"""Egress-observation evaluator shared by NFT-SEC-02 and NFT-SEC-05 (AZ-437).

Both scenarios verify the same invariant: **no packets leave the e2e
Docker network** from the SUT container. NFT-SEC-02 reads the Docker
network-stats counter over a 5-min Derkachi replay. NFT-SEC-05 runs a
``nslookup`` probe inside the SUT container's network namespace and
checks that (a) the lookup fails and (b) no UDP-53 packets escape the
host's outbound interface during the probe.

The observation pattern is identical in both cases: take a *before*
counter snapshot, run the workload, take an *after* snapshot, assert
``after - before == 0`` for the relevant counter family. The runner is
responsible for the actual ``docker network inspect`` / ``ip -s link``
collection; this helper only performs the delta + verdict logic so the
scenario code stays tight and the verdict logic is unit-testable in
isolation.

DNS-resolution outcome categories follow the spec's wording (NXDOMAIN,
timeout, "no servers can be reached") + a generic "other failure" bucket
for resolver implementations that emit a different string but still
fail. A *success* outcome — i.e. an actual A record returned — is the
only failing case.

Public-boundary discipline: does NOT import any
``src/gps_denied_onboard`` symbol.
"""

from __future__ import annotations

import csv
from dataclasses import dataclass
from enum import Enum
from pathlib import Path


class DnsLookupOutcome(str, Enum):
    """The runner-classified outcome of a ``nslookup`` probe."""

    NXDOMAIN = "nxdomain"
    TIMEOUT = "timeout"
    NO_SERVERS = "no_servers_can_be_reached"
    OTHER_FAILURE = "other_failure"
    SUCCESS = "success"  # the only outcome that fails the AC


FAILING_DNS_OUTCOMES: frozenset[DnsLookupOutcome] = frozenset(
    {
        DnsLookupOutcome.NXDOMAIN,
        DnsLookupOutcome.TIMEOUT,
        DnsLookupOutcome.NO_SERVERS,
        DnsLookupOutcome.OTHER_FAILURE,
    }
)


@dataclass(frozen=True)
class EgressCounterSnapshot:
    """One snapshot of egress-byte / packet counters on the SUT-facing interface."""

    egress_packets_to_internal_net: int
    egress_packets_to_other_destinations: int
    udp53_egress_packets: int

    def __post_init__(self) -> None:
        for field_name in (
            "egress_packets_to_internal_net",
            "egress_packets_to_other_destinations",
            "udp53_egress_packets",
        ):
            value = getattr(self, field_name)
            if value < 0:
                raise ValueError(
                    f"egress counter {field_name!r} cannot be negative; got {value}"
                )


@dataclass(frozen=True)
class NoEgressReport:
    """NFT-SEC-02 verdict — zero packets to non-internal destinations during the window."""

    before: EgressCounterSnapshot
    after: EgressCounterSnapshot
    window_label: str  # e.g. "5min-derkachi-replay"

    @property
    def delta_other_destinations(self) -> int:
        return (
            self.after.egress_packets_to_other_destinations
            - self.before.egress_packets_to_other_destinations
        )

    @property
    def delta_internal(self) -> int:
        return (
            self.after.egress_packets_to_internal_net
            - self.before.egress_packets_to_internal_net
        )

    @property
    def passes(self) -> bool:
        return self.delta_other_destinations == 0


@dataclass(frozen=True)
class DnsBlackholeReport:
    """NFT-SEC-05 verdict — lookup fails AND no UDP-53 packets escape."""

    before: EgressCounterSnapshot
    after: EgressCounterSnapshot
    lookup_outcome: DnsLookupOutcome
    sidecar_healthy: bool

    @property
    def delta_udp53(self) -> int:
        return self.after.udp53_egress_packets - self.before.udp53_egress_packets

    @property
    def passes_lookup(self) -> bool:
        return self.lookup_outcome in FAILING_DNS_OUTCOMES

    @property
    def passes_udp_silence(self) -> bool:
        return self.delta_udp53 == 0

    @property
    def passes(self) -> bool:
        return (
            self.sidecar_healthy and self.passes_lookup and self.passes_udp_silence
        )


def evaluate_no_egress(
    before: EgressCounterSnapshot,
    after: EgressCounterSnapshot,
    *,
    window_label: str,
) -> NoEgressReport:
    """AC-1 verdict for NFT-SEC-02."""
    return NoEgressReport(before=before, after=after, window_label=window_label)


def evaluate_dns_blackhole(
    before: EgressCounterSnapshot,
    after: EgressCounterSnapshot,
    *,
    lookup_outcome: DnsLookupOutcome,
    sidecar_healthy: bool,
) -> DnsBlackholeReport:
    """AC-2 + AC-3 verdict for NFT-SEC-05."""
    return DnsBlackholeReport(
        before=before,
        after=after,
        lookup_outcome=lookup_outcome,
        sidecar_healthy=sidecar_healthy,
    )


def write_no_egress_csv_evidence(out_path: Path, report: NoEgressReport) -> Path:
    out_path.parent.mkdir(parents=True, exist_ok=True)
    with out_path.open("w", newline="") as fh:
        writer = csv.writer(fh)
        writer.writerow(
            [
                "window_label",
                "before_other",
                "after_other",
                "delta_other",
                "before_internal",
                "after_internal",
                "delta_internal",
                "passes",
            ]
        )
        writer.writerow(
            [
                report.window_label,
                report.before.egress_packets_to_other_destinations,
                report.after.egress_packets_to_other_destinations,
                report.delta_other_destinations,
                report.before.egress_packets_to_internal_net,
                report.after.egress_packets_to_internal_net,
                report.delta_internal,
                "true" if report.passes else "false",
            ]
        )
    return out_path


def write_dns_blackhole_csv_evidence(
    out_path: Path, report: DnsBlackholeReport
) -> Path:
    out_path.parent.mkdir(parents=True, exist_ok=True)
    with out_path.open("w", newline="") as fh:
        writer = csv.writer(fh)
        writer.writerow(
            [
                "sidecar_healthy",
                "lookup_outcome",
                "passes_lookup",
                "before_udp53",
                "after_udp53",
                "delta_udp53",
                "passes_udp_silence",
                "passes",
            ]
        )
        writer.writerow(
            [
                "true" if report.sidecar_healthy else "false",
                report.lookup_outcome.value,
                "true" if report.passes_lookup else "false",
                report.before.udp53_egress_packets,
                report.after.udp53_egress_packets,
                report.delta_udp53,
                "true" if report.passes_udp_silence else "false",
                "true" if report.passes else "false",
            ]
        )
    return out_path