feat: add function and task to get version of used dependency

Fixes #20

src/cli.ts

@@ -16,8 +16,10 @@ import {Api} from '@openstapps/gitlab-api';
 import {Logger} from '@openstapps/logger';
 import * as commander from 'commander';
 import {existsSync, readFileSync} from 'fs';
-import {join} from 'path';
+import {join, resolve} from 'path';
+import {cwd, stdout} from 'process';
 import {GITLAB_API_URL} from './configuration';
+import {getUsedVersionMajorMinor} from './tasks/get-used-version';
 import {remind} from './tasks/remind';
 import {tidy} from './tasks/tidy';
 import {unlabel} from './tasks/unlabel';
@@ -63,6 +65,17 @@ commander
     Logger.ok('Done!');
   });
 
+commander
+  .command('get-used-version <dependency> [path]')
+  .action(async (dependency, path) => {
+    let fallbackPath = cwd();
+    if (typeof path === 'string' && path.length > 0) {
+      fallbackPath = resolve(path);
+    }
+
+    stdout.write(await getUsedVersionMajorMinor(fallbackPath, dependency), process.exit);
+  });
+
 commander
   .parse(process.argv);
 

src/tasks/get-used-version.ts

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2019 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+import {existsSync, PathLike} from 'fs';
+import {join} from 'path';
+import {readFilePromisified} from '../common';
+
+/**
+ * Get used version of a dependency of a project referenced by a path
+ *
+ * @param path Path to a Node.js project directory
+ * @param dependency Dependency to get used version of
+ */
+export async function getUsedVersion(path: PathLike, dependency: string): Promise<string> {
+  if (!existsSync(join(path.toString(), 'package.json'))) {
+    throw new Error(`'package.json' does not exist in '${path}'. Not a Node.js project?`);
+  }
+
+  const buffer = await readFilePromisified(join(path.toString(), 'package.json'));
+  const content = buffer.toString();
+  const pkgJson = JSON.parse(content);
+
+  if (typeof pkgJson.dependencies !== 'object') {
+    throw new Error(`Project in '${path}' has no dependencies!`);
+  }
+
+  if (typeof pkgJson.dependencies[dependency] !== 'string') {
+    throw new Error(`Project in '${path}' does not depend on '${dependency}'.`);
+  }
+
+  return pkgJson.dependencies[dependency];
+}
+
+/**
+ * Get 'MAJOR.MINOR' part of a used version
+ *
+ * See [[getUsedVersion]].
+ *
+ * @param path see [[getUsedVersion]]
+ * @param dependency see [[getUsedVersion]]
+ */
+export async function getUsedVersionMajorMinor(path: PathLike, dependency: string): Promise<string> {
+  const versionMatch = (await getUsedVersion(path, dependency)).match(/([0-9]+\.[0-9]+)\.[0-9]+/);
+
+  if (versionMatch === null) {
+    throw new Error(`Used version of '${dependency}' of project in '${path}' could not be determined.`);
+  }
+
+  return versionMatch[1];
+}