// @ts-check
"use strict";

import cluster from "node:cluster";
import { createWriteStream, existsSync, readFileSync } from "node:fs";
import { mkdir, rm } from "node:fs/promises";
import http from "node:http";
import https from "node:https";
import os from "node:os";
import path from "node:path";
import { fileURLToPath } from "node:url";

const __dirname = path.dirname(fileURLToPath(import.meta.url));
const PORT = Number(process.env.PORT || 3000);
const CHUNK_SIZE = 64 * 1024;
const INDEX_PATH = path.join(__dirname, "index.html");
const SERVERS_CONFIG_PATH = path.join(__dirname, "servers.json");
const FLAGS_DIR = path.join(__dirname, "flags");
// const FLAG_API_URL = "https://flagcdn.com";
const FLAG_API_URL = "https://flagicons.lipis.dev/flags/4x3";

const serversConfig = loadServersConfig();

if (cluster.isPrimary) {
  await ensureConfiguredFlags(serversConfig.servers);

  const workerCount = Number(process.env.WORKERS || os.cpus().length);
  console.log(`Master ${process.pid} запущен, форкаем ${workerCount} воркеров`);

  for (let i = 0; i < workerCount; i += 1) cluster.fork();
  cluster.on("exit", (worker) => {
    console.log(`Воркер ${worker.process.pid} упал, перезапуск`);
    cluster.fork();
  });
} else {
  const server = http.createServer((req, res) => {
    handleRequest(req, res);
  });

  server.listen(PORT, () => {
    console.log(`Воркер ${process.pid} слушает порт ${PORT}`);
  });
}

/**
 * Загружает общий список серверов. Один и тот же файл можно синхронизировать на
 * все инстансы, а текущий сервер выбирать через SERVER_ID.
 */
function loadServersConfig() {
  try {
    const raw = readFileSync(SERVERS_CONFIG_PATH, "utf8");
    const config = JSON.parse(raw);
    if (!Array.isArray(config.servers) || config.servers.length === 0) {
      throw new Error("servers must be a non-empty array");
    }
    return config;
  } catch (error) {
    console.warn(`Не удалось прочитать servers.json: ${error.message}`);
    return {
      currentServerId: "local",
      servers: [
        {
          id: "local",
          name: "Localhost",
          address: `http://localhost:${PORT}`,
          country: "Local",
          countryCode: "un",
        },
      ],
    };
  }
}

/**
 * Скачивает недостающие SVG-флаги при старте. Если API недоступен, сервер
 * продолжит работу, а карточка покажет текстовый код страны.
 */
async function ensureConfiguredFlags(servers) {
  await mkdir(FLAGS_DIR, { recursive: true });

  await Promise.all(
    servers
      .filter((server) => server.countryCode)
      .map(async (server) => {
        const code = String(server.countryCode).toLowerCase();
        const targetPath = path.join(FLAGS_DIR, `${code}.svg`);
        if (existsSync(targetPath)) return;

        try {
          await downloadFile(`${FLAG_API_URL}/${code}.svg`, targetPath);
          console.log(`Флаг ${code.toUpperCase()} сохранен в flags/`);
        } catch (error) {
          console.warn(`Не удалось скачать флаг ${code}: ${error.message}`);
        }
      }),
  );
}

function downloadFile(url, targetPath) {
  return new Promise((resolve, reject) => {
    const file = createWriteStream(targetPath);
    https
      .get(url, (response) => {
        if (response.statusCode !== 200) {
          file.close();
          rm(targetPath, { force: true }).finally(() => {});
          reject(new Error(`HTTP ${response.statusCode}`));
          return;
        }
        response.pipe(file);
        file.on("finish", () => {
          file.close(resolve);
        });
      })
      .on("error", (error) => {
        file.close();
        rm(targetPath, { force: true }).finally(() => {});
        reject(error);
      });
  });
}

function handleRequest(req, res) {
  const requestUrl = new URL(req.url || "/", `http://${req.headers.host}`);

