import crypto from "node:crypto";
import fs from "node:fs/promises";
import os from "node:os";
import path from "node:path";
import { resolveStateDir } from "../config/paths.js";

const STORE_VERSION = 2;

type TelegramUpdateOffsetState = {
  version: number;
  lastUpdateId: number | null;
  botId: string | null;
};

function normalizeAccountId(accountId?: string) {
  const trimmed = accountId?.trim();
  if (!trimmed) {
    return "default";
  }
  return trimmed.replace(/[^a-z0-9._-]+/gi, "_");
}

function resolveTelegramUpdateOffsetPath(
  accountId?: string,
  env: NodeJS.ProcessEnv = process.env,
): string {
  const stateDir = resolveStateDir(env, os.homedir);
  const normalized = normalizeAccountId(accountId);
  return path.join(stateDir, "telegram", `update-offset-${normalized}.json`);
}

function extractBotIdFromToken(token?: string): string | null {
  const trimmed = token?.trim();
  if (!trimmed) {
    return null;
  }
  const [rawBotId] = trimmed.split(":", 1);
  if (!rawBotId || !/^\d+$/.test(rawBotId)) {
    return null;
  }
  return rawBotId;
}

function safeParseState(raw: string): TelegramUpdateOffsetState | null {
  try {
    const parsed = JSON.parse(raw) as {
      version?: number;
      lastUpdateId?: number | null;
      botId?: string | null;
    };
    if (parsed?.version !== STORE_VERSION && parsed?.version !== 1) {
      return null;
    }
    if (parsed.lastUpdateId !== null && typeof parsed.lastUpdateId !== "number") {
      return null;
    }
    if (
      parsed.version === STORE_VERSION &&
      parsed.botId !== null &&
      typeof parsed.botId !== "string"
    ) {
      return null;
    }
    return {
      version: STORE_VERSION,
      lastUpdateId: parsed.lastUpdateId ?? null,
      botId: parsed.version === STORE_VERSION ? (parsed.botId ?? null) : null,
    };
  } catch {
    return null;
  }
}

export async function readTelegramUpdateOffset(params: {
  accountId?: string;
  botToken?: string;
  env?: NodeJS.ProcessEnv;
}): Promise<number | null> {
  const filePath = resolveTelegramUpdateOffsetPath(params.accountId, params.env);
  try {
    const raw = await fs.readFile(filePath, "utf-8");
    const parsed = safeParseState(raw);
    const expectedBotId = extractBotIdFromToken(params.botToken);
    if (expectedBotId && parsed?.botId && parsed.botId !== expectedBotId) {
      return null;
    }
    if (expectedBotId && parsed?.botId === null) {
      return null;
    }
    return parsed?.lastUpdateId ?? null;
  } catch (err) {
    const code = (err as { code?: string }).code;
    if (code === "ENOENT") {
      return null;
    }
    return null;
  }
}

export async function writeTelegramUpdateOffset(params: {
  accountId?: string;
  updateId: number;
  botToken?: string;
  env?: NodeJS.ProcessEnv;
}): Promise<void> {
  const filePath = resolveTelegramUpdateOffsetPath(params.accountId, params.env);
  const dir = path.dirname(filePath);
  await fs.mkdir(dir, { recursive: true, mode: 0o700 });
  const tmp = path.join(dir, `${path.basename(filePath)}.${crypto.randomUUID()}.tmp`);
  const payload: TelegramUpdateOffsetState = {
    version: STORE_VERSION,
    lastUpdateId: params.updateId,
    botId: extractBotIdFromToken(params.botToken),
  };
  await fs.writeFile(tmp, `${JSON.stringify(payload, null, 2)}\n`, {
    encoding: "utf-8",
  });
  await fs.chmod(tmp, 0o600);
  await fs.rename(tmp, filePath);
}

export async function deleteTelegramUpdateOffset(params: {
  accountId?: string;
  env?: NodeJS.ProcessEnv;
}): Promise<void> {
  const filePath = resolveTelegramUpdateOffsetPath(params.accountId, params.env);
  try {
    await fs.unlink(filePath);
  } catch (err) {
    const code = (err as { code?: string }).code;
    if (code === "ENOENT") {
      return;
    }
    throw err;
  }
}