#!/usr/bin/env python3
import argparse
import json
import struct
import sys
from datetime import datetime, timezone

from pymodbus.client import ModbusSerialClient


def decode_float_abcd(registers):
    if len(registers) != 2:
        raise ValueError(f"Expected 2 registers, got {len(registers)}")

    raw = registers[0].to_bytes(2, "big") + registers[1].to_bytes(2, "big")
    return struct.unpack(">f", raw)[0]


def read_float(client, address, device_id):
    rr = client.read_input_registers(
        address=address,
        count=2,
        device_id=device_id,
    )

    if rr.isError():
        raise RuntimeError(f"Modbus error at address {address}: {rr}")

    return decode_float_abcd(rr.registers)


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--port", default="/dev/ttyRS485")
    parser.add_argument("--slave", type=int, default=1)
    parser.add_argument("--baud", type=int, default=9600)
    parser.add_argument("--parity", default="N")
    parser.add_argument("--stopbits", type=int, default=1)
    parser.add_argument("--bytesize", type=int, default=8)
    parser.add_argument("--timeout", type=float, default=1.5)
    args = parser.parse_args()

    client = ModbusSerialClient(
        port=args.port,
        baudrate=args.baud,
        parity=args.parity,
        stopbits=args.stopbits,
        bytesize=args.bytesize,
        timeout=args.timeout,
    )

    if not client.connect():
        print("[ERROR] Cannot open Modbus serial port", file=sys.stderr)
        return 2

    try:
        voltage_v = read_float(client, 0, args.slave)
        current_a = read_float(client, 6, args.slave)
        active_power_w = read_float(client, 12, args.slave)
        frequency_hz = read_float(client, 70, args.slave)
        import_kwh = read_float(client, 72, args.slave)
        export_kwh = read_float(client, 74, args.slave)

        payload = {
            "ts": datetime.now(timezone.utc).isoformat(),
            "source": "revpi_sdm120m",
            "meter_model": "Eastron SDM120-M",
            "meter_id": f"modbus_{args.slave}",
            "port": args.port,
            "slave": args.slave,
            "baud": args.baud,
            "voltage_l1_v": round(voltage_v, 3),
            "current_l1_a": round(current_a, 3),
            "power_total_kw": round(active_power_w / 1000.0, 6),
            "frequency_hz": round(frequency_hz, 3),
            "import_kwh": round(import_kwh, 3),
            "export_kwh": round(export_kwh, 3),
            "comm_ok": True,
        }

        print(json.dumps(payload, indent=2, ensure_ascii=False))
        return 0

    except Exception as exc:
        error_payload = {
            "ts": datetime.now(timezone.utc).isoformat(),
            "source": "revpi_sdm120m",
            "meter_model": "Eastron SDM120-M",
            "meter_id": f"modbus_{args.slave}",
            "port": args.port,
            "slave": args.slave,
            "baud": args.baud,
            "comm_ok": False,
            "error_text": f"{type(exc).__name__}: {exc}",
        }
        print(json.dumps(error_payload, indent=2, ensure_ascii=False))
        return 1

    finally:
        client.close()


if __name__ == "__main__":
    sys.exit(main())