"""관리자 대시보드 집계 — ChatMessage(assistant 행)에 이미 쌓인 토큰·비용·시간을 모아서 줌.

  GET /api/v1/admin/stats?from=YYYY-MM-DD&to=YYYY-MM-DD
    → { totals, byUser[], byDay[] }   (is_superuser 만. 아니면 403 FORBIDDEN)

새로 모으는 건 없음. 기간 기본은 최근 30일(to 포함).
"""

from datetime import date, datetime, time, timedelta

from django.db.models import Avg, Count, F, Sum
from django.db.models.functions import TruncDate
from django.utils import timezone
from rest_framework.response import Response
from rest_framework.views import APIView

from apps.chat.models import ChatMessage
from common.envelope import CodedError

MAX_DAYS = 366


def _parse_range(request) -> tuple[date, date]:
    today = timezone.localdate()
    raw_from, raw_to = request.query_params.get("from"), request.query_params.get("to")
    try:
        d_to = date.fromisoformat(raw_to) if raw_to else today
        d_from = date.fromisoformat(raw_from) if raw_from else d_to - timedelta(days=29)
    except ValueError:
        raise CodedError(400, "VALIDATION_ERROR", "from/to 는 YYYY-MM-DD 여야 해")
    if d_from > d_to:
        raise CodedError(400, "VALIDATION_ERROR", "from 이 to 보다 늦어")
    if (d_to - d_from).days >= MAX_DAYS:
        raise CodedError(400, "VALIDATION_ERROR", f"기간은 최대 {MAX_DAYS}일")
    return d_from, d_to


def _agg(qs):
    """공통 집계 — 요청 수·토큰·비용·평균 응답시간."""
    return qs.aggregate(
        requests=Count("id"),
        input_tokens=Sum("input_tokens"),
        output_tokens=Sum("output_tokens"),
        cost_usd=Sum("cost_usd"),
        avg_elapsed_ms=Avg("elapsed_ms"),
    )


def _row(d: dict) -> dict:
    return {
        "requests": d["requests"] or 0,
        "inputTokens": d["input_tokens"] or 0,
        "outputTokens": d["output_tokens"] or 0,
        "totalTokens": (d["input_tokens"] or 0) + (d["output_tokens"] or 0),
        "costUsd": round(d["cost_usd"] or 0.0, 6),
        "avgElapsedMs": round(d["avg_elapsed_ms"]) if d["avg_elapsed_ms"] is not None else None,
    }


class AdminStatsView(APIView):
    def get(self, request):
        if not request.user.is_superuser:
            raise CodedError(403, "FORBIDDEN", "관리자만 볼 수 있어")
        d_from, d_to = _parse_range(request)
        tz = timezone.get_current_timezone()
        start = datetime.combine(d_from, time.min, tzinfo=tz)
        end = datetime.combine(d_to + timedelta(days=1), time.min, tzinfo=tz)
        base = ChatMessage.objects.filter(role="assistant", created_at__gte=start, created_at__lt=end)

        by_user = (
            base.values(user_id=F("session__user_id"), email=F("session__user__email"), name=F("session__user__user_name"))
            .annotate(
                requests=Count("id"),
                input_tokens=Sum("input_tokens"),
                output_tokens=Sum("output_tokens"),
                cost_usd=Sum("cost_usd"),
                avg_elapsed_ms=Avg("elapsed_ms"),
                sessions=Count("session_id", distinct=True),
            )
            .order_by("-cost_usd", "-requests")
        )
        by_day = (
            base.annotate(day=TruncDate("created_at", tzinfo=tz))
            .values("day")
            .annotate(
                requests=Count("id"),
                input_tokens=Sum("input_tokens"),
                output_tokens=Sum("output_tokens"),
                cost_usd=Sum("cost_usd"),
                avg_elapsed_ms=Avg("elapsed_ms"),
            )
            .order_by("day")
        )
        return Response(
            {
                "from": d_from.isoformat(),
                "to": d_to.isoformat(),
                "totals": {**_row(_agg(base)), "users": base.values("session__user_id").distinct().count(),
                           "sessions": base.values("session_id").distinct().count()},
                "byUser": [
                    {"userId": r["user_id"], "email": r["email"], "name": r["name"] or "", "sessions": r["sessions"], **_row(r)}
                    for r in by_user
                ],
                "byDay": [{"day": r["day"].isoformat(), **_row(r)} for r in by_day],
            }
        )