"""Tests for agent.error_classifier — structured API error classification."""

import pytest
from agent.error_classifier import (
    ClassifiedError,
    FailoverReason,
    classify_api_error,
    _extract_status_code,
    _extract_error_body,
    _extract_error_code,
    _classify_402,
)


# ── Helper: mock API errors ────────────────────────────────────────────

class MockAPIError(Exception):
    """Simulates an OpenAI SDK APIStatusError."""
    def __init__(self, message, status_code=None, body=None):
        super().__init__(message)
        self.status_code = status_code
        self.body = body or {}


class MockTransportError(Exception):
    """Simulates a transport-level error with a specific type name."""
    pass


class ReadTimeout(MockTransportError):
    pass


class ConnectError(MockTransportError):
    pass


class RemoteProtocolError(MockTransportError):
    pass


class ServerDisconnectedError(MockTransportError):
    pass


# ── Test: FailoverReason enum ──────────────────────────────────────────

class TestFailoverReason:
    def test_all_reasons_have_string_values(self):
        for reason in FailoverReason:
            assert isinstance(reason.value, str)

    def test_enum_members_exist(self):
        expected = {
            "auth", "auth_permanent", "billing", "rate_limit",
            "overloaded", "server_error", "timeout",
            "context_overflow", "payload_too_large",
            "model_not_found", "format_error",
            "thinking_signature", "long_context_tier", "unknown",
        }
        actual = {r.value for r in FailoverReason}
        assert expected == actual


# ── Test: ClassifiedError ──────────────────────────────────────────────

class TestClassifiedError:
    def test_is_auth_property(self):
        e1 = ClassifiedError(reason=FailoverReason.auth)
        assert e1.is_auth is True

        e2 = ClassifiedError(reason=FailoverReason.auth_permanent)
        assert e2.is_auth is True

        e3 = ClassifiedError(reason=FailoverReason.billing)
        assert e3.is_auth is False

    def test_defaults(self):
        e = ClassifiedError(reason=FailoverReason.unknown)
        assert e.retryable is True
        assert e.should_compress is False
        assert e.should_rotate_credential is False
        assert e.should_fallback is False
        assert e.status_code is None
        assert e.message == ""


# ── Test: Status code extraction ───────────────────────────────────────

class TestExtractStatusCode:
    def test_from_status_code_attr(self):
        e = MockAPIError("fail", status_code=429)
        assert _extract_status_code(e) == 429

    def test_from_status_attr(self):
        class ErrWithStatus(Exception):
            status = 503
        assert _extract_status_code(ErrWithStatus()) == 503

    def test_from_cause_chain(self):
        inner = MockAPIError("inner", status_code=401)
        outer = Exception("outer")
        outer.__cause__ = inner
        assert _extract_status_code(outer) == 401

    def test_none_when_missing(self):
        assert _extract_status_code(Exception("generic")) is None

    def test_rejects_non_http_status(self):
        """Integers outside 100-599 on .status should be ignored."""
        class ErrWeirdStatus(Exception):
            status = 42
        assert _extract_status_code(ErrWeirdStatus()) is None


# ── Test: Error body extraction ────────────────────────────────────────

class TestExtractErrorBody:
    def test_from_body_attr(self):
        e = MockAPIError("fail", body={"error": {"message": "bad"}})
        assert _extract_error_body(e) == {"error": {"message": "bad"}}

    def test_empty_when_no_body(self):
        assert _extract_error_body(Exception("generic")) == {}


# ── Test: Error code extraction ────────────────────────────────────────

class TestExtractErrorCode:
    def test_from_nested_error_code(self):
        body = {"error": {"code": "rate_limit_exceeded"}}
        assert _extract_error_code(body) == "rate_limit_exceeded"

    def test_from_nested_error_type(self):
        body = {"error": {"type": "invalid_request_error"}}
        assert _extract_error_code(body) == "invalid_request_error"

    def test_from_top_level_code(self):
        body = {"code": "model_not_found"}
        assert _extract_error_code(body) == "model_not_found"

    def test_empty_when_no_code(self):
        assert _extract_error_code({}) == ""
        assert _extract_error_code({"error": {"message": "oops"}}) == ""


# ── Test: 402 disambiguation ───────────────────────────────────────────

class TestClassify402:
    """The critical 402 billing vs rate_limit disambiguation."""

