"""
oO ML Serving — Phase 1: LinUCB contextual bandit.

Contract:
  POST /score                     LinUCB d=5 (baseline, kept as shadow-eligible)
  POST /score/egreedy             ε-greedy v1, d=7 (active — ADR-0007)
  POST /score/egreedy/v2          ε-greedy v2, d=12, profile features (shadow — ADR-0012)
  POST /reward, /reward/egreedy, /reward/egreedy/v2
  GET  /stats/{user_id}           LinUCB stats
  GET  /stats/egreedy/{user_id}   ε-greedy v1 stats
  GET  /stats/egreedy/v2/{user_id}  ε-greedy v2 stats
  POST /reset/{user_id}           clear all per-user bandit state
  GET  /features/{user_id}        last 100 scored feature vectors
  POST /generate                  LLM tip candidates via LiteLLM
  GET  /health                    { ok }

Features (d=5):
  hour_sin, hour_cos  — cyclical time-of-day encoding
  is_overdue          — 0 or 1
  task_age_days       — days since due date (clipped 0–30, normalised 0–1)
  priority_norm       — Todoist priority 1–4, normalised to 0–1
"""

from __future__ import annotations

import json
import math
import os
import time
from collections import deque
from contextlib import asynccontextmanager
from pathlib import Path
from typing import Optional, Deque

import httpx
import numpy as np
import sentry_sdk
import structlog
import structlog.contextvars
from fastapi import FastAPI, HTTPException, Request
from pydantic import BaseModel
from starlette.middleware.base import BaseHTTPMiddleware

import logging_config
import nats_consumer
from prompts import get_prompt

logging_config.configure()

_SENTRY_DSN = os.getenv("SENTRY_DSN")
if _SENTRY_DSN:
    sentry_sdk.init(dsn=_SENTRY_DSN, environment=os.getenv("ENV", "development"))

log = structlog.get_logger()


@asynccontextmanager
async def lifespan(app: FastAPI):
    await nats_consumer.start(STATE_DIR)
    yield
    await nats_consumer.stop()


app = FastAPI(title="oO ML Serving", version="1.0.0", lifespan=lifespan)


class _TracingMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request: Request, call_next):
        structlog.contextvars.clear_contextvars()
        traceparent = request.headers.get("traceparent", "")
        if traceparent:
            parts = traceparent.split("-")
            trace_id = parts[1] if len(parts) == 4 and len(parts[1]) == 32 else None
            if trace_id:
                structlog.contextvars.bind_contextvars(trace_id=trace_id)
        return await call_next(request)


app.add_middleware(_TracingMiddleware)

LITELLM_URL = os.getenv("LITELLM_URL", "http://localhost:4000")
LITELLM_MASTER_KEY = os.getenv("LITELLM_MASTER_KEY", "sk-oo-dev")

STATE_DIR = Path(os.getenv("STATE_DIR", "/tmp/oo-bandit-state"))
STATE_DIR.mkdir(parents=True, exist_ok=True)

ALPHA = 1.0   # LinUCB exploration coefficient
D = 5         # LinUCB feature dimension
D7 = 7        # ε-greedy v1 feature dimension (adds day-of-week cyclical encoding)
D12 = 12      # ε-greedy v2 feature dimension (adds 5 profile features — ADR-0012)
EPSILON = 0.1 # ε-greedy exploration rate
FEATURE_HISTORY_SIZE = 100  # per-user ring buffer


# ── Per-user in-memory feature history ────────────────────────────────────
_feature_history: dict[str, deque] = {}

def get_feature_history(user_id: str) -> deque:
    if user_id not in _feature_history:
        _feature_history[user_id] = deque(maxlen=FEATURE_HISTORY_SIZE)
    return _feature_history[user_id]


# ── Feature helpers ────────────────────────────────────────────────────────

def build_feature_vector(features: dict) -> np.ndarray:
    hour = features.get("hour_of_day", 12)
    hour_sin = math.sin(2 * math.pi * hour / 24)
    hour_cos = math.cos(2 * math.pi * hour / 24)
    is_overdue = float(bool(features.get("is_overdue", False)))
    age = min(float(features.get("task_age_days", 0)), 30.0) / 30.0
    priority = (float(features.get("priority", 1)) - 1.0) / 3.0
    return np.array([hour_sin, hour_cos, is_overdue, age, priority], dtype=np.float64)


