import * as React from 'react';
import {
  Box,
  TextField,
  Button,
  Typography,
  IconButton,
  CircularProgress,
  Link,
  InputAdornment,
  alpha,
} from '@mui/material';
import VisibilityIcon from '@mui/icons-material/Visibility';
import VisibilityOffIcon from '@mui/icons-material/VisibilityOff';
import CheckRoundedIcon from '@mui/icons-material/CheckRounded';
import ArrowBackRoundedIcon from '@mui/icons-material/ArrowBackRounded';
import { useTheme } from '@mui/material/styles';

export type AuthMode = "login" | "register";

export interface AuthPageProps {
  mode: AuthMode;
  onBack(): void;
  onSwitchMode(): void;
  login(username: string, password: string): Promise<void>;
  register(username: string, password: string): Promise<void>;
  loading: boolean;
  error: string | null;
  currentUser: any;
}

const FEATURES = [
  "OpenAPI-driven admin for accounts, expenses, tags & payors",
  "Import bank statements with live pipeline progress",
  "Entity & tag enrichment for clean, comparable data",
];

export function AuthPage({
  mode,
  onBack,
  onSwitchMode,
  login,
  register,
  loading,
  error,
  currentUser,
}: AuthPageProps) {
  const theme = useTheme();
  const [username, setUsername] = React.useState('');
  const [password, setPassword] = React.useState('');
  const [showPassword, setShowPassword] = React.useState(false);
  const [fieldErrors, setFieldErrors] = React.useState<{ username?: string; password?: string }>({});

  const isLogin = mode === "login";

  React.useEffect(() => {
    if (currentUser) onBack();
  }, [currentUser, onBack]);

  const validate = (): boolean => {
    const next: { username?: string; password?: string } = {};
    if (!username.trim()) next.username = "Username is required";
    else if (username.trim().length < 3) next.username = "Username must be at least 3 characters";
    if (!password) next.password = "Password is required";
    else if (password.length < 6) next.password = "Password must be at least 6 characters";
    setFieldErrors(next);
    return Object.keys(next).length === 0;
  };

  const handleSubmit = async (e: React.FormEvent) => {
    e.preventDefault();
    if (!validate()) return;
    if (isLogin) {
      await login(username.trim(), password);
    } else {
      await register(username.trim(), password);
    }
  };

  const handleSwitch = () => {
    setFieldErrors({});
    onSwitchMode();
  };

  const form = (
    <Box sx={{ width: '100%', maxWidth: 400 }}>
      <IconButton onClick={onBack} sx={{ mb: 2, border: '1px solid', borderColor: 'divider' }} aria-label="Go back">
        <ArrowBackRoundedIcon fontSize="small" />
      </IconButton>

      <Typography variant="h4" fontWeight={700} gutterBottom sx={{ letterSpacing: '-0.02em' }}>
        {isLogin ? "Sign in to Khata" : "Create your account"}
      </Typography>

      <Typography variant="body2" color="text.secondary" sx={{ mb: 3 }}>
        {isLogin
          ? "Welcome back. Enter your credentials to continue."
          : "Start managing your ledger in a few seconds."}
      </Typography>

      <form onSubmit={handleSubmit} noValidate>
        <Box sx={{ display: 'flex', flexDirection: 'column', gap: 2 }}>
          <TextField
            fullWidth
            label="Username"
            type="text"
            value={username}
            onChange={(e) => {
              setUsername(e.target.value);
              if (fieldErrors.username) setFieldErrors((p) => ({ ...p, username: undefined }));
            }}
            error={!!fieldErrors.username}
            helperText={fieldErrors.username}
            autoComplete="username"
            autoFocus
          />
          <TextField
            fullWidth
            label="Password"
            type={showPassword ? 'text' : 'password'}
            value={password}
            onChange={(e) => {
              setPassword(e.target.value);
              if (fieldErrors.password) setFieldErrors((p) => ({ ...p, password: undefined }));
            }}
            error={!!fieldErrors.password}
            helperText={fieldErrors.password}
            autoComplete={isLogin ? 'current-password' : 'new-password'}
            InputProps={{
              endAdornment: (
                <InputAdornment position="end">
                  <IconButton
                    aria-label={showPassword ? 'Hide password' : 'Show password'}
                    onClick={() => setShowPassword((s) => !s)}
                    edge="end"
                    size="small"
                    sx={{ border: 'none' }}
                  >
                    {showPassword ? <VisibilityOffIcon fontSize="small" /> : <VisibilityIcon fontSize="small" />}
                  </IconButton>
                </InputAdornment>
              ),
            }}
          />