    def test_billing_exhaustion(self):
        """Plain 402 = billing."""
        result = _classify_402(
            "payment required",
            lambda reason, **kw: ClassifiedError(reason=reason, **kw),
        )
        assert result.reason == FailoverReason.billing
        assert result.should_rotate_credential is True

    def test_transient_usage_limit(self):
        """402 with 'usage limit' + 'try again' = rate limit, not billing."""
        result = _classify_402(
            "usage limit exceeded. try again in 5 minutes",
            lambda reason, **kw: ClassifiedError(reason=reason, **kw),
        )
        assert result.reason == FailoverReason.rate_limit
        assert result.should_rotate_credential is True

    def test_quota_with_retry(self):
        """402 with 'quota' + 'retry' = rate limit."""
        result = _classify_402(
            "quota exceeded, please retry after the window resets",
            lambda reason, **kw: ClassifiedError(reason=reason, **kw),
        )
        assert result.reason == FailoverReason.rate_limit

    def test_quota_without_retry(self):
        """402 with just 'quota' but no transient signal = billing."""
        result = _classify_402(
            "quota exceeded",
            lambda reason, **kw: ClassifiedError(reason=reason, **kw),
        )
        assert result.reason == FailoverReason.billing

    def test_insufficient_credits(self):
        result = _classify_402(
            "insufficient credits to complete request",
            lambda reason, **kw: ClassifiedError(reason=reason, **kw),
        )
        assert result.reason == FailoverReason.billing


# ── Test: Full classification pipeline ─────────────────────────────────

class TestClassifyApiError:
    """End-to-end classification tests."""

    # ── Auth errors ──

    def test_401_classified_as_auth(self):
        e = MockAPIError("Unauthorized", status_code=401)
        result = classify_api_error(e, provider="openrouter")
        assert result.reason == FailoverReason.auth
        assert result.should_rotate_credential is True
        # 401 is non-retryable on its own — credential rotation runs
        # before the retryability check in the agent loop.
        assert result.retryable is False
        assert result.should_fallback is True

    def test_403_classified_as_auth(self):
        e = MockAPIError("Forbidden", status_code=403)
        result = classify_api_error(e, provider="anthropic")
        assert result.reason == FailoverReason.auth
        assert result.should_fallback is True

    def test_403_key_limit_classified_as_billing(self):
        """OpenRouter 403 'key limit exceeded' is billing, not auth."""
        e = MockAPIError("Key limit exceeded for this key", status_code=403)
        result = classify_api_error(e, provider="openrouter")
        assert result.reason == FailoverReason.billing
        assert result.should_rotate_credential is True
        assert result.should_fallback is True

    def test_403_spending_limit_classified_as_billing(self):
        e = MockAPIError("spending limit reached", status_code=403)
        result = classify_api_error(e, provider="openrouter")
        assert result.reason == FailoverReason.billing

    # ── Billing ──

    def test_402_plain_billing(self):
        e = MockAPIError("Payment Required", status_code=402)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.billing
        assert result.retryable is False

    def test_402_transient_usage_limit(self):
        e = MockAPIError("usage limit exceeded, try again later", status_code=402)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.rate_limit
        assert result.retryable is True

    # ── Rate limit ──

    def test_429_rate_limit(self):
        e = MockAPIError("Too Many Requests", status_code=429)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.rate_limit
        assert result.should_fallback is True

    def test_alibaba_rate_increased_too_quickly(self):
        """Alibaba/DashScope returns a unique throttling message.

        Port from anomalyco/opencode#21355.
        """
        msg = (
            "Upstream error from Alibaba: Request rate increased too quickly. "
            "To ensure system stability, please adjust your client logic to "
            "scale requests more smoothly over time."
        )
        e = MockAPIError(msg, status_code=400)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.rate_limit
        assert result.retryable is True
        assert result.should_rotate_credential is True

    # ── Server errors ──

    def test_500_server_error(self):
        e = MockAPIError("Internal Server Error", status_code=500)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.server_error
        assert result.retryable is True

    def test_502_server_error(self):
        e = MockAPIError("Bad Gateway", status_code=502)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.server_error

    def test_503_overloaded(self):
        e = MockAPIError("Service Unavailable", status_code=503)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.overloaded

    def test_529_anthropic_overloaded(self):
        e = MockAPIError("Overloaded", status_code=529)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.overloaded

    # ── Model not found ──

    def test_404_model_not_found(self):
        e = MockAPIError("model not found", status_code=404)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.model_not_found
        assert result.should_fallback is True
        assert result.retryable is False

    def test_404_generic(self):
        e = MockAPIError("Not Found", status_code=404)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.model_not_found