# ── Per-user bandit state (disjoint LinUCB, global arm) ───────────────────

# ── LinUCB state helpers ───────────────────────────────────────────────────

def state_path(user_id: str) -> Path:
    safe = "".join(c if c.isalnum() else "_" for c in user_id)
    return STATE_DIR / f"{safe}.json"


def load_state(user_id: str) -> tuple[np.ndarray, np.ndarray, dict]:
    """Returns (A, b, meta). A is DxD, b is D-vector."""
    p = state_path(user_id)
    if p.exists():
        raw = json.loads(p.read_text())
        A = np.array(raw["A"], dtype=np.float64)
        b = np.array(raw["b"], dtype=np.float64)
        meta = raw.get("meta", {})
        return A, b, meta
    return np.identity(D, dtype=np.float64), np.zeros(D, dtype=np.float64), {}


def save_state(user_id: str, A: np.ndarray, b: np.ndarray, meta: dict) -> None:
    p = state_path(user_id)
    p.write_text(json.dumps({"A": A.tolist(), "b": b.tolist(), "meta": meta}))


# ── ε-greedy state helpers (d=7, extended features) ───────────────────────

def build_feature_vector_7(features: dict, day_of_week: int = 0) -> np.ndarray:
    """d=7: base 5 features + day-of-week cyclical encoding."""
    base = build_feature_vector(features)
    dow_sin = math.sin(2 * math.pi * day_of_week / 7)
    dow_cos = math.cos(2 * math.pi * day_of_week / 7)
    return np.append(base, [dow_sin, dow_cos])


def state7_path(user_id: str) -> Path:
    safe = "".join(c if c.isalnum() else "_" for c in user_id)
    return STATE_DIR / f"{safe}_egreedy.json"


def load_state7(user_id: str) -> tuple[np.ndarray, np.ndarray, dict]:
    """Returns (A, b, meta) for ε-greedy d=7 policy."""
    p = state7_path(user_id)
    if p.exists():
        raw = json.loads(p.read_text())
        A = np.array(raw["A"], dtype=np.float64)
        b = np.array(raw["b"], dtype=np.float64)
        return A, b, raw.get("meta", {})
    return np.identity(D7, dtype=np.float64), np.zeros(D7, dtype=np.float64), {}


def save_state7(user_id: str, A: np.ndarray, b: np.ndarray, meta: dict) -> None:
    p = state7_path(user_id)
    p.write_text(json.dumps({"A": A.tolist(), "b": b.tolist(), "meta": meta}))


# ── ε-greedy v2 state helpers (d=12, profile features — ADR-0012) ─────────
#
# Normalization choices (see ADR-0012):
#   completion_rate_30d   — already 0–1, passthrough; null → 0
#   dismiss_rate_30d      — already 0–1, passthrough; null → 0
#   mean_dwell_ms_30d     — clipped to [0, 600_000 ms] (10 min), then /600_000
#   preferred_hour        — circular alignment with context hour:
#                             (cos(2π·(now − pref)/24) + 1) / 2  → 0–1
#                           captures "is the user's habitual peak near now?"
#                           null → 0.5 (neutral)
#   tip_volume_30d        — log1p(n) / log1p(100), clipped to [0, 1]

_DWELL_CLIP_MS = 600_000.0  # 10 minutes
_VOLUME_LOG_MAX = math.log1p(100.0)


def _profile_value(profile: Optional[dict], key: str) -> Optional[float]:
    if not profile:
        return None
    v = profile.get(key)
    if v is None:
        return None
    try:
        return float(v)
    except (TypeError, ValueError):
        return None


def _norm_rate(v: Optional[float]) -> float:
    return 0.0 if v is None else max(0.0, min(1.0, v))


def _norm_dwell(v: Optional[float]) -> float:
    if v is None:
        return 0.0
    return max(0.0, min(1.0, v / _DWELL_CLIP_MS))


def _norm_volume(v: Optional[float]) -> float:
    if v is None or v <= 0:
        return 0.0
    return min(1.0, math.log1p(float(v)) / _VOLUME_LOG_MAX)


