package handler

import (
	"fmt"
	"io"
	"mime"
	"mime/multipart"
	"path/filepath"
	"strings"

	"github.com/enterprise-ai-platform/server/internal/config"
)

// ValidateFile checks file size, extension, and MIME type.
// Returns nil if valid, or an error message if invalid.
func ValidateFile(header *multipart.FileHeader, allowedExtensions []string, maxSize int64) string {
	if header.Size > maxSize {
		return fmt.Sprintf("文件大小超出限制，最大支持 %dMB", maxSize/(1024*1024))
	}

	ext := strings.ToLower(filepath.Ext(header.Filename))
	if ext != "" {
		ext = ext[1:] // strip leading "."
	}

	extAllowed := false
	for _, e := range allowedExtensions {
		if strings.EqualFold(e, ext) {
			extAllowed = true
			break
		}
	}
	if !extAllowed {
		return fmt.Sprintf("不支持的文件类型：.%s，仅支持：%s", ext, strings.Join(allowedExtensions, "、"))
	}

	// Verify MIME type matches extension
	mimeType := header.Header.Get("Content-Type")
	if mimeType != "" {
		extMime, err := mime.ExtensionsByType(mimeType)
		if err == nil && len(extMime) > 0 {
			mimeAllowed := false
			for _, e := range extMime {
				if strings.EqualFold(strings.TrimPrefix(e, "."), ext) {
					mimeAllowed = true
					break
				}
			}
			if !mimeAllowed && !strings.HasPrefix(mimeType, "text/") && !strings.HasPrefix(mimeType, "application/") {
				return "文件类型与实际内容不匹配"
			}
		}
	}

	return "" // valid
}

// AllowedDocumentExtensions returns the list of allowed document file extensions.
func AllowedDocumentExtensions() []string {
	return []string{"pdf", "docx", "txt", "md", "csv", "xlsx"}
}

// AllowedDocumentMaxSize returns the max file size for document uploads.
func AllowedDocumentMaxSize() int64 {
	return config.MaxFileSize
}

// ReadAllWithLimit reads all content from r up to maxSize bytes.
// Returns error if content exceeds maxSize.
func ReadAllWithLimit(r io.Reader, maxSize int64) ([]byte, error) {
	limited := &io.LimitedReader{R: r, N: maxSize + 1}
	data, err := io.ReadAll(limited)
	if err != nil {
		return nil, err
	}
	if limited.N == 0 {
		return nil, fmt.Errorf("文件内容超出 %dMB 限制", maxSize/(1024*1024))
	}
	return data, nil
}