# /config/pyscript/ess_set_power.py
import struct 

@service
def ess_set_power(hub="openEMS", slave=1, power_w=0.0):
    """
    706 = SetActivePowerEquals (float32 BE)
    Laden = negativ, Entladen = positiv.
    """

    ADDR_EQUALS = 706

    def float_to_regs_be(val: float):
        b = struct.pack(">f", float(val))  # Big Endian
        return [(b[0] << 8) | b[1], (b[2] << 8) | b[3]]  # [hi, lo]

    try:
        p = float(power_w)
    except Exception:
        p = 0.0

    regs = float_to_regs_be(p)
    log.info(f"OpenEMS ESS Ziel: {p:.1f} W -> {ADDR_EQUALS} -> {regs}")

    service.call("modbus", "write_register", hub=hub, slave=slave, address=ADDR_EQUALS, value=regs)