/*
 * Copyright 2015 Google LLC
 *
 * 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 com.google.cloud;

import static com.google.common.base.MoreObjects.firstNonNull;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.api.client.http.GenericUrl;
import com.google.api.client.http.HttpHeaders;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpRequestFactory;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.GenericJson;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.JsonObjectParser;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.client.util.Charsets;
import com.google.api.core.ApiClock;
import com.google.api.core.BetaApi;
import com.google.api.core.CurrentMillisClock;
import com.google.api.core.InternalApi;
import com.google.api.gax.core.GaxProperties;
import com.google.api.gax.retrying.RetrySettings;
import com.google.api.gax.rpc.FixedHeaderProvider;
import com.google.api.gax.rpc.HeaderProvider;
import com.google.api.gax.rpc.NoHeaderProvider;
import com.google.auth.Credentials;
import com.google.auth.oauth2.GoogleCredentials;
import com.google.cloud.spi.ServiceRpcFactory;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterables;
import com.google.common.io.Files;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.nio.charset.Charset;
import java.util.Locale;
import java.util.Map;
import java.util.Objects;
import java.util.ServiceLoader;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.threeten.bp.Duration;

/**
 * Abstract class representing service options.
 *
 * @param <ServiceT> the service subclass
 * @param <OptionsT> the {@code ServiceOptions} subclass corresponding to the service
 */
public abstract class ServiceOptions<ServiceT extends Service<OptionsT>,
    OptionsT extends ServiceOptions<ServiceT, OptionsT>> implements Serializable {

  public static final String CREDENTIAL_ENV_NAME = "GOOGLE_APPLICATION_CREDENTIALS";

  private static final String DEFAULT_HOST = "https://www.googleapis.com";
  private static final String LEGACY_PROJECT_ENV_NAME = "GCLOUD_PROJECT";
  private static final String PROJECT_ENV_NAME = "GOOGLE_CLOUD_PROJECT";

  private static final RetrySettings DEFAULT_RETRY_SETTINGS = getDefaultRetrySettingsBuilder()
      .build();
  private static final RetrySettings NO_RETRY_SETTINGS = getDefaultRetrySettingsBuilder()
      .setMaxAttempts(1).build();

  private static final long serialVersionUID = 9198896031667942014L;

  private final String projectId;
  private final String host;
  private final RetrySettings retrySettings;
  private final String serviceRpcFactoryClassName;
  private final String serviceFactoryClassName;
  private final ApiClock clock;
  protected Credentials credentials;
  private final TransportOptions transportOptions;
  private final HeaderProvider headerProvider;

  private transient ServiceRpcFactory<OptionsT> serviceRpcFactory;
  private transient ServiceFactory<ServiceT, OptionsT> serviceFactory;
  private transient ServiceT service;
  private transient ServiceRpc rpc;

  /**
   * Builder for {@code ServiceOptions}.
   *
   * @param <ServiceT> the service subclass
   * @param <OptionsT> the {@code ServiceOptions} subclass corresponding to the service
   * @param <B> the {@code ServiceOptions} builder
   */
  public abstract static class Builder<ServiceT extends Service<OptionsT>,
      OptionsT extends ServiceOptions<ServiceT, OptionsT>,
      B extends Builder<ServiceT, OptionsT, B>> {

    private String projectId;
    private String host;
    protected Credentials credentials;
    private RetrySettings retrySettings;
    private ServiceFactory<ServiceT, OptionsT> serviceFactory;
    private ServiceRpcFactory<OptionsT> serviceRpcFactory;
    private ApiClock clock;
    private TransportOptions transportOptions;
    private HeaderProvider headerProvider;

    @InternalApi("This class should only be extended within google-cloud-java")
    protected Builder() {}

    @InternalApi("This class should only be extended within google-cloud-java")
    protected Builder(ServiceOptions<ServiceT, OptionsT> options) {
      projectId = options.projectId;
      host = options.host;
      credentials = options.credentials;
      retrySettings = options.retrySettings;
      serviceFactory = options.serviceFactory;
      serviceRpcFactory = options.serviceRpcFactory;
      clock = options.clock;
      transportOptions = options.transportOptions;
    }

    protected abstract ServiceOptions<ServiceT, OptionsT> build();

    @SuppressWarnings("unchecked")
    protected B self() {
      return (B) this;
    }


    /**
     * Sets the service factory.
     */
    public B setServiceFactory(ServiceFactory<ServiceT, OptionsT> serviceFactory) {
      this.serviceFactory = serviceFactory;
      return self();
    }


    /**
     * Sets the service's clock. The clock is mainly used for testing purpose. {@link ApiClock}
     * will be replaced by Java8's {@code java.time.Clock}.
     *
     * @param clock the clock to set
     * @return the builder
     */
    public B setClock(ApiClock clock) {
      this.clock = clock;
      return self();
    }


