package storage

import (
	"fmt"
	"net"
	"net/url"
	"strings"
)

// ValidateThreadsFetchableURL ensures Meta servers can download an image for publish.
func ValidateThreadsFetchableURL(raw string) error {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return fmt.Errorf("圖片網址不可為空")
	}
	parsed, err := url.Parse(raw)
	if err != nil || parsed.Scheme == "" || parsed.Host == "" {
		return fmt.Errorf("圖片網址格式無效")
	}
	scheme := strings.ToLower(parsed.Scheme)
	if scheme != "https" && scheme != "http" {
		return fmt.Errorf("圖片網址必須是 http 或 https")
	}
	host := strings.ToLower(parsed.Hostname())
	if host == "" {
		return fmt.Errorf("圖片網址缺少主機名稱")
	}
	if isPrivateOrLoopbackHost(host) {
		return fmt.Errorf(
			"圖片網址 %s 無法被 Threads 伺服器存取（localhost / 內網）。請將 HAIXUN_STORAGE_S3_PUBLIC_BASE_URL 設為公開 HTTPS，例如 https://你的網域/api/v1/public/assets",
			raw,
		)
	}
	if scheme != "https" {
		return fmt.Errorf("Threads 附圖網址建議使用 HTTPS（目前為 %s）", scheme)
	}
	return nil
}

func isPrivateOrLoopbackHost(host string) bool {
	if host == "localhost" {
		return true
	}
	ip := net.ParseIP(host)
	if ip == nil {
		return false
	}
	return ip.IsLoopback() || ip.IsPrivate() || ip.IsLinkLocalUnicast()
}