"""Session digest — Tier 1 -> Tier 2 promotion (design §3, §4; T04).

Compresses a session's events into a small, durable digest: outcome heuristic,
cost totals, tool histogram, and counts of error/retry/test/edit/human markers,
plus a few key snippets. Writing the digest sets ``analyzed_at``, which is what
makes a session evictable under budget-based retention (design §5).

Signal extraction beyond this digest is intentionally out of scope here — it
belongs to the Detect phase (PRD §6.2).
"""

from __future__ import annotations

import collections
import json
import re
from typing import Any

from .schema import Session, SessionEvent

# Substrings in tool_result bodies / summaries that suggest a failure.
_FAIL_HINTS = ("error", "failed", "exception", "traceback", "fatal", "non-zero")
# Substrings suggesting a clean test pass.
_PASS_HINTS = ("passed", "0 failed", "ok", "success")

# A line that is numbered source content from a Read result (`cat -n` style),
# e.g. "229\t    raise InfospaceError(" — code text, never a runtime error.
_NUMBERED_LINE_RE = re.compile(r"^\s*\d+\t")
# Top-level keys that mark a JSON tool-result as an actual error (vs. success).
_JSON_ERROR_KEYS = ("error", "errors", "detail")

# Normalization patterns so the same error collapses to one fingerprint
# regardless of paths / ids / counts (WP-0006 T01).
_UUID_RE = re.compile(r"\b[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\b", re.I)
_HEXADDR_RE = re.compile(r"\b0x[0-9a-f]+\b", re.I)
_PATH_RE = re.compile(r"(?:/[\w.\-]+)+/?|[A-Za-z]:\\[\w.\\\-]+")
_NUM_RE = re.compile(r"\b\d+\b")
_WS_RE = re.compile(r"\s+")
_ERR_SAMPLE_MAX = 200
_ERR_FP_MAX = 160


def infer_outcome(events: list[SessionEvent], blobs: dict[str, str] | None = None) -> str:
    """Heuristic outcome label across flavors (design OQ2).

    - ``abandoned`` if the session has no assistant output at all.
    - ``fail`` if the last substantive signal is an error / failing test.
    - ``success`` if it ends on assistant output or a passing test.
    - ``unknown`` otherwise.
    """
    blobs = blobs or {}
    assistant = [e for e in events if e.kind == "assistant_msg"]
    if not assistant:
        return "abandoned"

    # Look at error and test signals; weight the latest ones.
    last_fail = _last_index(events, lambda e: e.kind == "error")
    last_test = _last_index(events, lambda e: e.kind == "test_run")
    last_completion = _last_index(events, lambda e: e.kind in ("completion", "assistant_msg"))

    test_passed = None
    if last_test is not None:
        # inspect the nearest following tool_result body for pass/fail hints
        body = _nearby_result_body(events, last_test, blobs)
        if body:
            low = body.lower()
            if any(h in low for h in _FAIL_HINTS):
                test_passed = False
            elif any(h in low for h in _PASS_HINTS):
                test_passed = True

    if test_passed is False and (last_test or 0) >= (last_completion or 0):
        return "fail"
    if last_fail is not None and last_completion is not None and last_fail > last_completion:
        return "fail"
    if test_passed is True:
        return "success"
    if last_completion is not None:
        return "success"
    return "unknown"


def build_digest(session: Session, events: list[SessionEvent],
                 blobs: dict[str, str] | None = None) -> dict[str, Any]:
    """Produce the compact Tier 2 digest dict for a session."""
    blobs = blobs or {}
    kind_counts = collections.Counter(e.kind for e in events)
    tool_hist = collections.Counter(e.tool for e in events if e.tool)
    retries = kind_counts.get("retry", 0)
    outcome = infer_outcome(events, blobs)

    return {
        "session_uid": session.session_uid,
        "flavor": session.flavor,
        "repo": session.repo,
        "domain": session.domain,
        "model": session.model,
        "started_at": session.started_at,
        "ended_at": session.ended_at,
        "outcome": outcome,
        "cost": {
            "input_tokens": session.cost.input_tokens,
            "output_tokens": session.cost.output_tokens,
            "cache_tokens": session.cost.cache_tokens,
            "wall_clock_s": session.cost.wall_clock_s,
            "turns": session.cost.turns,
            "retries": retries,
        },
        "event_count": len(events),
        "kind_counts": dict(kind_counts),
        "tool_histogram": dict(tool_hist),
        "markers": {
            "errors": kind_counts.get("error", 0),
            "retries": retries,
            "test_runs": kind_counts.get("test_run", 0),
            "edits": kind_counts.get("edit", 0),
            "human_interventions": kind_counts.get("human_intervention", 0),
        },
        "first_prompt": _first_prompt(events, blobs),
        "last_assistant": _last_assistant(events, blobs),
        "error_snippets": _error_snippets(events, blobs),
        "schema_version": session.schema_version,
    }


def analyze(store, session_uid: str) -> dict[str, Any]:
    """Read a session from the store, write its digest, return the digest."""
    session = store.get_session(session_uid)
    if session is None:
        raise KeyError(session_uid)
    events = store.get_events(session_uid)
    blobs = {e.payload_ref: _read_blob(store, e.payload_ref)
             for e in events if e.payload_ref}
    digest = build_digest(session, events, blobs)
    store.write_digest(session_uid, digest)
    return digest


