CSS extraction and code-splitting

closes #388

src/core/create_compilers/WebpackCompiler.ts

@@ -0,0 +1,48 @@
+import * as path from 'path';
+import relative from 'require-relative';
+import { CompileResult } from './interfaces';
+import WebpackResult from './WebpackResult';
+
+let webpack: any;
+
+export class WebpackCompiler {
+	_: any;
+
+	constructor(config: string) {
+		if (!webpack) webpack = relative('webpack', process.cwd());
+		this._ = webpack(require(path.resolve(config)));
+	}
+
+	oninvalid(cb: (filename: string) => void) {
+		this._.hooks.invalid.tap('sapper', cb);
+	}
+
+	compile(): Promise<CompileResult> {
+		return new Promise((fulfil, reject) => {
+			this._.run((err: Error, stats: any) => {
+				if (err) {
+					reject(err);
+					process.exit(1);
+				}
+
+				const result = new WebpackResult(stats);
+
+				if (result.errors.length) {
+					// TODO print errors
+					// console.error(stats.toString({ colors: true }));
+					reject(new Error(`Encountered errors while building app`));
+				}
+
+				else {
+					fulfil(result);
+				}
+			});
+		});
+	}
+
+	watch(cb: (err?: Error, stats?: any) => void) {
+		this._.watch({}, (err?: Error, stats?: any) => {
+			cb(err, stats && new WebpackResult(stats));
+		});
+	}
+}