"""IOmeter reading."""

import json
from dataclasses import dataclass
from datetime import datetime
from typing import List


@dataclass
class Register:
    """Represents a meter register reading."""

    obis: str
    value: float
    unit: str


@dataclass
class MeterReading:
    """Represents a point-in-time reading."""

    time: datetime
    registers: List[Register]

    def get_register_by_obis(self, obis: str) -> Register | None:
        """Get register by OBIS code."""
        return next((reg for reg in self.registers if reg.obis == obis), None)


@dataclass
class Meter:
    """Represents the meter device."""

    number: str
    reading: MeterReading


@dataclass
class Reading:
    """Top level class representing a complete meter reading."""

    meter: Meter
    typename: str = "iometer.reading.v1"

    # OBIS code constants
    TOTAL_CONSUMPTION_OBIS = "01-00:01.08.00*ff"
    TOTAL_PRODUCTION_OBIS = "01-00:02.08.00*ff"
    CURRENT_POWER_OBIS = "01-00:10.07.00*ff"
    CURRENT_POWER_OBIS_ALT = "01-00:24.07.00*ff"

    @classmethod
    def from_json(cls, json_str: str) -> "Reading":
        """Create Reading instance from JSON string."""
        data = json.loads(json_str)

        # Create registers
        registers = [
            Register(obis=reg["obis"], value=reg["value"], unit=reg["unit"])
            for reg in data["meter"]["reading"]["registers"]
        ]

        # Create meter reading
        meter_reading = MeterReading(
            time=datetime.fromisoformat(
                data["meter"]["reading"]["time"].replace("Z", "+00:00")
            ),
            registers=registers,
        )

        # Create meter
        meter = Meter(number=data["meter"]["number"], reading=meter_reading)

        # Create reading
        return cls(meter=meter)

    def to_json(self) -> str:
        """Convert the status to JSON string"""
        return json.dumps(
            {
                "__typename": self.typename,
                "meter": {
                    "number": self.meter.number,
                    "reading": {
                        "time": self.meter.reading.time.strftime("%Y-%m-%dT%H:%M:%SZ"),
                        "registers": [
                            {
                                "obis": register.obis,
                                "value": register.value,
                                "unit": register.unit,
                            }
                            for register in self.meter.reading.registers
                        ],
                    },
                },
            }
        )

    def get_total_consumption(self) -> float | None:
        """Get total consumption in Wh."""
        register = self.meter.reading.get_register_by_obis(self.TOTAL_CONSUMPTION_OBIS)
        return register.value if register else None

    def get_total_production(self) -> float | None:
        """Get total production in Wh.

        Returns None if OBIS is not found, otherwise the value in Wh as float.
        """
        register = self.meter.reading.get_register_by_obis(self.TOTAL_PRODUCTION_OBIS)
        return register.value if register else None

    def get_current_power(self) -> float | None:
        """Get current power consumption in W.

        Prefer 10.07.00 OBIS, it is missing in some meters.
        These meters falsely report 24.07.00 OBIS as current power.

        Returns None if neither OBIS is found, otherwise the value in W as float.
        """
        register = self.meter.reading.get_register_by_obis(self.CURRENT_POWER_OBIS)
        if register:
            return register.value
        register_alt = self.meter.reading.get_register_by_obis(
            self.CURRENT_POWER_OBIS_ALT
        )
        return register_alt.value if register_alt else None

    def __str__(self) -> str:
        return self.to_json()