          {error && (
            <Typography color="error" variant="body2" sx={{ mt: 0.5 }}>
              {error}
            </Typography>
          )}

          <Button
            fullWidth
            type="submit"
            variant="contained"
            size="large"
            sx={{ mt: 1, fontWeight: 600 }}
            disabled={loading}
          >
            {loading ? (
              <CircularProgress size={20} color="inherit" />
            ) : isLogin ? (
              "Sign In"
            ) : (
              "Create Account"
            )}
          </Button>
        </Box>
      </form>

      <Typography variant="body2" color="text.secondary" align="center" sx={{ mt: 3 }}>
        {isLogin ? "Don't have an account?" : "Already have an account?"}{' '}
        <Link component="button" underline="hover" color="primary" onClick={handleSwitch} sx={{ fontWeight: 600 }}>
          {isLogin ? "Register" : "Sign In"}
        </Link>
      </Typography>
    </Box>
  );

  return (
    <Box
      sx={{
        minHeight: 'calc(100vh - 64px)',
        display: 'flex',
        alignItems: 'center',
        justifyContent: 'center',
        p: { xs: 2, md: 4 },
      }}
    >
      <Box
        sx={{
          width: '100%',
          maxWidth: 960,
          display: 'grid',
          gridTemplateColumns: { xs: '1fr', md: '5fr 6fr' },
          borderRadius: 3,
          overflow: 'hidden',
          border: '1px solid',
          borderColor: 'divider',
          backgroundColor: 'background.paper',
          boxShadow: (t) =>
            `0 12px 40px ${alpha(t.palette.common.black, t.palette.mode === 'dark' ? 0.4 : 0.08)}`,
        }}
      >
        {/* LEFT BRAND PANEL */}
        <Box
          sx={{
            display: { xs: 'none', md: 'flex' },
            flexDirection: 'column',
            justifyContent: 'space-between',
            p: 4,
            background: 'linear-gradient(150deg, #635BFF 0%, #4F46E5 55%, #3B82F6 100%)',
            color: '#fff',
          }}
        >
          <Box>
            <Typography variant="h6" fontWeight={700} sx={{ letterSpacing: '-0.02em' }}>
              Khata
            </Typography>
            <Typography sx={{ mt: 3, fontSize: '1.25rem', fontWeight: 600, lineHeight: 1.4, maxWidth: 320 }}>
              The intelligent, extensible financial ledger for your cashflow.
            </Typography>
          </Box>

          <Box sx={{ display: 'flex', flexDirection: 'column', gap: 1.5 }}>
            {FEATURES.map((f) => (
              <Box key={f} sx={{ display: 'flex', gap: 1.5, alignItems: 'flex-start' }}>
                <CheckRoundedIcon sx={{ fontSize: 18, mt: 0.25, color: alpha('#fff', 0.9) }} />
                <Typography variant="body2" sx={{ color: alpha('#fff', 0.92), lineHeight: 1.5 }}>
                  {f}
                </Typography>
              </Box>
            ))}
          </Box>
        </Box>

        {/* RIGHT FORM PANEL */}
        <Box sx={{ p: { xs: 3, md: 5 }, display: 'flex', justifyContent: 'center', alignItems: 'center' }}>
          {form}
        </Box>
      </Box>
    </Box>
  );
}