aurelia/aurelia

/* eslint-disable @typescript-eslint/strict-boolean-expressions */
import { Controller } from "@aurelia/runtime-html";
import { Observable, Subscription } from 'rxjs';

import { Store, STORE } from './store';
import { Class } from '@aurelia/kernel';

export interface ConnectToSettings<T, R = T> {
  onChanged?: string;
  selector: ((store: Store<T>) => Observable<R>) | MultipleSelector<T, R>;
  /**
   * the function to be called for setup of the state subscription, typically an Aurelia lifecycle hook
   */
  setup?: string;
  target?: string;
  /**
   * the function to be called for teardown of the state subscription, typically an Aurelia lifecycle hook
   */
  teardown?: string;
}

export interface MultipleSelector<T, R = T> {
  [key: string]: ((store: Store<T>) => Observable<R>);
}

const defaultSelector = <T>(store: Store<T>) => store.state;

// eslint-disable-next-line @typescript-eslint/no-explicit-any
export function connectTo<T, R = any>(settings?: ((store: Store<T>) => Observable<R>) | ConnectToSettings<T, R>) {
  const _settings = {
    selector: (typeof settings === 'function' ? settings : defaultSelector),
    ...settings
  } as unknown as ConnectToSettings<T>;

  function getSource(store: Store<T>, selector: (((store: Store<T>) => Observable<R>))): Observable<unknown> {
    const source = selector(store);

    if (source instanceof Observable) {
      return source;
    }

    return store.state;
  }

  function createSelectors() {
    const isSelectorObj = typeof _settings.selector === "object";
    const fallbackSelector = {
      [_settings.target || 'state']: _settings.selector || defaultSelector
    };

    return Object.entries({
      ...((isSelectorObj ? _settings.selector : fallbackSelector) as MultipleSelector<T>)
    }).map(([target, selector]) => ({
      targets: _settings.target && isSelectorObj ? [_settings.target, target] : [target],
      selector,
      // numbers are the starting index to slice all the change handling args,
      // which are prop name, new state and old state
      changeHandlers: {
        [_settings.onChanged ?? '']: 1,
        [`${_settings.target ?? target}Changed`]: _settings.target ? 0 : 1,
        propertyChanged: 0
      }
    }));
  }

  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  return function <TClass extends Class<unknown>>(target: any, context: ClassDecoratorContext<TClass>) {
    const originalSetup = typeof settings === 'object' && settings.setup
      ? target.prototype[settings.setup]
      : target.prototype.binding;
    const originalTeardown = typeof settings === 'object' && settings.teardown
      ? target.prototype[settings.teardown]
      : target.prototype.unbinding;

    target.prototype[typeof settings === 'object' && settings.setup !== undefined ? settings.setup : 'binding'] = function () {
      if (typeof settings === 'object' &&
        typeof settings.onChanged === 'string' &&
        !(settings.onChanged in this)) {
        // Provided onChanged handler does not exist on target VM
        throw new Error('Provided onChanged handler does not exist on target VM');
      }

      const store = Controller.getCached(this)
        ? Controller.getCached(this)!.container.get<Store<T>>(Store)
        : STORE.container.get<Store<T>>(Store); // TODO: need to get rid of this helper for classic unit tests

      this._stateSubscriptions = createSelectors().map(s => getSource(store, s.selector as any).subscribe((state: unknown) => {
        const lastTargetIdx = s.targets.length - 1;
        // eslint-disable-next-line default-param-last
        const oldState = s.targets.reduce((accu = {}, curr) => accu[curr], this);

        Object.entries(s.changeHandlers).forEach(([handlerName, args]) => {
          if (handlerName in this) {
            this[handlerName](...[ s.targets[lastTargetIdx], state, oldState ].slice(args, 3));
          }
        });

        s.targets.reduce((accu, curr, idx) => {
          accu[curr] = idx === lastTargetIdx ? state : accu[curr] || {};
          return accu[curr];
        }, this);
      }));

      if (originalSetup) {
        // eslint-disable-next-line prefer-rest-params
        return originalSetup.apply(this, arguments);
      }
    };

    target.prototype[typeof settings === 'object' && settings.teardown ? settings.teardown : 'unbinding'] = function () {
      if (this._stateSubscriptions && Array.isArray(this._stateSubscriptions)) {
        this._stateSubscriptions.forEach((sub: Subscription) => {
          if (sub instanceof Subscription && sub.closed === false) {
            sub.unsubscribe();
          }
        });
      }

      if (originalTeardown) {
        // eslint-disable-next-line prefer-rest-params
        return originalTeardown.apply(this, arguments);
      }
    };
  };
}