Correct cost aggregation logic to resolve diff in monthly cost

src/cost.test.ts

@@ -0,0 +1,201 @@
+import AWS from 'aws-sdk';
+import { AWSConfig } from './config';
+import { getRawCostByService, getTotalCosts } from './cost';
+import AWSMock from 'aws-sdk-mock';
+import dayjs from 'dayjs';
+
+// Use Apr 2024 (30 days) as the 'last month'
+// Thus 'today' is someday in May 2024
+const costDataLength = 65;
+const fixedToday = '2024-05-11'; // cost of 'this month' will be sum of 10 days from May 1 to May 10 ('today' is omitted because its cost is incomplete)
+const fixedFirstDay = dayjs(fixedToday).subtract(costDataLength, 'day');
+
+const generateMockPricingData = () => {
+  const resultsByTime = [];
+  for (let i = 0; i < costDataLength; i++) {
+    const date = dayjs(fixedFirstDay).add(i, 'day').format('YYYY-MM-DD');
+    const month = dayjs(date).month(); // 0-indexed (0 = January, 1 = February, etc.)
+    let service1Cost;
+
+    switch (month) {
+      case 2: // March
+        service1Cost = 0.9;
+        break;
+      case 3: // April
+        service1Cost = 1.0; // Total cost of service1 in April will be 30.00
+        break;
+      case 4: // May
+        service1Cost = 1.1;
+        break;
+      default:
+        service1Cost = 0.0; // Default cost if none of the above
+    }
+
+    resultsByTime.push({
+      TimePeriod: {
+        Start: date,
+        End: dayjs(date).add(1, 'day').format('YYYY-MM-DD'),
+      },
+      Groups: [
+        {
+          Keys: ['service1'],
+          Metrics: {
+            UnblendedCost: {
+              Amount: String(service1Cost),
+              Unit: 'USD',
+            },
+          },
+        },
+        {
+          Keys: ['service2'],
+          Metrics: {
+            UnblendedCost: {
+              Amount: String(service1Cost * 100),
+              Unit: 'USD',
+            },
+          },
+        },
+      ],
+    });
+  }
+  return { ResultsByTime: resultsByTime };
+};
+
+describe('Cost Functions', () => {
+  beforeAll(() => {
+    AWSMock.setSDKInstance(AWS);
+  });
+
+  afterAll(() => {
+    AWSMock.restore();
+  });
+
+  beforeEach(() => {
+    jest.useFakeTimers('modern');
+    jest.setSystemTime(new Date(fixedToday).getTime());
+  });
+
+  afterEach(() => {
+    jest.useRealTimers();
+  });
+
+  describe('getRawCostByService', () => {
+    it('should return raw cost by service', async () => {
+      const awsConfig: AWSConfig = {
+        credentials: {
+          accessKeyId: 'testAccessKeyId',
+          secretAccessKey: 'testSecretAccessKey',
+          sessionToken: 'testSessionToken',
+        },
+        region: 'us-east-1',
+      };
+
+      const mockPricingData = generateMockPricingData();
+
+      AWSMock.mock('CostExplorer', 'getCostAndUsage', (params, callback) => {
+        callback(null, mockPricingData);
+      });
+
+      const rawCostByService = await getRawCostByService(awsConfig);
+
+      const expectedRawCostByService = {
+        service1: {},
+        service2: {},
+      };
+      for (let i = 0; i < costDataLength; i++) {
+        const date = dayjs(fixedFirstDay).add(i, 'day').format('YYYY-MM-DD');
+        const month = dayjs(date).month();
+        let service1Cost;
+
+        switch (month) {
+          case 2: // March
+            service1Cost = 0.9;
+            break;
+          case 3: // April
+            service1Cost = 1.0; // Total cost of service1 in April will be 30.00
+            break;
+          case 4: // May
+            service1Cost = 1.1;
+            break;
+          default:
+            service1Cost = 0.0; // Default cost if none of the above
+        }
+
+        expectedRawCostByService.service1[date] = service1Cost;
+        expectedRawCostByService.service2[date] = service1Cost * 100;
+      }
+
+      expect(rawCostByService).toEqual(expectedRawCostByService);
+
+      AWSMock.restore('CostExplorer');
+    });
+  });
+
+  describe('getTotalCosts', () => {
+    it('should return total costs', async () => {
+      const awsConfig: AWSConfig = {
+        credentials: {
+          accessKeyId: 'testAccessKeyId',
+          secretAccessKey: 'testSecretAccessKey',
+          sessionToken: 'testSessionToken',
+        },
+        region: 'us-east-1',
+      };
+
+      const mockPricingData = generateMockPricingData();
+
+      AWSMock.mock('CostExplorer', 'getCostAndUsage', (params, callback) => {
+        callback(null, mockPricingData);
+      });
+
+      const totalCosts = await getTotalCosts(awsConfig);
+
+      const expectedTotalCosts = {
+        totals: {
+          lastMonth: 30 * (1 + 100), // Apr
+          thisMonth: 10 * (1.1 + 110), // sum of May 1..May 10
+          last7Days: 7 * 1.1 + 7 * 110, // sum of May 4..May 10
+          yesterday: 1.1 + 110, // on May 10
+        },
+        totalsByService: {
+          lastMonth: {
+            // Apr
+            service1: 30.0,
+            service2: 3000.0,
+          },
+          thisMonth: {
+            service1: 11.0, // 10 days of May
+            service2: 1100.0,
+          },
+          last7Days: {
+            service1: 7.7,
+            service2: 770.0,
+          },
+          yesterday: {
+            service1: 1.1,
+            service2: 110.0,
+          },
+        },
+      };
+
+      const roundToTwoDecimals = (num: number) => Math.round(num * 100) / 100;
+
+      Object.keys(totalCosts.totals).forEach((key) => {
+        expect(roundToTwoDecimals(totalCosts.totals[key])).toBeCloseTo(
+          expectedTotalCosts.totals[key],
+          1,
+        );
+      });
+
+      Object.keys(totalCosts.totalsByService).forEach((period) => {
+        Object.keys(totalCosts.totalsByService[period]).forEach((service) => {
+          expect(
+            roundToTwoDecimals(totalCosts.totalsByService[period][service]),
+          ).toBeCloseTo(expectedTotalCosts.totalsByService[period][service], 1);
+        });
+      });
+
+      AWSMock.restore('CostExplorer');
+    });
+  });
+});