    # ── Payload too large ──

    def test_413_payload_too_large(self):
        e = MockAPIError("Request Entity Too Large", status_code=413)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.payload_too_large
        assert result.should_compress is True

    # ── Context overflow ──

    def test_400_context_length(self):
        e = MockAPIError("context length exceeded: 250000 > 200000", status_code=400)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow
        assert result.should_compress is True

    def test_400_too_many_tokens(self):
        e = MockAPIError("This model's maximum context is 128000 tokens, too many tokens", status_code=400)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    def test_400_prompt_too_long(self):
        e = MockAPIError("prompt is too long: 300000 tokens > 200000 maximum", status_code=400)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    def test_400_generic_large_session(self):
        """Generic 400 with large session → context overflow heuristic."""
        e = MockAPIError(
            "Error",
            status_code=400,
            body={"error": {"message": "Error"}},
        )
        result = classify_api_error(e, approx_tokens=100000, context_length=200000)
        assert result.reason == FailoverReason.context_overflow

    def test_400_generic_small_session_is_format_error(self):
        """Generic 400 with small session → format error, not context overflow."""
        e = MockAPIError(
            "Error",
            status_code=400,
            body={"error": {"message": "Error"}},
        )
        result = classify_api_error(e, approx_tokens=1000, context_length=200000)
        assert result.reason == FailoverReason.format_error

    # ── Server disconnect + large session ──

    def test_disconnect_large_session_context_overflow(self):
        """Server disconnect with large session → context overflow."""
        e = Exception("server disconnected without sending complete message")
        result = classify_api_error(e, approx_tokens=150000, context_length=200000)
        assert result.reason == FailoverReason.context_overflow
        assert result.should_compress is True

    def test_disconnect_small_session_timeout(self):
        """Server disconnect with small session → timeout."""
        e = Exception("server disconnected without sending complete message")
        result = classify_api_error(e, approx_tokens=5000, context_length=200000)
        assert result.reason == FailoverReason.timeout

    # ── Provider-specific: Anthropic thinking signature ──

    def test_anthropic_thinking_signature(self):
        e = MockAPIError(
            "thinking block has invalid signature",
            status_code=400,
        )
        result = classify_api_error(e, provider="anthropic")
        assert result.reason == FailoverReason.thinking_signature
        assert result.retryable is True

    def test_non_anthropic_400_with_signature_not_classified_as_thinking(self):
        """400 with 'signature' but from non-Anthropic → format error."""
        e = MockAPIError("invalid signature", status_code=400)
        result = classify_api_error(e, provider="openrouter", approx_tokens=0)
        # Without "thinking" in the message, it shouldn't be thinking_signature
        assert result.reason != FailoverReason.thinking_signature

    # ── Provider-specific: Anthropic long-context tier ──

    def test_anthropic_long_context_tier(self):
        e = MockAPIError(
            "Extra usage is required for long context requests over 200k tokens",
            status_code=429,
        )
        result = classify_api_error(e, provider="anthropic", model="claude-sonnet-4")
        assert result.reason == FailoverReason.long_context_tier
        assert result.should_compress is True

    def test_normal_429_not_long_context(self):
        """Normal 429 without 'extra usage' + 'long context' → rate_limit."""
        e = MockAPIError("Too Many Requests", status_code=429)
        result = classify_api_error(e, provider="anthropic")
        assert result.reason == FailoverReason.rate_limit

    # ── Transport errors ──

    def test_read_timeout(self):
        e = ReadTimeout("Read timed out")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.timeout
        assert result.retryable is True

    def test_connect_error(self):
        e = ConnectError("Connection refused")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.timeout

    def test_connection_error_builtin(self):
        e = ConnectionError("Connection reset by peer")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.timeout

    def test_timeout_error_builtin(self):
        e = TimeoutError("timed out")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.timeout

