depents/src/Injector.ts

import 'reflect-metadata';
import { ERR_NO_INITIALIZE_WITH_PRIORITY, ERR_NO_INJECTION_TOKEN } from './Strings';
import { Constructor, Type, SingletonDefinition, InjectionError, InjectionResolutionError } from './Internals';

class _Injector {

  private injectionQueue: any[] = []
  private singletonDefinitions: SingletonDefinition[] = []

  private singletonObjects: { [classname in string]: any } = {}
  private tokenLookupTable: { [token in string]: Constructor<any> } = {}

  private initialized = false

  /**
   * Resolves instances by injecting required services
   * @param {Type<any>} request
   * @returns {T}
   */
  public resolve<T>(request: Constructor<T>): T {
    if (!this.initialized) {
      this.initialize()
      this.initialized = true
    }

    return this.singletonObjects[request.name] as any
  }

  public async resolveAsync<T>(target: Type<T>): Promise<T> {
    if (!this.initialized) {
      this.initialize()
      this.initialized = true
    }

    return this.singletonObjects[target.name] as any
  }

  private initialize = () => {
    this.createSingletons()
    this.injectDependencies()
    this.initializeSingletons()
    this.cleanup()
  }

  private createSingletons = () => {
    this.singletonDefinitions.forEach(def => {
      const obj = new def.ctor()

      if (def.initializationPriority != undefined && !obj.initialize) {
        throw new InjectionError(ERR_NO_INITIALIZE_WITH_PRIORITY(def.ctor))
      }

      this.singletonObjects[def.ctor.name] = obj
    })
  }

  private injectDependencies = () => {
    this.injectionQueue.forEach(inj => {

      if (inj.token.name in this.tokenLookupTable) { //injection alias was used
        inj.token = this.tokenLookupTable[inj.token.name]
      }

      if (this.singletonObjects[inj.token.name]) {
        this.singletonObjects[inj.receiver.constructor.name][inj.key] = this.singletonObjects[inj.token.name]
      } else {
        throw new InjectionResolutionError(ERR_NO_INJECTION_TOKEN(inj.injectionType))
      }
    })
  }

  private initializeSingletons = () => {
    this.singletonDefinitions
      .sort((a, b) => (b.initializationPriority ?? 0) - (a.initializationPriority ?? 0))
      .map(def => this.singletonObjects[def.ctor.name])
      .forEach(obj => obj.initialize ? obj.initialize() : undefined)
  }

  private cleanup = () => {
    while (this.singletonDefinitions.length > 0)
      this.singletonDefinitions.pop()
    while (this.injectionQueue.length > 0)
      this.injectionQueue.pop()
  }
}

/**
 * The Injector stores services and resolves requested instances.
 */
export const Injector = new _Injector()