"""Tests for gateway.platforms.telegram_network – fallback transport layer.

Background
----------
api.telegram.org resolves to an IP (e.g. 149.154.166.110) that is unreachable
from some networks.  The workaround: route TCP through a different IP in the
same Telegram-owned 149.154.160.0/20 block (e.g. 149.154.167.220) while
keeping TLS SNI and the Host header as api.telegram.org so Telegram's edge
servers still accept the request.  This is the programmatic equivalent of:

    curl --resolve api.telegram.org:443:149.154.167.220 https://api.telegram.org/bot<token>/getMe

The TelegramFallbackTransport implements this: try the primary (DNS-resolved)
path first, and on ConnectTimeout / ConnectError fall through to configured
fallback IPs in order, then "stick" to whichever IP works.
"""

import httpx
import pytest

from gateway.platforms import telegram_network as tnet


# ---------------------------------------------------------------------------
# Helpers
# ---------------------------------------------------------------------------

class FakeTransport(httpx.AsyncBaseTransport):
    """Records calls and raises / returns based on a host→action mapping."""

    def __init__(self, calls, behavior):
        self.calls = calls
        self.behavior = behavior
        self.closed = False

    async def handle_async_request(self, request: httpx.Request) -> httpx.Response:
        self.calls.append(
            {
                "url_host": request.url.host,
                "host_header": request.headers.get("host"),
                "sni_hostname": request.extensions.get("sni_hostname"),
                "path": request.url.path,
            }
        )
        action = self.behavior.get(request.url.host, "ok")
        if action == "timeout":
            raise httpx.ConnectTimeout("timed out")
        if action == "connect_error":
            raise httpx.ConnectError("connect error")
        if isinstance(action, Exception):
            raise action
        return httpx.Response(200, request=request, text="ok")

    async def aclose(self) -> None:
        self.closed = True


def _fake_transport_factory(calls, behavior):
    """Returns a factory that creates FakeTransport instances."""
    instances = []

    def factory(**kwargs):
        t = FakeTransport(calls, behavior)
        instances.append(t)
        return t

    factory.instances = instances
    return factory


def _telegram_request(path="/botTOKEN/getMe"):
    return httpx.Request("GET", f"https://api.telegram.org{path}")


# ═══════════════════════════════════════════════════════════════════════════
# IP parsing & validation
# ═══════════════════════════════════════════════════════════════════════════

class TestParseFallbackIpEnv:
    def test_filters_invalid_and_ipv6(self, caplog):
        ips = tnet.parse_fallback_ip_env("149.154.167.220, bad, 2001:67c:4e8:f004::9,149.154.167.220")
        assert ips == ["149.154.167.220", "149.154.167.220"]
        assert "Ignoring invalid Telegram fallback IP" in caplog.text
        assert "Ignoring non-IPv4 Telegram fallback IP" in caplog.text

    def test_none_returns_empty(self):
        assert tnet.parse_fallback_ip_env(None) == []

    def test_empty_string_returns_empty(self):
        assert tnet.parse_fallback_ip_env("") == []

    def test_whitespace_only_returns_empty(self):
        assert tnet.parse_fallback_ip_env("  ,  , ") == []

    def test_single_valid_ip(self):
        assert tnet.parse_fallback_ip_env("149.154.167.220") == ["149.154.167.220"]

    def test_multiple_valid_ips(self):
        ips = tnet.parse_fallback_ip_env("149.154.167.220, 149.154.167.221")
        assert ips == ["149.154.167.220", "149.154.167.221"]

    def test_rejects_leading_zeros(self, caplog):
        """Leading zeros are ambiguous (octal?) so ipaddress rejects them."""
        ips = tnet.parse_fallback_ip_env("149.154.167.010")
        assert ips == []
        assert "Ignoring invalid" in caplog.text


class TestNormalizeFallbackIps:
    def test_deduplication_happens_at_transport_level(self):
        """_normalize does not dedup; TelegramFallbackTransport.__init__ does."""
        raw = ["149.154.167.220", "149.154.167.220"]
        assert tnet._normalize_fallback_ips(raw) == ["149.154.167.220", "149.154.167.220"]

    def test_empty_strings_skipped(self):
        assert tnet._normalize_fallback_ips(["", "  ", "149.154.167.220"]) == ["149.154.167.220"]


