/** @file
 *  @brief Generic Attribute Profile handling.
 */

/*
 * Copyright (c) 2015 Intel Corporation
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1) Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *
 * 2) Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * 3) Neither the name of Intel Corporation nor the names of its contributors
 * may be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
#ifndef __BT_GATT_H
#define __BT_GATT_H

#include <misc/util.h>
#include <bluetooth/conn.h>
#include <bluetooth/uuid.h>

/* GATT attribute permission bitfield values */

/** @def BT_GATT_PERM_READ
 *  @brief Attribute read permission.
 */
#define BT_GATT_PERM_READ			0x01
/** @def BT_GATT_PERM_WRITE
 *  @brief Attribute write permission.
 */
#define BT_GATT_PERM_WRITE			0x02
/** @def BT_GATT_PERM_READ_ENCRYPT
 *  @brief Attribute read permission with encryption.
 *
 *  If set, requires encryption for read access.
 */
#define BT_GATT_PERM_READ_ENCRYPT		0x04
/** @def BT_GATT_PERM_WRITE_ENCRYPT
 *  @brief Attribute write permission with encryption.
 *
 *  If set, requires encryption for write access.
 */
#define BT_GATT_PERM_WRITE_ENCRYPT		0x08
/** @def BT_GATT_PERM_READ_AUTHEN
 *  @brief Attribute read permission with authentication.
 *
 *  If set, requires encryption using authenticated link-key for read access.
 */
#define BT_GATT_PERM_READ_AUTHEN		0x10
/** @def BT_GATT_PERM_WRITE_AUTHEN
 *  @brief Attribute write permission with authentication.
 *
 *  If set, requires encryption using authenticated link-key for write access.
 */
#define BT_GATT_PERM_WRITE_AUTHEN		0x20
/** @def BT_GATT_PERM_AUTHOR
 *  @brief Attribute authorization permission.
 */
#define BT_GATT_PERM_AUTHOR			0x40

/* GATT attribute flush flags */
/** @def BT_GATT_FLUSH_DISCARD
 *  @brief Attribute flush discard flag.
 */
#define BT_GATT_FLUSH_DISCARD			0x00
/** @def BT_GATT_FLUSH_DISCARD
 *  @brief Attribute flush syncronize flag.
 */
#define BT_GATT_FLUSH_SYNC			0x01

/** @brief GATT Attribute structure. */
struct bt_gatt_attr {
	/** Attribute UUID */
	const struct bt_uuid	*uuid;
	/** Attribute read callback */
	int			(*read)(struct bt_conn *conn,
					const struct bt_gatt_attr *attr,
					void *buf, uint16_t len,
					uint16_t offset);
	/** Attribute write callback */
	int			(*write)(struct bt_conn *conn,
					 const struct bt_gatt_attr *attr,
					 const void *buf, uint16_t len,
					 uint16_t offset);
	/** Attribute flush callback */
	int			(*flush)(struct bt_conn *conn,
					 const struct bt_gatt_attr *attr,
					 uint8_t flags);
	/** Attribute user data */
	void			*user_data;
	/** Attribute handle */
	uint16_t		handle;
	/** Attribute permissions */
	uint8_t			perm;
};

/** @brief Service Attribute Value. */
struct bt_gatt_service {
	/** Service UUID. */
	const struct bt_uuid	*uuid;
};

/** @brief Include Attribute Value. */
struct bt_gatt_include {
	/** Service UUID. */
	const struct bt_uuid	*uuid;
	/** Service start handle. */
	uint16_t		start_handle;
	/** Service end handle. */
	uint16_t		end_handle;
};