def _norm_preferred_hour(pref: Optional[float], now_hour: int) -> float:
    if pref is None:
        return 0.5  # neutral when the user has no established peak yet
    delta = (float(pref) - float(now_hour)) * (2.0 * math.pi / 24.0)
    return (math.cos(delta) + 1.0) / 2.0


def build_feature_vector_12(
    features: dict,
    day_of_week: int = 0,
    profile: Optional[dict] = None,
) -> np.ndarray:
    """d=12: egreedy-v1's 7 dims + 5 normalized profile features (ADR-0012)."""
    base7 = build_feature_vector_7(features, day_of_week)
    now_hour = int(features.get("hour_of_day", 12))
    profile_dims = np.array(
        [
            _norm_rate(_profile_value(profile, "completion_rate_30d")),
            _norm_rate(_profile_value(profile, "dismiss_rate_30d")),
            _norm_dwell(_profile_value(profile, "mean_dwell_ms_30d")),
            _norm_preferred_hour(_profile_value(profile, "preferred_hour"), now_hour),
            _norm_volume(_profile_value(profile, "tip_volume_30d")),
        ],
        dtype=np.float64,
    )
    return np.concatenate([base7, profile_dims])


def state12_path(user_id: str) -> Path:
    safe = "".join(c if c.isalnum() else "_" for c in user_id)
    return STATE_DIR / f"{safe}_egreedy_v2.json"


def load_state12(user_id: str) -> tuple[np.ndarray, np.ndarray, dict]:
    p = state12_path(user_id)
    if p.exists():
        raw = json.loads(p.read_text())
        A = np.array(raw["A"], dtype=np.float64)
        b = np.array(raw["b"], dtype=np.float64)
        return A, b, raw.get("meta", {})
    return np.identity(D12, dtype=np.float64), np.zeros(D12, dtype=np.float64), {}


def save_state12(user_id: str, A: np.ndarray, b: np.ndarray, meta: dict) -> None:
    p = state12_path(user_id)
    p.write_text(json.dumps({"A": A.tolist(), "b": b.tolist(), "meta": meta}))


# ── API models ─────────────────────────────────────────────────────────────

class CandidateFeatures(BaseModel):
    hour_of_day: int = 12
    is_overdue: bool = False
    task_age_days: float = 0.0
    priority: int = 1


class Candidate(BaseModel):
    id: str
    content: str
    source: str
    source_id: Optional[str] = None
    features: CandidateFeatures = CandidateFeatures()


class Context(BaseModel):
    hour_of_day: int = 12
    day_of_week: int = 0


class ScoreRequest(BaseModel):
    user_id: str
    candidates: list[Candidate]
    context: Context = Context()
    # User-level features computed by the API (#81 phase A). Accepted, logged,
    # but not yet consumed by the bandit — extending the feature vector
    # changes `D` and resets every user's learned state, which is a deliberate
    # follow-up (phase B), not a side effect of this PR.
    profile_features: Optional[dict] = None


class ScoreResponse(BaseModel):
    tip_id: str
    score: float
    policy: str


class RewardRequest(BaseModel):
    user_id: str
    tip_id: str
    reward: float          # +1 done, +0.5 helpful, 0 snooze, -0.5 not_helpful, -1 dismiss
    features: CandidateFeatures
    day_of_week: int = 0   # included so egreedy can train dow features correctly
    # Profile features at the time the tip was served. Ignored by /reward and
    # /reward/egreedy; consumed by /reward/egreedy/v2 so the ridge update uses
    # the same feature vector as the matching /score/egreedy/v2 call.
    profile_features: Optional[dict] = None


class RewardResponse(BaseModel):
    ok: bool


class PromptContext(BaseModel):
    tasks: list[dict] = []
    hour_of_day: int = 12
    day_of_week: int = 0
    extra: dict = {}


class GenerateRequest(BaseModel):
    user_id: str
    context: PromptContext = PromptContext()
    n: int = 3
    prompt_version: Optional[str] = None  # None → server default (env DEFAULT_PROMPT_VERSION)
    # User-level features (#81 phase A). Accepted by the contract; not yet
    # injected into the prompt — that's a #84-style prompt-design decision.
    profile_features: Optional[dict] = None


class TipCandidate(BaseModel):
    id: str
    content: str
    source: str = "llm"
    rationale: Optional[str] = None


class GenerateResponse(BaseModel):
    candidates: list[TipCandidate]
    model: str
    prompt_version: str
    prompt_tokens: int = 0
    completion_tokens: int = 0


