// Heartbeat record storage and batch-flush interface.

#pragma once

#include <cstdint>

#include <functional>

#include <vector>

struct HeartbeatRecord {

  uint64_t deviceId;    // unique device identifier

  uint64_t timestampMs; // record timestamp in milliseconds since epoch

  int16_t  rssi;        // received signal strength in dBm

};

// Buffers device heartbeat records and flushes them to persistent storage in

// batches. Flush fires when the buffer reaches kMaxBatchSize, or when

// flushPending() is called by the periodic timer.

class HeartbeatStore {

public:

  static constexpr std::size_t kMaxBatchSize = 64; // maximum records per flush batch

  using FlushCallback = std::function<void(std::vector<HeartbeatRecord>)>;

  // Parameters:

  //   cb - callback invoked with the batch whenever a flush occurs

  // Returns: new HeartbeatStore ready to accept records

  explicit HeartbeatStore(FlushCallback cb) : onFlush_(std::move(cb)) {}

  // Parameters:

  //   rec - heartbeat record to append; triggers flush when buffer is at capacity

  // Returns: void

  void append(const HeartbeatRecord& rec);

  // Parameters: none

  // Returns: void; flushes any buffered records immediately (called by timer)

  void flushPending();

private:

  std::vector<HeartbeatRecord> records_; // in-flight record buffer

  FlushCallback onFlush_;                // caller-supplied flush sink

};