#pragma once
#include <ArduinoJson.h>
#include <stdint.h>
#include <stddef.h>

// JSON wire format: {"id":<int>,"data":{"BT":<float>,"ET":<float>}}
// Nested document needs two object allocations:
//   root   → 2 keys: "id", "data"
//   "data" → 2 keys: "BT", "ET"
static constexpr size_t TELEMETRY_DOC_SIZE = JSON_OBJECT_SIZE(2) + JSON_OBJECT_SIZE(2);
static constexpr size_t TELEMETRY_BUF_LEN  = 96;  // worst case: ~75 chars + null

// Serialise a telemetry frame into buf[bufLen].
// Returns number of bytes written (0 on failure / overflow).
inline size_t buildTelemetryJson(char* buf, size_t bufLen, int id, float bt, float et) {
    StaticJsonDocument<TELEMETRY_DOC_SIZE> doc;
    doc["id"]         = id;
    doc["data"]["BT"] = bt;
    doc["data"]["ET"] = et;
    size_t len = serializeJson(doc, buf, bufLen);
    // serializeJson truncates and null-terminates; len==bufLen-1 means overflow
    if (len == 0 || len >= bufLen) return 0;
    return len;
}