# ── Endpoints ──────────────────────────────────────────────────────────────

@app.get("/health")
def health():
    return {
        "ok": True,
        "nats": {
            "enabled": bool(nats_consumer.NATS_URL),
            "consumers": nats_consumer.consumer_health,
        },
    }


_RETRY_SUFFIX = (
    "\n\nYour previous response was not valid JSON. "
    "Reply ONLY with the JSON array — no prose, no markdown fences."
)

_MAX_GENERATE_RETRIES = 2


def _parse_llm_json(raw: str) -> list[dict]:
    """Strip markdown fences and parse JSON array. Raises ValueError on failure."""
    text = raw.strip()
    if text.startswith("```"):
        parts = text.split("```")
        text = parts[1] if len(parts) > 1 else text
        if text.startswith("json"):
            text = text[4:]
    return json.loads(text)


@app.post("/generate", response_model=GenerateResponse)
async def generate(req: GenerateRequest) -> GenerateResponse:
    """Generate tip candidates via LiteLLM → tip-generator alias.

    Retries up to _MAX_GENERATE_RETRIES times on malformed JSON, appending
    a correction hint to the conversation so the model can self-correct.
    """
    try:
        prompt_template = get_prompt(req.prompt_version)
    except KeyError as e:
        raise HTTPException(status_code=422, detail=f"Unknown prompt_version: {e.args[0]}")
    user_msg = prompt_template.build_user(req.context, req.n)
    messages: list[dict] = [
        {"role": "system", "content": prompt_template.system},
        {"role": "user", "content": user_msg},
    ]
    headers = {"Authorization": f"Bearer {LITELLM_MASTER_KEY}"}
    last_parse_error: str = ""
    last_raw: str = ""
    total_usage: dict = {"prompt_tokens": 0, "completion_tokens": 0}
    model_used = "tip-generator"

    async with httpx.AsyncClient(timeout=30.0) as client:
        for attempt in range(1 + _MAX_GENERATE_RETRIES):
            payload = {"model": "tip-generator", "messages": messages, "temperature": 0.7}
            try:
                resp = await client.post(
                    f"{LITELLM_URL}/chat/completions",
                    json=payload,
                    headers=headers,
                )
                resp.raise_for_status()
            except httpx.HTTPStatusError as e:
                raise HTTPException(status_code=502, detail=f"LiteLLM error: {e.response.text}")
            except httpx.RequestError as e:
                raise HTTPException(status_code=503, detail=f"LiteLLM unreachable: {e}")

            data = resp.json()
            usage = data.get("usage", {})
            total_usage["prompt_tokens"] += usage.get("prompt_tokens", 0)
            total_usage["completion_tokens"] += usage.get("completion_tokens", 0)
            model_used = data.get("model", "tip-generator")

            last_raw = data["choices"][0]["message"]["content"]
            try:
                items = _parse_llm_json(last_raw)
                break
            except (json.JSONDecodeError, ValueError) as e:
                last_parse_error = str(e)
                # Feed the bad reply back so the model can self-correct
                messages.append({"role": "assistant", "content": last_raw})
                messages.append({"role": "user", "content": _RETRY_SUFFIX})
        else:
            raise HTTPException(
                status_code=502,
                detail=f"LLM returned invalid JSON after {_MAX_GENERATE_RETRIES} retries: "
                       f"{last_parse_error}\n{last_raw[:200]}",
            )

    candidates = [
        TipCandidate(
            id=item.get("id", f"tip-{i}"),
            content=item.get("content", ""),
            rationale=item.get("rationale"),
        )
        for i, item in enumerate(items)
    ]

    return GenerateResponse(
        candidates=candidates,
        model=model_used,
        prompt_version=prompt_template.version,
        prompt_tokens=total_usage["prompt_tokens"],
        completion_tokens=total_usage["completion_tokens"],
    )


@app.post("/score", response_model=ScoreResponse)
def score(req: ScoreRequest) -> ScoreResponse:
    if not req.candidates:
        raise HTTPException(status_code=422, detail="No candidates")