/* Characteristic Properties Bitfield values */

/** @def BT_GATT_CHRC_BROADCAST
 *  @brief Characteristic broadcast property.
 *
 *  If set, permits broadcasts of the Characteristic Value using Server
 *  Characteristic Configuration Descriptor.
 */
#define BT_GATT_CHRC_BROADCAST			0x01
/** @def BT_GATT_CHRC_READ
 *  @brief Characteristic read property.
 *
 *  If set, permits reads of the Characteristic Value.
 */
#define BT_GATT_CHRC_READ			0x02
/** @def BT_GATT_CHRC_WRITE_WITHOUT_RESP
 *  @brief Characteristic write without response property.
 *
 *  If set, permits write of the Characteristic Value without response.
 */
#define BT_GATT_CHRC_WRITE_WITHOUT_RESP		0x04
/** @def BT_GATT_CHRC_WRITE
 *  @brief Characteristic write with response property.
 *
 *  If set, permits write of the Characteristic Value with response.
 */
#define BT_GATT_CHRC_WRITE			0x08
/** @def BT_GATT_CHRC_NOTIFY
 *  @brief Characteristic notify property.
 *
 *  If set, permits notifications of a Characteristic Value without
 *  acknowledgment.
 */
#define BT_GATT_CHRC_NOTIFY			0x10
/** @def BT_GATT_CHRC_INDICATE
 *  @brief Characteristic indicate property.
 *
 * If set, permits indications of a Characteristic Value with acknowledgment.
 */
#define BT_GATT_CHRC_INDICATE			0x20
/** @def BT_GATT_CHRC_AUTH
 *  @brief Characteristic Authenticated Signed Writes property.
 *
 *  If set, permits signed writes to the Characteristic Value.
 */
#define BT_GATT_CHRC_AUTH			0x40
/** @def BT_GATT_CHRC_EXT_PROP
 *  @brief Characteristic Extended Properties property.
 *
 * If set, additional characteristic properties are defined in the
 * Characteristic Extended Properties Descriptor.
 */
#define BT_GATT_CHRC_EXT_PROP			0x80

/** @brief Characteristic Attribute Value. */
struct bt_gatt_chrc {
	/** Characteristic UUID. */
	const struct bt_uuid	*uuid;
	/** Characteristic value handle. */
	uint16_t		value_handle;
	/** Characteristic properties. */
	uint8_t			properties;
};

/* Characteristic Extended Properties Bitfield values */
#define BT_GATT_CEP_RELIABLE_WRITE		0x0001
#define BT_GATT_CEP_WRITABLE_AUX		0x0002

/** @brief Characteristic Extended Properties Attribute Value. */
struct bt_gatt_cep {
	/** Characteristic Extended properties */
	uint16_t		properties;
};

/** @brief Characteristic User Description Attribute Value. */
struct bt_gatt_cud {
	/** Characteristic User Description string. */
	char			*string;
};

/* Client Characteristic Configuration Values */

/** @def BT_GATT_CCC_NOTIFY
 *  @brief Client Characteristic Configuration Notification.
 *
 *  If set, changes to Characteristic Value shall be notified.
 */
#define BT_GATT_CCC_NOTIFY			0x0001
/** @def BT_GATT_CCC_INDICATE
 *  @brief Client Characteristic Configuration Indication.
 *
 *  If set, changes to Characteristic Value shall be indicated.
 */
#define BT_GATT_CCC_INDICATE			0x0002

/* Client Characteristic Configuration Attribute Value */
struct bt_gatt_ccc {
	/** Client Characteristic Configuration flags */
	uint16_t		flags;
};

/* Server API */

/** @brief Register attribute database.
 *
 *  Register GATT attribute database table. Applications can make use of
 *  macros such as BT_GATT_PRIMARY_SERVICE, BT_GATT_CHARACTERISTIC,
 *  BT_GATT_DESCRIPTOR, etc.
 *
 *  @param attrs Database table containing the available attributes.
 *  @param count Size of the database table.
 */
void bt_gatt_register(const struct bt_gatt_attr *attrs, size_t count);

enum {
	BT_GATT_ITER_STOP = 0,
	BT_GATT_ITER_CONTINUE,
};

/** @brief Attribute iterator callback.
 *
 *  @param attr Attribute found.
 *  @param user_data Data given.
 *
 *  @return BT_GATT_ITER_CONTINUE if should continue to the next attribute
 *  or BT_GATT_ITER_STOP to stop.
 */
typedef uint8_t (*bt_gatt_attr_func_t)(const struct bt_gatt_attr *attr,
				       void *user_data);

/** @brief Attribute iterator.
 *
 *  Iterate attributes in the given range.
 *
 *  @param start_handle Start handle.
 *  @param end_handle End handle.
 *  @param func Callback function.
 *  @param user_data Data to pass to the callback.
 */
void bt_gatt_foreach_attr(uint16_t start_handle, uint16_t end_handle,
			  bt_gatt_attr_func_t func, void *user_data);