src/cost.ts

@@ -1,5 +1,9 @@
 import AWS from 'aws-sdk';
 import dayjs from 'dayjs';
+import isSameOrAfter from 'dayjs/plugin/isSameOrAfter';
+import isSameOrBefore from 'dayjs/plugin/isSameOrBefore';
+dayjs.extend(isSameOrAfter);
+dayjs.extend(isSameOrBefore);
 import { AWSConfig } from './config';
 import { showSpinner } from './logger';
 
@@ -15,7 +19,7 @@ export async function getRawCostByService(
   showSpinner('Getting pricing data');
 
   const costExplorer = new AWS.CostExplorer(awsConfig);
-  const endDate = dayjs().subtract(1, 'day');
+  const endDate = dayjs(); // `endDate` is set to 'today' but its cost be omitted because of API spec (see: https://docs.aws.amazon.com/aws-cost-management/latest/APIReference/API_GetCostAndUsage.html#API_GetCostAndUsage_RequestSyntax)
   const startDate = endDate.subtract(65, 'day');
 
   const groupByConfig = [
@@ -74,7 +78,7 @@ export async function getRawCostByService(
       const filterKeys = group.Keys;
       const serviceName = filterKeys.find((key) => !/^\d{12}$/.test(key)); // AWS service name is non-12-digits string
       const cost = group.Metrics.UnblendedCost.Amount;
-      const costDate = day.TimePeriod.End;
+      const costDate = day.TimePeriod.Start; // must be set to `Start` not `End` because the end of `Period` parameter will be omitted (see: https://docs.aws.amazon.com/aws-cost-management/latest/APIReference/API_GetCostAndUsage.html#API_GetCostAndUsage_RequestSyntax)
 
       costByService[serviceName] = costByService[serviceName] || {};
       costByService[serviceName][costDate] = parseFloat(cost);
@@ -118,8 +122,8 @@ function calculateServiceTotals(
 
   const startOfLastMonth = dayjs().subtract(1, 'month').startOf('month');
   const startOfThisMonth = dayjs().startOf('month');
-  const startOfLast7Days = dayjs().subtract(7, 'day');
-  const startOfYesterday = dayjs().subtract(1, 'day');
+  const startOfLast7Days = dayjs().subtract(7, 'day').startOf('day');
+  const startOfYesterday = dayjs().subtract(1, 'day').startOf('day');
 
   for (const service of Object.keys(rawCostByService)) {
     const servicePrices = rawCostByService[service];
@@ -142,8 +146,8 @@ function calculateServiceTotals(
       }
 
       if (
-        dateObj.isSame(startOfLast7Days, 'week') &&
-        !dateObj.isSame(startOfYesterday, 'day')
+        dateObj.isSameOrAfter(startOfLast7Days) &&
+        dateObj.isSameOrBefore(dayjs().startOf('day'))
       ) {
         last7DaysServiceTotal += price;
       }