# MQTT usage

## Callbacks and tuning

The following snippets extend a sketch that already owns long-lived `HADevice`, `HAMqtt`, and entity objects. Configure callbacks, discovery metadata, and availability before `mqtt.begin(...)`; call the publishing snippets later from normal application logic.

`HAMqtt` supports optional callbacks and PubSubClient tuning:

```cpp
// These callbacks are registered before mqtt.begin(...).
void onMessage(const char* topic, const uint8_t* payload, uint16_t length) { /* ... */ }
void onConnected() { /* ... */ }
void onDisconnected() { /* ... */ }
void onStateChanged(HAMqtt::ConnectionState state) { /* ... */ }

void setup() {
    // A successful reconnect creates a new MQTT session, so onConnected runs again.
    mqtt.onMessage(onMessage);
    mqtt.onConnected(onConnected);
    mqtt.onDisconnected(onDisconnected);
    mqtt.onStateChanged(onStateChanged);
    mqtt.setBufferSize(512);   // Increase only when a larger MQTT packet is required.
    mqtt.setKeepAlive(60);     // Seconds; the default is 15.
    mqtt.begin("192.168.1.50", "user", "pass");
}
```

## Custom subscriptions

Subscribe after each successful connection (for example in `onConnected`), because subscriptions are tied to the MQTT session:

```cpp
void onConnected() {
    // MQTT subscriptions belong to this session and must be restored after reconnecting.
    mqtt.subscribe("my/custom/topic");
}
```

Handle payloads in `onMessage`.

## Publishing arbitrary payloads

```cpp
// Call after mqtt.begin(...); retain controls whether the broker keeps this value.
void publishApplicationState() {
    mqtt.publish("customTopic", "payload", false);  // Not retained.
    mqtt.publish("customTopic", "payload", true);   // Retained.
}
```

## Availability

**Shared availability (recommended):** one availability topic for the whole device — works well with **Last Will** (LWT):

```cpp
// Configure device-wide availability before mqtt.begin(...).
void configureSharedAvailability() {
    device.enableSharedAvailability();
    device.setPayloadAvailable("up");
    device.setPayloadNotAvailable("down");
    device.enableLastWill();   // Broker publishes offline when TCP drops.
    // device.setAvailability(false);  // Optional: start as offline.
}
```

**Per-entity availability:** call `someEntity.setAvailability(true/false)` on each type. Does not use LWT the same way as shared mode; see examples under `examples/availability/`.

Custom per-entity payloads are supported:

```cpp
// Configure the relevant entity before mqtt.begin(...).
void configureSensorAvailability() {
    sensor.setPayloadAvailable("ready");
    sensor.setPayloadNotAvailable("lost");
}
```

For multi-topic availability discovery, add full MQTT topics and a mode:

```cpp
// `sensor` is the entity whose availability depends on these external topics.
void configureExternalAvailability() {
    sensor.setAvailabilityMode("all");
    sensor.addAvailabilityEntry("bridge/status");
    sensor.addAvailabilityEntry("sensor/status", "{{ value_json.state }}");
}
```

## Discovery helpers by entity

Common entity discovery metadata is available on most entity classes:

```cpp
// `entity` is an entity type that supports these common discovery fields.
void configureCommonDiscovery(HABaseDeviceType& entity) {
    entity.setEnabledByDefault(false);
    entity.setEntityPicture("https://example.com/entity.png");
    entity.setQos(1);
    entity.setEncoding("utf-8");
    entity.setEntityCategory("diagnostic");
}
```

Read-only sensor presentation/template helpers:

```cpp
// `sensor` is a read-only HASensor instance.
void configureSensorPresentation(HASensor& sensor) {
    sensor.setSuggestedDisplayPrecision(2);
    sensor.setValueTemplate("{{ value_json.temperature }}");
    sensor.setJsonAttributesTemplate("{{ value_json.attrs | tojson }}");
    sensor.setLastResetValueTemplate("{{ value_json.last_reset }}");
    sensor.setDeviceClass("enum");
    sensor.setOptions("idle;charging;discharging;fault");
}
```

