package handler

import (
	"encoding/base64"
	"errors"
	"strings"
	"unicode/utf8"
)

const (
	maxTextMessageLength = 2000
	maxImageMessageSize  = 5 * 1024 * 1024
)

func validateMessageContent(messageType, content string) (string, error) {
	switch messageType {
	case "text":
		content = strings.TrimSpace(content)
		if content == "" {
			return "", errors.New("消息内容不能为空")
		}
		if utf8.RuneCountInString(content) > maxTextMessageLength {
			return "", errors.New("单条文本消息不能超过 2000 字")
		}
		return content, nil
	case "image":
		parts := strings.SplitN(content, ",", 2)
		if len(parts) != 2 {
			return "", errors.New("图片格式无效")
		}
		if parts[0] != "data:image/jpeg;base64" && parts[0] != "data:image/png;base64" && parts[0] != "data:image/gif;base64" {
			return "", errors.New("仅支持 jpg、png、gif 图片")
		}
		bytes, err := base64.StdEncoding.DecodeString(parts[1])
		if err != nil || len(bytes) == 0 {
			return "", errors.New("图片内容无效")
		}
		if len(bytes) > maxImageMessageSize {
			return "", errors.New("图片不能超过 5 MB")
		}
		return content, nil
	default:
		return "", errors.New("不支持的消息类型")
	}
}