import { createHmac, randomBytes, timingSafeEqual } from "node:crypto";

export type LinkTokenPayloadV1 = {
  v: 1;
  teamId: string;
  userId: string;
  nonce: string;
  exp: number;
};

const TOKEN_TTL_SEC = Number(process.env.TELEGRAM_LINK_TOKEN_TTL_SEC || 10 * 60);

function base64UrlEncode(input: Buffer | string) {
  return Buffer.from(input)
    .toString("base64")
    .replace(/\+/g, "-")
    .replace(/\//g, "_")
    .replace(/=+$/g, "");
}

function base64UrlDecode(input: string) {
  const normalized = input.replace(/-/g, "+").replace(/_/g, "/");
  const pad = normalized.length % 4;
  const padded = pad === 0 ? normalized : normalized + "=".repeat(4 - pad);
  return Buffer.from(padded, "base64");
}

export function requireLinkSecret() {
  const secret = String(process.env.TELEGRAM_LINK_SECRET || process.env.TELEGRAM_BOT_TOKEN || "").trim();
  if (!secret) {
    throw createError({ statusCode: 500, statusMessage: "TELEGRAM_LINK_SECRET or TELEGRAM_BOT_TOKEN is required" });
  }
  return secret;
}

export function requireBotUsername() {
  const botUsername = String(process.env.TELEGRAM_BOT_USERNAME || "").trim().replace(/^@/, "");
  if (!botUsername) {
    throw createError({ statusCode: 500, statusMessage: "TELEGRAM_BOT_USERNAME is required" });
  }
  return botUsername;
}

function sign(input: string, secret: string) {
  return createHmac("sha256", secret).update(input).digest();
}

export function issueLinkToken(input: { teamId: string; userId: string }) {
  const secret = requireLinkSecret();
  const payload: LinkTokenPayloadV1 = {
    v: 1,
    teamId: input.teamId,
    userId: input.userId,
    nonce: randomBytes(12).toString("hex"),
    exp: Math.floor(Date.now() / 1000) + Math.max(60, TOKEN_TTL_SEC),
  };
  const payloadRaw = JSON.stringify(payload);
  const payloadEncoded = base64UrlEncode(payloadRaw);
  const sig = base64UrlEncode(sign(payloadEncoded, secret));
  const token = `${payloadEncoded}.${sig}`;
  return { token, payload };
}

export function verifyLinkToken(token: string): LinkTokenPayloadV1 | null {
  const raw = String(token || "").trim();
  if (!raw) return null;

  const dotIdx = raw.indexOf(".");
  if (dotIdx <= 0 || dotIdx >= raw.length - 1) return null;

  const payloadEncoded = raw.slice(0, dotIdx);
  const sigEncoded = raw.slice(dotIdx + 1);

  try {
    const secret = requireLinkSecret();
    const expected = sign(payloadEncoded, secret);
    const actual = base64UrlDecode(sigEncoded);
    if (actual.length !== expected.length || !timingSafeEqual(actual, expected)) {
      return null;
    }

    const payload = JSON.parse(base64UrlDecode(payloadEncoded).toString("utf8")) as LinkTokenPayloadV1;
    if (!payload || payload.v !== 1) return null;
    if (!payload.teamId || !payload.userId || !payload.nonce || !payload.exp) return null;
    if (Math.floor(Date.now() / 1000) > payload.exp) return null;
    return payload;
  } catch {
    return null;
  }
}

export function extractLinkTokenFromStartText(text: string) {
  const trimmed = String(text || "").trim();
  if (!trimmed.startsWith("/start")) return null;
  const parts = trimmed.split(/\s+/).filter(Boolean);
  if (parts.length < 2) return null;
  const arg = parts[1] || "";
  if (!arg.startsWith("link_")) return null;
  return arg.slice("link_".length);
}

export function buildTelegramStartUrl(token: string) {
  const botUsername = requireBotUsername();
  return `https://t.me/${botUsername}?start=link_${token}`;
}

export function getTelegramChatIdFromUpdate(update: any): string | null {
  const candidates = [
    update?.message?.chat?.id,
    update?.business_message?.chat?.id,
    update?.edited_business_message?.chat?.id,
    update?.business_connection?.user_chat_id,
  ];
  for (const c of candidates) {
    if (c == null) continue;
    const v = String(c).trim();
    if (v) return v;
  }
  return null;
}

export function getBusinessConnectionFromUpdate(update: any): {
  id: string;
  userChatId: string | null;
  isEnabled: boolean | null;
  canReply: boolean | null;
  raw: any;
} | null {
  const bc = (update?.business_connection ?? null) as any;
  if (!bc || typeof bc !== "object") return null;

  const id = String(bc.id ?? "").trim();
  if (!id) return null;

  const userChatId = bc.user_chat_id != null ? String(bc.user_chat_id) : null;
  const isEnabled = typeof bc.is_enabled === "boolean" ? bc.is_enabled : null;
  const canReply = typeof bc.can_reply === "boolean"
    ? bc.can_reply
    : typeof bc.rights?.can_reply === "boolean"
      ? bc.rights.can_reply
      : null;

  return {
    id,
    userChatId,
    isEnabled,
    canReply,
    raw: bc,
  };
}