/** @brief Generic Read Attribute value helper.
 *
 *  Read attribute value storing the result into buffer.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value.
 *  @param buf_len Buffer length.
 *  @param offset Start offset.
 *  @param value Attribute value.
 *  @param value_len Length of the attribute value.
 *
 *  @return int number of bytes read in case of success or negative values in
 *  case of error.
 */
int bt_gatt_attr_read(struct bt_conn *conn, const struct bt_gatt_attr *attr,
		      void *buf, uint16_t buf_len, uint16_t offset,
		      const void *value, uint16_t value_len);

/** @brief Read Service Attribute helper.
 *
 *  Read service attribute value storing the result into buffer after
 *  enconding it.
 *  NOTE: Only use this with attributes which user_data is a bt_uuid.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return int number of bytes read in case of success or negative values in
 *  case of error.
 */
int bt_gatt_attr_read_service(struct bt_conn *conn,
			      const struct bt_gatt_attr *attr,
			      void *buf, uint16_t len, uint16_t offset);

/** @def BT_GATT_SERVICE
 *  @brief Generic Service Declaration Macro.
 *
 *  Helper macro to declare a service attribute.
 *
 *  @param _handle Service attribute handle.
 *  @param _uuid Service attribute type.
 *  @param _data Service attribute value.
 */
#define BT_GATT_SERVICE(_handle, _uuid, _service)			\
{									\
	.handle = _handle,						\
	.uuid = _uuid,							\
	.perm = BT_GATT_PERM_READ,					\
	.read = bt_gatt_attr_read_service,				\
	.user_data = _service,						\
}

/** @def BT_GATT_PRIMARY_SERVICE
 *  @brief Primary Service Declaration Macro.
 *
 *  Helper macro to declare a primary service attribute.
 *
 *  @param _handle Service attribute handle.
 *  @param _service Service attribute value.
 */
#define BT_GATT_PRIMARY_SERVICE(_handle, _service)			\
{									\
	.handle = _handle,						\
	.uuid = (&(struct bt_uuid) { .type = BT_UUID_16,		\
				     .u16 = BT_UUID_GATT_PRIMARY }),	\
	.perm = BT_GATT_PERM_READ,					\
	.read = bt_gatt_attr_read_service,				\
	.user_data = _service,						\
}

/** @def BT_GATT_SECONDARY_SERVICE
 *  @brief Secondary Service Declaration Macro.
 *
 *  Helper macro to declare a secondary service attribute.
 *
 *  @param _handle Service attribute handle.
 *  @param _service Service attribute value.
 */
#define BT_GATT_SECONDARY_SERVICE(_handle, _service)			\
{									\
	.handle = _handle,						\
	.uuid = (&(struct bt_uuid) { .type = BT_UUID_16,		\
				     .u16 = BT_UUID_GATT_SECONDARY }),	\
	.perm = BT_GATT_PERM_READ,					\
	.read = bt_gatt_attr_read_service,				\
	.user_data = _service,						\
}

/** @brief Read Include Attribute helper.
 *
 *  Read include service attribute value storing the result into buffer after
 *  enconding it.
 *  NOTE: Only use this with attributes which user_data is a bt_gatt_include.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return int number of bytes read in case of success or negative values in
 *  case of error.
 */
int bt_gatt_attr_read_included(struct bt_conn *conn,
			       const struct bt_gatt_attr *attr,
			       void *buf, uint16_t len, uint16_t offset);

/** @def BT_GATT_INCLUDE_SERVICE
 *  @brief Include Service Declaration Macro.
 *
 *  Helper macro to declare a include service attribute.
 *
 *  @param _handle Service attribute handle.
 *  @param _service Service attribute value.
 */
#define BT_GATT_INCLUDE_SERVICE(_handle, _service)			\
{									\
	.handle = _handle,						\
	.uuid = (&(struct bt_uuid) { .type = BT_UUID_16,		\
				     .u16 = BT_UUID_GATT_INCLUDE }),	\
	.perm = BT_GATT_PERM_READ,					\
	.read = bt_gatt_attr_read_included,				\
	.user_data = _service,						\
}

/** @brief Read Characteristic Attribute helper.
 *
 *  Read characteristic attribute value storing the result into buffer after
 *  enconding it.
 *  NOTE: Only use this with attributes which user_data is a bt_gatt_chrc.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return number of bytes read in case of success or negative values in
 *  case of error.
 */
int bt_gatt_attr_read_chrc(struct bt_conn *conn,
			   const struct bt_gatt_attr *attr, void *buf,
			   uint16_t len, uint16_t offset);

