//! Deterministic-vs-transient failure classification for compaction
//! LLM calls.
//!
//! The *policy* lives here, shared across harnesses; per-harness error types
//! and their wrapping (e.g. kigi's `SamplingError` →
//! `CompactFailure(acp::Error)`) stay in thin host wrappers that delegate the
//! status/message decisions to these functions.

/// Whether a compaction-call failure is worth retrying.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum FailureKind {
    /// Retrying the same payload will hit the same failure — the retry loop
    /// should bail without sleeping or re-issuing.
    Deterministic,
    /// Failure may resolve on retry (network blips, 5xx, rate limits).
    Transient,
}

impl FailureKind {
    pub fn is_deterministic(self) -> bool {
        matches!(self, Self::Deterministic)
    }
}

/// True when an error message indicates a context-window overflow.
///
/// Backends report this inconsistently with no stable error code, so the match
/// is on message text. Re-sending the same payload always fails, so callers
/// must not retry.
pub fn is_context_length_error(message: &str) -> bool {
    let m = message.to_ascii_lowercase();
    m.contains("too long for this model")
        || m.contains("prompt is too long")
        || m.contains("maximum prompt length")
        || m.contains("maximum context length")
        || m.contains("context_length_exceeded")
}

/// Classify an HTTP API failure (status + message) for the compaction retry
/// loop.
///
/// A context-length overflow message is deterministic regardless of status,
/// because backends sometimes dress it as a synthesized 500.
pub fn classify_http_status(status: u16, message: &str) -> FailureKind {
    if is_context_length_error(message)
        || ((400..500).contains(&status) && status != 408 && status != 429)
    {
        FailureKind::Deterministic
    } else {
        FailureKind::Transient
    }
}

/// Classify a provider-style stream error event (`ResponseError` /
/// `ResponseFailed.error`) for the compaction retry loop.
///
/// `code` is the structured `code` field on the event: typically a numeric HTTP
/// status as a string, but some providers send error-type strings like
/// `"invalid_request_error"` instead, and that marker can also arrive buried in
/// `message` alone. It always means a schema violation, which re-sending the
/// same payload cannot fix.
pub fn classify_stream_event_error(code: Option<&str>, message: &str) -> FailureKind {
    if matches!(code, Some("invalid_request_error")) || message.contains("invalid_request_error") {
        return FailureKind::Deterministic;
    }

    if let Some(status_code) = code.and_then(|c| c.parse::<u16>().ok())
        && (400..500).contains(&status_code)
        && status_code != 408
        && status_code != 429
    {
        return FailureKind::Deterministic;
    }

    // Size overflow arrives here with no parseable code (`code="none"`); the
    // message is the only signal that re-sending cannot help.
    if is_context_length_error(message) {
        return FailureKind::Deterministic;
    }

    FailureKind::Transient
}

#[cfg(test)]
mod tests {
    use super::*;

    fn det_status(status: u16) -> bool {
        classify_http_status(status, "test").is_deterministic()
    }

    #[test]
    fn http_4xx_is_deterministic_except_408_and_429() {
        assert!(det_status(400));
        assert!(det_status(401));
        assert!(det_status(403));
        assert!(det_status(404));
        assert!(det_status(413));
        assert!(!det_status(408));
        assert!(!det_status(429));
        assert!(!det_status(500));
        assert!(!det_status(502));
        assert!(!det_status(503));
    }

    #[test]
    fn http_500_with_context_length_message_is_deterministic() {
        // The sampler synthesizes status=500 from a streamed size overflow, so
        // status alone reads transient; the message must still short-circuit.
        assert!(
            classify_http_status(
                500,
                "API error (status 500 Internal Server Error): \
                 The prompt is too long for this model's context window."
            )
            .is_deterministic()
        );
    }

    #[test]
    fn stream_event_invalid_request_error_marker_is_deterministic() {
        assert!(
            classify_stream_event_error(
                Some("invalid_request_error"),
                "messages.27.content.1: ..."
            )
            .is_deterministic()
        );
        assert!(
            classify_stream_event_error(
                Some("400"),
                "Provider returned invalid_request_error: messages.X..."
            )
            .is_deterministic()
        );
        assert!(
            classify_stream_event_error(None, "messages.X.content.Y: invalid_request_error: ...")
                .is_deterministic()
        );
    }

    #[test]
    fn stream_event_numeric_codes_match_http_classification() {
        let det = |c: &str| classify_stream_event_error(Some(c), "msg").is_deterministic();
        assert!(det("400"));
        assert!(det("401"));
        assert!(det("403"));
        assert!(det("404"));
        assert!(!det("408"));
        assert!(!det("429"));
        assert!(!det("500"));
        assert!(!det("503"));
    }

    #[test]
    fn stream_event_unknown_code_defaults_to_transient() {
        assert!(!classify_stream_event_error(None, "msg").is_deterministic());
        assert!(!classify_stream_event_error(Some("error"), "msg").is_deterministic());
        assert!(!classify_stream_event_error(Some("overloaded_error"), "msg").is_deterministic());
    }

    #[test]
    fn stream_event_context_length_message_is_deterministic() {
        assert!(
            classify_stream_event_error(
                None,
                "The prompt is too long for this model's context window."
            )
            .is_deterministic()
        );
    }

    #[test]
    fn context_length_error_matches_known_messages() {
        for msg in [
            "The prompt is too long for this model's context window.",
            "prompt is too long: 250000 tokens > 200000 maximum",
            "exceeds the maximum prompt length",
            "This model's maximum context length is 128000 tokens",
            "error code: context_length_exceeded",
        ] {
            assert!(is_context_length_error(msg), "should match: {msg}");
        }
        for msg in [
            "internal server error",
            "rate limited",
            "connection reset by peer",
        ] {
            assert!(!is_context_length_error(msg), "should not match: {msg}");
        }
    }
}