  setCorsHeaders(res);
  if (req.method === "OPTIONS") {
    res.writeHead(204);
    res.end();
    return;
  }

  if (requestUrl.pathname === "/" && req.method === "GET") {
    sendHtml(res);
    return;
  }

  if (requestUrl.pathname === "/api/servers" && req.method === "GET") {
    sendJson(res, buildServersPayload(req));
    return;
  }

  if (requestUrl.pathname === "/ping" && req.method === "GET") {
    sendJson(res, {
      ok: true,
      serverId: getCurrentServer(req).id,
      now: Date.now(),
    });
    return;
  }

  if (requestUrl.pathname.startsWith("/flags/") && req.method === "GET") {
    sendFlag(requestUrl.pathname, res);
    return;
  }

  if (requestUrl.pathname === "/download" && req.method === "GET") {
    handleDownload(req, res);
    return;
  }

  if (requestUrl.pathname === "/upload" && req.method === "POST") {
    handleUpload(req, res);
    return;
  }

  res.writeHead(404, { "Content-Type": "text/plain; charset=utf-8" });
  res.end("Not found");
}

function setCorsHeaders(res) {
  res.setHeader("Access-Control-Allow-Origin", "*");
  res.setHeader("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
  res.setHeader("Access-Control-Allow-Headers", "Content-Type, Cache-Control");
}

function sendHtml(res) {
  const indexHtml = readFileSync(INDEX_PATH);
  res.writeHead(200, {
    "Content-Type": "text/html; charset=utf-8",
    "Cache-Control": "no-store",
  });
  res.end(indexHtml);
}

function sendJson(res, data) {
  res.writeHead(200, {
    "Content-Type": "application/json; charset=utf-8",
    "Cache-Control": "no-store",
  });
  res.end(JSON.stringify(data));
}

function sendFlag(pathname, res) {
  const fileName = path.basename(pathname);
  const flagPath = path.join(FLAGS_DIR, fileName);

  if (!fileName.endsWith(".svg") || !existsSync(flagPath)) {
    res.writeHead(404, { "Content-Type": "text/plain; charset=utf-8" });
    res.end("Flag not found");
    return;
  }

  res.writeHead(200, {
    "Content-Type": "image/svg+xml; charset=utf-8",
    "Cache-Control": "public, max-age=86400",
  });
  res.end(readFileSync(flagPath));
}

function handleDownload(req, res) {
  res.writeHead(200, {
    "Content-Type": "application/octet-stream",
    "Cache-Control": "no-store",
  });

  const chunk = Buffer.alloc(CHUNK_SIZE);
  let finished = false;

  function writeChunk() {
    if (finished) return;

    while (true) {
      const ok = res.write(chunk);
      if (!ok) {
        res.once("drain", writeChunk);
        return;
      }
    }
  }

  writeChunk();
  req.on("close", () => {
    finished = true;
    res.end();
  });
}

function handleUpload(req, res) {
  let totalBytes = 0;
  req.on("data", (chunk) => {
    totalBytes += chunk.length;
  });
  req.on("end", () => {
    res.writeHead(200, { "Content-Type": "text/plain; charset=utf-8" });
    res.end(String(totalBytes));
  });
}

function buildServersPayload(req) {
  const current = getCurrentServer(req);
  return {
    current,
    servers: serversConfig.servers.map((server) => ({
      ...server,
      flagUrl: server.countryCode
        ? `/flags/${String(server.countryCode).toLowerCase()}.svg`
        : null,
    })),
  };
}

function getCurrentServer(req) {
  const envServerId = process.env.SERVER_ID || serversConfig.currentServerId;
  const byEnv = serversConfig.servers.find((server) => server.id === envServerId);
  if (byEnv) return byEnv;

  const requestHost = req.headers.host;
  const byHost = serversConfig.servers.find((server) => {
    try {
      return new URL(server.address).host === requestHost;
    } catch {
      return false;
    }
  });

  return byHost || serversConfig.servers[0];
}