// Copyright IBM Corp. 2019,2020. All Rights Reserved.
// Node module: @inward/example-context
// This file is licensed under the MIT License.
// License text available at https://opensource.org/licenses/MIT

import {
  BindingAddress,
  ConfigurationResolver,
  Context,
  ContextBindings,
  DefaultConfigurationResolver,
  inject,
  ResolutionOptions,
  ValueOrPromise,
} from '@inward/context';

/**
 * A custom configuration resolver that looks up env variables first
 */
class EnvConfigResolver extends DefaultConfigurationResolver
  implements ConfigurationResolver {
  constructor(@inject.context() public readonly context: Context) {
    super(context);
  }

  /**
   * Try to find a matching env variable (case insensitive)
   * @param key The binding key
   */
  private getFromEnvVars(key: string) {
    let val;
    let found;
    for (const k in process.env) {
      if (k.toUpperCase() === key.toUpperCase()) {
        val = process.env[k];
        found = k;
        break;
      }
    }
    if (val == null) return val;
    console.log(
      'Loading configuration for binding "%s" from env variable "%s"',
      key,
      found,
    );
    try {
      return JSON.parse(val);
    } catch (err) {
      return val;
    }
  }

  getConfigAsValueOrPromise<ConfigValueType>(
    key: BindingAddress<unknown>,
    configPath?: string,
    resolutionOptions?: ResolutionOptions,
  ): ValueOrPromise<ConfigValueType | undefined> {
    const val = this.getFromEnvVars(key.toString());
    if (val != null) return val;
    return super.getConfigAsValueOrPromise(key, configPath, resolutionOptions);
  }
}

export async function main() {
  const ctx = new Context();
  ctx.bind(ContextBindings.CONFIGURATION_RESOLVER).toClass(EnvConfigResolver);

  // Configure `foo` with `{bar: 'abc'}`
  // To override it with env var, use `foo='{"bar":"abc"}'`.
  ctx.configure('foo').to({bar: 'abc'});

  const fooConfig = await ctx.getConfig('foo');
  console.log(fooConfig);

  ctx.configure('bar').to('xyz');
  const barConfig = ctx.getConfigSync('bar');
  console.log(barConfig);
}

if (require.main === module) {
  main().catch(err => {
    console.error(err);
    process.exit(1);
  });
}