# ═══════════════════════════════════════════════════════════════════════════
# Request rewriting
# ═══════════════════════════════════════════════════════════════════════════

class TestRewriteRequestForIp:
    def test_preserves_host_and_sni(self):
        request = _telegram_request()
        rewritten = tnet._rewrite_request_for_ip(request, "149.154.167.220")

        assert rewritten.url.host == "149.154.167.220"
        assert rewritten.headers["host"] == "api.telegram.org"
        assert rewritten.extensions["sni_hostname"] == "api.telegram.org"
        assert rewritten.url.path == "/botTOKEN/getMe"

    def test_preserves_method_and_path(self):
        request = httpx.Request("POST", "https://api.telegram.org/botTOKEN/sendMessage")
        rewritten = tnet._rewrite_request_for_ip(request, "149.154.167.220")

        assert rewritten.method == "POST"
        assert rewritten.url.path == "/botTOKEN/sendMessage"


# ═══════════════════════════════════════════════════════════════════════════
# Fallback transport – core behavior
# ═══════════════════════════════════════════════════════════════════════════

class TestFallbackTransport:
    """Primary path fails → try fallback IPs → stick to whichever works."""

    @pytest.mark.asyncio
    async def test_falls_back_on_connect_timeout_and_becomes_sticky(self, monkeypatch):
        calls = []
        behavior = {"api.telegram.org": "timeout", "149.154.167.220": "ok"}
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport(["149.154.167.220"])
        resp = await transport.handle_async_request(_telegram_request())

        assert resp.status_code == 200
        assert transport._sticky_ip == "149.154.167.220"
        # First attempt was primary (api.telegram.org), second was fallback
        assert calls[0]["url_host"] == "api.telegram.org"
        assert calls[1]["url_host"] == "149.154.167.220"
        assert calls[1]["host_header"] == "api.telegram.org"
        assert calls[1]["sni_hostname"] == "api.telegram.org"

        # Second request goes straight to sticky IP
        calls.clear()
        resp2 = await transport.handle_async_request(_telegram_request())
        assert resp2.status_code == 200
        assert calls[0]["url_host"] == "149.154.167.220"

    @pytest.mark.asyncio
    async def test_falls_back_on_connect_error(self, monkeypatch):
        calls = []
        behavior = {"api.telegram.org": "connect_error", "149.154.167.220": "ok"}
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport(["149.154.167.220"])
        resp = await transport.handle_async_request(_telegram_request())

        assert resp.status_code == 200
        assert transport._sticky_ip == "149.154.167.220"

    @pytest.mark.asyncio
    async def test_does_not_fallback_on_non_connect_error(self, monkeypatch):
        """Errors like ReadTimeout are not connection issues — don't retry."""
        calls = []
        behavior = {"api.telegram.org": httpx.ReadTimeout("read timeout"), "149.154.167.220": "ok"}
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport(["149.154.167.220"])

        with pytest.raises(httpx.ReadTimeout):
            await transport.handle_async_request(_telegram_request())

        assert [c["url_host"] for c in calls] == ["api.telegram.org"]

    @pytest.mark.asyncio
    async def test_all_ips_fail_raises_last_error(self, monkeypatch):
        calls = []
        behavior = {"api.telegram.org": "timeout", "149.154.167.220": "timeout"}
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport(["149.154.167.220"])

        with pytest.raises(httpx.ConnectTimeout):
            await transport.handle_async_request(_telegram_request())

        assert [c["url_host"] for c in calls] == ["api.telegram.org", "149.154.167.220"]
        assert transport._sticky_ip is None

    @pytest.mark.asyncio
    async def test_multiple_fallback_ips_tried_in_order(self, monkeypatch):
        calls = []
        behavior = {
            "api.telegram.org": "timeout",
            "149.154.167.220": "timeout",
            "149.154.167.221": "ok",
        }
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport(["149.154.167.220", "149.154.167.221"])
        resp = await transport.handle_async_request(_telegram_request())

        assert resp.status_code == 200
        assert transport._sticky_ip == "149.154.167.221"
        assert [c["url_host"] for c in calls] == [
            "api.telegram.org",
            "149.154.167.220",
            "149.154.167.221",
        ]

    @pytest.mark.asyncio
    async def test_sticky_ip_tried_first_but_falls_through_if_stale(self, monkeypatch):
        """If the sticky IP stops working, the transport retries others."""
        calls = []
        behavior = {
            "api.telegram.org": "timeout",
            "149.154.167.220": "ok",
            "149.154.167.221": "ok",
        }
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport(["149.154.167.220", "149.154.167.221"])