    /**
     * Sets the project ID. If no project ID is set, {@link #getDefaultProjectId()} will be used to
     * attempt getting the project ID from the environment.
     *
     * @return the builder
     */
    public B setProjectId(String projectId) {
      this.projectId = projectId;
      return self();
    }


    /**
     * Sets service host.
     *
     * @return the builder
     */
    public B setHost(String host) {
      this.host = host;
      return self();
    }

    /**
     * Sets the service authentication credentials. If no credentials are set,
     * {@link GoogleCredentials#getApplicationDefault()} will be used to attempt getting credentials
     * from the environment. Use {@link NoCredentials#getInstance()} to skip authentication, this is
     * typically useful when using local service emulators.
     *
     * @param credentials authentication credentials, should not be {@code null}
     * @return the builder
     * @throws NullPointerException if {@code credentials} is {@code null}. To disable
     * authentication use {@link NoCredentials#getInstance()}
     */
    public B setCredentials(Credentials credentials) {
      this.credentials = checkNotNull(credentials);
      return self();
    }


    /**
     * Sets configuration parameters for request retries.
     *
     * @return the builder
     */
    public B setRetrySettings(RetrySettings retrySettings) {
      this.retrySettings = retrySettings;
      return self();
    }


    /**
     * Sets the factory for rpc services.
     *
     * @return the builder
     */
    public B setServiceRpcFactory(ServiceRpcFactory<OptionsT> serviceRpcFactory) {
      this.serviceRpcFactory = serviceRpcFactory;
      return self();
    }

    /**
     * Sets the transport options.
     *
     * @return the builder
     */
    public B setTransportOptions(TransportOptions transportOptions) {
      this.transportOptions = transportOptions;
      return self();
    }

    /**
     * Sets the static header provider. The header provider will be called during client
     * construction only once. The headers returned by the provider will be cached and supplied as
     * is for each request issued by the constructed client. Some reserved headers can be overridden
     * (e.g. Content-Type) or merged with the default value (e.g. User-Agent) by the underlying
     * transport layer.
     *
     * @param headerProvider the header provider
     * @return the builder
     */
    @BetaApi
    public B setHeaderProvider(HeaderProvider headerProvider) {
      this.headerProvider = headerProvider;
      return self();
    }
  }

  @InternalApi("This class should only be extended within google-cloud-java")
  protected ServiceOptions(Class<? extends ServiceFactory<ServiceT, OptionsT>> serviceFactoryClass,
      Class<? extends ServiceRpcFactory<OptionsT>> rpcFactoryClass,
      Builder<ServiceT, OptionsT, ?> builder,
      ServiceDefaults<ServiceT, OptionsT> serviceDefaults) {
    projectId = builder.projectId != null ? builder.projectId : getDefaultProject();
    if (projectIdRequired()) {
      checkArgument(
          projectId != null,
          "A project ID is required for this service but could not be determined from the builder "
              + "or the environment.  Please set a project ID using the builder.");
    }
    host = firstNonNull(builder.host, getDefaultHost());
    credentials = builder.credentials != null ? builder.credentials : defaultCredentials();
    retrySettings = firstNonNull(builder.retrySettings, getDefaultRetrySettings());
    serviceFactory = firstNonNull(builder.serviceFactory,
        getFromServiceLoader(serviceFactoryClass, serviceDefaults.getDefaultServiceFactory()));
    serviceFactoryClassName = serviceFactory.getClass().getName();
    serviceRpcFactory = firstNonNull(builder.serviceRpcFactory,
        getFromServiceLoader(rpcFactoryClass, serviceDefaults.getDefaultRpcFactory()));
    serviceRpcFactoryClassName = serviceRpcFactory.getClass().getName();
    clock = firstNonNull(builder.clock, CurrentMillisClock.getDefaultClock());
    transportOptions = firstNonNull(builder.transportOptions,
        serviceDefaults.getDefaultTransportOptions());
    headerProvider = firstNonNull(builder.headerProvider, new NoHeaderProvider());
  }

  /**
   * Returns whether a service requires a project ID. This method may be overridden in
   * service-specific Options objects.
   *
   * @return true if a project ID is required to use the service, false if not
   */
  protected boolean projectIdRequired() {
    return true;
  }

  private static GoogleCredentials defaultCredentials() {
    try {
      return GoogleCredentials.getApplicationDefault();
    } catch (Exception ex) {
      return null;
    }
  }


  protected String getDefaultHost() {
    return DEFAULT_HOST;
  }


  protected String getDefaultProject() {
    return getDefaultProjectId();
  }

  /**
   * Returns the default project ID, or {@code null} if no default project ID could be found. This
   * method returns the first available project ID among the following sources:
   * <ol>
   *   <li>The project ID specified by the GOOGLE_CLOUD_PROJECT environment variable
   *   <li>The App Engine project ID
   *   <li>The project ID specified in the JSON credentials file pointed by the
   *   {@code GOOGLE_APPLICATION_CREDENTIALS} environment variable
   *   <li>The Google Cloud SDK project ID
   *   <li>The Compute Engine project ID
   * </ol>
   */
  public static String getDefaultProjectId() {
    String projectId = System.getProperty(PROJECT_ENV_NAME, System.getenv(PROJECT_ENV_NAME));
    if (projectId == null) {
      projectId =
          System.getProperty(LEGACY_PROJECT_ENV_NAME, System.getenv(LEGACY_PROJECT_ENV_NAME));
    }
    if (projectId == null) {
      projectId = getAppEngineProjectId();
    }
    if (projectId == null) {
      projectId = getServiceAccountProjectId();
    }
    return projectId != null ? projectId : getGoogleCloudProjectId();
  }

