"""数据总览接口（客迹视觉 V1：周期卡 + 趋势双线 + 渠道分布）。

?range=today|7d|30d（默认 7d，非法值回落默认）+ ?site=（可选，缺省聚合全部站点）。
- 周期卡四指标全口径排除爬虫，与上一个等长周期比较出 delta_pct（today 比昨天）；
  上期值为 0 时 delta 为 null（前端显示 —）。
- 趋势为日粒度：历史位读 DailyStat 聚合（缺日补零），今天一位用 daily_counts 实时值
  （聚合作业未跑也不缺当日）——与 refresh_daily 共享口径（Task8 审查结论）。
- channels 按窗口内会话入口分类聚合，pct = 占已分类会话比（列表含 direct/unknown，
  总和 ≈ 1；未重算出分类行的历史会话不计入）。
- 最近访问不在本接口做：前端调既有 /api/admin/visitors?page=1 取前 5 行。
"""
from datetime import datetime, time, timedelta

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

from tracker.api.envelope import EnvelopeMixin, ok
from tracker.models import DailyStat, Event, Site, SourceClassification, VisitSession, Visitor
from tracker.services.stats import daily_counts

RANGE_DAYS = {"today": 1, "7d": 7, "30d": 30}
CARD_KEYS = ("visitors", "visits", "avg_stay_ms", "returning")


def _window_stats(site, start, end):
    """窗口四指标（site=None 聚合全部站点；全口径排除爬虫）。

    visitors 按 Event distinct visitor（与 daily_counts 的 uv 同源，跨日不重复计）；
    visits 按会话 started_at 落窗；avg_stay_ms = Sum(stay_ms)/会话数（0 保护）；
    returning = visitors - 窗口内新访客（first_seen_at 落窗；异常数据下限 0）。
    """
    ev = Event.objects.filter(is_bot=False,
                              occurred_at__gte=start, occurred_at__lt=end)
    vs = VisitSession.objects.filter(visitor__is_bot=False,
                                     started_at__gte=start, started_at__lt=end)
    vis = Visitor.objects.filter(is_bot=False,
                                 first_seen_at__gte=start, first_seen_at__lt=end)
    if site is not None:
        ev = ev.filter(site=site)
        vs = vs.filter(site=site)
        vis = vis.filter(site=site)
    agg = vs.aggregate(n=Count("id"), stay=Sum("stay_ms"))
    sessions = agg["n"]
    visitors = ev.values("visitor").distinct().count()
    new_visitors = vis.count()
    return {"visitors": visitors,
            "visits": sessions,
            "avg_stay_ms": round((agg["stay"] or 0) / sessions) if sessions else 0,
            "returning": max(visitors - new_visitors, 0)}


def _delta(cur, prev):
    """环比百分比（保留 1 位小数）；上期值为 0 无意义 → None。"""
    if prev == 0:
        return None
    return round((cur - prev) / prev * 100, 1)


class OverviewView(EnvelopeMixin, APIView):
    def get(self, request):
        site = None
        sid = request.query_params.get("site")
        if sid:
            site = Site.objects.filter(site_id=sid).first()
            if not site:
                return Response({"code": 404, "data": None,
                                 "message": "site_not_found"}, status=404)
        days = RANGE_DAYS.get(request.query_params.get("range", "7d"), 7)
        today = timezone.localdate()
        # 当前窗口与上期等长窗口（上海自然日对齐：[T-N+1, T+1) 与 [T-2N+1, T-N+1)）
        cur_start = timezone.make_aware(
            datetime.combine(today - timedelta(days=days - 1), time.min))
        cur_end = timezone.make_aware(
            datetime.combine(today + timedelta(days=1), time.min))
        prev_start = cur_start - timedelta(days=days)

        cur = _window_stats(site, cur_start, cur_end)
        prev = _window_stats(site, prev_start, cur_start)
        online = self._active_now(site)
        return ok({
            "header": {"online": online, "active_now": online},   # active_now 兼容保留
            "cards": {k: {"value": cur[k], "delta_pct": _delta(cur[k], prev[k])}
                      for k in CARD_KEYS},
            "trend": self._trend(site, today, days),
            "channels": self._channels(site, cur_start, cur_end),
        })

    @staticmethod
    def _active_now(site):
        # 5 分钟内有行为的访客（last_seen_at 有 site,-last_seen_at 索引；不用无索引的 received_at）
        q = Visitor.objects.filter(is_bot=False,
                                   last_seen_at__gt=timezone.now() - timedelta(minutes=5))
        if site is not None:
            q = q.filter(site=site)
        return q.count()

    def _trend(self, site, today, days):
        """窗口每日 [{date, uv, sessions}]：历史位读 DailyStat（缺日补零），
        今天一位用 daily_counts 实时值覆盖——聚合作业未跑也不缺当日。"""
        start = today - timedelta(days=days - 1)
        qs = DailyStat.objects.filter(date__gte=start, date__lte=today)
        if site is not None:
            qs = qs.filter(site=site)
        rows = {r["date"]: r for r in qs.values("date").annotate(
            uv=Sum("uv"), sessions=Sum("sessions"))}
        out = []
        for i in range(days):
            date = start + timedelta(days=i)
            if date == today:
                counts = daily_counts(site, today)
                out.append({"date": date.isoformat(),
                            "uv": counts["uv"], "sessions": counts["sessions"]})
            else:
                r = rows.get(date, {})
                out.append({"date": date.isoformat(),
                            "uv": r.get("uv") or 0, "sessions": r.get("sessions") or 0})
        return out

    def _channels(self, site, start, end):
        """窗口内会话按 session_entry 分类聚合（session.started_at 落窗）。
        从分类表正向聚合 + Count(distinct session)：无唯一约束下分类表偶发同键重复行
        也不会把同一会话计两次。pct = 占已分类会话比（含 direct/unknown，总和 ≈ 1；
        无分类行的会话——未重算的历史数据——不计入）。"""
        q = SourceClassification.objects.filter(
            scope="session_entry",
            session__visitor__is_bot=False,
            session__started_at__gte=start, session__started_at__lt=end)
        if site is not None:
            q = q.filter(site=site)
        rows = list(q.values("channel")
                    .annotate(n=Count("session", distinct=True))
                    .order_by("-n", "channel"))   # 平局时次序跨请求稳定
        total = sum(r["n"] for r in rows)
        return [{"channel": r["channel"] or "unknown", "sessions": r["n"],
                 "pct": round(r["n"] / total, 4) if total else 0.0}
                for r in rows]