"use client";

import { useState } from "react";
import { useRouter } from "next/navigation";
import Link from "next/link";
import { toast } from "sonner";
import { api, AdminError, type Me } from "@/lib/api";
import { Button } from "@/components/ui/button";
import { Input } from "@/components/ui/input";

export default function LoginPage() {
  const router = useRouter();
  const [email, setEmail] = useState("");
  const [password, setPassword] = useState("");
  const [otp, setOtp] = useState("");
  const [stage, setStage] = useState<"credentials" | "otp">("credentials");
  const [busy, setBusy] = useState(false);
  const [error, setError] = useState<string | null>(null);

  // Once authenticated, only admins may proceed. Non-admins are signed back
  // out so an ordinary account can't sit in an authenticated-but-forbidden
  // state against the admin origin.
  async function gateAdmin(user: Me) {
    if (user.role === "admin") {
      router.replace("/users");
      return;
    }
    await api.logout().catch(() => {});
    setError("This account doesn't have admin access.");
    setStage("credentials");
  }

  async function onCredentials(e: React.FormEvent) {
    e.preventDefault();
    setError(null);
    setBusy(true);
    try {
      const res = await api.login(email.trim(), password);
      if (res.kind === "otp_required") {
        setStage("otp");
        toast("We emailed you a verification code.");
      } else {
        await gateAdmin(res.user);
      }
    } catch (err) {
      setError(err instanceof AdminError ? err.message : "Could not sign in.");
    } finally {
      setBusy(false);
    }
  }

  async function onOtp(e: React.FormEvent) {
    e.preventDefault();
    setError(null);
    setBusy(true);
    try {
      const user = await api.verifyLoginOtp(email.trim(), password, otp.trim());
      await gateAdmin(user);
    } catch (err) {
      setError(err instanceof AdminError ? err.message : "Invalid code.");
    } finally {
      setBusy(false);
    }
  }

  return (
    <AuthShell title="Admin sign in">
      {stage === "credentials" ? (
        <form onSubmit={onCredentials} className="space-y-4">
          <Field label="Email">
            <Input
              type="email"
              autoComplete="email"
              required
              value={email}
              onChange={(e) => setEmail(e.target.value)}
            />
          </Field>
          <Field label="Password">
            <Input
              type="password"
              autoComplete="current-password"
              required
              value={password}
              onChange={(e) => setPassword(e.target.value)}
            />
          </Field>
          {error ? <p className="text-sm text-destructive">{error}</p> : null}
          <Button type="submit" disabled={busy} className="w-full">
            {busy ? "Signing in…" : "Sign in"}
          </Button>
          <p className="text-center text-sm text-muted-foreground">
            <Link href="/forgot-password" className="hover:text-foreground">
              Forgot your password?
            </Link>
          </p>
        </form>
      ) : (
        <form onSubmit={onOtp} className="space-y-4">
          <p className="text-sm text-muted-foreground">
            Enter the verification code we emailed to {email}.
          </p>
          <Field label="Verification code">
            <Input
              inputMode="numeric"
              autoFocus
              required
              value={otp}
              onChange={(e) => setOtp(e.target.value)}
            />
          </Field>
          {error ? <p className="text-sm text-destructive">{error}</p> : null}
          <Button type="submit" disabled={busy} className="w-full">
            {busy ? "Verifying…" : "Verify & sign in"}
          </Button>
          <button
            type="button"
            onClick={() => {
              setStage("credentials");
              setOtp("");
              setError(null);
            }}
            className="w-full text-center text-sm text-muted-foreground hover:text-foreground"
          >
            Back
          </button>
        </form>
      )}
    </AuthShell>
  );
}

export function AuthShell({
  title,
  children,
}: {
  title: string;
  children: React.ReactNode;
}) {
  return (
    <main className="flex min-h-screen items-center justify-center px-4">
      <div className="w-full max-w-sm">
        <div className="mb-6 text-center">
          <p className="text-xs uppercase tracking-[0.2em] text-primary">
            Prabhupāda Says
          </p>
          <h1 className="mt-1 text-xl font-semibold text-foreground">{title}</h1>
        </div>
        <div className="rounded-2xl border border-border bg-card p-6 shadow-sm">
          {children}
        </div>
      </div>
    </main>
  );
}

export function Field({
  label,
  children,
}: {
  label: string;
  children: React.ReactNode;
}) {
  return (
    <label className="block space-y-1.5">
      <span className="text-sm font-medium text-foreground">{label}</span>
      {children}
    </label>
  );
}