add CodeBuilder utility for easier codegen

src/utils/CodeBuilder.js

@@ -0,0 +1,29 @@
+const LINE = {};
+const BLOCK = {};
+
+export default class CodeBuilder {
+	constructor () {
+		this.result = '';
+		this.last = null;
+	}
+
+	addLine ( line ) {
+		if ( this.last === BLOCK ) {
+			this.result += `\n\n${line}`;
+		} else {
+			this.result += `\n${line}`;
+		}
+
+		this.last = LINE;
+	}
+
+	addBlock ( block ) {
+		this.result += `\n\n${block}`;
+
+		this.last = BLOCK;
+	}
+
+	toString () {
+		return this.result.trim();
+	}
+}

src/utils/__test__.js

@@ -1,5 +1,6 @@
 import * as assert from 'assert';
 import deindent from './deindent.js';
+import CodeBuilder from './CodeBuilder.js';
 
 describe( 'deindent', () => {
 	it( 'deindents a simple string', () => {
@@ -34,3 +35,87 @@ describe( 'deindent', () => {
 		assert.equal( deindented, `before\n\tline one\n\tline two\nafter` );
 	});
 });
+
+describe( 'CodeBuilder', () => {
+	it( 'creates an empty block', () => {
+		const builder = new CodeBuilder();
+		assert.equal( builder.toString(), '' );
+	});
+
+	it( 'creates a block with a line', () => {
+		const builder = new CodeBuilder();
+
+		builder.addLine( 'var answer = 42;' );
+		assert.equal( builder.toString(), 'var answer = 42;' );
+	});
+
+	it( 'creates a block with two lines', () => {
+		const builder = new CodeBuilder();
+
+		builder.addLine( 'var problems = 99;' );
+		builder.addLine( 'var answer = 42;' );
+		assert.equal( builder.toString(), 'var problems = 99;\nvar answer = 42;' );
+	});
+
+	it( 'adds newlines around blocks', () => {
+		const builder = new CodeBuilder();
+
+		builder.addLine( '// line 1' );
+		builder.addLine( '// line 2' );
+		builder.addBlock( deindent`
+			if ( foo ) {
+				bar();
+			}
+		` );
+		builder.addLine( '// line 3' );
+		builder.addLine( '// line 4' );
+
+		assert.equal( builder.toString(), deindent`
+			// line 1
+			// line 2
+
+			if ( foo ) {
+				bar();
+			}
+
+			// line 3
+			// line 4
+		` );
+	});
+
+	it( 'nests codebuilders with correct indentation', () => {
+		const child = new CodeBuilder();
+
+		child.addBlock( deindent`
+			var obj = {
+				answer: 42
+			};
+		` );
+
+		const builder = new CodeBuilder();
+
+		builder.addLine( '// line 1' );
+		builder.addLine( '// line 2' );
+		builder.addBlock( deindent`
+			if ( foo ) {
+				${child}
+			}
+		` );
+		builder.addLine( '// line 3' );
+		builder.addLine( '// line 4' );
+
+		assert.equal( builder.toString(), deindent`
+			// line 1
+			// line 2
+
+			if ( foo ) {
+				var obj = {
+					answer: 42
+				};
+			}
+
+			// line 3
+			// line 4
+		` );
+	});
+});