import TestRepoBackend from './test-repo/Implementation';

export function resolveBackend(config) {
  const name = config.getIn(['backend', 'name']);
  if (name == null) {
    throw 'No backend defined in configuration';
  }

  switch (name) {
    case 'test-repo':
      return new Backend(new TestRepoBackend(config));
    default:
      throw `Backend not found: ${name}`;
  }
}

class Backend {
  constructor(implementation, authStore = null) {
    this.implementation = implementation;
    this.authStore = authStore;
    if (this.implementation == null) {
      throw 'Cannot instantiate a Backend with no implementation';
    }
  }

  currentUser() {
    if (this.user) { return this.user; }
    return this.authStore && this.authStore.retrieve();
  }

  authComponent() {
    return this.implementation.authComponent();
  }

  authenticate(state) {
    return this.implementation.authenticate(state);
  }
}

export const currentBackend = (function() {
  let backend = null;

  return (config) => {
    if (backend) { return backend; }
    if (config.get('backend')) {
      return backend = resolveBackend(config);
    }
  };
})();