/**
 * JWT를 decoding하면 만료시간을 읽을 수 있다.
 * JWT는 3부분으로 구성 : Header.Payload.Signature
 * Payload 부분에 만료시간(exp)이 있다.
 */
"use client";

import { useEffect, useRef, useState } from "react";
import { authService } from "@/src/entities/auth";
import { CLAIM_NAME } from "@/src/shared/config";
import { getCookie } from "@/src/shared/lib";

interface JwtPayload {
  sub?: string; // 토큰 subject. 일반적으로 사용자 식별자나 주체 정보
  exp?: number; // 만료 시각(Unix timestamp, 초 단위)
  iat?: number; // 토큰 발급 시각(Unix timestamp, 초 단위)
  [key: string]: unknown; // 그 외 JWT payload에 포함될 수 있는 추가 클레임
}

interface JwtState {
  token: string; // 쿠키에서 읽어온 JWT 원본 문자열
  payload: JwtPayload | null; // JWT를 파싱한 payload 객체
  exp: number | null; // payload에서 추출한 exp 값
  expDateLocal: string | null; // exp를 로컬 시간 문자열로 변환한 값
  remainingMs: number | null; // 현재 시각 기준 남은 시간(ms)
  error: string | null; // 쿠키 없음, 파싱 실패 등 오류 메시지
}

const initialJwtState: JwtState = {
  token: "",
  payload: null,
  exp: null,
  expDateLocal: null,
  remainingMs: null,
  error: null,
};

function parseJwt(token: string): JwtPayload {
  const parts = token.split(".");
  if (parts.length !== 3) {
    throw new Error("유효한 JWT 형식이 아닙니다.");
  }

  const base64Url = parts[1] ?? ""; // Payload를 가져온다.
  const base64 = base64Url.replace(/-/g, "+").replace(/_/g, "/");
  const padded = base64.padEnd(Math.ceil(base64.length / 4) * 4, "=");
  const jsonPayload = decodeURIComponent(
    atob(padded)
      .split("")
      .map((char) => `%${char.charCodeAt(0).toString(16).padStart(2, "0")}`)
      .join("")
  );

  return JSON.parse(jsonPayload) as JwtPayload;
}

function formatRemainingMs(remainingMs: number | null): string {
  if (remainingMs === null) return "-";
  if (remainingMs <= 0) return "만료됨";

  const totalSeconds = Math.floor(remainingMs / 1000);
  const hours = Math.floor(totalSeconds / 3600);
  const minutes = Math.floor((totalSeconds % 3600) / 60);
  const seconds = totalSeconds % 60;

  return `${hours}시간 ${minutes}분 ${seconds}초`;
}

function readJwtState(): JwtState {
  const token = getCookie(CLAIM_NAME) ?? "";

  if (!token) {
    return {
      token: "",
      payload: null,
      exp: null,
      expDateLocal: null,
      remainingMs: null,
      error: `${CLAIM_NAME} 쿠키가 없습니다.`,
    };
  }

  try {
    const payload = parseJwt(token);

    if (typeof payload.exp !== "number") {
      return {
        token,
        payload,
        exp: null,
        expDateLocal: null,
        remainingMs: null,
        error: "JWT payload에 exp 값이 없습니다.",
      };
    }

    const expMs = payload.exp * 1000;

    return {
      token,
      payload,
      exp: payload.exp,
      expDateLocal: new Date(expMs).toLocaleString(),
      remainingMs: Math.max(expMs - Date.now(), 0),
      error: null,
    };
  } catch (error) {
    return {
      token,
      payload: null,
      exp: null,
      expDateLocal: null,
      remainingMs: null,
      error:
        error instanceof Error
          ? error.message
          : "JWT 파싱 중 오류가 발생했습니다.",
    };
  }
}

export default function Page() {
  const [jwtState, setJwtState] = useState<JwtState>(initialJwtState);
  const isRefreshingRef = useRef(false);

  const handleSilentRefresh = async () => {
    try {
      await authService.silentRefresh();
    } catch (error) {
      console.error("Manual silent refresh failed:", error);
    } finally {
      setJwtState(readJwtState());
    }
  };

  useEffect(() => {
    const syncJwtState = async () => {
      const nextState = readJwtState();

      if (
        nextState.remainingMs !== null &&
        nextState.remainingMs > 0 &&
        nextState.remainingMs < 5 * 60 * 1000 &&
        !isRefreshingRef.current
      ) {
        isRefreshingRef.current = true;
        try {
          await authService.silentRefresh();
        } catch (error) {
          console.error("JWT test silent refresh failed:", error);
        }
      }

      setJwtState(readJwtState());

      if (
        nextState.remainingMs === null ||
        nextState.remainingMs >= 5 * 60 * 1000 ||
        nextState.remainingMs <= 0
      ) {
        isRefreshingRef.current = false;
      }
    };

    void syncJwtState();
    const timer = window.setInterval(() => {
      void syncJwtState();
    }, 1000);

    return () => window.clearInterval(timer);
  }, []);

  return (
    <div className="space-y-4 p-8 text-base">
      <h1 className="text-2xl font-bold">JWT Exp Test</h1>

      <button
        type="button"
        className="rounded bg-blue-600 px-4 py-2 text-white hover:bg-blue-700"
        onClick={() => {
          void handleSilentRefresh();
        }}
      >
        Silent Refresh 호출
      </button>

      <div className="rounded border p-4">
        <div className="font-semibold">쿠키명</div>
        <div>{CLAIM_NAME}</div>
      </div>

      <div className="rounded border p-4">
        <div className="font-semibold">exp</div>
        <div>{jwtState.exp ?? "-"}</div>
      </div>

      <div className="rounded border p-4">
        <div className="font-semibold">만료시각</div>
        <div>{jwtState.expDateLocal ?? "-"}</div>
      </div>

      <div className="rounded border p-4">
        <div className="font-semibold">남은시간</div>
        <div>{formatRemainingMs(jwtState.remainingMs)}</div>
      </div>

      <div className="rounded border p-4">
        <div className="font-semibold">상태</div>
        <div>{jwtState.error ?? "정상"}</div>
      </div>

      <div className="rounded border p-4">
        <div className="font-semibold">payload</div>
        <pre className="overflow-auto whitespace-pre-wrap break-all text-sm">
          {jwtState.payload ? JSON.stringify(jwtState.payload, null, 2) : "-"}
        </pre>
      </div>
    </div>
  );
}