/** @def BT_GATT_CHARACTERISTIC
 *  @brief Characteristic Declaration Macro.
 *
 *  Helper macro to declare a characteristic attribute.
 *
 *  @param _handle Characteristic attribute handle.
 *  @param _value Characteristic attribute value.
 */
#define BT_GATT_CHARACTERISTIC(_handle, _value)				\
{									\
	.handle = _handle,						\
	.uuid = (&(struct bt_uuid) { .type = BT_UUID_16,		\
				     .u16 = BT_UUID_GATT_CHRC }),	\
	.perm = BT_GATT_PERM_READ,					\
	.read = bt_gatt_attr_read_chrc,					\
	.user_data = _value,						\
}

/** @brief GATT CCC configuration entry. */
struct bt_gatt_ccc_cfg {
	/** Config peer address. */
	bt_addr_le_t		peer;
	/** Config peer value. */
	uint16_t		value;
	/** Config valid flag. */
	uint8_t			valid;
};

/* Internal representation of CCC value */
struct _bt_gatt_ccc {
	struct bt_gatt_ccc_cfg	*cfg;
	size_t			cfg_len;
	uint16_t		value;
	uint16_t		value_handle;
	void			(*cfg_changed)(uint16_t value);
};

/** @brief Read Client Characteristic Configuration Attribute helper.
 *
 *  Read CCC attribute value storing the result into buffer after
 *  enconding it.
 *  NOTE: Only use this with attributes which user_data is a _bt_gatt_ccc.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return number of bytes read in case of success or negative values in
 *  case of error.
 */
int bt_gatt_attr_read_ccc(struct bt_conn *conn,
			  const struct bt_gatt_attr *attr, void *buf,
			  uint16_t len, uint16_t offset);

/** @brief Write Client Characteristic Configuration Attribute helper.
 *
 *  Write value in the buffer into CCC attribute.
 *  NOTE: Only use this with attributes which user_data is a _bt_gatt_ccc.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return number of bytes written in case of success or negative values in
 *  case of error.
 */
int bt_gatt_attr_write_ccc(struct bt_conn *conn,
			   const struct bt_gatt_attr *attr, const void *buf,
			   uint16_t len, uint16_t offset);

/** @def BT_GATT_CCC
 *  @brief Client Characteristic Configuration Declaration Macro.
 *
 *  Helper macro to declare a CCC attribute.
 *
 *  @param _handle Descriptor attribute handle.
 *  @param _value_handle Characteristic attribute value handle.
 *  @param _cfg Initial configuration.
 *  @param _cfg_changed Configuration changed callback.
 */
#define BT_GATT_CCC(_handle, _value_handle, _cfg, _cfg_changed)		\
{									\
	.handle = _handle,						\
	.uuid = (&(struct bt_uuid) { .type = BT_UUID_16,		\
				     .u16 = BT_UUID_GATT_CCC }),	\
	.perm = BT_GATT_PERM_READ | BT_GATT_PERM_WRITE,			\
	.read = bt_gatt_attr_read_ccc,					\
	.write = bt_gatt_attr_write_ccc,				\
	.user_data = (&(struct _bt_gatt_ccc) { .cfg = _cfg,		\
					       .cfg_len = ARRAY_SIZE(_cfg), \
					       .value_handle = _value_handle, \
					       .cfg_changed = _cfg_changed, }),\
}

/** @brief Read Characteristic Extended Properties Attribute helper
 *
 *  Read CEP attribute value storing the result into buffer after
 *  enconding it.
 *  NOTE: Only use this with attributes which user_data is a bt_gatt_cep.
 *
 *  @param conn Connection object
 *  @param attr Attribute to read
 *  @param buf Buffer to store the value read
 *  @param len Buffer length
 *  @param offset Start offset
 *
 *  @return number of bytes read in case of success or negative values in
 *  case of error.
 */
int bt_gatt_attr_read_cep(struct bt_conn *conn,
			  const struct bt_gatt_attr *attr, void *buf,
			  uint16_t len, uint16_t offset);

