Sub2API v1.0 - AI API 网关（二开初始版本，基于上游 Wei-Shaw/sub2api）

backend/internal/service/video_billing_resolution.go

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+package service
+
+import "strings"
+
+const (
+	VideoBillingResolution480P  = "480p"
+	VideoBillingResolution720P  = "720p"
+	VideoBillingResolution1080P = "1080p"
+)
+
+// xAI 视频生成按秒计费，duration 请求参数允许 1-15 秒；未指定时上游默认生成 8 秒。
+// 计费时长必须与上游实际消耗对齐，否则用户可通过拉长 duration 套利（提交时长由用户控制）。
+const (
+	VideoBillingMinDurationSeconds     = 1
+	VideoBillingMaxDurationSeconds     = 15
+	VideoBillingDefaultDurationSeconds = 8
+)
+
+// NormalizeVideoBillingDurationSecondsOrDefault 归一化计费用视频时长：
+// 未指定（<=0）按上游默认 8 秒计，超出上游允许区间按边界收敛。
+func NormalizeVideoBillingDurationSecondsOrDefault(durationSeconds int) int {
+	if durationSeconds <= 0 {
+		return VideoBillingDefaultDurationSeconds
+	}
+	if durationSeconds < VideoBillingMinDurationSeconds {
+		return VideoBillingMinDurationSeconds
+	}
+	if durationSeconds > VideoBillingMaxDurationSeconds {
+		return VideoBillingMaxDurationSeconds
+	}
+	return durationSeconds
+}
+
+// LookupVideoBillingResolution 归一化分辨率并报告是否为已知档位。
+// 配置解析路径必须用它而不是 OrDefault：把无法识别的档位（如 "4k"、拼错的
+// "1080i"）静默折算成 480p，会让管理员配的高分辨率单价被挂到低分辨率档上。
+func LookupVideoBillingResolution(resolution string) (string, bool) {
+	switch strings.ToLower(strings.TrimSpace(resolution)) {
+	case "480", "480p", "sd":
+		return VideoBillingResolution480P, true
+	case "720", "720p", "hd":
+		return VideoBillingResolution720P, true
+	case "1080", "1080p", "full_hd", "full-hd", "fhd":
+		return VideoBillingResolution1080P, true
+	default:
+		return "", false
+	}
+}
+
+// NormalizeVideoBillingResolutionOrDefault 用于运行时计费：上游回传的分辨率
+// 缺失或无法识别时按最低档兜底，保证请求仍可计费。
+func NormalizeVideoBillingResolutionOrDefault(resolution string) string {
+	if normalized, ok := LookupVideoBillingResolution(resolution); ok {
+		return normalized
+	}
+	return VideoBillingResolution480P
+}