# Collection of procedures related to ESLs
# 2018 furrtek - furrtek.org
# See LICENSE

def crc16(data):
    result = 0x8408
    poly = 0x8408

    for by in data:
        result ^= by
        for bi in range(0, 8):
            if (result & 1):
                result >>= 1
                result ^= poly
            else:
                result >>= 1

    return result

def terminate_frame(frame, pp16, repeats):
    crc = crc16(frame)
    if pp16:
    	frame[0:0] = [0x00, 0x00, 0x00, 0x40]	# Prepend special PP16 header
    frame.append(crc & 255)
    frame.append((crc // 256) & 255)
    frame.append(repeats & 255)             # This is used by the transmitter, it's not part of the transmitted data
    frame.append((repeats // 256) & 255)    # This is used by the transmitter, it's not part of the transmitted data

def make_raw_frame(protocol, PLID, cmd):
    frame = [protocol, PLID[3], PLID[2], PLID[1], PLID[0], cmd]
    return frame

def make_mcu_frame(PLID, cmd):
    frame = [0x85, PLID[3], PLID[2], PLID[1], PLID[0], 0x34, 0x00, 0x00, 0x00, cmd]
    return frame

def append_word(frame, value):
    frame.append(value // 256)
    frame.append(value & 255)
    
def get_plid(barcode):
    PLID = [0] * 4
    if len(barcode) != 17:
        return PLID
    id_value = int(barcode[2:7]) + (int(barcode[7:12]) << 16)
    PLID[0] = (id_value >> 8) & 0xFF
    PLID[1] = id_value & 0xFF
    PLID[2] = (id_value >> 24) & 0xFF
    PLID[3] = (id_value >> 16) & 0xFF
    return PLID

def make_ping_frame(PLID, pp16, repeats):
    frame = make_raw_frame(0x85, PLID, 0x17)	# 0x97 ?
    frame.append(0x01)
    frame.append(0x00)
    frame.append(0x00)
    frame.append(0x00)
    for b in range(0, 22):
        frame.append(0x01)
    terminate_frame(frame, pp16, repeats)
    return frame

def make_refresh_frame(PLID, pp16):
    frame = make_mcu_frame(PLID, 0x01)
    for b in range(0, 22):
        frame.append(0x00)
    terminate_frame(frame, pp16, 1)
    return frame