Add support for supplying multiple label files

- Fixes #49

This change introduces support for any number of `--labels` arguments to
be supplied. The behavior is the same as before, with regards to http(s)
urls or local paths, and after they are all collected, they will be
merged. Any items with a duplicate name and different property values
will throw an error. Otherwise they will be merged and then applied.

bin/github-label-sync.js

@@ -19,7 +19,8 @@ program
 	.option(
 		'-l, --labels <path>',
 		'the path or URL to look for the label configuration in. Default: labels.json',
-		'labels.json'
+		getLabelFiles,
+		[ ]
 	)
 	.option(
 		'-d, --dry-run',
@@ -41,29 +42,44 @@ if (program.args.length !== 1) {
 	program.help();
 }
 
+function getLabelFiles(value, previous) {
+	return previous.concat([value]);
+}
+
 function readLabels() {
-	if (program.labels.indexOf('http://') === 0 || program.labels.indexOf('https://') === 0) {
-		const got = require('got');
+	if (program.labels.length === 0) {
+		program.labels = [ 'labels.json' ];
+	}
 
-		return got(program.labels, { json: true }).then((response) => response.body).catch(() => {
-			console.error(chalk.red(`Downloading labels from ${program.labels} failed`));
-			process.exit(1);
-		});
+	const files = [];
 
-	} else {
-		// Resolve the label configuration path
-		if (!/^[\/\~]/.test(program.labels)) {
-			program.labels = path.resolve(process.cwd(), program.labels);
-		}
+	program.labels.forEach((file) => {
+		if (file.indexOf('http://') === 0 || file.indexOf('https://') === 0) {
+			const got = require('got');
 
-		// Load the labels
-		try {
-			return Promise.resolve(require(program.labels));
-		} catch (error) {
-			console.error(chalk.red(`No labels were found in ${program.labels}`));
-			process.exit(1);
+			files.push(got(file, { json: true }).then((response) => response.body).catch(() => {
+				console.error(chalk.red(`Downloading labels from ${file} failed`));
+				process.exit(1);
+			}));
+
+		} else {
+			// Resolve the label configuration path
+			if (!/^[\/\~]/.test(file)) {
+				file = path.resolve(process.cwd(), file);
+			}
+
+			// Load the labels
+			try {
+				files.push(Promise.resolve(require(file)));
+			} catch (error) {
+				console.error(chalk.red(`No labels were found in ${file}`));
+				process.exit(1);
+			}
 		}
-	}
+
+	});
+
+	return Promise.all(files);
 }
 
 // Apply some log formatting
@@ -79,16 +95,45 @@ const format = {
 	}
 };
 
+// Merge our lists together
+function merge(files) {
+	const data = {};
+	const labels = [];
+
+	files.forEach((file) => {
+		if (!Array.isArray(file)) {
+			return;
+		}
+
+		file.forEach((label) => {
+			if (data[label.name] !== null && data[label.name] !== '') {
+				data[label.name] = label;
+			} else {
+				if (JSON.stringify(data[label.name]) !== JSON.stringify(label)) {
+					console.error(chalk.red(`Conflicting label names were found: ${label.name}`));
+					process.exit(1);
+				}
+			}
+		});
+	});
+
+	Object.keys(data).forEach((key) => {
+		labels.push(data[key]);
+	});
+
+	return labels;
+}
+
 // Pull together all the options
 function resolveOptions() {
-	return readLabels().then((labels) => {
+	return readLabels().then((files) => {
 		return {
 			accessToken: program.accessToken,
 			allowAddedLabels: program.allowAddedLabels,
 			dryRun: program.dryRun,
 			endpoint: program.endpoint,
 			format: format,
-			labels: labels,
+			labels: merge(files),
 			log: console,
 			repo: program.args[0]
 		};