"""
Write Tool - 文件写入工具

参考：vendor/opencode/packages/opencode/src/tool/write.ts

核心功能：
- 创建新文件或覆盖现有文件
- 支持追加模式（append）
- 生成 diff 预览
"""

from pathlib import Path
from typing import Optional
import difflib

from agent.tools import tool, ToolResult, ToolContext


@tool(description="写入文件内容（创建新文件、覆盖现有文件或追加内容）")
async def write_file(
    file_path: str,
    content: str,
    append: bool = False,
    context: Optional[ToolContext] = None
) -> ToolResult:
    """
    写入文件

    参考 OpenCode 实现，并添加追加模式支持

    Args:
        file_path: 文件路径
        content: 文件内容
        append: 是否追加模式（默认 False，覆盖写入）
        context: 工具上下文

    Returns:
        ToolResult: 写入结果
    """
    # 解析路径
    path = Path(file_path)
    if not path.is_absolute():
        path = Path.cwd() / path

    # 检查是否为目录
    if path.exists() and path.is_dir():
        return ToolResult(
            title="路径错误",
            output=f"路径是目录，不是文件: {file_path}",
            error="Path is a directory"
        )

    # 读取旧内容（如果存在）
    existed = path.exists()
    old_content = ""
    if existed:
        try:
            with open(path, 'r', encoding='utf-8') as f:
                old_content = f.read()
        except Exception:
            old_content = ""

    # 确定最终内容
    if append and existed:
        new_content = old_content + content
    else:
        new_content = content

    # 生成 diff
    if existed and old_content:
        diff = _create_diff(str(path), old_content, new_content)
    else:
        diff = f"(新建文件: {path.name})"

    # 确保父目录存在
    path.parent.mkdir(parents=True, exist_ok=True)

    # 写入文件
    try:
        with open(path, 'w', encoding='utf-8') as f:
            f.write(new_content)
    except Exception as e:
        return ToolResult(
            title="写入失败",
            output=f"无法写入文件: {str(e)}",
            error=str(e)
        )

    # 统计
    lines = new_content.count('\n')

    # 构建操作描述
    if append and existed:
        operation = "追加内容到"
    elif existed:
        operation = "覆盖"
    else:
        operation = "创建"

    return ToolResult(
        title=path.name,
        output=f"文件写入成功 ({operation})\n\n{diff}",
        metadata={
            "existed": existed,
            "append": append,
            "lines": lines,
            "diff": diff
        },
        long_term_memory=f"{operation}文件 {path.name}"
    )


def _create_diff(filepath: str, old_content: str, new_content: str) -> str:
    """生成 unified diff"""
    old_lines = old_content.splitlines(keepends=True)
    new_lines = new_content.splitlines(keepends=True)

    diff_lines = list(difflib.unified_diff(
        old_lines,
        new_lines,
        fromfile=f"a/{filepath}",
        tofile=f"b/{filepath}",
        lineterm=''
    ))

    if not diff_lines:
        return "(无变更)"

    return ''.join(diff_lines)