    A, b, meta = load_state(req.user_id)
    try:
        A_inv = np.linalg.inv(A)
    except np.linalg.LinAlgError:
        A_inv = np.identity(D, dtype=np.float64)

    theta = A_inv @ b

    best_id = None
    best_score = -float("inf")
    best_features: dict = {}

    for candidate in req.candidates:
        feat_dict = {
            "hour_of_day": req.context.hour_of_day,
            "is_overdue": candidate.features.is_overdue,
            "task_age_days": candidate.features.task_age_days,
            "priority": candidate.features.priority,
        }
        x = build_feature_vector(feat_dict)
        exploit = float(theta @ x)
        explore = ALPHA * math.sqrt(float(x @ A_inv @ x))
        ucb = exploit + explore
        if ucb > best_score:
            best_score = ucb
            best_id = candidate.id
            best_features = feat_dict

    # Log to feature history ring buffer
    history = get_feature_history(req.user_id)
    history.append({
        "ts": time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime()),
        "features": best_features,
        "score": best_score,
        "tip_id": best_id,
    })

    # Update meta stats
    meta["pulls"] = meta.get("pulls", 0) + 1
    meta["last_updated"] = time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())
    save_state(req.user_id, A, b, meta)

    return ScoreResponse(tip_id=best_id, score=best_score, policy="linucb-v1")


@app.post("/reward", response_model=RewardResponse)
def reward(req: RewardRequest) -> RewardResponse:
    A, b, meta = load_state(req.user_id)
    feat_dict = {
        "hour_of_day": req.features.hour_of_day,
        "is_overdue": req.features.is_overdue,
        "task_age_days": req.features.task_age_days,
        "priority": req.features.priority,
    }
    x = build_feature_vector(feat_dict)
    A += np.outer(x, x)
    b += req.reward * x

    # Track cumulative reward in meta
    meta["cumulative_reward"] = meta.get("cumulative_reward", 0.0) + req.reward
    meta["reward_count"] = meta.get("reward_count", 0) + 1
    meta["last_updated"] = time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())

    save_state(req.user_id, A, b, meta)
    return RewardResponse(ok=True)


@app.post("/score/egreedy", response_model=ScoreResponse)
def score_egreedy(req: ScoreRequest) -> ScoreResponse:
    """ε-greedy policy with d=7 features (adds day-of-week encoding).

    Exploration: pick uniformly at random with probability ε.
    Exploitation: pick argmax of linear payoff estimate θ·x.
    Differs from LinUCB in: no UCB bonus, richer feature space.
    """
    if not req.candidates:
        raise HTTPException(status_code=422, detail="No candidates")

    A, b, meta = load_state7(req.user_id)
    try:
        A_inv = np.linalg.inv(A)
    except np.linalg.LinAlgError:
        A_inv = np.identity(D7, dtype=np.float64)
    theta = A_inv @ b

    dow = req.context.day_of_week
    exploring = np.random.random() < EPSILON

    if exploring:
        chosen = req.candidates[np.random.randint(len(req.candidates))]
        feat_dict = {
            "hour_of_day": req.context.hour_of_day,
            "is_overdue": chosen.features.is_overdue,
            "task_age_days": chosen.features.task_age_days,
            "priority": chosen.features.priority,
        }
        x = build_feature_vector_7(feat_dict, dow)
        best_score = float(theta @ x)
        best_id = chosen.id
    else:
        best_id = None
        best_score = -float("inf")
        feat_dict = {}
        for candidate in req.candidates:
            fd = {
                "hour_of_day": req.context.hour_of_day,
                "is_overdue": candidate.features.is_overdue,
                "task_age_days": candidate.features.task_age_days,
                "priority": candidate.features.priority,
            }
            x = build_feature_vector_7(fd, dow)
            s = float(theta @ x)
            if s > best_score:
                best_score = s
                best_id = candidate.id
                feat_dict = fd

    history = get_feature_history(req.user_id)
    history.append({
        "ts": time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime()),
        "features": {**feat_dict, "day_of_week": dow, "exploring": exploring},
        "score": best_score,
        "tip_id": best_id,
        "policy": "egreedy-v1",
    })

    meta["pulls"] = meta.get("pulls", 0) + 1
    meta["explore_count"] = meta.get("explore_count", 0) + int(exploring)
    meta["last_updated"] = time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())
    save_state7(req.user_id, A, b, meta)

    return ScoreResponse(tip_id=best_id, score=best_score, policy="egreedy-v1")


