const mongoose = require("mongoose");

const actionSchema = new mongoose.Schema({
  updated: Number,
});
const Action = mongoose.model("Action", actionSchema);

const userSchema = new mongoose.Schema({ name: String });

async function updateAction() {
  try {
    await Action.updateOne({}, { $set: { updated: 1 } }, { upsert: true });

    console.log("✅ Cập nhật thành công");
  } catch (err) {
    console.error("❌ Lỗi cập nhật:", err);
  }
}

const connectDB = async () => {
  try {
    const conn = await mongoose.connect(process.env.MONGODB_URI);
    console.log(`✅ MongoDB Connected:[ ${conn.connection.host} ]`);

    // Lấy db sau khi connect thành công
    const db = mongoose.connection.db;

    // admin is the database admin interface used to run server commands
    const admin = db.admin();
    const isMaster = await admin.command({ isMaster: 1 });

    // Only create a ChangeStream when connected to a replica set.
    // On standalone servers the $changeStream aggregation stage isn't supported
    // and attempting to watch() will emit an 'error' event that can crash the
    // process if not handled. Guard and add defensive error handling.
    if (isMaster && isMaster.setName) {
      try {
        const changeStream = db.watch([
          {
            $match: {
              "ns.coll": { $ne: "actions" }, // bỏ qua collection "actions"
            },
          },
        ]);

        changeStream.on("change", async (change) => {
          try {
            console.log("📢 Change detected:", change);
            await updateAction();
          } catch (e) {
            console.error("Error handling change event:", e);
          }
        });

        // Defensive: listen for errors so they don't bubble as unhandled
        changeStream.on("error", (err) => {
          console.warn(
            "⚠️ ChangeStream error — disabling change stream:",
            err && err.message ? err.message : err,
          );
          try {
            changeStream.close();
          } catch (e) {
            /* ignore */
          }
        });
      } catch (e) {
        // If watch() throws synchronously (older drivers/servers) skip it.
        console.log(
          "ℹ️ ChangeStream not initialized (watch() failed):",
          e.message || e,
        );
      }
    } else {
      console.log("ℹ️ ChangeStream skipped (no replica set detected)");
    }
  } catch (error) {
    console.error(`Error: ${error.message}`);
    process.exit(1);
  }
};

module.exports = connectDB;