode = !register;
    setRegister(newMode);
    setFieldErrors({});
    setServerError(null);
    window.history.replaceState(
      {},
      '',
      newMode ? '/login?mode=register' : '/login'
    );
  };

  const validate = (): boolean => {
    const errs: FieldError = {};
    if (!EMAIL_RE.test(email.trim())) errs.email = 'Enter a valid email address';
    if (!password) errs.password = 'Password is required';
    if (register && !username.trim()) errs.username = 'Username is required';
    setFieldErrors(errs);
    return Object.keys(errs).length === 0;
  };

  const submit = async (e: Event) => {
    e.preventDefault();
    setServerError(null);
    if (submitting) return;
    if (!validate()) return;
    setSubmitting(true);
    const body = register
      ? { username: username.trim(), password, email: email.trim() }
      : { email: email.trim(), password };
    try {
      const res = await apiFetch(register ? '/web/auth/register' : '/web/auth/login', {
        refreshOn401: false,
        ...jsonBody(body),
      });
      if (res.ok) {
        const data = (await res.json()) as { user?: User };
        if (data?.user) {
          setAuthed(data.user);
          navigate(next);
          return;
        }
        throw new ApiError(0, 'Something went wrong');
      }
      const err = await toApiError(res);
      throw err;
    } catch (err) {
      const msg = err instanceof ApiError ? err.message : 'Something went wrong';
      setServerError(msg);
    } finally {
      setSubmitting(false);
    }
  };

  const origin = typeof window !== 'undefined' ? window.location.origin : '';

  return (
    <div className="min-h-screen flex flex-col items-center justify-center p-6">
      <a href="#login-main" className="skip-link">
        Skip to content
      </a>
      <main id="login-main" className="w-full max-w-[400px] card p-6 sm:p-8" tabIndex={-1}>
        <div className="flex flex-col items-center text-center">
          <div className="logo-tile mb-4" aria-hidden="true">
            <svg width="26" height="26" viewBox="0 0 24 24" fill="none">
              <path
                d="M4 20h4l10.5-10.5a2.83 2.83 0 10-4-4L4 16v4z"
                stroke="currentColor"
                strokeWidth="2"
                strokeLinejoin="round"
              />
              <path d="M13.5 6.5l4 4" stroke="currentColor" strokeWidth="2" />
            </svg>
          </div>
          <h1 className="text-[24px] font-bold leading-[1.25]" style={{ margin: 0 }}>
            KeepNote
          </h1>
          <p className="mt-1 mb-6" style={{ color: 'var(--dn-muted)', fontSize: 15 }}>
            Your notes on Dcntrlized
          </p>
        </div>

        <form onSubmit={submit} noValidate>
          <div className="mb-4">
            <label className="field-label" htmlFor="email">
              Email
            </label>
            <input
              ref={emailRef}
              id="email"
              className="field"
              type="email"
              value={email}
              placeholder="john@example.org"
              autoComplete="email"
              inputMode="email"
              autoCapitalize="none"
              spellcheck={false}
              aria-invalid={!!fieldErrors.email}
              aria-describedby={fieldErrors.email ? 'email-error' : undefined}
              onInput={(e) => setEmail((e.target as HTMLInputElement).value)}
            />
            {fieldErrors.email && (
              <p id="email-error" className="mt-1 text-[13px]" style={{ color: 'var(--dn-bad)' }} role="alert">
                {fieldErrors.email}
              </p>
            )}
          </div>

          {register && (
            <div className="mb-4">
              <label className="field-label" htmlFor="username">
                Username
              </label>
              <input
                id="username"
                className="field"
                type="text"
                value={username}
                placeholder="johndoe"
                autoComplete="username"
                autoCapitalize="none"
                spellcheck={false}
                aria-invalid={!!fieldErrors.username}
                aria-describedby={fieldErrors.username ? 'username-error' : undefined}
                onInput={(e) => setUsername((e.target as HTMLInputElement).value)}
              />
              {fieldErrors.username && (
                <p id="username-error" className="mt-1 text-[13px]" style={{ color: 'var(--dn-bad)' }} role="alert">
                  {fieldErrors.username}
                </p>
              )}
            </div>
          )}

          <div className="mb-5">
            <label className="field-label" htmlFor="password">
              Password
            </label>
            <input
              id="password"
              className="field"
              type="password"
              value={password}
              placeholder="••••••••"
              autoComplete={register ? 'new-password' : 'current-password'}
              aria-invalid={!!fieldErrors.password}
              aria-describedby={fieldErrors.password ? 'password-error' : undefined}
              onInput={(e) => setPassword((e.target as HTMLInputElement).value)}
            />
            {fieldErrors.password && (
              <p id="password-error" className="mt-1 text-[13px]" style={{ color: 'var(--dn-bad)' }} role="alert">
                {fieldErrors.password}
              </p>
            )}
          </div>

          {serverError && (
            <div className="mb-4 banner banner-error" role="alert">
              {serverError}
            </div>
          )}

          <button type="submit" className="btn btn-primary w-full" disabled={submitting}>
            {submitting && <Spinner />}
            {register ? 'Create account' : 'Sign in'}
          </button>
        </form>

        <button
          type="button"
          className="mt-3 w-full"
          aria-pressed={register}
          style={{ minHeight: 44, color: 'var(--dn-accent)', fontWeight: 600, background: 'transparent', border: 'none', cursor: 'pointer' }}
          onClick={toggleMode}
        >
          {register ? 'Already have an account? Sign in' : 'New here? Create an account'}
        </button>
      </main>

      <footer
        className="w-full max-w-[400px] mt-6 flex items-center gap-2"
        role="status"
        style={{ color: 'var(--dn-muted)', fontSize: 12, minHeight: 44 }}
      >
        <span
          aria-hidden="true"
          style={{
            width: 8,
            height: 8,
            borderRadius: '50%',
            background:
              probe === 'connected' ? 'var(--dn-ok)' : probe === 'unreachable' ? 'var(--dn-bad)' : 'var(--dn-muted)',
            flex: 'none',
          }}
        />
        {probe === 'checking' && <span>Checking connection…</span>}
        {probe === 'connected' && (
          <span className="mono truncate" title={origin}>
            Connected to {origin}
          </span>
        )}
        {probe === 'unreachable' && (
          <>
            <span>Server unreachable</span>
            <button
              type="button"
              className="banner-action"
              style={{ marginLeft: 'auto', minHeight: 44 }}
              onClick={probeServer}
            >
              Retry
            </button>
          </>
        )}
      </footer>
    </div>
  );
}