#ifndef mqtt_h__included
#define mqtt_h__included

// re-define to 1 to enable server functionality
#ifndef MQTT_SERVER
# define MQTT_SERVER 0
#endif

// re-rdefine to 0 to disable client functionality
#ifndef MQTT_CLIENT
# define MQTT_CLIENT 1
#endif


#include <stdint.h>
#include <stdbool.h>

typedef struct _MQTTHandle MQTTHandle;

typedef struct {
    char *hostname;  /**< Hostname to connect to, will do DNS resolution */
    uint16_t port;   /**< Port the broker listens on, set to 0 for 1883 default */

    char *client_id; /**< Client identification */
    bool clean_session; /**< Set to true to reset the session on reconnect */

    char *username;  /**< User name, set to NULL to connect anonymously */
    char *password;  /**< Password, set to NULL to connect without password */

    char *last_will_topic;   /**< last will topic that is automatically published on connection loss */
    char *last_will_message; /**< last will message */
    bool last_will_retain;   /**< tell server to retain last will message */
} MQTTConfig;

typedef enum {
    MQTT_STATUS_OK = 0, /**< All ok, no error */
    MQTT_STATUS_ERROR   /**< Error, action did not succeed, error handler will be called */
} MQTTStatus;

typedef enum {
    MQTT_QOS_0 = 0, /**< At most once, drop message if nobody is listening, no ACK */
    MQTT_QOS_1,     /**< At least once, wait for ACK from broker */
    MQTT_QOS_2,     /**< Exactly once, do triple way handshake with broker */
} MQTTQosLevel;

typedef enum {
    MQTT_Error_Host_Not_Found,         /**< Host could not be resolved */
    MQTT_Error_Connection_Refused,     /**< Connection was refused, wrong port? */
    MQTT_Error_Broker_Disconnected,    /**< Broker went down, perhaps restart? */
    MQTT_Error_Authentication,         /**< Authentication error, wrong or missing username/password? */
    MQTT_Error_Protocol_Not_Supported, /**< Broker does not speak MQTT protocol 3.1.1 (aka version 4) */
    MQTT_Error_Connection_Reset        /**< Network connection reset, perhaps network went down? */
} MQTTErrorCode;

/** Error handler callback
 *
 * Return true if the handle should be freed, false to keep it
 */
typedef bool (*MQTTErrorHandler)(MQTTHandle *handle, MQTTConfig *config, MQTTErrorCode code);

/** Event handler callback */
typedef void (*MQTTEventHandler)(MQTTHandle *handle, void *context);

/** publish event callback */
typedef void (*MQTTPublishEventHandler)(MQTTHandle *handle, char *topic, char *payload);

/**
 * Connect to MQTT broker
 *
 * @param config: MQTT configuration
 * @param callback: Success callback
 * @param callback_context: Context pointer for the callback
 * @param error_callback: Callback function to call on errors
 * @returns handle to mqtt connection or NULL on error
 *
 * If the error handler is called with Host not found or Connection refused,
 * the handler is in charge of freeing the handle by returning true
 * or re-trying by changing settings and calling mqtt_reconnect() and returning false
 */
MQTTHandle *mqtt_connect(MQTTConfig *config, MQTTEventHandler callback, void *callback_context, MQTTErrorHandler error_callback);

/**
 * Re-Connect to MQTT broker
 *
 * Usually called in the MQTTErrorHandler callback, if called on a working
 * connection the connection will be disconnected before reconnecting.
 *
 * If there were registered subscriptions they will be re-instated after
 * a successful reconnect.
 *
 * @param handle: MQTT Handle from `mqtt_connect`
 * @param callback: Success callback
 * @param callback_context: Context pointer for the callback
 * @returns: Status code
 */
MQTTStatus mqtt_reconnect(MQTTHandle *handle, MQTTEventHandler callback, void *callback_context);

/**
 * Subscribe to a topic
 *
 * @param handle: MQTT Handle from `mqtt_connect`
 * @param topic: Topic to subscribe
 * @param qos_level: Maximum qos level to subscribe to
 * @param callback: Callback function to call when receiving something for that topic
 * @returns: Status code
 */
MQTTStatus mqtt_subscribe(MQTTHandle *handle, char *topic, MQTTQosLevel qos_level, MQTTPublishEventHandler callback);

/**
 * Un-Subscribe from a topic
 *
 * @param handle: MQTT Handle from `mqtt_connect`
 * @param topic: Topic to unsubscribe
 * @returns: Status code
 */
MQTTStatus mqtt_unsubscribe(MQTTHandle *handle, char *topic);

/**
 * Publish something to the broker
 *
 * @param handle: MQTT Handle from `mqtt_connect`
 * @param topic: Topic to publish to
 * @param payload: Message payload to publish
 * @returns: Status code
 */
MQTTStatus mqtt_publish(MQTTHandle *handle, char *topic, char *payload, MQTTQosLevel qos_level);

/**
 * Disconnect from MQTT broker
 *
 * @param handle: MQTT Handle from `mqtt_connect`
 * @returns: Status code
 *
 * @attention: do not use the handle after calling this function,
 *             all resources will be freed, this handle is now invalid!
 */
MQTTStatus mqtt_disconnect(MQTTHandle *handle, MQTTEventHandler callback, void *callback_context);

#endif /* mqtt_h__included */