import logging
import os
import secrets
from datetime import timedelta
from dataclasses import dataclass

from django.conf import settings
from django.contrib.auth.hashers import check_password, make_password
from django.utils import timezone

from apps.accounts.models import OtpChannel, OtpPurpose, PhoneOTP

logger = logging.getLogger(__name__)


@dataclass
class OtpSendResult:
    request_id: str
    expires_at: str


class OtpRateLimitError(RuntimeError):
    def __init__(self, retry_after_seconds: int):
        super().__init__("Too many OTP requests. Try again later.")
        self.retry_after_seconds = retry_after_seconds


class OtpCooldownError(RuntimeError):
    def __init__(self, retry_after_seconds: int):
        super().__init__("Please wait before requesting another code.")
        self.retry_after_seconds = retry_after_seconds


class BaseOtpProvider:
    def send_sms(self, to_number: str, message: str) -> None:
        raise NotImplementedError

    def send_whatsapp(self, to_number: str, message: str) -> None:
        raise NotImplementedError


class ConsoleOtpProvider(BaseOtpProvider):
    def send_sms(self, to_number: str, message: str) -> None:
        logger.info("OTP SMS to %s: %s", to_number, message)

    def send_whatsapp(self, to_number: str, message: str) -> None:
        logger.info("OTP WhatsApp to %s: %s", to_number, message)


class TwilioOtpProvider(BaseOtpProvider):
    def __init__(self) -> None:
        self.account_sid = os.getenv("TWILIO_ACCOUNT_SID")
        self.auth_token = os.getenv("TWILIO_AUTH_TOKEN")
        self.from_number = os.getenv("TWILIO_FROM_NUMBER")
        self.whatsapp_from = os.getenv("TWILIO_WHATSAPP_FROM")

    def _assert_config(self) -> None:
        if not self.account_sid or not self.auth_token or not self.from_number:
            raise ValueError("Twilio credentials are not configured")

    def send_sms(self, to_number: str, message: str) -> None:
        self._assert_config()
        raise NotImplementedError("Twilio SMS adapter not implemented yet")

    def send_whatsapp(self, to_number: str, message: str) -> None:
        self._assert_config()
        if not self.whatsapp_from:
            raise ValueError("Twilio WhatsApp sender is not configured")
        raise NotImplementedError("Twilio WhatsApp adapter not implemented yet")


class UnifonicOtpProvider(BaseOtpProvider):
    def __init__(self) -> None:
        self.app_sid = os.getenv("UNIFONIC_APP_SID")
        self.sender_id = os.getenv("UNIFONIC_SENDER_ID")
        self.whatsapp_sender = os.getenv("UNIFONIC_WHATSAPP_SENDER")

    def _assert_config(self) -> None:
        if not self.app_sid or not self.sender_id:
            raise ValueError("Unifonic credentials are not configured")

    def send_sms(self, to_number: str, message: str) -> None:
        self._assert_config()
        raise NotImplementedError("Unifonic SMS adapter not implemented yet")

    def send_whatsapp(self, to_number: str, message: str) -> None:
        self._assert_config()
        if not self.whatsapp_sender:
            raise ValueError("Unifonic WhatsApp sender is not configured")
        raise NotImplementedError("Unifonic WhatsApp adapter not implemented yet")


PROVIDERS = {
    "console": ConsoleOtpProvider,
    "twilio": TwilioOtpProvider,
    "unifonic": UnifonicOtpProvider,
}


def get_provider() -> BaseOtpProvider:
    provider_key = settings.OTP_PROVIDER
    provider_cls = PROVIDERS.get(provider_key)
    if not provider_cls:
        raise ValueError(f"Unknown OTP provider: {provider_key}")
    return provider_cls()


def generate_code(length: int = 6) -> str:
    digits = "0123456789"
    return "".join(secrets.choice(digits) for _ in range(length))


def create_and_send_otp(phone_number: str, channel: str, purpose: str = OtpPurpose.AUTH) -> OtpSendResult:
    provider = get_provider()
    now = timezone.now()
    window_minutes = getattr(settings, "OTP_WINDOW_MINUTES", 15)
    max_per_window = getattr(settings, "OTP_MAX_PER_WINDOW", 5)
    cooldown_seconds = getattr(settings, "OTP_RESEND_COOLDOWN_SECONDS", 60)

    window_start = now - timedelta(minutes=window_minutes)
    recent_qs = PhoneOTP.objects.filter(phone_number=phone_number, created_at__gte=window_start)
    if recent_qs.count() >= max_per_window:
        oldest_recent = recent_qs.order_by("created_at").first()
        if oldest_recent:
            retry_after = int((oldest_recent.created_at + timedelta(minutes=window_minutes) - now).total_seconds())
        else:
            retry_after = cooldown_seconds
        raise OtpRateLimitError(retry_after_seconds=max(retry_after, cooldown_seconds))

    latest = (
        PhoneOTP.objects.filter(phone_number=phone_number, channel=channel)
        .order_by("-created_at")
        .first()
    )
    if latest and latest.verified_at is None:
        elapsed = (now - latest.created_at).total_seconds()
        if elapsed < cooldown_seconds:
            raise OtpCooldownError(retry_after_seconds=int(cooldown_seconds - elapsed))

    code = generate_code()
    otp = PhoneOTP.objects.create(
        phone_number=phone_number,
        channel=channel,
        purpose=purpose,
        provider=settings.OTP_PROVIDER,
        code_hash=make_password(code),
        expires_at=PhoneOTP.expiry_at(),
    )

    message = f"Your verification code is {code}. It expires in {settings.OTP_EXPIRY_MINUTES} minutes."
    if channel == OtpChannel.SMS:
        provider.send_sms(phone_number, message)
    elif channel == OtpChannel.WHATSAPP:
        provider.send_whatsapp(phone_number, message)
    else:
        raise ValueError("Unsupported OTP channel")

    return OtpSendResult(request_id=str(otp.id), expires_at=otp.expires_at.isoformat())


def verify_otp(otp: PhoneOTP, code: str) -> bool:
    if otp.verified_at or otp.is_expired():
        return False
    otp.attempt_count += 1
    if otp.attempt_count > otp.max_attempts:
        otp.save(update_fields=["attempt_count"])
        return False
    if not check_password(code, otp.code_hash):
        otp.save(update_fields=["attempt_count"])
        return False
    otp.verified_at = timezone.now()
    otp.save(update_fields=["verified_at", "attempt_count"])
    return True