"""知识分类 API：GET /api/v1/knowledge/categories、GET /api/v1/knowledge/stats"""

from functools import lru_cache
from typing import Any

import structlog
from fastapi import APIRouter

from app.api.response import ApiError, ok
from app.config import settings
from app.models.knowledge import UNCATEGORIZED, TaxonomyCategory, load_taxonomy
from app.services.qdrant import ALL_COLLECTIONS, COLLECTION_L1, QdrantService

logger = structlog.get_logger()

router = APIRouter(prefix="/api/v1", tags=["knowledge"])

# 类目分布统计的分页大小
_STATS_SCROLL_PAGE_SIZE = 100

# 模块级懒加载单例，避免每请求重建 QdrantService
_qdrant: QdrantService | None = None


def _get_qdrant() -> QdrantService:
    global _qdrant
    if _qdrant is None:
        _qdrant = QdrantService()
    return _qdrant


@lru_cache(maxsize=1)
def _get_taxonomy() -> list[TaxonomyCategory]:
    """加载并缓存 taxonomy 类目集（进程内只加载一次）"""
    return load_taxonomy(settings.taxonomy_path)


@router.get("/knowledge/categories")
async def list_categories() -> dict[str, Any]:
    """返回完整知识分类类目集"""
    categories = _get_taxonomy()
    return ok({"categories": [c.model_dump() for c in categories], "count": len(categories)})


@router.get("/knowledge/stats")
async def knowledge_stats() -> dict[str, Any]:
    """返回四层集合规模与 L1 类目分布统计"""
    service = _get_qdrant()
    try:
        collections = {collection: await service.count(collection) for collection in ALL_COLLECTIONS}
        categories = await _aggregate_l1_categories(service)
    except Exception as exc:
        logger.error("获取知识库统计失败", error=str(exc))
        raise ApiError(2000, f"获取知识库统计失败: {exc}") from exc
    return ok(
        {
            "collections": collections,
            "categories": categories,
            "uncategorized_count": categories.get(UNCATEGORIZED, 0),
            "documents_total": collections[COLLECTION_L1],
        }
    )


async def _aggregate_l1_categories(service: QdrantService) -> dict[str, int]:
    """分页遍历 L1 文档，按 category 聚合文档数（空类目归入 uncategorized）"""
    categories: dict[str, int] = {}
    offset: str | None = None
    while True:
        items, offset = await service.scroll_l1(limit=_STATS_SCROLL_PAGE_SIZE, offset=offset)
        for item in items:
            category = item.get("category") or UNCATEGORIZED
            categories[category] = categories.get(category, 0) + 1
        if offset is None:
            return categories