"""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
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")


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),
        "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 _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 ""