From d61df97d8d7ce4e6e522fd506a12390dd81f34ef Mon Sep 17 00:00:00 2001
From: Rich-Harris <richard.a.harris@gmail.com>
Date: Wed, 8 Jun 2016 10:56:49 -0400
Subject: [PATCH] auto-install rollup-watch if requested

---
 bin/getRollupWatch.js | 43 +++++++++++++++++++++++++++++++++++++++++++
 bin/handleError.js    |  8 ++++++++
 bin/runRollup.js      | 37 ++++++++++++++++++++++++++++---------
 3 files changed, 79 insertions(+), 9 deletions(-)
 create mode 100644 bin/getRollupWatch.js

diff --git a/bin/getRollupWatch.js b/bin/getRollupWatch.js
new file mode 100644
index 0000000..d830023
--- /dev/null
+++ b/bin/getRollupWatch.js
@@ -0,0 +1,43 @@
+var chalk = require( 'chalk' );
+var relative = require( 'require-relative' );
+
+module.exports = function getRollupWatch () {
+	try {
+		watch = relative( 'rollup-watch', process.cwd() );
+		return Promise.resolve( watch );
+	} catch ( err ) {
+		if ( err.code === 'MODULE_NOT_FOUND' ) {
+			return installRollupWatch().then( () => {
+				return relative( 'rollup-watch', process.cwd() );
+			});
+		} else {
+			return Promise.reject( err );
+		}
+	}
+};
+
+function installRollupWatch () {
+	console.error( 'rollup --watch depends on the rollup-watch package, which could not be found. You can install it globally with ' + chalk.cyan( 'npm install -g rollup-watch' ) + '. Do this now? ' + chalk.green.bold( '[y/n]' ) );
+
+	process.stdin.setEncoding( 'utf8' );
+
+	return new Promise( ( fulfil, reject ) => {
+		process.stdin.on( 'readable', function () {
+			var chunk = process.stdin.read();
+			if ( !chunk ) return;
+
+			if ( /^y(?:es)?$/i.test( chunk ) ) {
+				console.error( 'installing rollup-watch...' );
+				child = require( 'child_process' ).exec( 'npm install --global rollup-watch', err => {
+					if ( err ) {
+						reject( err );
+					} else {
+						fulfil();
+					}
+				});
+			} else {
+				reject( new Error( 'aborted' ) );
+			}
+		});
+	});
+}
diff --git a/bin/handleError.js b/bin/handleError.js
index b7cd224..33ee847 100644
--- a/bin/handleError.js
+++ b/bin/handleError.js
@@ -27,6 +27,14 @@ var handlers = {
 
 	DUPLICATE_IMPORT_OPTIONS: function ( err ) {
 		console.error( chalk.red( 'use --input, or pass input path as argument' ) );
+	},
+
+	ROLLUP_WATCH_NOT_INSTALLED: function ( err ) {
+		console.error( chalk.red( 'failed to find or install rollup-watch' ) );
+	},
+
+	WATCHER_MISSING_INPUT_OR_OUTPUT: function ( err ) {
+		console.error( chalk.red( 'must specify --input and --output when using rollup --watch' ) );
 	}
 };
 
diff --git a/bin/runRollup.js b/bin/runRollup.js
index 46ac35c..91a3df4 100644
--- a/bin/runRollup.js
+++ b/bin/runRollup.js
@@ -1,8 +1,9 @@
 require( 'source-map-support' ).install();
 
 var path = require( 'path' );
-var relative = require( 'require-relative' );
 var handleError = require( './handleError' );
+var getRollupWatch = require( './getRollupWatch' );
+var chalk = require( 'chalk' );
 var rollup = require( '../' );
 
 // log to stderr to keep `rollup main.js > bundle.js` from breaking
@@ -129,16 +130,34 @@ function execute ( options, command ) {
 
 	try {
 		if ( command.watch ) {
-			var watch;
-
-			try {
-				watch = relative( 'rollup-watch', process.cwd() );
-			} catch ( err ) {
-				// TODO offer to install rollup-watch
-				throw err;
+			if ( !options.entry || !options.dest ) {
+				handleError({ code: 'WATCHER_MISSING_INPUT_OR_OUTPUT' });
 			}
 
-			watch( options );
+			getRollupWatch()
+				.then( watch => {
+					const watcher = watch( rollup, options );
+
+					watcher.on( 'event', event => {
+						switch ( event.code ) {
+							case 'STARTING':
+								console.error( 'checking rollup-watch version...' );
+								break;
+
+							case 'BUILD_START':
+								console.error( 'bundling...' );
+								break;
+
+							case 'BUILD_END':
+								console.error( 'bundled in ' + event.duration + 'ms. Watching for changes...' );
+								break;
+
+							default:
+								console.error( 'unknown event', event );
+						}
+					});
+				})
+				.catch( handleError );
 		} else {
 			bundle( options ).catch( handleError );
 		}