Feature/write form from type (#114)

* feat(rxformmapper): create form from type

* test(rxformmapper): test fromType method

* docs: add fromType documentation

Author: KernelPanic92

README.md

@@ -163,6 +163,14 @@ This method converts our class instance into reactive form instance
 this.form = formMapper.writeForm(new Post());
 ```
 
+### fromType
+
+This method converts our class type into reactive form instance
+
+```typescript
+this.form = formMapper.fromType(Post);
+```
+
 ### readForm
 
 This method converts our form instance into specific class instance

projects/rx-form-mapper/src/lib/services/rx-form-mapper.service.ts

@@ -9,7 +9,19 @@ import { ValidatorResolver } from './validator-resolver';
 
 @Injectable()
 export class RxFormMapper {
-	constructor(private readonly customMapperResolver: CustomMapperResolver, private readonly validatorResolver: ValidatorResolver) {}
+	public constructor(
+		private readonly customMapperResolver: CustomMapperResolver,
+		private readonly validatorResolver: ValidatorResolver
+	) {}
+
+	public fromType<T>(type: Type<T>): FormGroup {
+		if (isNil(type)) {
+			throw new Error('type cannot be inferred implicitly');
+		}
+
+		const formWriter = new FormWriter(void(0), this.customMapperResolver, this.validatorResolver);
+		return ModelBinder.instance.getMetadata(type).accept(formWriter) as FormGroup;
+	}
 
 	public writeForm<T>(value: T): FormGroup;
 	public writeForm<T>(value: T, type: Type<T>): FormGroup;

projects/rx-form-mapper/src/lib/tests/rx-form-mapper.spec.ts

@@ -40,11 +40,29 @@ describe('RxFormMapper', () => {
 		expect(formMapper.writeForm(new Test(), Test)).toBeTruthy();
 	}));
 
-	it('writeModel should not accept undefined type', inject([RxFormMapper], (mapper: RxFormMapper) => {
+	it('fromType should create form', inject([RxFormMapper], (formMapper: RxFormMapper) => {
+		class Test {
+			@FormControl()
+			public name: string;
+		}
+
+		expect(formMapper.fromType(Test).get('name')).toBeTruthy();
+	}));
+
+	it('fromType should throw error', inject([RxFormMapper], (formMapper: RxFormMapper) => {
+		class Test {
+			@FormControl()
+			public name: string;
+		}
+
+		expect(() => formMapper.fromType(null)).toThrow();
+	}));
+
+	it('writeForm should not accept undefined type', inject([RxFormMapper], (mapper: RxFormMapper) => {
 		expect(() => mapper.writeForm(null, null)).toThrow();
 	}));
 
-	it('writeModel should return FormGroup', inject([RxFormMapper], (mapper: RxFormMapper) => {
+	it('writeForm should return FormGroup', inject([RxFormMapper], (mapper: RxFormMapper) => {
 		class TestClass {}
 		expect(mapper.writeForm(null, TestClass) instanceof NgFormGroup).toBeTruthy();
 	}));