    # ── Error code classification ──

    def test_error_code_resource_exhausted(self):
        e = MockAPIError(
            "Resource exhausted",
            body={"error": {"code": "resource_exhausted", "message": "Too many requests"}},
        )
        result = classify_api_error(e)
        assert result.reason == FailoverReason.rate_limit

    def test_error_code_model_not_found(self):
        e = MockAPIError(
            "Model not available",
            body={"error": {"code": "model_not_found"}},
        )
        result = classify_api_error(e)
        assert result.reason == FailoverReason.model_not_found

    def test_error_code_context_length_exceeded(self):
        e = MockAPIError(
            "Context too large",
            body={"error": {"code": "context_length_exceeded"}},
        )
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    # ── Message-only patterns (no status code) ──

    def test_message_billing_pattern(self):
        e = Exception("insufficient credits to complete this request")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.billing

    def test_message_rate_limit_pattern(self):
        e = Exception("rate limit reached for this model")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.rate_limit

    def test_message_auth_pattern(self):
        e = Exception("invalid api key provided")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.auth

    def test_message_model_not_found_pattern(self):
        e = Exception("gpt-99 is not a valid model")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.model_not_found

    def test_message_context_overflow_pattern(self):
        e = Exception("maximum context length exceeded")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    # ── Message-only usage limit disambiguation (no status code) ──

    def test_message_usage_limit_transient_is_rate_limit(self):
        """'usage limit' + 'try again' with no status code → rate_limit, not billing."""
        e = Exception("usage limit exceeded, try again in 5 minutes")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.rate_limit
        assert result.retryable is True
        assert result.should_rotate_credential is True
        assert result.should_fallback is True

    def test_message_usage_limit_no_retry_signal_is_billing(self):
        """'usage limit' with no transient signal and no status code → billing."""
        e = Exception("usage limit reached")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.billing
        assert result.retryable is False
        assert result.should_rotate_credential is True

    def test_message_quota_with_reset_window_is_rate_limit(self):
        """'quota' + 'resets at' with no status code → rate_limit."""
        e = Exception("quota exceeded, resets at midnight UTC")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.rate_limit
        assert result.retryable is True

    def test_message_limit_exceeded_with_wait_is_rate_limit(self):
        """'limit exceeded' + 'wait' with no status code → rate_limit."""
        e = Exception("key limit exceeded, please wait before retrying")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.rate_limit
        assert result.retryable is True

    # ── Unknown / fallback ──

    def test_generic_exception_is_unknown(self):
        e = Exception("something weird happened")
        result = classify_api_error(e)
        assert result.reason == FailoverReason.unknown
        assert result.retryable is True

    # ── Format error ──

    def test_400_descriptive_format_error(self):
        """400 with descriptive message (not context overflow) → format error."""
        e = MockAPIError(
            "Invalid value for parameter 'temperature': must be between 0 and 2",
            status_code=400,
            body={"error": {"message": "Invalid value for parameter 'temperature': must be between 0 and 2"}},
        )
        result = classify_api_error(e, approx_tokens=1000)
        assert result.reason == FailoverReason.format_error
        assert result.retryable is False

    def test_422_format_error(self):
        e = MockAPIError("Unprocessable Entity", status_code=422)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.format_error
        assert result.retryable is False

    def test_400_flat_body_descriptive_not_context_overflow(self):
        """Responses API flat body with descriptive error + large session → format error.

        The Codex Responses API returns errors in flat body format:
        {"message": "...", "type": "..."} without an "error" wrapper.
        A descriptive 400 must NOT be misclassified as context overflow
        just because the session is large.
        """
        e = MockAPIError(
            "Invalid 'input[index].name': string does not match pattern.",
            status_code=400,
            body={"message": "Invalid 'input[index].name': string does not match pattern.",
                  "type": "invalid_request_error"},
        )
        result = classify_api_error(e, approx_tokens=200000, context_length=400000, num_messages=500)
        assert result.reason == FailoverReason.format_error
        assert result.retryable is False

    def test_400_flat_body_generic_large_session_still_context_overflow(self):
        """Flat body with generic 'Error' message + large session → context overflow.

        Regression: the flat-body fallback must not break the existing heuristic
        for genuinely generic errors from providers that use flat bodies.
        """
        e = MockAPIError(
            "Error",
            status_code=400,
            body={"message": "Error"},
        )
        result = classify_api_error(e, approx_tokens=100000, context_length=200000)
        assert result.reason == FailoverReason.context_overflow

    # ── Peer closed + large session ──

    def test_peer_closed_large_session(self):
        e = Exception("peer closed connection without sending complete message")
        result = classify_api_error(e, approx_tokens=130000, context_length=200000)
        assert result.reason == FailoverReason.context_overflow

