Replace duplicated raw export size calculations with a shared estimator

src/client/app/redux/thunks/exportThunk.ts

@@ -25,6 +25,7 @@ import { createAppThunk } from './appThunk';
 import { selectAnythingFetching } from '../../redux/selectors/apiSelectors';
 import { RootState } from '../../store';
 import { find, sortBy } from 'lodash';
+import { estimateRawExportSizeMB } from '../../../../common/RawExportFileSize';
 
 const selectCanExport = (state: RootState) => {
 	const fetchInProgress = selectAnythingFetching(state);
@@ -134,10 +135,7 @@ export const exportRawReadings = createAppThunk(
 		// the wrong value. The time to do this is small compared to most raw exports (if file is large
 		// when it matters).
 		const count = await dispatch(metersApi.endpoints.lineReadingsCount.initiate({ meterIDs, timeInterval })).unwrap();
-		// Estimated file size in MB. Note that changing the language effects the size about +/- 8%.
-		// This is just a decent estimate for larger files.
-		// This estimate is also present in src/server/routes/readings.js and must be kept consistent between files.
-		const fileSize = (count * 0.082 / 1000);
+		const fileSize = estimateRawExportSizeMB(count);
 		// Decides if the readings should be exported, true if should.
 		let shouldDownload = false;
 		if (fileSize <= adminState.defaultWarningFileSize) {

src/common/RawExportFileSize.d.ts

@@ -0,0 +1,14 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/**
+ * Estimates the size of a raw export in MB based on the number of readings.
+ * Note that changing the language effects the size about +/- 8%.
+ * This is just a decent estimate for larger files.
+ * @param readingCount - The number of readings to estimate.
+ * @returns The estimated size in MB.
+ */
+export function estimateRawExportSizeMB(readingCount: number): number;

src/common/RawExportFileSize.js

@@ -0,0 +1,22 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+const ESTIMATED_MB_PER_RAW_READING = 8.2e-5;
+
+/**
+ * Estimates the size of a raw export in MB based on the number of readings.
+ * Note that changing the language effects the size about +/- 8%.
+ * This is just a decent estimate for larger files.
+ * @param readingCount - The number of readings to estimate.
+ * @returns The estimated size in MB.
+ */
+function estimateRawExportSizeMB(readingCount) {
+	return readingCount * ESTIMATED_MB_PER_RAW_READING;
+}
+
+module.exports = {
+	estimateRawExportSizeMB
+};

src/server/routes/readings.js

@@ -16,6 +16,7 @@ const { isTokenAuthorized } = require('../util/userRoles');
 const Preferences = require('../models/Preferences');
 const User = require('../models/User');
 const { success, failure } = require('./response');
+const { estimateRawExportSizeMB } = require('../../common/RawExportFileSize');
 
 const router = express.Router();
 
@@ -111,11 +112,9 @@ router.get('/line/raw/meter/:meter_id', optionalAuthMiddleware, async (req, res)
 			timeInterval = TimeInterval.fromString(req.query.timeInterval);
 			// Check if user is allowed to export.
 			let shouldDownload = false;
-			// Estimated file size. The full explanation of the estimate used can be found in the client.
-			// This estimate is also present in src/client/app/redux/thunks/exportThunk.ts and must be kept consistent between files.
 			// This count only checks a single meterID, while client testing checks multiple meterIDs, so the estimate is slightly different.
 			const count = await Reading.getCountByMeterIDAndDateRange(meterID, timeInterval.startTimestamp, timeInterval.endTimestamp, conn);
-			const fileSize = (count * 0.082 / 1000);
+			const fileSize = estimateRawExportSizeMB(count);
 			const preferences = await Preferences.get(conn);
 			if (fileSize <= preferences.defaultFileSizeLimit) {
 				// File size within limit, anyone can download.

src/server/test/util/rawExportFileSizeTests.js

@@ -0,0 +1,27 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+const { expect, mocha } = require('../common');
+const { estimateRawExportSizeMB } = require('../../../common/RawExportFileSize');
+const DELTA = 1e-15;
+
+mocha.describe('Raw Export File Size Estimator', () => {
+	mocha.it('returns zero for zero readings', () => {
+		expect(estimateRawExportSizeMB(0)).to.be.closeTo(0, DELTA);
+	});
+
+	mocha.it('returns 0.082 MB for 1000 readings', () => {
+		expect(estimateRawExportSizeMB(1000)).to.be.closeTo(0.082, DELTA);
+	});
+
+	mocha.it('returns 0.11808 MB for 1440 readings', () => {
+		expect(estimateRawExportSizeMB(1440)).to.be.closeTo(0.11808, DELTA);
+	});
+
+	mocha.it('returns 0.71832 MB for 8760 readings', () => {
+		expect(estimateRawExportSizeMB(8760)).to.be.closeTo(0.71832, DELTA);
+	});
+});