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createApp.ts
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createApp.ts
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import { UseCase, UseCaseType } from '.';
import { composeMiddlewares } from './composeMiddlewares';
import { Context, Middleware } from './interfaces';
/**
* A DYAL app
* @example
* ```typescript
* const app = createApp(dependencies);
* const commandBus: CommandBus = createCommandBus();
* commandBus.register('CountCommand', countCommandHandler);
* app.on('command').use(commandBus.middleware);
*
* export interface CountCommandResult {
* total: number;
* }
*
* const countCommand: CountCommand = {
* type: 'command',
* name: 'CountCommand',
* payload: {
* count: 5,
* },
* };
*
* const result = await app.execute<CountCommandResult>(countCommand);
* ```
*/
export interface DyalApp {
/**
*
* @param target It's the kind of use case your middleware will be called for. Can be `query`, `command` or `all`
* @example
* ```typescript
* app.on('command').use(commandHandlerMiddleware);
* ```
*/
on(target: UseCaseType): {
/**
*
* @param middleware middleware to add to the app stack
* @returns void
* @example
* ```typescript
* app.on('all').use(middleware);
* ```
*/
use(middleware: Middleware): void;
};
/**
*
* @param middleware middleware to add to the app stack
* @returns void
* @example
* ```typescript
* app.use(middleware);
* ```
*/
use(middleware: Middleware): void;
/**
* @param useCase The useCase to execute.
* @type R The useCase's return type.
* @returns R
* @example
* ```typescript
* const app = createApp(dependencies);
* const commandBus: CommandBus = createCommandBus();
* commandBus.register('CountCommand', countCommandHandler);
* app.on('command').use(commandBus.middleware);
*
* export interface CountCommandResult {
* total: number;
* }
*
* const countCommand: CountCommand = {
* type: 'command',
* name: 'CountCommand',
* payload: {
* count: 5,
* },
* };
*
* const result = await app.execute<CountCommandResult>(countCommand);
* ```
*/
execute<R>(useCase: UseCase): Promise<R>;
}
/**
* @param dependencies Your app dependencies like repositories, logger, database connection, etc...
* @returns CQRSApp
* @example
* ```typescript
* const dependencies: AppDependencies = { logger: console.log };
* const app = createApp(dependencies);
* app.use(loggerMiddleware);
* const commandResult = await app.execute(commands);
* const queryResult = await app.execute(query);
* ```
*/
export function createApp<D>(dependencies: D): DyalApp {
const middlewares: { target: UseCaseType; middleware: Middleware }[] = [];
function use(target: UseCaseType, middleware: Middleware) {
if (typeof middleware !== 'function') {
throw new TypeError('Middleware must be composed of functions');
}
middlewares.push({ target, middleware });
}
return {
on: (target: UseCaseType) => {
return {
use: (middleware: Middleware) => {
use(target, middleware);
},
};
},
use: (middleware: Middleware) => {
use('all', middleware);
},
execute: async <R>(useCase: UseCase): Promise<R> => {
const targetMiddlewares = middlewares.reduce(
(selectedMids: Middleware[], mid) => {
if (mid.target === 'all' || mid.target === useCase.type) {
selectedMids.push(mid.middleware);
}
return selectedMids;
},
[],
);
const midStack = composeMiddlewares(targetMiddlewares);
const context: Context<D, UseCase, R> = {
dependencies,
useCase,
result: undefined,
};
await midStack(context);
if (!context.result) {
throw new RangeError(
'No result to return. At least one middleware must write the ctx.result object',
);
}
return context.result;
},
};
}