    # ── Chinese error messages ──

    def test_chinese_context_overflow(self):
        e = MockAPIError("超过最大长度限制", status_code=400)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    # ── vLLM / local inference server error messages ──

    def test_vllm_max_model_len_overflow(self):
        """vLLM's 'exceeds the max_model_len' error → context_overflow."""
        e = MockAPIError(
            "The engine prompt length 1327246 exceeds the max_model_len 131072. "
            "Please reduce prompt.",
            status_code=400,
        )
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    def test_vllm_prompt_length_exceeds(self):
        """vLLM prompt length error → context_overflow."""
        e = MockAPIError(
            "prompt length 200000 exceeds maximum model length 131072",
            status_code=400,
        )
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    def test_vllm_input_too_long(self):
        """vLLM 'input is too long' error → context_overflow."""
        e = MockAPIError("input is too long for model", status_code=400)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    def test_ollama_context_length_exceeded(self):
        """Ollama 'context length exceeded' error → context_overflow."""
        e = MockAPIError("context length exceeded", status_code=400)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    def test_llamacpp_slot_context(self):
        """llama.cpp / llama-server 'slot context' error → context_overflow."""
        e = MockAPIError(
            "slot context: 4096 tokens, prompt 8192 tokens — not enough space",
            status_code=400,
        )
        result = classify_api_error(e)
        assert result.reason == FailoverReason.context_overflow

    # ── Result metadata ──

    def test_provider_and_model_in_result(self):
        e = MockAPIError("fail", status_code=500)
        result = classify_api_error(e, provider="openrouter", model="gpt-5")
        assert result.provider == "openrouter"
        assert result.model == "gpt-5"
        assert result.status_code == 500

    def test_message_extracted(self):
        e = MockAPIError(
            "outer",
            status_code=500,
            body={"error": {"message": "Internal server error occurred"}},
        )
        result = classify_api_error(e)
        assert result.message == "Internal server error occurred"


# ── Test: Adversarial / edge cases (from live testing) ─────────────────

class TestAdversarialEdgeCases:
    """Edge cases discovered during live testing with real SDK objects."""

    def test_empty_exception_message(self):
        result = classify_api_error(Exception(""))
        assert result.reason == FailoverReason.unknown
        assert result.retryable is True

    def test_500_with_none_body(self):
        e = MockAPIError("fail", status_code=500, body=None)
        result = classify_api_error(e)
        assert result.reason == FailoverReason.server_error

    def test_non_dict_body(self):
        """Some providers return strings instead of JSON."""
        class StringBodyError(Exception):
            status_code = 400
            body = "just a string"
        result = classify_api_error(StringBodyError("bad"))
        assert result.reason == FailoverReason.format_error

    def test_list_body(self):
        class ListBodyError(Exception):
            status_code = 500
            body = [{"error": "something"}]
        result = classify_api_error(ListBodyError("server error"))
        assert result.reason == FailoverReason.server_error

    def test_circular_cause_chain(self):
        """Must not infinite-loop on circular __cause__."""
        e = Exception("circular")
        e.__cause__ = e
        result = classify_api_error(e)
        assert result.reason == FailoverReason.unknown

    def test_three_level_cause_chain(self):
        inner = MockAPIError("inner", status_code=429)
        middle = Exception("middle")
        middle.__cause__ = inner
        outer = RuntimeError("outer")
        outer.__cause__ = middle
        result = classify_api_error(outer)
        assert result.status_code == 429
        assert result.reason == FailoverReason.rate_limit

    def test_400_with_rate_limit_text(self):
        """Some providers send rate limits as 400 instead of 429."""
        e = MockAPIError(
            "rate limit policy",
            status_code=400,
            body={"error": {"message": "rate limit exceeded on this model"}},
        )
        result = classify_api_error(e, provider="openrouter")
        assert result.reason == FailoverReason.rate_limit

    def test_400_with_billing_text(self):
        """Some providers send billing errors as 400."""
        e = MockAPIError(
            "billing",
            status_code=400,
            body={"error": {"message": "insufficient credits for this request"}},
        )
        result = classify_api_error(e)
        assert result.reason == FailoverReason.billing

    def test_200_with_error_body(self):
        """200 status with error in body — should be unknown, not crash."""
        class WeirdSuccess(Exception):
            status_code = 200
            body = {"error": {"message": "loading"}}
        result = classify_api_error(WeirdSuccess("model loading"))
        assert result.reason == FailoverReason.unknown

    def test_ollama_context_size_exceeded(self):
        e = MockAPIError(
            "Error",
            status_code=400,
            body={"error": {"message": "context size has been exceeded"}},
        )
        result = classify_api_error(e, provider="ollama")
        assert result.reason == FailoverReason.context_overflow

