#!/usr/bin/env python3
import sys

def read_file(filepath):
    """读取文件内容，返回行列表"""
    try:
        with open(filepath, 'r', encoding='utf-8') as f:
            return f.readlines()
    except FileNotFoundError:
        print(f"错误：文件 '{filepath}' 不存在")
        sys.exit(1)

def get_context(line, pos, context_len=10):
    """获取字符上下文"""
    start = max(0, pos - context_len)
    end = min(len(line), pos + context_len + 1)
    prefix = "..." if start > 0 else ""
    suffix = "..." if end < len(line) else ""
    return prefix + line[start:end] + suffix

def compare_files(file1, file2):
    """比较两个文件，输出详细差异"""
    lines1 = read_file(file1)
    lines2 = read_file(file2)
    
    print(f"比较文件: {file1} vs {file2}")
    print("=" * 80)
    
    max_lines = max(len(lines1), len(lines2))
    differences = 0
    
    for line_num in range(max_lines):
        line1 = lines1[line_num] if line_num < len(lines1) else None
        line2 = lines2[line_num] if line_num < len(lines2) else None
        
        if line1 is None:
            print(f"\n[新增行] 第 {line_num + 1} 行")
            print(f"        + {repr(line2)}")
            differences += 1
            continue
        
        if line2 is None:
            print(f"\n[删除行] 第 {line_num + 1} 行")
            print(f"        - {repr(line1)}")
            differences += 1
            continue
        
        if line1 == line2:
            continue
        
        # 行内容不同，逐字符比较
        print(f"\n[差异行] 第 {line_num + 1} 行")
        
        max_chars = max(len(line1), len(line2))
        for char_pos in range(max_chars):
            char1 = line1[char_pos] if char_pos < len(line1) else None
            char2 = line2[char_pos] if char_pos < len(line2) else None
            
            if char1 == char2:
                continue
            
            # 找到差异字符
            context1 = get_context(line1, char_pos) if line1 else ""
            context2 = get_context(line2, char_pos) if line2 else ""
            
            print(f"        字符位置 {char_pos + 1}:")
            if char1 is not None:
                print(f"          - {repr(char1)} | 上下文: {repr(context1)}")
            else:
                print(f"          - (缺失)")
            if char2 is not None:
                print(f"          + {repr(char2)} | 上下文: {repr(context2)}")
            else:
                print(f"          + (缺失)")
            differences += 1
            
            # 跳过一些连续差异，避免输出过多
            while char_pos + 1 < max_chars:
                next_char1 = line1[char_pos + 1] if char_pos + 1 < len(line1) else None
                next_char2 = line2[char_pos + 1] if char_pos + 1 < len(line2) else None
                if next_char1 != next_char2:
                    char_pos += 1
                else:
                    break
    
    print("\n" + "=" * 80)
    print(f"比较完成，共发现 {differences} 处差异")

def main():
    if len(sys.argv) != 3:
        print("用法: python diff.py <文件1> <文件2>")
        sys.exit(1)
    
    file1 = sys.argv[1]
    file2 = sys.argv[2]
    
    compare_files(file1, file2)

if __name__ == "__main__":
    main()