3 files changed, 119 insertions, 0 deletions
diff --git a/packages/monorepo-scripts/package.json b/packages/monorepo-scripts/package.json
index 4a2cf52e1..09b7a340d 100644
--- a/packages/monorepo-scripts/package.json
+++ b/packages/monorepo-scripts/package.json
@@ -7,6 +7,7 @@
     "scripts": {
         "build:watch": "tsc -w",
         "deps_versions": "node ./lib/deps_versions.js",
+        "publish:prepublish": "yarn build; node ./lib/custom_prepublish.js",
         "convert_changelogs": "yarn build; node ./lib/convert_changelogs.js",
         "lint": "tslint --project . 'src/**/*.ts'",
         "clean": "shx rm -rf lib",
diff --git a/packages/monorepo-scripts/src/custom_prepublish.ts b/packages/monorepo-scripts/src/custom_prepublish.ts
new file mode 100644
index 000000000..7f0e186bd
--- /dev/null
+++ b/packages/monorepo-scripts/src/custom_prepublish.ts
@@ -0,0 +1,117 @@
+#!/usr/bin/env node
+
+import * as fs from 'fs';
+import lernaGetPackages = require('lerna-get-packages');
+import * as _ from 'lodash';
+import * as moment from 'moment';
+import * as path from 'path';
+import { exec as execAsync } from 'promisify-child-process';
+import semverSort = require('semver-sort');
+
+import { Changelog, Changes, UpdatedPackage } from './types';
+import { utils } from './utils';
+
+const MONOREPO_ROOT_PATH = path.join(__dirname, '../../..');
+const TODAYS_TIMESTAMP = moment().unix();
+
+(async () => {
+    const updatedPublicPackages = await getPublicLernaUpdatedPackagesAsync();
+    const updatedPackageNames = _.map(updatedPublicPackages, pkg => pkg.name);
+
+    const allLernaPackages = lernaGetPackages(MONOREPO_ROOT_PATH);
+    const relevantLernaPackages = _.filter(allLernaPackages, pkg => {
+        return _.includes(updatedPackageNames, pkg.package.name);
+    });
+    _.each(relevantLernaPackages, lernaPackage => {
+        const changelogJSONPath = path.join(lernaPackage.location, 'CHANGELOG.json');
+        const changelogJSON = getChangelogJSONOrCreateIfMissing(lernaPackage.package.name, changelogJSONPath);
+        let changelogs: Changelog[];
+        try {
+            changelogs = JSON.parse(changelogJSON);
+        } catch (err) {
+            throw new Error(
+                `${lernaPackage.package.name}'s CHANGELOG.json contains invalid JSON. Please fix and try again.`,
+            );
+        }
+
+        const currentVersion = lernaPackage.package.version;
+        const shouldAddNewEntry = shouldAddNewChangelogEntry(changelogs);
+        if (shouldAddNewEntry) {
+            // Create a new entry for a patch version with generic changelog entry.
+            const nextPatchVersion = utils.getNextPatchVersion(currentVersion);
+            const newChangelogEntry: Changelog = {
+                timestamp: TODAYS_TIMESTAMP,
+                version: nextPatchVersion,
+                changes: [
+                    {
+                        note: 'Dependencies updated',
+                    },
+                ],
+            };
+            changelogs = [newChangelogEntry, ...changelogs];
+        } else {
+            // Update existing entry with timestamp
+            const lastEntry = changelogs[0];
+            if (_.isUndefined(lastEntry.timestamp)) {
+                lastEntry.timestamp = TODAYS_TIMESTAMP;
+            }
+            // Check version number is correct.
+            const proposedNextVersion = lastEntry.version;
+            lastEntry.version = updateVersionNumberIfNeeded(currentVersion, proposedNextVersion);
+            changelogs[0] = lastEntry;
+        }
+
+        // Save updated CHANGELOG.json
+        fs.writeFileSync(changelogJSONPath, JSON.stringify(changelogs, null, '\t'));
+        // Generate updated CHANGELOG.md
+        const changelogMd = generateChangelogMd(changelogs);
+    });
+})().catch(err => {
+    utils.log(err);
+    process.exit(1);
+});
+
+async function getPublicLernaUpdatedPackagesAsync(): Promise<UpdatedPackage[]> {
+    const result = await execAsync(`./node_modules/lerna/bin/lerna.js updated --json`, { cwd: MONOREPO_ROOT_PATH });
+    const updatedPackages = JSON.parse(result.stdout);
+    const updatedPublicPackages = _.filter(updatedPackages, updatedPackage => !updatedPackage.private);
+    return updatedPublicPackages;
+}
+
+function updateVersionNumberIfNeeded(currentVersion: string, proposedNextVersion: string) {
+    console.log('currentVersion', currentVersion);
+    console.log('proposedNextVersion', proposedNextVersion);
+    if (proposedNextVersion === currentVersion) {
+        return utils.getNextPatchVersion(currentVersion);
+    }
+    const sortedVersions = semverSort.desc([proposedNextVersion, currentVersion]);
+    if (sortedVersions[0] !== proposedNextVersion) {
+        return utils.getNextPatchVersion(currentVersion);
+    }
+    return proposedNextVersion;
+}
+
+function getChangelogJSONOrCreateIfMissing(packageName: string, changelogPath: string): string {
+    let changelogJSON: string;
+    try {
+        changelogJSON = fs.readFileSync(changelogPath, 'utf-8');
+        return changelogJSON;
+    } catch (err) {
+        // If none exists, create new, empty one.
+        const emptyChangelogJSON = JSON.stringify([]);
+        fs.writeFileSync(changelogPath, emptyChangelogJSON);
+        return emptyChangelogJSON;
+    }
+}
+
+function shouldAddNewChangelogEntry(changelogs: Changelog[]): boolean {
+    if (_.isEmpty(changelogs)) {
+        return true;
+    }
+    const lastEntry = changelogs[0];
+    return !!lastEntry.isPublished;
+}
+
+function generateChangelogMd(changelogs: Changelog[]): string {
+    return '';
+}
diff --git a/packages/monorepo-scripts/src/globals.d.ts b/packages/monorepo-scripts/src/globals.d.ts
index 1d49559f2..90adc0b78 100644
--- a/packages/monorepo-scripts/src/globals.d.ts
+++ b/packages/monorepo-scripts/src/globals.d.ts
@@ -11,6 +11,7 @@ declare interface LernaPackage {
     location: string;
     package: {
         private?: boolean;
+        version: string;
         name: string;
         main?: string;
         config?: {