package message

import (
	"encoding/base64"
	"errors"
	"strings"

	"aichat/utils"
)

const maxImageSize = 4 * 1024 * 1024

var allowedImageTypes = map[string]bool{
	"image/jpeg": true,
	"image/png":  true,
	"image/webp": true,
	"image/gif":  true,
}

func normalizeImageDataURI(raw string) (string, error) {
	comma := strings.Index(raw, ",")
	if comma < 0 {
		return "", errors.New("图片 base64 数据格式错误")
	}

	meta := strings.ToLower(strings.TrimSpace(raw[5:comma]))
	payload := strings.TrimSpace(raw[comma+1:])
	if payload == "" {
		return "", errors.New("图片 base64 数据不能为空")
	}
	parts := strings.Split(meta, ";")
	if len(parts) < 2 || !utils.Contains(parts[1:], "base64") {
		return "", errors.New("图片 data URI 必须使用 base64 编码")
	}

	mime := parts[0]
	if !allowedImageTypes[mime] {
		return "", errors.New("图片格式不支持，仅支持 jpeg/png/webp/gif")
	}

	decoded, err := base64.StdEncoding.DecodeString(payload)
	if err != nil {
		return "", errors.New("图片 base64 数据无效")
	}
	if len(decoded) > maxImageSize {
		return "", errors.New("图片过大，请选择小于 4MB 的图片")
	}

	return "data:" + mime + ";base64," + payload, nil
}