import { useRef, useState } from "react";
import { Form, useActionData, useLoaderData, useNavigation } from "react-router";
import { useTranslation } from "react-i18next";
import { useRootData } from "~/utils/data/useRootData";
import { AuthShell } from "~/components/auth/AuthShell";
import { Button } from "~/ui/components/Button";
import { Checkbox } from "~/ui/components/Checkbox";
import { InputOtp } from "~/ui/components/InputOtp";
import { LinkButton } from "~/ui/components/LinkButton";
import { TextInput } from "~/ui/components/TextInput";
import type { ActionData, LoaderData } from "~/routeModules/auth/login-mfa.impl";

// D-D0a — 2FA-Code-Eingabe nach Davids Subframe-Design ("_2FA _ Code Entry"): Logo + Card
// (Bestaetigung in zwei Schritten) + 6-stellige InputOtp + "Geraet vertrauen"-Checkbox + Bestaetigen +
// Recovery-Code-Toggle. An die bestehende login-mfa-Action verdrahtet (code/recoveryCode/rememberDevice/csrf).
// Die 6 OTP-Boxen werden zu einem hidden "code"-Feld kombiniert (Auto-Advance, Paste, Backspace).

const OTP_LENGTH = 6;

export default function LoginMfaRoute() {
  const { t } = useTranslation();
  const { csrf } = useRootData();
  const data = useLoaderData<LoaderData>();
  const actionData = useActionData<ActionData>();
  const navigation = useNavigation();
  const isSubmitting = navigation.state !== "idle";

  const [digits, setDigits] = useState<string[]>(Array(OTP_LENGTH).fill(""));
  const [trustDevice, setTrustDevice] = useState(false);
  const [showRecovery, setShowRecovery] = useState(false);
  const inputs = useRef<(HTMLInputElement | null)[]>([]);
  const code = digits.join("");

  function handleChange(index: number, raw: string) {
    const clean = raw.replace(/\D/g, "");
    setDigits((prev) => {
      const next = [...prev];
      if (!clean) {
        next[index] = "";
        return next;
      }
      // Einzelzeichen ODER Paste (z.B. "123456") ab dieser Box vorwaerts fuellen.
      for (let k = 0; k < clean.length && index + k < OTP_LENGTH; k++) {
        next[index + k] = clean[k];
      }
      return next;
    });
    if (clean) {
      inputs.current[Math.min(index + clean.length, OTP_LENGTH - 1)]?.focus();
    }
  }

  function handleKeyDown(index: number, event: React.KeyboardEvent<HTMLInputElement>) {
    if (event.key === "Backspace" && !digits[index] && index > 0) {
      inputs.current[index - 1]?.focus();
      setDigits((prev) => {
        const next = [...prev];
        next[index - 1] = "";
        return next;
      });
    }
  }

  const errorState = Boolean(actionData?.error && navigation.state === "idle");

  return (
    <AuthShell
      title={t("account.loginMfa.twoStepTitle")}
      subtitle={t("account.loginMfa.codeSubtitle")}
      logoIconOnly
      subtitleStrong
      dataUiId="ui.auth.loginMfa.page"
    >
      <Form method="post" noValidate className="flex w-full flex-col gap-4" data-ui-id="ui.auth.loginMfa.form">
        {csrf ? <input type="hidden" name="csrf" value={csrf} readOnly /> : null}
        <input type="hidden" name="redirectTo" value={data.redirectTo} readOnly />
        <input type="hidden" name="code" value={code} readOnly />
        <input type="hidden" name="rememberDevice" value={trustDevice ? "on" : ""} readOnly />

        {!showRecovery ? (
          <div className="flex w-full flex-col items-center py-2">
            <InputOtp state={errorState ? "error" : "default"} helperText={t("account.loginMfa.codeHelper")}>
              {Array.from({ length: OTP_LENGTH }).map((_, i) => (
                <InputOtp.OtpInputItem key={i} error={errorState}>
                  <InputOtp.Input
                    className="h-auto w-12 flex-none self-stretch"
                    ref={(el) => {
                      inputs.current[i] = el;
                    }}
                    value={digits[i]}
                    onChange={(event) => handleChange(i, event.target.value)}
                    onKeyDown={(event) => handleKeyDown(i, event)}
                    inputMode="numeric"
                    autoComplete={i === 0 ? "one-time-code" : "off"}
                    maxLength={OTP_LENGTH}
                    aria-label={`${t("account.loginMfa.fields.authenticatorCode")} ${i + 1}`}
                    data-ui-id={i === 0 ? "ui.auth.loginMfa.code" : undefined}
                  />
                </InputOtp.OtpInputItem>
              ))}
            </InputOtp>
          </div>
        ) : (
          <TextInput className="h-auto w-full flex-none" fillContainer showLabel label={t("account.loginMfa.fields.recoveryCode")}>
            <TextInput.Input
              name="recoveryCode"
              autoFocus
              autoComplete="off"
              placeholder={t("account.loginMfa.fields.recoveryCode")}
              disabled={isSubmitting}
              data-ui-id="ui.auth.loginMfa.recoveryCode"
            />
          </TextInput>
        )}

        <Checkbox
          label={t("account.loginMfa.trustDevice")}
          checked={trustDevice}
          onCheckedChange={setTrustDevice}
          data-ui-id="ui.auth.loginMfa.rememberDevice"
        />

        <Button type="submit" loading={isSubmitting} disabled={isSubmitting} data-ui-id="ui.auth.loginMfa.submit">
          {t("account.loginMfa.confirm")}
        </Button>

        {errorState ? (
          <p className="text-center text-body-small-regular-0 font-body-small-regular-0 text-text-feedback-negative" role="alert">
            {actionData?.error}
          </p>
        ) : null}
      </Form>

      <div className="flex w-full items-center justify-center">
        <LinkButton
          size="small"
          hideIcon
          onClick={() => setShowRecovery((v) => !v)}
          data-ui-id="ui.auth.loginMfa.useRecoveryCode"
        >
          {showRecovery ? t("account.loginMfa.useAuthenticator") : t("account.loginMfa.useRecoveryCode")}
        </LinkButton>
      </div>
    </AuthShell>
  );
}