refactor: apply consistently the same interface pattern for view models and use case output data

Author: adbayb

README.md

@@ -103,6 +103,7 @@ Having all of your infrastructure code in a single source code tree means that i
 - [Domain-Driven Design tactical design and Clean Architecture (video)](https://www.youtube.com/watch?v=hf_XBb5cSoA).
 - [Pull-based vs push-based approach managing use case output](https://softwareengineering.stackexchange.com/a/420360) or [why presenters (push-based) should be preferred to returned use case values (pull-based)](https://lukemorton.tech/articles/nuances-in-clean-architecture). TLDR; Communication from Controller to Presenter is meant to go through the application layer, making the Controller do part of the Presenters job is likely a domain/application leak.
 - [Single responsibility principle and mixing presenter/controller](https://stackoverflow.com/questions/64415618/clean-architecture-controller-and-presenter-should-always-be-separate-classes-o). TLDR; Not mixing them allows better flexibility later if some other ways of displaying data (i.e. presenters) should be supported (Web, CLI, JSON, ...).
+- [The "Real" Repository Pattern in Android](https://proandroiddev.com/the-real-repository-pattern-in-android-efba8662b754).
 
 <br>
 

modules/catalog/src/GetProducts/adapters/GetProductsPresenter.ts

@@ -15,21 +15,30 @@ export const createGetProductsPresenter: PresenterFactory<
 > = (onViewModelChange) => {
 	return {
 		display(input) {
-			const viewModel: GetProductsViewModel = input.map((item) => {
-				if (item instanceof Error) {
-					return { payload: formatError(item), type: "failure" };
-				}
+			const viewModel: GetProductsViewModel = input.map(
+				({ payload, type }) => {
+					if (type === "failure") {
+						return {
+							payload: formatError(payload),
+							type: "failure",
+						};
+					}
 
-				return { payload: formatProduct(item), type: "success" };
-			});
+					return { payload: formatProduct(payload), type: "success" };
+				},
+			);
 
 			onViewModelChange(viewModel);
 		},
 	};
 };
 
-// eslint-disable-next-line unicorn/prefer-native-coercion-functions
-const formatError = (input: Extract<GetProductsOutputData[number], Error>) => {
+type GetProductOutputData = GetProductsOutputData[number];
+
+const formatError = (
+	input: Extract<GetProductOutputData, { type: "failure" }>["payload"],
+	// eslint-disable-next-line unicorn/prefer-native-coercion-functions
+) => {
 	return String(input);
 };
 
@@ -38,7 +47,7 @@ const formatProduct = ({
 	brand,
 	price,
 	thumbnail,
-}: Exclude<GetProductsOutputData[number], Error>) => {
+}: Extract<GetProductOutputData, { type: "success" }>["payload"]) => {
 	return {
 		title: title.toLocaleUpperCase(),
 		brand,

modules/catalog/src/GetProducts/adapters/GetProductsViewModel.ts

@@ -8,4 +8,4 @@ export type GetProductsViewModel = ViewModel<
 		thumbnail: string;
 	},
 	string
->;
+>[];

modules/catalog/src/GetProducts/useCases/GetProductsUseCase.ts

@@ -17,7 +17,7 @@ export type GetProductsOutputData = UseCaseOutputData<
 		thumbnail: string;
 	},
 	Error
->;
+>[];
 
 export type GetProductsInteractor = UseCaseInteractor<GetProductsInputData>;
 
