http-url-generator.ts

import { Inject, Injectable, InjectionToken, Optional } from '@angular/core';
import { Pluralizer } from '../utils/interfaces';

/**
 * Known resource URLS for specific entity types.
 * Each entity's resource URLS are endpoints that
 * target single entity and multi-entity HTTP operations.
 * Used by the `DefaultHttpUrlGenerator`.
 */
export abstract class EntityHttpResourceUrls {
  [entityName: string]: HttpResourceUrls;
}

/**
 * Resource URLS for HTTP operations that target single entity
 * and multi-entity endpoints.
 */
export interface HttpResourceUrls {
  /**
   * The URL path for a single entity endpoint, e.g, `some-api-root/hero/`
   * such as you'd use to add a hero.
   * Example: `httpClient.post<Hero>('some-api-root/hero/', addedHero)`.
   * Note trailing slash (/).
   */
  entityResourceUrl: string;
  /**
   * The URL path for a multiple-entity endpoint, e.g, `some-api-root/heroes/`
   * such as you'd use when getting all heroes.
   * Example: `httpClient.get<Hero[]>('some-api-root/heroes/')`
   * Note trailing slash (/).
   */
  collectionResourceUrl: string;
}

/**
 * Generate the base part of an HTTP URL for
 * single entity or entity collection resource
 */
export abstract class HttpUrlGenerator {
  /**
   * Return the base URL for a single entity resource,
   * e.g., the base URL to get a single hero by its id
   */
  abstract entityResource(entityName: string, root: string): string;

  /**
   * Return the base URL for a collection resource,
   * e.g., the base URL to get all heroes
   */
  abstract collectionResource(entityName: string, root: string): string;

  /**
   * Register known single-entity and collection resource URLs for HTTP calls
   * @param entityHttpResourceUrls {EntityHttpResourceUrls} resource urls for specific entity type names
   */
  abstract registerHttpResourceUrls(
    entityHttpResourceUrls: EntityHttpResourceUrls
  ): void;
}

@Injectable()
export class DefaultHttpUrlGenerator implements HttpUrlGenerator {
  /**
   * Known single-entity and collection resource URLs for HTTP calls.
   * Generator methods returns these resource URLs for a given entity type name.
   * If the resources for an entity type name are not know, it generates
   * and caches a resource name for future use
   */
  protected knownHttpResourceUrls: EntityHttpResourceUrls = {};

  constructor(private pluralizer: Pluralizer) {}

  /**
   * Get or generate the entity and collection resource URLs for the given entity type name
   * @param entityName {string} Name of the entity type, e.g, 'Hero'
   * @param root {string} Root path to the resource, e.g., 'some-api`
   */
  protected getResourceUrls(
    entityName: string,
    root: string
  ): HttpResourceUrls {
    let resourceUrls = this.knownHttpResourceUrls[entityName];
    if (!resourceUrls) {
      const nRoot = normalizeRoot(root);
      resourceUrls = {
        entityResourceUrl: `${nRoot}/${entityName}/`.toLowerCase(),
        collectionResourceUrl: `${nRoot}/${this.pluralizer.pluralize(
          entityName
        )}/`.toLowerCase()
      };
      this.registerHttpResourceUrls({ [entityName]: resourceUrls });
    }
    return resourceUrls;
  }

  /**
   * Create the path to a single entity resource
   * @param entityName {string} Name of the entity type, e.g, 'Hero'
   * @param root {string} Root path to the resource, e.g., 'some-api`
   * @returns complete path to resource, e.g, 'some-api/hero'
   */
  entityResource(entityName: string, root: string): string {
    return this.getResourceUrls(entityName, root).entityResourceUrl;
  }

  /**
   * Create the path to a multiple entity (collection) resource
   * @param entityName {string} Name of the entity type, e.g, 'Hero'
   * @param root {string} Root path to the resource, e.g., 'some-api`
   * @returns complete path to resource, e.g, 'some-api/heroes'
   */
  collectionResource(entityName: string, root: string): string {
    return this.getResourceUrls(entityName, root).collectionResourceUrl;
  }

  /**
   * Register known single-entity and collection resource URLs for HTTP calls
   * @param entityHttpResourceUrls {EntityHttpResourceUrls} resource urls for specific entity type names
   * Well-formed resource urls end in a '/';
   * Note: this method does not ensure that resource urls are well-formed.
   */
  registerHttpResourceUrls(
    entityHttpResourceUrls: EntityHttpResourceUrls
  ): void {
    this.knownHttpResourceUrls = {
      ...this.knownHttpResourceUrls,
      ...(entityHttpResourceUrls || {})
    };
  }
}

/** Remove leading & trailing spaces or slashes */
export function normalizeRoot(root: string) {
  return root.replace(/^[\/\s]+|[\/\s]+$/g, '');
}