    def test_connection_refused_error(self):
        e = ConnectionRefusedError("Connection refused: localhost:11434")
        result = classify_api_error(e, provider="ollama")
        assert result.reason == FailoverReason.timeout

    def test_body_message_enrichment(self):
        """Body message must be included in pattern matching even when
        str(error) doesn't contain it (OpenAI SDK APIStatusError)."""
        e = MockAPIError(
            "Usage limit",  # str(e) = "usage limit"
            status_code=402,
            body={"error": {"message": "Usage limit reached, try again in 5 minutes"}},
        )
        result = classify_api_error(e)
        # "try again" is only in body, not in str(e)
        assert result.reason == FailoverReason.rate_limit

    def test_disconnect_pattern_ordering(self):
        """Disconnect + large session must beat generic transport catch."""
        class FakeRemoteProtocol(Exception):
            pass
        # Type name isn't in _TRANSPORT_ERROR_TYPES but message has disconnect pattern
        e = Exception("peer closed connection without sending complete message")
        result = classify_api_error(e, approx_tokens=150000, context_length=200000)
        assert result.reason == FailoverReason.context_overflow
        assert result.should_compress is True

    def test_credit_balance_too_low(self):
        e = MockAPIError(
            "Credits low",
            status_code=402,
            body={"error": {"message": "Your credit balance is too low"}},
        )
        result = classify_api_error(e, provider="anthropic")
        assert result.reason == FailoverReason.billing

    def test_deepseek_402_chinese(self):
        """Chinese billing message should still match billing patterns."""
        # "余额不足" doesn't match English billing patterns, but 402 defaults to billing
        e = MockAPIError("余额不足", status_code=402)
        result = classify_api_error(e, provider="deepseek")
        assert result.reason == FailoverReason.billing

    def test_openrouter_wrapped_context_overflow_in_metadata_raw(self):
        """OpenRouter wraps provider errors in metadata.raw JSON string."""
        e = MockAPIError(
            "Provider returned error",
            status_code=400,
            body={
                "error": {
                    "message": "Provider returned error",
                    "code": 400,
                    "metadata": {
                        "raw": '{"error":{"message":"context length exceeded: 50000 > 32768"}}'
                    }
                }
            },
        )
        result = classify_api_error(e, provider="openrouter", approx_tokens=10000)
        assert result.reason == FailoverReason.context_overflow
        assert result.should_compress is True

    def test_openrouter_wrapped_rate_limit_in_metadata_raw(self):
        e = MockAPIError(
            "Provider returned error",
            status_code=400,
            body={
                "error": {
                    "message": "Provider returned error",
                    "metadata": {
                        "raw": '{"error":{"message":"Rate limit exceeded. Please retry after 30s."}}'
                    }
                }
            },
        )
        result = classify_api_error(e, provider="openrouter")
        assert result.reason == FailoverReason.rate_limit

    def test_thinking_signature_via_openrouter(self):
        """Thinking signature errors proxied through OpenRouter must be caught."""
        e = MockAPIError(
            "thinking block has invalid signature",
            status_code=400,
        )
        # provider is openrouter, not anthropic — old code missed this
        result = classify_api_error(e, provider="openrouter", model="anthropic/claude-sonnet-4")
        assert result.reason == FailoverReason.thinking_signature

    def test_generic_400_large_by_message_count(self):
        """Many small messages (>80) should trigger context overflow heuristic."""
        e = MockAPIError(
            "Error",
            status_code=400,
            body={"error": {"message": "Error"}},
        )
        # Low token count but high message count
        result = classify_api_error(
            e, approx_tokens=5000, context_length=200000, num_messages=100,
        )
        assert result.reason == FailoverReason.context_overflow

    def test_disconnect_large_by_message_count(self):
        """Server disconnect with 200+ messages should trigger context overflow."""
        e = Exception("server disconnected without sending complete message")
        result = classify_api_error(
            e, approx_tokens=5000, context_length=200000, num_messages=250,
        )
        assert result.reason == FailoverReason.context_overflow

    def test_openrouter_wrapped_model_not_found_in_metadata_raw(self):
        e = MockAPIError(
            "Provider returned error",
            status_code=400,
            body={
                "error": {
                    "message": "Provider returned error",
                    "metadata": {
                        "raw": '{"error":{"message":"The model gpt-99 does not exist"}}'
                    }
                }
            },
        )
        result = classify_api_error(e, provider="openrouter")
        assert result.reason == FailoverReason.model_not_found