/** @def BT_GATT_CEP
 *  @brief Characteristic Extended Properties Declaration Macro.
 *
 *  Helper macro to declare a CEP attribute.
 *
 *  @param _handle Descriptor attribute handle.
 *  @param _value Descriptor attribute value.
 */
#define BT_GATT_CEP(_handle, _value)					\
{									\
	.handle = _handle,						\
	.uuid = (&(struct bt_uuid) { .type = BT_UUID_16,		\
				     .u16 = BT_UUID_GATT_CEP }),	\
	.perm = BT_GATT_PERM_READ,					\
	.read = bt_gatt_attr_read_cep,					\
	.user_data = _value,						\
}

/** @def BT_GATT_DESCRIPTOR
 *  @brief Descriptor Declaration Macro.
 *
 *  Helper macro to declare a descriptor attribute.
 *
 *  @param _handle Descriptor attribute handle.
 *  @param _value Descriptor attribute value.
 *  @param _perm Descriptor attribute access permissions.
 *  @param _read Descriptor attribute read callback.
 *  @param _write Descriptor attribute write callback.
 *  @param _value Descriptor attribute value.
 */
#define BT_GATT_DESCRIPTOR(_handle, _uuid, _perm, _read, _write, _value) \
{									\
	.handle = _handle,						\
	.uuid = _uuid,							\
	.perm = _perm,							\
	.read = _read,							\
	.write = _write,						\
	.user_data = _value,						\
}

/** @def BT_GATT_LONG_DESCRIPTOR
 *  @brief Descriptor Declaration Macro.
 *
 *  Helper macro to declare a descriptor attribute.
 *
 *  @param _handle Descriptor attribute handle.
 *  @param _value Descriptor attribute value.
 *  @param _perm Descriptor attribute access permissions.
 *  @param _read Descriptor attribute read callback.
 *  @param _write Descriptor attribute write callback.
 *  @param _flush Descriptor attribute flush callback.
 *  @param _value Descriptor attribute value.
 */
#define BT_GATT_LONG_DESCRIPTOR(_handle, _uuid, _perm, _read, _write, _flush, \
				_value)					\
{									\
	.handle = _handle,						\
	.uuid = _uuid,							\
	.perm = _perm,							\
	.read = _read,							\
	.write = _write,						\
	.flush = _flush,						\
	.user_data = _value,						\
}

/** @brief Notify attribute value change.
 *
 *  Send notification of attribute value change.
 *  Note: This function should only be called if CCC is declared with
 *  BT_GATT_CCC otherwise it cannot find a valid peer configuration.
 *
 *  @param handle Attribute handle.
 *  @param value Attribute value.
 *  @param len Attribute value length.
 */
void bt_gatt_notify(uint16_t handle, const void *data, uint16_t len);

/** @brief connected callback.
 *
 *  @param conn Connection object.
 */
void bt_gatt_connected(struct bt_conn *conn);

/** @brief disconnected callback.
 *
 *  @param conn Connection object.
 */
void bt_gatt_disconnected(struct bt_conn *conn);

/** @brief notification callback.
 *
 *  @param conn Connection object.
 *  @param handle Attribute handle.
 *  @param data Attribute data.
 *  @param length Attribute data length.
 */
void bt_gatt_notification(struct bt_conn *conn, uint16_t handle,
			  const void *data, uint16_t length);

/* Client API */

/** @brief Response callback function
 *
 *  @param conn Connection object.
 *  @param err Error code.
 */
typedef void (*bt_gatt_rsp_func_t)(struct bt_conn *conn, uint8_t err);

/** @brief Exchange MTU
 *
 * This client procedure can be used to set the MTU to the maximum possible
 * size the buffers can hold.
 * NOTE: Shall only be used once per connection.
 *
 *  @param conn Connection object.
 */
int bt_gatt_exchange_mtu(struct bt_conn *conn, bt_gatt_rsp_func_t func);

/** @brief GATT Discover Primary parameters */
struct bt_gatt_discover_params {
	/** Discover UUID type */
	struct bt_uuid *uuid;
	/** Discover attribute callback */
	bt_gatt_attr_func_t func;
	/** Discover destroy callback */
	void (*destroy)(void *user_data);
	/** Discover start handle */
	uint16_t start_handle;
	/** Discover end handle */
	uint16_t end_handle;
};