Writable entity template/payload helpers:

```cpp
// These names refer to the matching writable entity instances in the application.
void configureWritableEntities(HASwitch& mySwitch,
                               HANumber& myNumber,
                               HASelect& mySelect,
                               HAText& myText,
                               HAButton& myButton) {
    mySwitch.setPayloadOn("ENABLE");
    mySwitch.setPayloadOff("DISABLE");
    mySwitch.setStateOn("running");
    mySwitch.setStateOff("stopped");
    mySwitch.setValueTemplate("{{ value_json.state }}");
    mySwitch.setCommandTemplate("{{ value_json.command }}");

    myNumber.setPayloadReset("RESET");
    myNumber.setCommandTemplate("{{ value | float | round(1) }}");

    mySelect.setCommandTemplate("{{ value_json.choice }}");
    myText.setCommandTemplate("{{ value_json.text }}");
    myButton.setPayloadPress("PRESS");
}
```

## Compiler macros

Defined in `ArduinoHADefines.h` or via build flags.

- **`ARDUINOHA_DISABLE_STDFUNCTION`** — disables the default capturing-lambda and
  `std::bind` overloads on entity command APIs. Use it on targets without a complete
  `std::function` implementation or where code size/RAM matters (constrained AVR
  builds are the usual case). ESP8266/ESP32 support the overloads. `HAMqtt`
  lifecycle callbacks remain ordinary function pointers.
- **`ARDUINOHA_DEBUG`** — enables ArduinoHA logging by default and sets the initial maximum verbosity to `Debug`. Without this flag, structured logs are compiled in but remain disabled until you call `arduinoHASetLogEnabled(true)`.

Structured logging is available through a long-lived sink:

```cpp
class MyLogSink : public ArduinoHALogSink {
public:
    void log(const ArduinoHALogMessage& msg) override {
        Serial.print("[");
        Serial.print(arduinoHALogLevelTag(msg.level));
        Serial.print("][aha.");
        Serial.print(msg.subsystem);
        Serial.print("] ");
        Serial.println(msg.text);
    }
};

MyLogSink logSink;  // The installed sink must outlive ArduinoHA logging.

void setup() {
    Serial.begin(115200);
    arduinoHASetLogSink(&logSink);
    arduinoHASetLogEnabled(true);
    arduinoHASetLogLevel(ArduinoHALogLevel::Trace);
}
```

`arduinoHALog(...)` and `arduinoHALogf(...)` support subsystem-tagged messages such as `mqtt`, `discovery`, `availability`, `serializer`, `entity`, and `device`. Install a sink when you want those messages to join your application’s normal serial or structured log stream.

Applications that use Wi-Fi can register **`arduinoHASetNetworkStatusFn`** with a callback returning `WiFi.status()`. Publish failure diagnostics can then include the current Wi-Fi status without coupling ArduinoHA to a particular network library.

**Exclude unused device types** (saves flash from vtables), e.g.:

`EX_ARDUINOHA_BINARY_SENSOR`, `EX_ARDUINOHA_BUTTON`, `EX_ARDUINOHA_CAMERA`, `EX_ARDUINOHA_COVER`, `EX_ARDUINOHA_DEVICE_TRACKER`, `EX_ARDUINOHA_DEVICE_TRIGGER`, `EX_ARDUINOHA_FAN`, `EX_ARDUINOHA_HVAC`, `EX_ARDUINOHA_LIGHT`, `EX_ARDUINOHA_LOCK`, `EX_ARDUINOHA_NUMBER`, `EX_ARDUINOHA_SCENE`, `EX_ARDUINOHA_SELECT`, `EX_ARDUINOHA_SENSOR`, `EX_ARDUINOHA_SWITCH`, `EX_ARDUINOHA_TAG_SCANNER`