"""
文档加载器，使用 unstructured 库解析文档。
"""

import logging
import os
from pathlib import Path
from typing import Any, Dict, List, Optional, Union

from langchain_core.documents import Document
from unstructured.documents.elements import Element
from unstructured.partition.auto import partition

# 相对导入配置
from .config import RAG_OCR_LANGUAGES, RAG_DOC_LANGUAGES

logger = logging.getLogger(__name__)

# 模块加载时设置一次环境变量，避免重复设置
os.environ.setdefault("UNSTRUCTURED_LANGUAGE_CHECKS", "false")


class DocumentLoader:
    """从各种文件格式加载文档。"""

    SUPPORTED_EXTENSIONS = {
        ".pdf", ".docx", ".doc", ".txt", ".md",
        ".html", ".pptx", ".xlsx", ".json"
    }

    def __init__(
        self,
        extract_images: bool = False,
        strategy: str = "auto",
        ocr_languages: Optional[List[str]] = None,
        languages: Optional[List[str]] = None,
        include_page_breaks: bool = False,
        pdf_infer_table_structure: bool = True,
        partition_kwargs: Optional[Dict[str, Any]] = None,
    ):
        """
        Args:
            extract_images: 是否提取 PDF 中的图片
            strategy: 解析策略 (auto, fast, hi_res, ocr_only)
            ocr_languages: OCR 语言列表，如 ['chi_sim', 'eng']
            languages: 文档主语言，如 ['zh']（主要用于非 OCR 场景）
            include_page_breaks: 是否包含分页符
            pdf_infer_table_structure: 是否识别表格结构（需 hi_res 策略）
            partition_kwargs: 额外的 partition 参数字典（高级定制）
        """
        self.extract_images = extract_images
        self.strategy = strategy
        self.ocr_languages = ocr_languages or RAG_OCR_LANGUAGES
        self.languages = languages or RAG_DOC_LANGUAGES
        self.include_page_breaks = include_page_breaks
        self.pdf_infer_table_structure = pdf_infer_table_structure
        self.partition_kwargs = partition_kwargs or {}

    def _build_partition_kwargs(self, file_path: Path) -> Dict[str, Any]:
        """根据文件类型构建 partition 的参数。"""
        kwargs: Dict[str, Any] = {
            "include_page_breaks": self.include_page_breaks,
        }

        suffix = file_path.suffix.lower()

        # PDF 专用参数
        if suffix == ".pdf":
            kwargs.update({
                "strategy": self.strategy,
                "ocr_languages": self.ocr_languages,
                "extract_images_in_pdf": self.extract_images,
                "pdf_infer_table_structure": self.pdf_infer_table_structure,
            })

        # 所有文件适用的语言参数
        if self.languages:
            kwargs["languages"] = self.languages

        # 用户自定义参数覆盖默认值
        kwargs.update(self.partition_kwargs)

        return kwargs

    def _element_to_document(self, element: Element, file_path: Path) -> Optional[Document]:
        """将单个 Element 转换为 Document，同时保留关键元数据。"""
        text = getattr(element, "text", "")
        if not text or not text.strip():
            return None

        # 提取 unstructured 提供的元数据（根据实际需要选择）
        metadata = {
            "source": str(file_path),
            "file_name": file_path.name,
            "file_type": file_path.suffix.lower(),
            # 以下元数据来自 Element 对象，可能为 None
            "page_number": getattr(getattr(element, "metadata", None), "page_number", None),
            "category": getattr(getattr(element, "metadata", None), "category", None),
        }
        # 过滤掉值为 None 的元数据
        metadata = {k: v for k, v in metadata.items() if v is not None}

        return Document(page_content=text, metadata=metadata)

    def load_file(self, file_path: Union[str, Path]) -> List[Document]:
        """将单个文件加载为 LangChain Document 对象。"""
        file_path = Path(file_path).resolve()
        if not file_path.exists():
            raise FileNotFoundError(f"文件不存在: {file_path}")

        suffix = file_path.suffix.lower()
        if suffix not in self.SUPPORTED_EXTENSIONS:
            raise ValueError(
                f"不支持的文件扩展名: {suffix}。支持的格式: {self.SUPPORTED_EXTENSIONS}"
            )

        kwargs = self._build_partition_kwargs(file_path)

        try:
            elements = partition(filename=str(file_path), **kwargs)
        except Exception as e:
            logger.exception("解析文件 %s 失败", file_path)
            raise RuntimeError(f"文件解析失败: {file_path}") from e

        documents = []
        for elem in elements:
            doc = self._element_to_document(elem, file_path)
            if doc:
                documents.append(doc)

        if not documents:
            logger.warning("未从 %s 提取到文本内容", file_path)

        return documents

    def load_directory(
        self,
        directory_path: Union[str, Path],
        recursive: bool = True,
        fail_fast: bool = False
    ) -> List[Document]:
        """
        从目录加载所有支持的文件。

        Args:
            directory_path: 目录路径
            recursive: 是否递归子目录
            fail_fast: 遇到第一个失败时是否立即抛出异常
        """
        directory_path = Path(directory_path).resolve()
        if not directory_path.is_dir():
            raise NotADirectoryError(f"不是目录: {directory_path}")

        all_documents: List[Document] = []
        pattern = "**/*" if recursive else "*"

        for file_path in directory_path.glob(pattern):
            if not file_path.is_file():
                continue
            if file_path.suffix.lower() not in self.SUPPORTED_EXTENSIONS:
                continue

            try:
                docs = self.load_file(file_path)
                all_documents.extend(docs)
            except Exception as e:
                logger.error("加载 %s 失败: %s", file_path, e)
                if fail_fast:
                    raise

        return all_documents