import os
from typing import Tuple

def build_prompt(prefix: str, suffix: str) -> str:
    """
    构建用于代码补全的 Prompt。
    参考 completions-sample-code 的 extractPrompt 逻辑简化实现。
    """
    MAX_CONTEXT_LINES = 30
    
    prefix_lines = prefix.split('\n')
    suffix_lines = suffix.split('\n') if suffix else []
    
    recent_prefix = '\n'.join(prefix_lines[-MAX_CONTEXT_LINES:])
    recent_suffix = '\n'.join(suffix_lines[:5])

    prompt = f"""
You are a helpful writing assistant. Continue the text naturally based on the context.

Context (before cursor):
{recent_prefix}

Complete this:
{suffix if suffix else '(cursor here)'}

Continue:"""
    
    return prompt.strip()