/** @brief Discover Primary Service by Service UUID
 *
 *  This procedure is used by a client to discover a specific primary service on
 *  a server when only the Service UUID is known.
 *
 *  For each attribute found the callback is called which can then decide
 *  whether to continue discovering or stop.
 *
 *  @param conn Connection object.
 *  @param params Discover parameters.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_discover(struct bt_conn *conn,
		     struct bt_gatt_discover_params *params);

/** @brief Discover Characteristic
 *
 *  This procedure is used by a client to discover all characteristics on a
 *  server.
 *  Note: In case the UUID is set in the parameter it will be matched against
 *  the attributes found before calling the function callback.
 *
 *  For each attribute found the callback is called which can then decide
 *  whether to continue discovering or stop.
 *
 *  @param conn Connection object.
 *  @param params Discover parameters.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_discover_characteristic(struct bt_conn *conn,
				    struct bt_gatt_discover_params *params);

/** @brief Discover Descriptor
 *
 *  This procedure is used by a client to discover descriptors on a server.
 *  Note: In case the UUID is set in the parameter it will be matched against
 *  the attributes found before calling the function callback.
 *
 *  For each attribute found the callback is called which can then decide
 *  whether to continue discovering or stop.
 *
 *  @param conn Connection object.
 *  @param params Discover parameters.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_discover_descriptor(struct bt_conn *conn,
				struct bt_gatt_discover_params *params);

/** @brief Read callback function
 *
 *  @param conn Connection object.
 *  @param err Error code.
 *  @param data Attribute value data.
 *  @param length Attribute value length.
 */
typedef void (*bt_gatt_read_func_t)(struct bt_conn *conn, int err,
				    const void *data, uint16_t length);

/** @brief Read Attribute Value by handle
 *
 * This procedure read the attribute value and return it to the callback.
 *
 * @param conn Connection object.
 * @param handle Attribute handle.
 * @param offset Attribute data offset.
 * @param func Callback function.
 *
 * @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_read(struct bt_conn *conn, uint16_t handle, uint16_t offset,
		 bt_gatt_read_func_t func);

/** @brief Write Attribute Value by handle
 *
 * This procedure write the attribute value and return the result in the
 * callback in case it is set.
 *
 * @param conn Connection object.
 * @param handle Attribute handle.
 * @param data Data to be written.
 * @param length Data length.
 * @param func Callback function.
 *
 * @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_write(struct bt_conn *conn, uint16_t handle, const void *data,
		  uint16_t length, bt_gatt_rsp_func_t func);

/** @brief GATT Subscribe parameters */
struct bt_gatt_subscribe_params {
	bt_addr_le_t _peer;
	/** Subscribe value callback */
	bt_gatt_read_func_t func;
	/** Subscribe destroy callback */
	void (*destroy)(void *user_data);
	/** Subscribe value handle */
	uint16_t value_handle;
	struct bt_gatt_subscribe_params *_next;
};

/** @brief Subscribe Attribute Value Notification
 *
 * This procedure subscribe to value notification using the Client
 * Characteristic Configuration handle.
 *
 * @param conn Connection object.
 * @param handle CCC handle.
 * @param params Subscribe parameters.
 *
 * @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_subscribe(struct bt_conn *conn, uint16_t handle,
		      struct bt_gatt_subscribe_params *params);

/** @brief Unsubscribe Attribute Value Notification
 *
 * This procedure unsubscribe to value notification using the Client
 * Characteristic Configuration handle.
 *
 * @param conn Connection object.
 * @param handle CCC handle.
 * @param params Subscribe parameters.
 *
 * @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_unsubscribe(struct bt_conn *conn, uint16_t handle,
			struct bt_gatt_subscribe_params *params);

/** @brief Cancel GATT pending request
 *
 *  @param conn Connection object.
 */
void bt_gatt_cancel(struct bt_conn *conn);

/** @brief Read Multiple Attribute Values by set of handles
 *
 *  Routine to be used to retrieve set of attributes values determined by set of
 *  handles in one call.
 *
 *  @param conn Connection object.
 *  @param handles Set of valid handles to attributes.
 *  @param count Number of handles to be read.
 *  @param func User callback routine to get retrieved values.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_read_multiple(struct bt_conn *conn, const uint16_t *handles,
			  size_t count, bt_gatt_read_func_t func);

#endif /* __BT_GATT_H */