.

packages/web/src/lib/billing-helpers.ts

@@ -0,0 +1,109 @@
+import type { BillingWithChecks, Price, UsageMeter, Product } from "@flowglad/server"
+
+/**
+ * Computes the total usage credits for a given usage meter slug from the current subscription's feature items.
+ */
+export function computeUsageTotal(
+  usageMeterSlug: string,
+  currentSubscription:
+    | NonNullable<NonNullable<BillingWithChecks["currentSubscriptions"]>[number]>
+    | undefined,
+  pricingModel: BillingWithChecks["pricingModel"] | undefined,
+): number {
+  try {
+    if (!currentSubscription || !pricingModel?.usageMeters) return 0
+
+    const experimental = currentSubscription.experimental as
+      | { featureItems?: Array<{ type: string; usageMeterId: string; amount: number }> }
+      | undefined
+    const featureItems = experimental?.featureItems ?? []
+
+    if (featureItems.length === 0) return 0
+
+    // Build lookup map: usageMeterId -> slug
+    const usageMeterById: Record<string, string> = {}
+    for (const meter of pricingModel.usageMeters) {
+      usageMeterById[String(meter.id)] = String(meter.slug)
+    }
+
+    // Sum up usage credits for matching meter
+    let total = 0
+    for (const item of featureItems) {
+      if (item.type !== "usage_credit_grant") continue
+      const meterSlug = usageMeterById[item.usageMeterId]
+      if (meterSlug === usageMeterSlug) {
+        total += item.amount
+      }
+    }
+
+    return total
+  } catch {
+    return 0
+  }
+}
+
+/**
+ * Finds a usage meter by its slug from the pricing model.
+ */
+export function findUsageMeterBySlug(
+  usageMeterSlug: string,
+  pricingModel: BillingWithChecks["pricingModel"] | undefined,
+): { id: string; slug: string } | null {
+  if (!pricingModel?.usageMeters) return null
+
+  const usageMeter = pricingModel.usageMeters.find(
+    (meter: UsageMeter) => meter.slug === usageMeterSlug,
+  )
+
+  if (!usageMeter) return null
+
+  return {
+    id: String(usageMeter.id),
+    slug: String(usageMeter.slug),
+  }
+}
+
+/**
+ * Finds a usage price by its associated usage meter slug from the pricing model.
+ */
+export function findUsagePriceByMeterSlug(
+  usageMeterSlug: string,
+  pricingModel: BillingWithChecks["pricingModel"] | undefined,
+): Price | null {
+  if (!pricingModel?.products || !pricingModel?.usageMeters) return null
+
+  // Build lookup map: slug -> id
+  const meterIdBySlug = new Map(
+    pricingModel.usageMeters.map((meter: UsageMeter) => [meter.slug, meter.id]),
+  )
+
+  const usageMeterId = meterIdBySlug.get(usageMeterSlug)
+  if (!usageMeterId) return null
+
+  // Find price by meter ID
+  const usagePrice = pricingModel.products
+    .flatMap((product: Product) => product.prices ?? [])
+    .find(
+      (price: Price) => price.type === "usage" && price.usageMeterId === usageMeterId,
+    )
+
+  return usagePrice ?? null
+}
+
+/**
+ * Checks if a plan is a default (free) plan by looking up the price by slug.
+ */
+export function isDefaultPlanBySlug(
+  pricingModel: BillingWithChecks["pricingModel"] | null | undefined,
+  priceSlug: string | undefined,
+): boolean {
+  if (!pricingModel?.products || !priceSlug) return false
+
+  for (const product of pricingModel.products) {
+    const price = product.prices?.find((p: Price) => p.slug === priceSlug)
+    if (price) {
+      return product.default === true
+    }
+  }
+  return false
+}