Initial import of zappier-edge from zapier monorepo

src/credits.ts

@@ -0,0 +1,29 @@
+export interface CreditAdjustment {
+  id: string;
+  customerId: string;
+  cents: number;
+  reason: string;
+  agent: string;
+  at: string;
+}
+
+export class CreditLedger {
+  private rows: CreditAdjustment[] = [];
+
+  add(row: Omit<CreditAdjustment, 'id' | 'at'> & { id?: string; at?: string }): CreditAdjustment {
+    const rec: CreditAdjustment = {
+      id: row.id || `crd_${Date.now().toString(36)}`,
+      customerId: row.customerId,
+      cents: row.cents,
+      reason: row.reason,
+      agent: row.agent,
+      at: row.at || new Date().toISOString(),
+    };
+    this.rows.unshift(rec);
+    return rec;
+  }
+
+  list(customerId?: string): CreditAdjustment[] {
+    return customerId ? this.rows.filter((r) => r.customerId === customerId) : this.rows;
+  }
+}