/*
 * Copyright (c) 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.helidon.service.configuration.microprofile.config;

import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

import io.helidon.service.configuration.api.ServiceConfiguration;

import org.eclipse.microprofile.config.spi.ConfigSource;

/**
 * A {@link ConfigSource} implementation that wraps the {@linkplain
 * ServiceConfiguration#getInstance(String)
 * <code>ServiceConfiguration</code> in effect}.
 *
 * @author <a href="mailto:laird.nelson@oracle.com">Laird Nelson</a>
 *
 * @see #getValue(String)
 *
 * @see #getProperties()
 */
public class ServiceConfigurationConfigSource implements ConfigSource {


  /*
   * Instance fields.
   */


  /**
   * The {@link ServiceConfiguration} this {@link
   * ServiceConfigurationConfigSource} wraps.
   *
   * <p>This field may be {@code null}.</p>
   *
   * @see ServiceConfiguration#getInstance(String)
   */
  private final ServiceConfiguration sc;

  /**
   * The service identifier for which a {@linkplain
   * ServiceConfiguration#getInstance(String)
   * <code>ServiceConfiguration</code> should be retrieved}, and also
   * the {@linkplain #getName() name of this
   * <code>ConfigSource</code>} implementation.
   *
   * <p>This field will never be {@code null}.</p>
   *
   * @see #getName()
   */
  private final String name;


  /*
   * Constructors.
   */


  /**
   * Creates a new {@link ServiceConfigurationConfigSource}.
   *
   * <p>The name of this {@link ServiceConfigurationConfigSource} will
   * be equal to the value of the {@linkplain
   * java.lang.System#getProperties() system property} named by
   * concatenating this {@link ServiceConfigurationConfigSource}'s
   * {@linkplain Class#getSimpleName() simple class name} converted to
   * {@linkplain String#toLowerCase() lowercase} with {@code
   * .serviceIdentifier}, or, if that is {@code null}, the {@linkplain
   * Class#getSimpleName() simple class name} converted to {@linkplain
   * String#toLowerCase() lowercase} itself.</p>
   *
   * @see #ServiceConfigurationConfigSource(ServiceConfiguration)
   */
  protected ServiceConfigurationConfigSource() {
    this(null);
  }

  /**
   * Creates a new {@link ServiceConfigurationConfigSource}.
   *
   * @param serviceConfiguration the {@link ServiceConfiguration} this
   * {@link ServiceConfigurationConfigSource} will wrap.  If this
   * parameter is {@code null}, then the service identifier for which
   * to {@linkplain ServiceConfiguration#getInstance(String) find} a
   * {@link ServiceConfiguration} will be determined by first trying
   * to use the value of the {@linkplain
   * java.lang.System#getProperties() system property} named by
   * concatenating this {@link ServiceConfigurationConfigSource}'s
   * {@linkplain Class#getSimpleName() simple class name} converted to
   * {@linkplain String#toLowerCase() lowercase} with {@code
   * .serviceIdentifier}, and then, if that is {@code null} (as it
   * commonly may be) by simply using this {@link
   * ServiceConfigurationConfigSource}'s {@linkplain
   * Class#getSimpleName() simple class name} converted to {@linkplain
   * String#toLowerCase() lowercase}.  The result of invoking {@link
   * ServiceConfiguration#getInstance(String)} on this value will then
   * be used as if it had been passed directly.
   *
   * @see ServiceConfiguration#getInstance(String)
   *
   * @see ServiceConfiguration#getServiceIdentifier()
   */
  protected ServiceConfigurationConfigSource(final ServiceConfiguration serviceConfiguration) {
    super();
    if (serviceConfiguration == null) {
      final String lowerCaseSimpleClassName = this.getClass().getSimpleName().toLowerCase();
      this.name = System.getProperty(lowerCaseSimpleClassName + ".serviceIdentifier", lowerCaseSimpleClassName);
      this.sc = ServiceConfiguration.getInstance(this.name);
    } else {
      this.name = serviceConfiguration.getServiceIdentifier();
      this.sc = serviceConfiguration;
    }
  }


  /*
   * Instance methods.
   */


  /**
   * Returns the name of this {@link
   * ServiceConfigurationConfigSource}.
   *
   * <p>This method never returns {@code null}.</p>
   *
   * @return the name of this {@link
   * ServiceConfigurationConfigSource}; never {@code null}
   */
  @Override
  public final String getName() {
    return this.name;
  }

  /**
   * Returns all property names known to this {@link
   * ServiceConfigurationConfigSource} by returning the result of
   * invoking the {@link ServiceConfiguration#getPropertyNames()}
   * method on the underlying {@link ServiceConfiguration}.
   *
   * <p>This method never returns {@code null}.</p>
   *
   * @return all property names known to this {@link
   * ServiceConfigurationConfigSource}; never {@code null}
   *
   * @see ServiceConfiguration#getPropertyNames()
   */
  @Override
  public final Set<String> getPropertyNames() {
    final Set<String> returnValue;
    if (this.sc == null) {
      returnValue = Collections.emptySet();
    } else {
      final Set<String> scPropertyNames = this.sc.getPropertyNames();
      if (scPropertyNames == null) {
        returnValue = Collections.emptySet();
      } else {
        returnValue = scPropertyNames;
      }
    }
    return returnValue;
  }

  /**
   * Returns a {@link Map} representing all properties known to this
   * {@link ServiceConfigurationConfigSource}.
   *
   * <p>This method never returns {@code null}.</p>
   *
   * <p>The {@link Map} that is returned is assembled using
   * invocations of the {@link
   * ServiceConfiguration#getPropertyNames()} and {@link
   * ServiceConfiguration#getProperty(String)} methods.</p>
   *
   * <p>The {@link Map} that is returned is immutable and
   * thread-safe.</p>
   *
   * @return a {@link Map} representing all properties known to this
   * {@link ServiceConfigurationConfigSource}; never {@code null}
   *
   * @see ServiceConfiguration#getPropertyNames()
   *
   * @see ServiceConfiguration#getProperty(String)
   */
  @Override
  public final Map<String, String> getProperties() {
    final Map<String, String> returnValue;
    if (this.sc == null) {
      returnValue = Collections.emptyMap();
    } else {
      final Collection<? extends String> propertyNames = this.sc.getPropertyNames();
      if (propertyNames == null || propertyNames.isEmpty()) {
        returnValue = Collections.emptyMap();
      } else {
        final Map<String, String> properties = new LinkedHashMap<>();
        for (final String propertyName : propertyNames) {
          if (propertyName != null) {
            properties.put(propertyName, this.sc.getProperty(propertyName));
          }
        }
        if (properties.isEmpty()) {
          returnValue = Collections.emptyMap();
        } else {
          returnValue = Collections.unmodifiableMap(properties);
        }
      }
    }
    return returnValue;
  }

  /**
   * Returns the value of the property identified by the supplied
   * {@code name}, or {@code null} if there is no such property or a
   * value could not be found for some reason.
   *
   * <p>This method may return {@code null}.</p>
   *
   * <p>This method returns the result of invoking the {@link
   * ServiceConfiguration#getProperty(String)} method with the
   * supplied {@code name}.</p>
   *
   * @param name the name of the property; may be {@code null} in
   * which case {@code null} will be returned
   *
   * @return a value for the named property, or {@code null}
   */
  @Override
  public final String getValue(final String name) {
    final String returnValue;
    if (this.sc == null) {
      returnValue = null;
    } else {
      returnValue = this.sc.getProperty(name);
    }
    return returnValue;
  }

}
