package tools

import (
	"context"
	"encoding/base64"
	"fmt"
	"os"
	"path/filepath"
	"regexp"

	"github.com/mark3labs/mcp-go/mcp"
)

const UploadFileName = "upload_file"

// filenameRegex restricts upload names to a safe, portable character set.
var filenameRegex = regexp.MustCompile(`^[a-zA-Z0-9._-]+$`)

// NewUploadFileTool returns the schema for the upload_file MCP Tool.
func NewUploadFileTool() mcp.Tool {
	return mcp.NewTool(UploadFileName,
		mcp.WithDescription("Upload a script or config file to ./data/uploads/ so it can be referenced by spark_submit later."),
		mcp.WithString("filename",
			mcp.Required(),
			mcp.Description("Plain file name without path separators (1-128 chars, [a-zA-Z0-9._-])"),
		),
		mcp.WithString("content",
			mcp.Required(),
			mcp.Description("File contents; text or base64-encoded binary"),
		),
		mcp.WithString("encoding",
			mcp.Description("Encoding of content"),
			mcp.Enum("text", "base64"),
			mcp.DefaultString("text"),
		),
	)
}

// UploadFileHandler writes user-provided content to DataDir/uploads/filename.
func (d *Deps) UploadFileHandler(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
	filename, err := req.RequireString("filename")
	if err != nil {
		return errResult("upload_file: " + err.Error()), nil
	}
	content, err := req.RequireString("content")
	if err != nil {
		return errResult("upload_file: " + err.Error()), nil
	}

	args := req.GetArguments()
	encoding := "text"
	if v, ok := args["encoding"].(string); ok && v != "" {
		encoding = v
	}
	if encoding != "text" && encoding != "base64" {
		return errResult(fmt.Sprintf("upload_file: invalid encoding %q", encoding)), nil
	}

	if err := validateUploadFilename(filename); err != nil {
		return errResult("upload_file: " + err.Error()), nil
	}

	var data []byte
	switch encoding {
	case "base64":
		decoded, err := base64.StdEncoding.DecodeString(content)
		if err != nil {
			return errResult("upload_file: decode base64: " + err.Error()), nil
		}
		data = decoded
	default:
		data = []byte(content)
	}

	final := filepath.Join(d.DataDir, "uploads", filename)
	if err := os.MkdirAll(filepath.Dir(final), 0o750); err != nil {
		return errResult("upload_file: create uploads dir: " + err.Error()), nil
	}
	if err := os.WriteFile(final, data, 0o640); err != nil {
		return errResult("upload_file: write file: " + err.Error()), nil
	}

	result := map[string]any{
		"path": fmt.Sprintf("uploads/%s", filename),
		"size": len(data),
	}
	return textResult(encodeJSON(result)), nil
}

func validateUploadFilename(filename string) error {
	if len(filename) == 0 || len(filename) > 128 {
		return fmt.Errorf("filename length must be 1-128")
	}
	if filepath.Base(filename) != filename {
		return fmt.Errorf("filename must not contain path separators or '..'")
	}
	if filename == "." || filename == ".." {
		return fmt.Errorf("filename must not be '.' or '..'")
	}
	if !filenameRegex.MatchString(filename) {
		return fmt.Errorf("filename contains invalid characters")
	}
	return nil
}