from fastapi import APIRouter, Depends, HTTPException
from sqlalchemy.orm import Session

from app.api.credentials import SNMP_CREDENTIAL_TYPE
from app.auth.dependencies import require_role
from app.core.secrets import decrypt_secret
from app.db.session import get_db
from app.models import Credential, User
from app.schemas.core import (
    SnmpDiscoveredInterfaceRead,
    SnmpDiscoveryItemRead,
    SnmpDiscoveryRead,
    SnmpDiscoveryRequest,
)
from app.services.snmp import DiscoveredSnmpDevice, SnmpCredential, SnmpDiscoveryError, discover_snmp_device

router = APIRouter(prefix="/discovery", tags=["discovery"])


@router.post("/snmp", response_model=SnmpDiscoveryRead)
def discover_snmp(
    payload: SnmpDiscoveryRequest,
    _: User = Depends(require_role("admin")),
    db: Session = Depends(get_db),
) -> SnmpDiscoveryRead:
    profile = db.get(Credential, payload.credential_profile_id)
    if profile is None or profile.credential_type != SNMP_CREDENTIAL_TYPE:
        raise HTTPException(status_code=404, detail="SNMP credential profile not found")

    extra = dict(profile.extra or {})
    version = str(extra.get("version") or "2c")
    if version != "2c":
        raise HTTPException(status_code=400, detail="SNMP discovery currently supports SNMPv2c profiles")

    community = decrypt_secret(profile.encrypted_secret)
    if not community:
        raise HTTPException(status_code=400, detail="SNMP credential profile has no usable community string")

    credential = SnmpCredential(
        community=community,
        port=int(extra.get("port") or 161),
        timeout_seconds=int(extra.get("timeout_seconds") or 5),
        retries=int(extra.get("retries") or 1),
    )
    try:
        discovered = discover_snmp_device(payload.host, credential)
    except SnmpDiscoveryError as exc:
        raise HTTPException(status_code=502, detail="SNMP discovery failed") from exc

    return _discovery_to_read(payload.credential_profile_id, discovered)


def _discovery_to_read(credential_profile_id: int, discovered: DiscoveredSnmpDevice) -> SnmpDiscoveryRead:
    interfaces = [
        SnmpDiscoveredInterfaceRead(
            index=interface.index,
            name=interface.name,
            description=interface.description,
            admin_status=interface.admin_status,
            oper_status=interface.oper_status,
            speed_bps=interface.speed_bps,
        )
        for interface in discovered.interfaces
    ]
    return SnmpDiscoveryRead(
        host=discovered.host,
        credential_profile_id=credential_profile_id,
        profile_key=discovered.profile_key,
        profile_name=discovered.profile_name,
        capabilities=discovered.capabilities,
        device_name=discovered.device_name,
        description=discovered.description,
        uptime_seconds=discovered.uptime_seconds,
        interfaces=interfaces,
        monitorable_items=_monitorable_items(discovered),
    )


def _monitorable_items(discovered: DiscoveredSnmpDevice) -> list[SnmpDiscoveryItemRead]:
    items = []
    if discovered.uptime_seconds is not None:
        items.append(
            SnmpDiscoveryItemRead(
                item_id="device.uptime",
                item_type="device_uptime",
                group="Device Health",
                label="Device uptime",
                unit="seconds",
            )
        )
    items.extend(
        SnmpDiscoveryItemRead(
            item_id=item.item_id,
            item_type=item.item_type,
            group=item.group,
            label=item.label,
            unit=item.unit,
        )
        for item in discovered.health_items
    )
    for interface in discovered.interfaces:
        group = f"Interface {interface.name}"
        item_prefix = f"interface.{interface.index}"
        items.extend(
            [
                SnmpDiscoveryItemRead(
                    item_id=f"{item_prefix}.status",
                    item_type="interface_status",
                    group=group,
                    label=f"{interface.name} status",
                ),
                SnmpDiscoveryItemRead(
                    item_id=f"{item_prefix}.traffic",
                    item_type="interface_traffic",
                    group=group,
                    label=f"{interface.name} traffic",
                    unit="bps",
                ),
                SnmpDiscoveryItemRead(
                    item_id=f"{item_prefix}.errors",
                    item_type="interface_errors",
                    group=group,
                    label=f"{interface.name} errors and discards",
                    unit="count",
                ),
            ]
        )
    return items