add prometheus metrics for temperaturesensors

CHANGELOG_LATEST.md

@@ -9,6 +9,7 @@ For more details go to [emsesp.org](https://emsesp.org/).
 - comfortpoint for BC400 [#2935](https://github.com/emsesp/EMS-ESP32/issues/2935)
 - customize device brand [#2784](https://github.com/emsesp/EMS-ESP32/issues/2784)
 - set model for ems-esp devices temperature, analog, etc. [#2958](https://github.com/emsesp/EMS-ESP32/discussions/2958)
+- prometheus metrics for temperaturesensors [#2962](https://github.com/emsesp/EMS-ESP32/issues/2962)
 
 ## Fixed
 

src/core/temperaturesensor.cpp

@@ -400,6 +400,15 @@ bool TemperatureSensor::get_value_info(JsonObject output, const char * cmd, cons
         return true;
     }
 
+    if (!strcmp(cmd, F_(metrics))) {
+        std::string metrics = get_metrics_prometheus();
+        if (!metrics.empty()) {
+            output["api_data"] = metrics;
+            return true;
+        }
+        return false;
+    }
+
     // this is for a specific sensor
     const char * attribute_s = Command::get_attribute(cmd);
 
@@ -414,6 +423,21 @@ bool TemperatureSensor::get_value_info(JsonObject output, const char * cmd, cons
     return false; // not found
 }
 
+// generate Prometheus metrics format from temperature values
+std::string TemperatureSensor::get_metrics_prometheus() {
+    std::string result;
+    result.reserve(sensors_.size() * 120);
+    char val[10];
+    for (auto & sensor : sensors_) {
+        result += (std::string) "# HELP emsesp_" + sensor.name() + " " + sensor.name() + ", "
+                  + EMSdevice::uom_to_string(EMSESP::system_.fahrenheit() ? DeviceValueUOM::FAHRENHEIT : DeviceValueUOM::DEGREES) + ", readable, visible\n";
+        result += (std::string) "# TYPE emsesp_" + sensor.name() + " gauge\n";
+        result +=
+            (std::string) "emsesp_" + sensor.name() + " " + Helpers::render_value(val, sensor.temperature_c, 10, EMSESP::system_.fahrenheit() ? 2 : 0) + "\n";
+    }
+    return result;
+}
+
 // note we don't add the device and state classes here, as we do in the custom entity service
 void TemperatureSensor::get_value_json(JsonObject output, const Sensor & sensor) {
     output["id"]       = sensor.id();

src/core/temperaturesensor.h

@@ -96,6 +96,8 @@ class TemperatureSensor {
     bool updated_values();
     bool get_value_info(JsonObject output, const char * cmd, const int8_t id = -1);
 
+    std::string get_metrics_prometheus();
+
     // return back reference to the sensor list, used by other classes
     std::vector<Sensor, AllocatorPSRAM<Sensor>> sensors() const {
         return sensors_;