# ---- helpers ---------------------------------------------------------------

def _last_index(events, pred):
    idx = None
    for i, e in enumerate(events):
        if pred(e):
            idx = i
    return idx


def _nearby_result_body(events, idx, blobs):
    for e in events[idx + 1: idx + 4]:
        if e.kind == "tool_result" and e.payload_ref in blobs:
            return blobs[e.payload_ref]
    return None


def _first_prompt(events, blobs):
    for e in events:
        if e.kind == "user_msg":
            return (blobs.get(e.payload_ref) or e.summary or "")[:280]
    return None


def _last_assistant(events, blobs):
    for e in reversed(events):
        if e.kind == "assistant_msg":
            return (blobs.get(e.payload_ref) or e.summary or "")[:280]
    return None


def _error_line(text: str) -> str:
    """Pick the most error-like line from a body.

    Prefers the *last* line matching a fail hint — in a Python traceback the
    actual exception is the final line, while the bare ``Traceback (most recent
    call last):`` header is just noise and is skipped.
    """
    lines = [ln.strip() for ln in text.splitlines() if ln.strip()]
    matches = [ln for ln in lines
               if any(h in ln.lower() for h in _FAIL_HINTS)
               and not ln.lower().startswith("traceback")]
    if matches:
        return matches[-1]
    # fall back to any fail-hint line (e.g. only the traceback header), else first
    any_hint = [ln for ln in lines if any(h in ln.lower() for h in _FAIL_HINTS)]
    return any_hint[-1] if any_hint else (lines[0] if lines else "")


def _error_fingerprint(text: str) -> str:
    """Stable, content-addressable key for an error, paths/ids/numbers removed."""
    s = _error_line(text).lower()
    s = _UUID_RE.sub("<uuid>", s)
    s = _HEXADDR_RE.sub("<addr>", s)
    s = _PATH_RE.sub("<path>", s)
    s = _NUM_RE.sub("<n>", s)
    return _WS_RE.sub(" ", s).strip()[:_ERR_FP_MAX]


def _error_body(event: SessionEvent, blobs: dict) -> str:
    """Best available text for a failed event."""
    if event.payload_ref and event.payload_ref in blobs:
        return blobs[event.payload_ref]
    return event.summary or ""


def _looks_like_file_read(body: str) -> bool:
    """True if the body is mostly numbered source lines (a Read result), not an error."""
    lines = [ln for ln in body.splitlines() if ln.strip()]
    if not lines:
        return False
    numbered = sum(1 for ln in lines if _NUMBERED_LINE_RE.match(ln))
    return numbered >= max(3, len(lines) // 2)


def _json_verdict(body: str):
    """Classify a JSON tool-result body: 'error', 'success', or None (not JSON).

    Hub MCP successes look like ``{"result": "..."}`` and mention 'error' deep
    inside summaries but are not failures ('success'). A payload with a top-level
    error key (``{"detail": ...}`` / ``{"error": ...}``) is 'error'. Non-JSON text
    returns None so the plain fail-hint heuristic still applies.
    """
    s = body.strip()
    if not s or s[0] not in "{[":
        return None
    try:
        obj = json.loads(s)
    except (ValueError, TypeError):
        return None
    if isinstance(obj, dict) and any(k in obj for k in _JSON_ERROR_KEYS):
        return "error"
    return "success"


def _is_failed(event: SessionEvent, blobs: dict) -> bool:
    if event.kind == "error":
        return True
    if event.kind == "tool_result":
        body = _error_body(event, blobs)
        if not body.strip():
            return False
        if _looks_like_file_read(body):
            return False
        verdict = _json_verdict(body)
        if verdict is not None:
            return verdict == "error"
        return any(h in body.lower() for h in _FAIL_HINTS)
    return False


def _error_snippets(events: list[SessionEvent], blobs: dict) -> list[dict]:
    """Collapse a session's failures into deduped, normalized error fingerprints.

    Durable in Tier 2 (the raw blobs may be evicted): each entry is
    ``{fingerprint, sample, count, tool}`` with same-fingerprint occurrences
    counted. Ordered by frequency (then first appearance) for stable output.
    """
    agg: dict[str, dict] = {}
    order: list[str] = []
    for e in events:
        if not _is_failed(e, blobs):
            continue
        body = _error_body(e, blobs)
        if not body.strip():
            continue
        fp = _error_fingerprint(body)
        if not fp:
            continue
        if fp not in agg:
            agg[fp] = {"fingerprint": fp, "sample": _error_line(body)[:_ERR_SAMPLE_MAX],
                       "count": 0, "tool": e.tool}
            order.append(fp)
        agg[fp]["count"] += 1
    snippets = [agg[fp] for fp in order]
    snippets.sort(key=lambda s: (-s["count"], order.index(s["fingerprint"])))
    return snippets


def _read_blob(store, ref):
    row = store.db.execute("SELECT path FROM blobs WHERE ref=?", (ref,)).fetchone()
    if not row:
        return ""
    try:
        with open(row["path"], "r", encoding="utf-8") as f:
            return f.read()
    except OSError:
        return ""