        # First request: primary fails → .220 works → becomes sticky
        await transport.handle_async_request(_telegram_request())
        assert transport._sticky_ip == "149.154.167.220"

        # Now .220 goes bad too
        calls.clear()
        behavior["149.154.167.220"] = "timeout"

        resp = await transport.handle_async_request(_telegram_request())
        assert resp.status_code == 200
        # Tried sticky (.220) first, then fell through to .221
        assert [c["url_host"] for c in calls] == ["149.154.167.220", "149.154.167.221"]
        assert transport._sticky_ip == "149.154.167.221"


class TestFallbackTransportPassthrough:
    """Requests that don't need fallback behavior."""

    @pytest.mark.asyncio
    async def test_non_telegram_host_bypasses_fallback(self, monkeypatch):
        calls = []
        behavior = {}
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport(["149.154.167.220"])
        request = httpx.Request("GET", "https://example.com/path")
        resp = await transport.handle_async_request(request)

        assert resp.status_code == 200
        assert calls[0]["url_host"] == "example.com"
        assert transport._sticky_ip is None

    @pytest.mark.asyncio
    async def test_empty_fallback_list_uses_primary_only(self, monkeypatch):
        calls = []
        behavior = {}
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport([])
        resp = await transport.handle_async_request(_telegram_request())

        assert resp.status_code == 200
        assert calls[0]["url_host"] == "api.telegram.org"

    @pytest.mark.asyncio
    async def test_primary_succeeds_no_fallback_needed(self, monkeypatch):
        calls = []
        behavior = {"api.telegram.org": "ok"}
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", _fake_transport_factory(calls, behavior))

        transport = tnet.TelegramFallbackTransport(["149.154.167.220"])
        resp = await transport.handle_async_request(_telegram_request())

        assert resp.status_code == 200
        assert transport._sticky_ip is None
        assert len(calls) == 1


class TestFallbackTransportInit:
    def test_deduplicates_fallback_ips(self, monkeypatch):
        monkeypatch.setattr(
            tnet.httpx, "AsyncHTTPTransport", lambda **kw: FakeTransport([], {})
        )
        transport = tnet.TelegramFallbackTransport(["149.154.167.220", "149.154.167.220"])
        assert transport._fallback_ips == ["149.154.167.220"]

    def test_filters_invalid_ips_at_init(self, monkeypatch):
        monkeypatch.setattr(
            tnet.httpx, "AsyncHTTPTransport", lambda **kw: FakeTransport([], {})
        )
        transport = tnet.TelegramFallbackTransport(["149.154.167.220", "not-an-ip"])
        assert transport._fallback_ips == ["149.154.167.220"]

    def test_uses_proxy_env_for_primary_and_fallback_transports(self, monkeypatch):
        seen_kwargs = []

        def factory(**kwargs):
            seen_kwargs.append(kwargs.copy())
            return FakeTransport([], {})

        for key in ("HTTPS_PROXY", "HTTP_PROXY", "ALL_PROXY", "https_proxy", "http_proxy", "all_proxy", "TELEGRAM_PROXY", "NO_PROXY", "no_proxy"):
            monkeypatch.delenv(key, raising=False)
        monkeypatch.setenv("HTTPS_PROXY", "http://proxy.example:8080")
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", factory)

        transport = tnet.TelegramFallbackTransport(["149.154.167.220"])

        assert transport._fallback_ips == ["149.154.167.220"]
        assert len(seen_kwargs) == 2
        assert all(kwargs["proxy"] == "http://proxy.example:8080" for kwargs in seen_kwargs)

    def test_no_proxy_bypasses_fallback_ip_cidr(self, monkeypatch):
        seen_kwargs = []

        def factory(**kwargs):
            seen_kwargs.append(kwargs.copy())
            return FakeTransport([], {})

        for key in ("HTTPS_PROXY", "HTTP_PROXY", "ALL_PROXY", "https_proxy", "http_proxy", "all_proxy", "TELEGRAM_PROXY", "NO_PROXY", "no_proxy"):
            monkeypatch.delenv(key, raising=False)
        monkeypatch.setenv("HTTPS_PROXY", "http://proxy.example:8080")
        monkeypatch.setenv("NO_PROXY", "149.154.160.0/20")
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", factory)

        transport = tnet.TelegramFallbackTransport(["149.154.167.220"])

        assert transport._fallback_ips == ["149.154.167.220"]
        assert len(seen_kwargs) == 2
        assert all("proxy" not in kwargs for kwargs in seen_kwargs)


class TestFallbackTransportClose:
    @pytest.mark.asyncio
    async def test_aclose_closes_all_transports(self, monkeypatch):
        factory = _fake_transport_factory([], {})
        monkeypatch.setattr(tnet.httpx, "AsyncHTTPTransport", factory)

        transport = tnet.TelegramFallbackTransport(["149.154.167.220", "149.154.167.221"])
        await transport.aclose()

