# Helpers for generating BLE advertising payloads
 
from micropython import const
import struct
import bluetooth
  
  # Advertising payloads are repeated packets of the following form:
  # 1 byte data length (N + 1)
  # 1 byte type (see constants below)
 # N bytes type-specific data
 
_ADV_TYPE_FLAGS = const(0x01)
_ADV_TYPE_NAME = const(0x09)
_ADV_TYPE_UUID16_COMPLETE = const(0x3)
_ADV_TYPE_UUID32_COMPLETE = const(0x5)
_ADV_TYPE_UUID128_COMPLETE = const(0x7)
_ADV_TYPE_UUID16_MORE = const(0x2)
_ADV_TYPE_UUID32_MORE = const(0x4)
_ADV_TYPE_UUID128_MORE = const(0x6)
_ADV_TYPE_APPEARANCE = const(0x19)
 

 # Generate a payload to be passed to gap_advertise(adv_data=...).
def advertising_payload(limited_disc=False, br_edr=False, name=None, services=None, appearance=0):
    payload = bytearray()
 
    def _append(adv_type, value):
        nonlocal payload
        payload += struct.pack("BB", len(value) + 1, adv_type) + value
     
    _append(
        _ADV_TYPE_FLAGS,
        struct.pack("B", (0x01 if limited_disc else 0x02) + (0x18 if br_edr else 0x04)),
    )
 
    if name:
        _append(_ADV_TYPE_NAME, name)
 
    if services:
        for uuid in services:
            b = bytes(uuid)
            if len(b) == 2:
                _append(_ADV_TYPE_UUID16_COMPLETE, b)
            elif len(b) == 4:
                _append(_ADV_TYPE_UUID32_COMPLETE, b)
            elif len(b) == 16:
                _append(_ADV_TYPE_UUID128_COMPLETE, b)
 
 # See org.bluetooth.characteristic.gap.appearance.xml
    if appearance:
        _append(_ADV_TYPE_APPEARANCE, struct.pack("<h", appearance))
     
    return payload
 
 
def decode_field(payload, adv_type):
    i = 0
    result = []
    while i + 1 < len(payload):
        if payload[i + 1] == adv_type:
            result.append(payload[i + 2 : i + payload[i] + 1])
        i += 1 + payload[i]
    return result
 
 
def decode_name(payload):
    n = decode_field(payload, _ADV_TYPE_NAME)
    return str(n[0], "utf-8") if n else ""
 
 
def decode_services(payload):
    services = []
    for u in decode_field(payload, _ADV_TYPE_UUID16_COMPLETE):
        services.append(bluetooth.UUID(struct.unpack("<h", u)[0]))
    for u in decode_field(payload, _ADV_TYPE_UUID32_COMPLETE):
        services.append(bluetooth.UUID(struct.unpack("<d", u)[0]))
    for u in decode_field(payload, _ADV_TYPE_UUID128_COMPLETE):
        services.append(bluetooth.UUID(u))
    return services
 
 
def demo():
    payload = advertising_payload(name="micropython", services=[bluetooth.UUID(0x181A), bluetooth.UUID("6E400001-B5A3-F393-E0A9-E50E24DCCA9E")],)
    print(payload)
    print(decode_name(payload))
    print(decode_services(payload))
 
 
if __name__ == "__main__":
    demo()