turnstone/app/services/diagnose/hypothesizer.py

"""Stage 3: Root-Cause Hypothesizer — LLM + RAG context."""
from __future__ import annotations

import json
import logging
from uuid import uuid4

from app.context.retriever import RetrievedContext
from app.services.diagnose._llm_client import call_llm, extract_first_json_array, strip_json_fences
from app.services.diagnose.models import (
    ClassifiedTimeline,
    EventCluster,
    Hypothesis,
    SeverityLabel,
)

logger = logging.getLogger(__name__)

_VALID_SEVERITIES: frozenset[str] = frozenset({"CRITICAL", "ERROR", "WARN", "INFO", "DEBUG"})

_SYSTEM_PROMPT = (
    "You are a Linux sysadmin log analyst. Analyze the following clustered log timeline "
    "and generate 2-4 root cause hypotheses as a JSON array.\n\n"
    "Each hypothesis must follow this exact JSON schema:\n"
    '{"title": str (≤80 chars), "description": str (2-4 sentences), '
    '"confidence": float (0.0-1.0), "severity": str (one of: CRITICAL, ERROR, WARN, INFO), '
    '"supporting_clusters": [str list of cluster IDs]}\n\n'
    "Return ONLY a valid JSON array. No prose, no markdown, no explanation outside the JSON."
)


def _coerce_float(val: object, default: float) -> float:
    """Safely coerce LLM output to float, returning default on failure."""
    try:
        return float(val)  # type: ignore[arg-type]
    except (TypeError, ValueError):
        return default


def _validate_severity(s: str) -> SeverityLabel:
    """Map a raw severity string to a valid SeverityLabel, defaulting to ERROR."""
    upper = s.upper()
    if upper == "WARNING":
        return "WARN"
    return upper if upper in _VALID_SEVERITIES else "ERROR"  # type: ignore[return-value]


def _cluster_summary(cluster: EventCluster, severity: str) -> str:
    """Build a condensed single-line summary of a cluster for the prompt."""
    sources = ", ".join(list(cluster.source_ids)[:3])
    patterns = ", ".join(list(cluster.pattern_tags)[:5])
    text_preview = cluster.representative_text[:200]
    summary = (
        f"[{severity}] {cluster.start_iso or 'unknown'} "
        f"({sources}) — {text_preview}"
    )
    if patterns:
        summary += f" [patterns: {patterns}]"
    return summary


class RootCauseHypothesizer:
    """Generate ranked root-cause hypotheses from a classified log timeline."""

    def __init__(self, max_hypotheses: int = 4) -> None:
        self._max_hypotheses = max_hypotheses

    def hypothesize(
        self,
        classified: ClassifiedTimeline,
        ctx: RetrievedContext,
        query: str,
        llm_url: str | None = None,
        llm_model: str | None = None,
        llm_api_key: str | None = None,
    ) -> list[Hypothesis]:
        """Generate hypotheses from a classified timeline and RAG context.

        Returns an empty list when no LLM is configured or there are no
        clusters to analyse.
        """
        if not llm_url or not llm_model:
            return []

        clusters = classified.timeline.clusters
        if not clusters:
            return []

        cluster_lines = [
            _cluster_summary(c, classified.cluster_severities.get(c.cluster_id, c.severity))
            for c in clusters
        ]
        cluster_block = "\n".join(cluster_lines)

        context_parts: list[str] = []
        for chunk in ctx.chunks[:5]:
            filename = chunk.get("filename", "unknown")
            text = chunk.get("text", "")[:300]
            context_parts.append(f"[{filename}] {text}")
        context_block = "\n".join(context_parts) if context_parts else "(none)"

        user_message = (
            f"Query: {query}\n\n"
            f"Context from runbooks and known patterns:\n{context_block}\n\n"
            f"Log timeline (clustered, {len(clusters)} clusters):\n{cluster_block}\n\n"
            f"Generate up to {self._max_hypotheses} hypotheses. Return JSON array only."
        )

        messages = [
            {"role": "system", "content": _SYSTEM_PROMPT},
            {"role": "user", "content": user_message},
        ]

        raw_response = call_llm(
            llm_url=llm_url,
            llm_model=llm_model,
            llm_api_key=llm_api_key,
            messages=messages,
        )
        if raw_response is None:
            return []

        return self._parse_response(raw_response)

    def _parse_response(self, raw: str) -> list[Hypothesis]:
        """Parse the LLM JSON response into a list of Hypothesis objects.

        Strips markdown code fences before parsing — some LLMs wrap JSON in
        triple-backtick fences despite being instructed not to.
        """
        try:
            # extract_first_json_array handles reasoning models that emit valid
            # JSON then repeat it inside a markdown fence block.
            data = json.loads(extract_first_json_array(strip_json_fences(raw)))
        except json.JSONDecodeError:
            logger.warning(
                "Hypothesizer: invalid JSON from LLM (truncated): %.120s", raw
            )
            return []

        if not isinstance(data, list):
            logger.warning(
                "Hypothesizer: expected JSON array, got %s", type(data).__name__
            )
            return []

        hypotheses: list[Hypothesis] = []
        for item in data[: self._max_hypotheses]:
            if not isinstance(item, dict):
                continue
            severity_raw = item.get("severity", "ERROR")
            severity = _validate_severity(str(severity_raw))
            hypothesis = Hypothesis(
                hypothesis_id=str(uuid4()),
                title=str(item.get("title", "Unknown"))[:80],
                description=str(item.get("description", "")),
                confidence=_coerce_float(item.get("confidence"), 0.5),
                supporting_cluster_ids=tuple(
                    str(x) for x in (item.get("supporting_clusters") or [])
                ),
                runbook_refs=(),
                severity=severity,
            )
            hypotheses.append(hypothesis)

        return hypotheses