Add option to merge extracted strings with existing translations (Thanks to @ocombe)

src/compilers/po.compiler.ts

@@ -0,0 +1,53 @@
+import { CompilerInterface } from './compiler.interface';
+import { TranslationCollection } from '../utils/translation.collection';
+
+import * as gettext from 'gettext-parser';
+
+export class PoCompiler implements CompilerInterface {
+
+	/**
+	 * Translation domain
+	 */
+	public domain = '';
+
+	public compile(collection: TranslationCollection): string {
+		const data = {
+			charset: 'utf-8',
+			headers: {
+				'mime-version': '1.0',
+				'content-type': 'text/plain; charset=utf-8',
+				'content-transfer-encoding': '8bit'
+			},
+			translations: {
+				'default': Object.keys(collection.values).reduce((translations, key) => {
+					translations[key] = {
+						msgid: key,
+						msgstr: collection.get(key)
+					};
+					return translations;
+				}, {})
+			}
+		};
+
+		return gettext.po.compile(data, 'utf-8');
+	}
+
+	public parse(contents: string): TranslationCollection {
+		const collection = new TranslationCollection();
+
+		const po = gettext.po.parse(contents, 'utf-8');
+		if (!po.translations.hasOwnProperty(this.domain)) {
+			return collection;
+		}
+
+		const values = Object.keys(po.translations[this.domain])
+			.filter(key => key.length > 0)
+			.reduce((values, key) => {
+				values[key] = po.translations[this.domain][key].msgstr.pop();
+				return values;
+			}, {});
+
+		return new TranslationCollection(values);
+	}
+
+}