@@ -34,13 +34,16 @@ export const createGetProductsInteractor: UseCaseInteractorFactory<
 
 			results.forEach(({ payload, type }) => {
 				if (type === "failure") {
-					presenterInput.push(payload);
+					presenterInput.push({ payload, type: "failure" });
 				} else {
 					presenterInput.push({
-						title: payload.title,
-						brand: payload.brand,
-						price: payload.price.value,
-						thumbnail: payload.thumbnail,
+						payload: {
+							title: payload.title,
+							brand: payload.brand,
+							price: payload.price.value,
+							thumbnail: payload.thumbnail,
+						},
+						type: "success",
 					});
 				}
 			});

modules/catalog/src/Product/entities/ProductEntity.ts

@@ -5,7 +5,6 @@ import {
 	success,
 } from "@clean-architecture/shared-kernel";
 import type {
-	DataTransferObject,
 	Entity,
 	EntityGatewayBoundary,
 	IdValueObject,
@@ -34,15 +33,15 @@ export type ProductEntityGatewayBoundary = EntityGatewayBoundary<{
 	toEntity: (input: ProductDataSourceBoundaryDto) => Result<ProductEntity>;
 }>;
 
-export type ProductEntityFactoryInput = DataTransferObject<{
+export type ProductEntityFactoryInput = {
 	id: string;
 	title: string;
 	brand: string;
 	category: string;
 	createdAt: string;
 	price: number;
 	thumbnail: string;
-}>;
+};
 
 export const createProductEntity = createEntityFactory<
 	ProductEntity,

modules/shared-kernel/src/DataTransferObject.ts

@@ -1,3 +1,3 @@
-import type { AnyRecord } from "./AnyRecord";
-
-export type DataTransferObject<Input extends AnyRecord = AnyRecord> = Input;
+export type DataTransferObject<SuccessInput, FailureInput> =
+	| { payload: FailureInput; type: "failure" }
+	| { payload: SuccessInput; type: "success" };

modules/shared-kernel/src/adapters/Presenter.ts

@@ -7,11 +7,11 @@ import type { ViewModel } from "./ViewModel";
  * The presenter implements the `UseCaseOutputBoundary` following the clean architecture [diagram](https://blog.cleancoder.com/uncle-bob/2012/08/13/the-clean-architecture.html).
  */
 export type Presenter<
-	OutputData extends UseCaseOutputData = UseCaseOutputData,
+	OutputData extends UseCaseOutputData | UseCaseOutputData[],
 > = UseCaseOutputBoundary<OutputData>;
 
 export type PresenterFactory<
 	Output extends Presenter<OutputData>,
-	OutputData extends UseCaseOutputData,
-	Model extends ViewModel,
+	OutputData extends UseCaseOutputData | UseCaseOutputData[],
+	Model extends ViewModel | ViewModel[],
 > = (onViewModelChange: (input: Model) => void) => Output;

modules/shared-kernel/src/adapters/ViewModel.ts

@@ -1,4 +1,8 @@
-export type ViewModel<SuccessInput = unknown, FailureInput = unknown> = (
-	| { payload: FailureInput; type: "failure" }
-	| { payload: SuccessInput; type: "success" }
-)[];
+import type { DataTransferObject } from "../DataTransferObject";
+
+type FailureInputConstraint = string;
+
+export type ViewModel<
+	SuccessInput = unknown,
+	FailureInput extends FailureInputConstraint = FailureInputConstraint,
+> = DataTransferObject<SuccessInput, FailureInput>;

modules/shared-kernel/src/frameworks/Hook.ts

@@ -2,7 +2,10 @@ import type { ViewModel } from "../adapters/ViewModel";
 import type { Controller } from "../adapters/Controller";
 import type { AnyInput } from "../AnyInput";
 
-export type Hook<C extends Controller<AnyInput>, VM extends ViewModel> = () => {
+export type Hook<
+	C extends Controller<AnyInput>,
+	VM extends ViewModel | ViewModel[],
+> = () => {
 	controller: C;
 	viewModel: VM;
 };

modules/shared-kernel/src/useCases/UseCaseInputData.ts

@@ -1,5 +1,3 @@
-import type { DataTransferObject } from "../DataTransferObject";
+import type { AnyRecord } from "../AnyRecord";
 
-export type UseCaseInputData<
-	Input extends DataTransferObject = DataTransferObject,
-> = DataTransferObject<Input>;
+export type UseCaseInputData<Input extends AnyRecord = AnyRecord> = Input;