feat(subscription-info): add find subscription id method

lib/subscription-info.js

@@ -457,6 +457,27 @@ class SubscriptionInfo {
     _isSubscriptionStatusCurrentlyActive(status) {
         return ACTIVE_SUBSCRIPTION_DESCRIPTIONS.includes(status.description)
     }
+
+    /**
+     * Reads the target subscription from the database, or uses the given subscription object
+     * to find the subscription id.
+     * 
+     * @param {Object|Array<String>} subscriptionOrIds subscription object or array of ids if subscription should be read from database
+     * @param {String} planId the target plan
+     * @returns {String}
+     */
+    async findSubscriptionIdByPlanId(subscriptionOrIds, planId) {
+        const subscription = await this._getOrReadSubscription(subscriptionOrIds)
+        const { status } = subscription
+
+        const subscriptionStatus = status.find(({ subscription_plan_id }) => subscription_plan_id == planId)
+
+        if (subscriptionStatus) {
+            return subscriptionStatus.subscription_id
+        } else {
+            return null
+        }
+    }
 }
 
 module.exports = SubscriptionInfo

test/spec/subscription-info.spec.js

@@ -754,4 +754,27 @@ describe('SubscriptionInfo', () => {
             expect(subscriptionTrail[0].description).to.equal('deleted')
         })
     })
+
+    describe('.findSubscriptionIdByPlanId', () => {
+        let subscriptionId
+        beforeEach(async () => {
+            subscriptionId = uuid()
+            const createPayload = Object.assign({}, subscriptionCreated,
+                {
+                    subscription_id: subscriptionId,
+                    passthrough: JSON.stringify(customData(ids)),
+                    event_time: new Date().toISOString()
+                }
+            )
+            await subscriptions.addSubscriptionCreatedStatus(createPayload)
+        })
+        it('returns the subscription id', async () => {
+            const id = await subscriptionInfo.findSubscriptionIdByPlanId(ids, '8')
+            expect(id).to.equal(subscriptionId)
+        })
+        it('returns null if no subscription id was found for plan', async () => {
+            const id = await subscriptionInfo.findSubscriptionIdByPlanId(ids, '18')
+            expect(id).to.be.null
+        })
+    })
 })