"""
文档解析器 — 支持 txt / pdf / docx / md / csv。

解析结果统一返回纯文本字符串，由调用方做分块处理。
"""
from __future__ import annotations

import csv
import io
import logging
import os
from typing import Optional

logger = logging.getLogger(__name__)


def parse_document(file_path: str, file_type: str) -> Optional[str]:
    """
    解析文档为纯文本。

    Args:
        file_path: 文件绝对路径
        file_type: 文件类型（txt / pdf / docx / md / csv）

    Returns:
        文本内容，解析失败返回 None
    """
    if not os.path.isfile(file_path):
        logger.warning("文件不存在: %s", file_path)
        return None

    parsers = {
        "txt": _parse_text,
        "md": _parse_text,
        "pdf": _parse_pdf,
        "docx": _parse_docx,
        "csv": _parse_csv,
    }
    parser = parsers.get(file_type)
    if not parser:
        logger.warning("不支持的文件类型: %s", file_type)
        return None

    try:
        text = parser(file_path)
        if text:
            text = text.strip()
        logger.info("文档解析完成: %s (%s, %d 字符)", file_path, file_type, len(text or ""))
        return text
    except Exception as e:
        logger.error("文档解析失败: %s (%s)", file_path, e, exc_info=True)
        return None


def _parse_text(file_path: str) -> str:
    """解析纯文本 / Markdown 文件。"""
    with open(file_path, "r", encoding="utf-8", errors="replace") as f:
        return f.read()


def _parse_pdf(file_path: str) -> str:
    """解析 PDF 文件。"""
    from pypdf import PdfReader

    reader = PdfReader(file_path)
    pages = []
    for page in reader.pages:
        text = page.extract_text()
        if text:
            pages.append(text)
    return "\n\n".join(pages)


def _parse_docx(file_path: str) -> str:
    """解析 Word 文档。"""
    from docx import Document as DocxDocument

    doc = DocxDocument(file_path)
    paragraphs = []
    for para in doc.paragraphs:
        if para.text and para.text.strip():
            paragraphs.append(para.text.strip())

    # 也提取表格内容
    for table in doc.tables:
        for row in table.rows:
            cells = [cell.text.strip() for cell in row.cells if cell.text.strip()]
            if cells:
                paragraphs.append(" | ".join(cells))

    return "\n\n".join(paragraphs)


def _parse_csv(file_path: str) -> str:
    """解析 CSV 文件为文本表格。"""
    rows = []
    with open(file_path, "r", encoding="utf-8", errors="replace") as f:
        reader = csv.reader(f)
        for row in reader:
            rows.append(" | ".join(cell.strip() for cell in row))
    return "\n".join(rows)