@app.post("/reward/egreedy", response_model=RewardResponse)
def reward_egreedy(req: RewardRequest) -> RewardResponse:
    """Update ε-greedy ridge estimator with observed reward."""
    A, b, meta = load_state7(req.user_id)
    feat_dict = {
        "hour_of_day": req.features.hour_of_day,
        "is_overdue": req.features.is_overdue,
        "task_age_days": req.features.task_age_days,
        "priority": req.features.priority,
    }
    x = build_feature_vector_7(feat_dict, day_of_week=req.day_of_week)
    A += np.outer(x, x)
    b += req.reward * x

    meta["cumulative_reward"] = meta.get("cumulative_reward", 0.0) + req.reward
    meta["reward_count"] = meta.get("reward_count", 0) + 1
    meta["last_updated"] = time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())
    save_state7(req.user_id, A, b, meta)
    return RewardResponse(ok=True)


@app.post("/score/egreedy/v2", response_model=ScoreResponse)
def score_egreedy_v2(req: ScoreRequest) -> ScoreResponse:
    """ε-greedy v2 — d=12, adds 5 normalized profile features (ADR-0012).

    Shadow-only until offline sim + rollout per ADR-0002 completes.
    Accepts the same ScoreRequest shape as v1; `profile_features` drives the
    extra 5 dims (defaults: zeros for rates/volume/dwell, 0.5 neutral for
    preferred_hour alignment).
    """
    if not req.candidates:
        raise HTTPException(status_code=422, detail="No candidates")

    A, b, meta = load_state12(req.user_id)
    try:
        A_inv = np.linalg.inv(A)
    except np.linalg.LinAlgError:
        A_inv = np.identity(D12, dtype=np.float64)
    theta = A_inv @ b

    dow = req.context.day_of_week
    exploring = np.random.random() < EPSILON

    if exploring:
        chosen = req.candidates[np.random.randint(len(req.candidates))]
        feat_dict = {
            "hour_of_day": req.context.hour_of_day,
            "is_overdue": chosen.features.is_overdue,
            "task_age_days": chosen.features.task_age_days,
            "priority": chosen.features.priority,
        }
        x = build_feature_vector_12(feat_dict, dow, req.profile_features)
        best_score = float(theta @ x)
        best_id = chosen.id
    else:
        best_id = None
        best_score = -float("inf")
        feat_dict = {}
        for candidate in req.candidates:
            fd = {
                "hour_of_day": req.context.hour_of_day,
                "is_overdue": candidate.features.is_overdue,
                "task_age_days": candidate.features.task_age_days,
                "priority": candidate.features.priority,
            }
            x = build_feature_vector_12(fd, dow, req.profile_features)
            s = float(theta @ x)
            if s > best_score:
                best_score = s
                best_id = candidate.id
                feat_dict = fd

    history = get_feature_history(req.user_id)
    history.append({
        "ts": time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime()),
        "features": {**feat_dict, "day_of_week": dow, "exploring": exploring},
        "score": best_score,
        "tip_id": best_id,
        "policy": "egreedy-v2",
    })

    meta["pulls"] = meta.get("pulls", 0) + 1
    meta["explore_count"] = meta.get("explore_count", 0) + int(exploring)
    meta["last_updated"] = time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())
    save_state12(req.user_id, A, b, meta)

    return ScoreResponse(tip_id=best_id, score=best_score, policy="egreedy-v2")


@app.post("/reward/egreedy/v2", response_model=RewardResponse)
def reward_egreedy_v2(req: RewardRequest) -> RewardResponse:
    """Update ε-greedy v2 ridge estimator using the d=12 feature vector."""
    A, b, meta = load_state12(req.user_id)
    feat_dict = {
        "hour_of_day": req.features.hour_of_day,
        "is_overdue": req.features.is_overdue,
        "task_age_days": req.features.task_age_days,
        "priority": req.features.priority,
    }
    x = build_feature_vector_12(feat_dict, req.day_of_week, req.profile_features)
    A += np.outer(x, x)
    b += req.reward * x

    meta["cumulative_reward"] = meta.get("cumulative_reward", 0.0) + req.reward
    meta["reward_count"] = meta.get("reward_count", 0) + 1
    meta["last_updated"] = time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())
    save_state12(req.user_id, A, b, meta)
    return RewardResponse(ok=True)


