/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */
import { Observable, of } from 'rxjs';
import { JsonValue, experimental as core_experimental, schema } from '../../../src';

export class NodeModuleJobRegistry<MinimumArgumentValueT extends JsonValue = JsonValue,
  MinimumInputValueT extends JsonValue = JsonValue,
  MinimumOutputValueT extends JsonValue = JsonValue,
> implements core_experimental.jobs.Registry<MinimumArgumentValueT,
  MinimumInputValueT,
  MinimumOutputValueT> {

  protected _resolve(name: string): string | null {
    try {
      return require.resolve(name);
    } catch (e) {
      if (e.code === 'MODULE_NOT_FOUND') {
        return null;
      }
      throw e;
    }
  }

  /**
   * Get a job description for a named job.
   *
   * @param name The name of the job.
   * @returns A description, or null if the job is not registered.
   */
  get<A extends MinimumArgumentValueT,
    I extends MinimumInputValueT,
    O extends MinimumOutputValueT,
    >(
    name: core_experimental.jobs.JobName,
  ): Observable<core_experimental.jobs.JobHandler<A, I, O> | null> {
    const [moduleName, exportName] = name.split(/#/, 2);

    const resolvedPath = this._resolve(moduleName);
    if (!resolvedPath) {
      return of(null);
    }

    const pkg = require(resolvedPath);
    const handler = pkg[exportName || 'default'];
    if (!handler) {
      return of(null);
    }

    function _getValue(...fields: unknown[]) {
      return fields.find(x => schema.isJsonSchema(x)) || true;
    }

    const argument = _getValue(pkg.argument, handler.argument);
    const input = _getValue(pkg.input, handler.input);
    const output = _getValue(pkg.output, handler.output);
    const channels = _getValue(pkg.channels, handler.channels);

    return of(Object.assign(handler.bind(undefined), {
      jobDescription: {
        argument,
        input,
        output,
        channels,
      },
    }));
  }
}