        # 1 primary + 2 fallback transports
        assert len(factory.instances) == 3
        assert all(t.closed for t in factory.instances)


# ═══════════════════════════════════════════════════════════════════════════
# Config layer – TELEGRAM_FALLBACK_IPS env → config.extra
# ═══════════════════════════════════════════════════════════════════════════

class TestConfigFallbackIps:
    def test_env_var_populates_config_extra(self, monkeypatch):
        from gateway.config import GatewayConfig, Platform, PlatformConfig, _apply_env_overrides

        monkeypatch.setenv("TELEGRAM_FALLBACK_IPS", "149.154.167.220,149.154.167.221")
        config = GatewayConfig(platforms={Platform.TELEGRAM: PlatformConfig(enabled=True, token="tok")})
        _apply_env_overrides(config)

        assert config.platforms[Platform.TELEGRAM].extra["fallback_ips"] == [
            "149.154.167.220", "149.154.167.221",
        ]

    def test_env_var_creates_platform_if_missing(self, monkeypatch):
        from gateway.config import GatewayConfig, Platform, _apply_env_overrides

        monkeypatch.setenv("TELEGRAM_FALLBACK_IPS", "149.154.167.220")
        config = GatewayConfig(platforms={})
        _apply_env_overrides(config)

        assert Platform.TELEGRAM in config.platforms
        assert config.platforms[Platform.TELEGRAM].extra["fallback_ips"] == ["149.154.167.220"]

    def test_env_var_strips_whitespace(self, monkeypatch):
        from gateway.config import GatewayConfig, Platform, PlatformConfig, _apply_env_overrides

        monkeypatch.setenv("TELEGRAM_FALLBACK_IPS", "  149.154.167.220 , 149.154.167.221  ")
        config = GatewayConfig(platforms={Platform.TELEGRAM: PlatformConfig(enabled=True, token="tok")})
        _apply_env_overrides(config)

        assert config.platforms[Platform.TELEGRAM].extra["fallback_ips"] == [
            "149.154.167.220", "149.154.167.221",
        ]

    def test_empty_env_var_does_not_populate(self, monkeypatch):
        from gateway.config import GatewayConfig, Platform, PlatformConfig, _apply_env_overrides

        monkeypatch.setenv("TELEGRAM_FALLBACK_IPS", "")
        config = GatewayConfig(platforms={Platform.TELEGRAM: PlatformConfig(enabled=True, token="tok")})
        _apply_env_overrides(config)

        assert "fallback_ips" not in config.platforms[Platform.TELEGRAM].extra


# ═══════════════════════════════════════════════════════════════════════════
# Adapter layer – _fallback_ips() reads config correctly
# ═══════════════════════════════════════════════════════════════════════════

class TestAdapterFallbackIps:
    def _make_adapter(self, extra=None):
        import sys
        from unittest.mock import MagicMock

        # Ensure telegram mock is in place
        if "telegram" not in sys.modules or not hasattr(sys.modules["telegram"], "__file__"):
            mod = MagicMock()
            mod.ext.ContextTypes.DEFAULT_TYPE = type(None)
            mod.constants.ParseMode.MARKDOWN_V2 = "MarkdownV2"
            mod.constants.ChatType.GROUP = "group"
            mod.constants.ChatType.SUPERGROUP = "supergroup"
            mod.constants.ChatType.CHANNEL = "channel"
            mod.constants.ChatType.PRIVATE = "private"
            for name in ("telegram", "telegram.ext", "telegram.constants", "telegram.request"):
                sys.modules.setdefault(name, mod)

        from gateway.config import PlatformConfig
        from gateway.platforms.telegram import TelegramAdapter

        config = PlatformConfig(enabled=True, token="test-token")
        if extra:
            config.extra.update(extra)
        return TelegramAdapter(config)