@app.get("/stats/egreedy/v2/{user_id}")
def stats_egreedy_v2(user_id: str):
    """ε-greedy v2 policy stats — pulls, cumulative reward, θ vector."""
    A, b, meta = load_state12(user_id)
    try:
        theta = (np.linalg.inv(A) @ b).tolist()
    except np.linalg.LinAlgError:
        theta = [0.0] * D12

    pulls = meta.get("pulls", 0)
    cumulative_reward = meta.get("cumulative_reward", 0.0)
    reward_count = meta.get("reward_count", 0)
    explore_count = meta.get("explore_count", 0)

    return {
        "user_id": user_id,
        "policy": "egreedy-v2",
        "pulls": pulls,
        "reward_count": reward_count,
        "cumulative_reward": cumulative_reward,
        "estimated_mean_reward": cumulative_reward / reward_count if reward_count > 0 else 0.0,
        "exploration_rate": explore_count / pulls if pulls > 0 else 0.0,
        "theta": theta,
        "feature_labels": [
            "hour_sin", "hour_cos", "is_overdue", "task_age", "priority",
            "dow_sin", "dow_cos",
            "completion_rate_30d", "dismiss_rate_30d", "mean_dwell_norm",
            "preferred_hour_alignment", "tip_volume_norm",
        ],
        "last_updated": meta.get("last_updated"),
    }


@app.get("/stats/egreedy/{user_id}")
def stats_egreedy(user_id: str):
    """ε-greedy policy stats — pulls, cumulative reward, θ vector."""
    A, b, meta = load_state7(user_id)
    try:
        theta = (np.linalg.inv(A) @ b).tolist()
    except np.linalg.LinAlgError:
        theta = [0.0] * D7

    pulls = meta.get("pulls", 0)
    cumulative_reward = meta.get("cumulative_reward", 0.0)
    reward_count = meta.get("reward_count", 0)
    explore_count = meta.get("explore_count", 0)

    return {
        "user_id": user_id,
        "policy": "egreedy-v1",
        "pulls": pulls,
        "reward_count": reward_count,
        "cumulative_reward": cumulative_reward,
        "estimated_mean_reward": cumulative_reward / reward_count if reward_count > 0 else 0.0,
        "exploration_rate": explore_count / pulls if pulls > 0 else 0.0,
        "theta": theta,
        "feature_labels": ["hour_sin", "hour_cos", "is_overdue", "task_age", "priority", "dow_sin", "dow_cos"],
        "last_updated": meta.get("last_updated"),
    }


@app.post("/reset/{user_id}", response_model=RewardResponse)
def reset(user_id: str) -> RewardResponse:
    """Reset per-user bandit state (admin action)."""
    p = state_path(user_id)
    if p.exists():
        p.unlink()
    p7 = state7_path(user_id)
    if p7.exists():
        p7.unlink()
    p12 = state12_path(user_id)
    if p12.exists():
        p12.unlink()
    if user_id in _feature_history:
        _feature_history[user_id].clear()
    return RewardResponse(ok=True)


@app.get("/stats/{user_id}")
def stats(user_id: str):
    """Return current LinUCB state summary for a user."""
    A, b, meta = load_state(user_id)
    try:
        A_inv = np.linalg.inv(A)
        theta = (A_inv @ b).tolist()
    except np.linalg.LinAlgError:
        theta = [0.0] * D

    pulls = meta.get("pulls", 0)
    cumulative_reward = meta.get("cumulative_reward", 0.0)
    reward_count = meta.get("reward_count", 0)
    estimated_mean = cumulative_reward / reward_count if reward_count > 0 else 0.0

    return {
        "user_id": user_id,
        "pulls": pulls,
        "reward_count": reward_count,
        "cumulative_reward": cumulative_reward,
        "estimated_mean_reward": estimated_mean,
        "theta": theta,
        "last_updated": meta.get("last_updated"),
    }


@app.get("/features/{user_id}")
def features(user_id: str):
    """Return recent feature vectors logged at scoring time."""
    history = get_feature_history(user_id)
    return {
        "user_id": user_id,
        "history": list(history),
    }