"""
语言检测服务

检测PDF文档的主要语言（中文/英文/混合）
用于决定使用哪种提取方法
"""

import pdfplumber
from typing import Dict, Any
from loguru import logger


def detect_language(pdf_path: str) -> str:
    """
    检测PDF主要语言
    
    策略：
    1. 提取前3页文本（代表性强）
    2. 统计中文字符比例
    3. 判断语言类型
    
    Args:
        pdf_path: PDF文件路径
    
    Returns:
        'chinese' | 'english' | 'mixed'
    """
    try:
        logger.info(f"开始语言检测: {pdf_path}")
        
        with pdfplumber.open(pdf_path) as pdf:
            # 提取前3页文本（或全部如果少于3页）
            sample_pages = min(3, len(pdf.pages))
            sample_text = ""
            
            for i in range(sample_pages):
                try:
                    page_text = pdf.pages[i].extract_text()
                    if page_text:
                        sample_text += page_text + "\n"
                except Exception as e:
                    logger.warning(f"第{i+1}页文本提取失败: {str(e)}")
                    continue
        
        # 检查是否有足够文本
        if len(sample_text.strip()) < 100:
            logger.warning("文本太少，默认使用英文处理")
            return 'english'
        
        # 统计中文字符比例
        chinese_chars = len([c for c in sample_text if '\u4e00' <= c <= '\u9fff'])
        total_chars = len([c for c in sample_text if c.strip()])
        
        if total_chars == 0:
            logger.warning("无有效字符，默认使用英文处理")
            return 'english'
        
        chinese_ratio = chinese_chars / total_chars
        
        logger.info(f"中文字符比例: {chinese_ratio:.2%} ({chinese_chars}/{total_chars})")
        
        # 判断语言
        # 阈值说明：
        # - > 30%: 判定为中文PDF（包括中英混合但中文为主）
        # - <= 30%: 判定为英文PDF
        if chinese_ratio > 0.3:
            language = 'chinese'
        else:
            language = 'english'
        
        logger.info(f"检测结果: {language}")
        return language
    
    except Exception as e:
        logger.error(f"语言检测失败: {str(e)}，默认使用英文处理")
        return 'english'


def detect_language_detailed(pdf_path: str) -> Dict[str, Any]:
    """
    详细的语言检测
    
    返回更多统计信息
    
    Args:
        pdf_path: PDF文件路径
    
    Returns:
        {
            "language": "chinese" | "english" | "mixed",
            "chinese_ratio": 0.65,
            "chinese_chars": 3500,
            "total_chars": 5000,
            "sample_pages": 3,
            "sample_text_length": 5000
        }
    """
    try:
        with pdfplumber.open(pdf_path) as pdf:
            sample_pages = min(3, len(pdf.pages))
            sample_text = ""
            
            for i in range(sample_pages):
                try:
                    page_text = pdf.pages[i].extract_text()
                    if page_text:
                        sample_text += page_text + "\n"
                except:
                    continue
        
        # 统计
        chinese_chars = len([c for c in sample_text if '\u4e00' <= c <= '\u9fff'])
        total_chars = len([c for c in sample_text if c.strip()])
        
        chinese_ratio = chinese_chars / total_chars if total_chars > 0 else 0
        
        # 判断语言
        if chinese_ratio > 0.3:
            language = 'chinese'
        elif chinese_ratio > 0.1:
            language = 'mixed'
        else:
            language = 'english'
        
        return {
            "language": language,
            "chinese_ratio": round(chinese_ratio, 4),
            "chinese_chars": chinese_chars,
            "total_chars": total_chars,
            "sample_pages": sample_pages,
            "sample_text_length": len(sample_text)
        }
    
    except Exception as e:
        logger.error(f"详细语言检测失败: {str(e)}")
        return {
            "language": "english",
            "error": str(e)
        }


def is_chinese_pdf(pdf_path: str, threshold: float = 0.3) -> bool:
    """
    简单判断是否为中文PDF
    
    Args:
        pdf_path: PDF文件路径
        threshold: 中文字符比例阈值，默认30%
    
    Returns:
        True if 中文字符比例 > threshold
    """
    language = detect_language(pdf_path)
    return language == 'chinese'