    def test_list_in_extra(self):
        adapter = self._make_adapter(extra={"fallback_ips": ["149.154.167.220"]})
        assert adapter._fallback_ips() == ["149.154.167.220"]

    def test_csv_string_in_extra(self):
        adapter = self._make_adapter(extra={"fallback_ips": "149.154.167.220,149.154.167.221"})
        assert adapter._fallback_ips() == ["149.154.167.220", "149.154.167.221"]

    def test_empty_extra(self):
        adapter = self._make_adapter()
        assert adapter._fallback_ips() == []

    def test_no_extra_attr(self):
        adapter = self._make_adapter()
        adapter.config.extra = None
        assert adapter._fallback_ips() == []

    def test_invalid_ips_filtered(self):
        adapter = self._make_adapter(extra={"fallback_ips": ["149.154.167.220", "not-valid"]})
        assert adapter._fallback_ips() == ["149.154.167.220"]


# ═══════════════════════════════════════════════════════════════════════════
# DoH auto-discovery
# ═══════════════════════════════════════════════════════════════════════════

def _doh_answer(*ips: str) -> dict:
    """Build a minimal DoH JSON response with A records."""
    return {"Answer": [{"type": 1, "data": ip} for ip in ips]}


class FakeDoHClient:
    """Mock httpx.AsyncClient for DoH queries."""

    def __init__(self, responses: dict):
        # responses: URL prefix → (status, json_body) | Exception
        self._responses = responses
        self.requests_made: list[dict] = []

    @staticmethod
    def _make_response(status, body, url):
        """Build an httpx.Response with a request attached (needed for raise_for_status)."""
        request = httpx.Request("GET", url)
        return httpx.Response(status, json=body, request=request)

    async def get(self, url, *, params=None, headers=None, **kwargs):
        self.requests_made.append({"url": url, "params": params, "headers": headers})
        for prefix, action in self._responses.items():
            if url.startswith(prefix):
                if isinstance(action, Exception):
                    raise action
                status, body = action
                return self._make_response(status, body, url)
        return self._make_response(200, {}, url)

    async def __aenter__(self):
        return self

    async def __aexit__(self, *args):
        pass


class TestDiscoverFallbackIps:
    """Tests for discover_fallback_ips() — DoH-based auto-discovery."""

    def _patch_doh(self, monkeypatch, responses, system_dns_ips=None):
        """Wire up fake DoH client and system DNS."""
        client = FakeDoHClient(responses)
        monkeypatch.setattr(tnet.httpx, "AsyncClient", lambda **kw: client)

        if system_dns_ips is not None:
            addrs = [(None, None, None, None, (ip, 443)) for ip in system_dns_ips]
            monkeypatch.setattr(tnet.socket, "getaddrinfo", lambda *a, **kw: addrs)
        else:
            def _fail(*a, **kw):
                raise OSError("dns failed")
            monkeypatch.setattr(tnet.socket, "getaddrinfo", _fail)
        return client

    @pytest.mark.asyncio
    async def test_google_and_cloudflare_ips_collected(self, monkeypatch):
        self._patch_doh(monkeypatch, {
            "https://dns.google": (200, _doh_answer("149.154.167.220")),
            "https://cloudflare-dns.com": (200, _doh_answer("149.154.167.221")),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert "149.154.167.220" in ips
        assert "149.154.167.221" in ips

    @pytest.mark.asyncio
    async def test_system_dns_ip_kept_when_doh_confirms(self, monkeypatch):
        """DoH-confirmed IPs are kept even when they match system DNS (#14520).

        The system-DNS IP is often the most reliable path; including it as a
        fallback lets the IP-rewrite retry recover from transient primary-path
        failures instead of jumping straight to the hardcoded seed list.
        """
        self._patch_doh(monkeypatch, {
            "https://dns.google": (200, _doh_answer("149.154.166.110", "149.154.167.220")),
            "https://cloudflare-dns.com": (200, _doh_answer("149.154.166.110")),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == ["149.154.166.110", "149.154.167.220"]

    @pytest.mark.asyncio
    async def test_doh_results_deduplicated(self, monkeypatch):
        self._patch_doh(monkeypatch, {
            "https://dns.google": (200, _doh_answer("149.154.167.220")),
            "https://cloudflare-dns.com": (200, _doh_answer("149.154.167.220")),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == ["149.154.167.220"]

