import ipaddress

from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.ext.asyncio import AsyncSession

from app.config import get_settings
from app.database import get_postgres_session
from app.deps.dns_setup_auth import require_dns_setup_auth
from app.schemas import DnsSetupRequest, DnsSetupResponse
from app.services.domain_provisioning import (
    build_deployment_dns_records,
    get_domain_by_name,
    validate_domain,
)

router = APIRouter(prefix="/dns-setup", tags=["dns-setup"])


def validate_mail_server_ip(value: str) -> str:
    candidate = value.strip()
    try:
        return str(ipaddress.ip_address(candidate))
    except ValueError as error:
        raise ValueError("Enter a valid IPv4 or IPv6 address.") from error


@router.post("/preview", response_model=DnsSetupResponse)
async def preview_dns_setup(
    payload: DnsSetupRequest,
    _: None = Depends(require_dns_setup_auth),
    session: AsyncSession = Depends(get_postgres_session),
) -> DnsSetupResponse:
    settings = get_settings()
    try:
        domain_name = validate_domain(payload.domain)
        mail_server_ip = validate_mail_server_ip(payload.mail_server_ip)
    except ValueError as error:
        raise HTTPException(
            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
            detail=str(error),
        ) from error

    domain = await get_domain_by_name(session, domain_name)
    sections = build_deployment_dns_records(
        domain_name=domain_name,
        mail_server_ip=mail_server_ip,
        dkim_selector=settings.dkim_selector,
        dkim_public_key=domain.dkim_public_key if domain else None,
        app_public_host=settings.app_public_host,
    )
    mail_host = f"mail.{domain_name}"
    return DnsSetupResponse(
        domain=domain_name,
        mail_host=mail_host,
        app_public_host=settings.app_public_host,
        mail_server_ip=mail_server_ip,
        is_platform_domain=domain_name == settings.platform_domain,
        sections=sections,
        notes=_build_notes(
            domain_name,
            settings.app_public_host,
            mail_server_ip,
        ),
    )


def _build_notes(
    domain_name: str,
    app_public_host: str,
    mail_server_ip: str,
) -> list[str]:
    return [
        "Add these records in Namecheap Advanced DNS for the zone.",
        f"Point mail.{domain_name} and {app_public_host} A records to {mail_server_ip}.",
        f"Keep the root {domain_name} A record on your main website server if it hosts the marketing site.",
        f"Set {domain_name} MX to mail.{domain_name} (priority 10) so inbound mail reaches Postfix on this host.",
        "Postfix accepts inbound mail on :25 and delivers outbound mail for the app over the Docker network.",
        f"Users open the web UI at https://{app_public_host} (Caddy terminates TLS).",
        f"Ask your VPS provider to set reverse DNS (PTR) for {mail_server_ip} → mail.{domain_name}.",
        "SPF, DKIM, and DMARC authenticate outbound mail signed by Agmail (selector agmail).",
    ]