CapabilityService.ts

interface Capability {
  isAllowed(args: Record<string, any>): boolean;
  get disallowReason(): string;

  get name(): string;
  
  get accountId(): string;
}

class CapabilityService extends Service {
  capabilities: Capability[];

  constructor() {
    super();

    this._registerCapabilities();
  }
  
  // the main method for checking the capability 
  hasCapability(capabilityName: string, args?: Record<string, any>) {
    const capability = this.capabilities.findBy('name', capabilityName);

    if (!capability) return false;

    return capability.isAllowed(args);
  }
  
  // in case user does not have a capability this method can be additonally used to display a message
  getDisallowReason(capabilityName: string) {
    return this.capabilities.findBy('name', capabilityName).disallowReason;
  }

  // main place to register capabilities that need to be calculated on the frontend
  private _registerCapabilities() {
    const capabilitiesToRegister = [
      new CanStartTrialCapability(getOwner(this))
    ];

    this.capabilities = [...this.capabilities, ...capabilitiesToRegister];
  }
  
  // main method for fetching capabilities by name, called in one of top-level routes
  async fetchCapabilities(capabilityNames: string[]) {
    // fetching from backend goes here
    const capabilitiesFromBackend = [
      { 
        name: 'can_start_trial',
        // this is ED's model method that would just alias to 'allowed' attribute returned from backend
        isAllowed() { return true; },
        disallowReason: null 
      },
    ];

    this.capabilities = [...this.capabilities, ...capabilitiesFromBackend]; 
  }

  // main method for fetching single capability, useful for computationally heavy logic
  async fetchCapability(capabilityName: string) {
    // fetching from backend goes here
    const capability = { name: 'can_see_trial_ended_banner', isAllowed: () => true, disallowReason: null };

    this.capabilities = [...this.capabilities, capability]; 
  }
}

// example of capability logic implemented on the frontend
class CanStartTrialCapability implements Capability {
  @service declare session: Service['session'];

  get accountId() { return this.session.currentAccount.id }

  name: 'can_start_trial';
  
  constructor(owner: EmberOwner) {
    setOwner(this, owner);
  }

  isAllowed(args: Record<string, any>) {
    return this.session.currentAccount.isPremium;
  }

  get disallowReason(): string {
    if(!this.isAllowed) return 'Not a premium account';
    return null;
  }
}