    @pytest.mark.asyncio
    async def test_doh_timeout_falls_back_to_seed(self, monkeypatch):
        self._patch_doh(monkeypatch, {
            "https://dns.google": httpx.TimeoutException("timeout"),
            "https://cloudflare-dns.com": httpx.TimeoutException("timeout"),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == tnet._SEED_FALLBACK_IPS

    @pytest.mark.asyncio
    async def test_doh_connect_error_falls_back_to_seed(self, monkeypatch):
        self._patch_doh(monkeypatch, {
            "https://dns.google": httpx.ConnectError("refused"),
            "https://cloudflare-dns.com": httpx.ConnectError("refused"),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == tnet._SEED_FALLBACK_IPS

    @pytest.mark.asyncio
    async def test_doh_malformed_json_falls_back_to_seed(self, monkeypatch):
        self._patch_doh(monkeypatch, {
            "https://dns.google": (200, {"Status": 0}),  # no Answer key
            "https://cloudflare-dns.com": (200, {"garbage": True}),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == tnet._SEED_FALLBACK_IPS

    @pytest.mark.asyncio
    async def test_one_provider_fails_other_succeeds(self, monkeypatch):
        self._patch_doh(monkeypatch, {
            "https://dns.google": httpx.TimeoutException("timeout"),
            "https://cloudflare-dns.com": (200, _doh_answer("149.154.167.220")),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == ["149.154.167.220"]

    @pytest.mark.asyncio
    async def test_system_dns_failure_keeps_all_doh_ips(self, monkeypatch):
        """If system DNS fails, nothing gets excluded — all DoH IPs kept."""
        self._patch_doh(monkeypatch, {
            "https://dns.google": (200, _doh_answer("149.154.166.110", "149.154.167.220")),
            "https://cloudflare-dns.com": (200, _doh_answer()),
        }, system_dns_ips=None)  # triggers OSError

        ips = await tnet.discover_fallback_ips()
        assert "149.154.166.110" in ips
        assert "149.154.167.220" in ips

    @pytest.mark.asyncio
    async def test_all_doh_ips_same_as_system_dns_kept(self, monkeypatch):
        """DoH agrees with system DNS — keep that IP instead of seed list (#14520).

        Previous behavior fell through to ``_SEED_FALLBACK_IPS`` here, but the
        seed addresses are not routable on every network.  When DoH confirms
        the system IP, that IP is the best candidate we have and should be
        used as the fallback target.
        """
        self._patch_doh(monkeypatch, {
            "https://dns.google": (200, _doh_answer("149.154.166.110")),
            "https://cloudflare-dns.com": (200, _doh_answer("149.154.166.110")),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == ["149.154.166.110"]

    @pytest.mark.asyncio
    async def test_cloudflare_gets_accept_header(self, monkeypatch):
        client = self._patch_doh(monkeypatch, {
            "https://dns.google": (200, _doh_answer("149.154.167.220")),
            "https://cloudflare-dns.com": (200, _doh_answer("149.154.167.221")),
        }, system_dns_ips=["149.154.166.110"])

        await tnet.discover_fallback_ips()

        cf_reqs = [r for r in client.requests_made if "cloudflare" in r["url"]]
        assert cf_reqs
        assert cf_reqs[0]["headers"]["Accept"] == "application/dns-json"

    @pytest.mark.asyncio
    async def test_non_a_records_ignored(self, monkeypatch):
        """AAAA records (type 28) and CNAME (type 5) should be skipped."""
        answer = {
            "Answer": [
                {"type": 5, "data": "telegram.org"},  # CNAME
                {"type": 28, "data": "2001:67c:4e8:f004::9"},  # AAAA
                {"type": 1, "data": "149.154.167.220"},  # A ✓
            ]
        }
        self._patch_doh(monkeypatch, {
            "https://dns.google": (200, answer),
            "https://cloudflare-dns.com": (200, _doh_answer()),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == ["149.154.167.220"]

    @pytest.mark.asyncio
    async def test_invalid_ip_in_doh_response_skipped(self, monkeypatch):
        answer = {"Answer": [
            {"type": 1, "data": "not-an-ip"},
            {"type": 1, "data": "149.154.167.220"},
        ]}
        self._patch_doh(monkeypatch, {
            "https://dns.google": (200, answer),
            "https://cloudflare-dns.com": (200, _doh_answer()),
        }, system_dns_ips=["149.154.166.110"])

        ips = await tnet.discover_fallback_ips()
        assert ips == ["149.154.167.220"]