  public static String getAppEngineAppId() {
    return System.getProperty("com.google.appengine.application.id");
  }

  private static String getActiveGoogleCloudConfig(File configDir) {
    String activeGoogleCloudConfig = null;
    try {
      activeGoogleCloudConfig =
          Files.readFirstLine(new File(configDir, "active_config"), Charset.defaultCharset());
    } catch (IOException ex) {
      // ignore
    }
    // if reading active_config failed or the file is empty we try default
    return firstNonNull(activeGoogleCloudConfig, "default");
  }

  protected static String getGoogleCloudProjectId() {
    File configDir;
    if (System.getenv().containsKey("CLOUDSDK_CONFIG")) {
      configDir = new File(System.getenv("CLOUDSDK_CONFIG"));
    } else if (isWindows() && System.getenv().containsKey("APPDATA")) {
      configDir = new File(System.getenv("APPDATA"), "gcloud");
    } else {
      configDir = new File(System.getProperty("user.home"), ".config/gcloud");
    }
    String activeConfig = getActiveGoogleCloudConfig(configDir);
    FileReader fileReader = null;
    try {
      fileReader = new FileReader(new File(configDir, "configurations/config_" + activeConfig));
    } catch (FileNotFoundException newConfigFileNotFoundEx) {
      try {
        fileReader = new FileReader(new File(configDir, "properties"));
      } catch (FileNotFoundException oldConfigFileNotFoundEx) {
        // ignore
      }
    }
    if (fileReader != null) {
      try (BufferedReader reader = new BufferedReader(fileReader)) {
        String line;
        String section = null;
        Pattern projectPattern = Pattern.compile("^project\\s*=\\s*(.*)$");
        Pattern sectionPattern = Pattern.compile("^\\[(.*)\\]$");
        while ((line = reader.readLine()) != null) {
          if (line.isEmpty() || line.startsWith(";")) {
            continue;
          }
          line = line.trim();
          Matcher matcher = sectionPattern.matcher(line);
          if (matcher.matches()) {
            section = matcher.group(1);
          } else if (section == null || section.equals("core")) {
            matcher = projectPattern.matcher(line);
            if (matcher.matches()) {
              return matcher.group(1);
            }
          }
        }
      } catch (IOException ex) {
        // ignore
      }
    }
    // return project id from metadata config
    return MetadataConfig.getProjectId();
  }

  private static boolean isWindows() {
    return System.getProperty("os.name").toLowerCase(Locale.ENGLISH).contains("windows");
  }

  protected static String getAppEngineProjectId() {
    String projectId = null;
    if (PlatformInformation.isOnGAEStandard7()) {
      projectId = getAppEngineProjectIdFromAppId();
    } else {
      //for GAE flex and standard Java 8 environment
      projectId = System.getenv("GOOGLE_CLOUD_PROJECT");
      if (projectId == null) {
        projectId = System.getenv("GCLOUD_PROJECT");
      }
      if (projectId == null) {
        projectId = getAppEngineProjectIdFromAppId();
      }
      if (projectId == null) {
        try {
          projectId = getAppEngineProjectIdFromMetadataServer();
        } catch (IOException ignore) {
          projectId = null;
        }
      }
    }
    return projectId;
  }

  protected static String getAppEngineProjectIdFromAppId() {
    String projectId = getAppEngineAppId();
    if (projectId != null && projectId.contains(":")) {
      int colonIndex = projectId.indexOf(":");
      projectId = projectId.substring(colonIndex + 1);
    }
    return projectId;
  }

  private static String getAppEngineProjectIdFromMetadataServer() throws IOException {
    String metadata = "http://metadata.google.internal";
    String projectIdURL = "/computeMetadata/v1/project/project-id";
    GenericUrl url = new GenericUrl(metadata + projectIdURL);

    HttpTransport netHttpTransport = new NetHttpTransport();
    HttpRequestFactory requestFactory = netHttpTransport.createRequestFactory();
    HttpRequest request = requestFactory.buildGetRequest(url)
            .setConnectTimeout(500)
            .setReadTimeout(500)
            .setHeaders(new HttpHeaders().set("Metadata-Flavor", "Google"));
    HttpResponse response = request.execute();
    return headerContainsMetadataFlavor(response) ? response.parseAsString() : null;
  }

  @InternalApi("Visible for testing")
  static boolean headerContainsMetadataFlavor(HttpResponse response) {
    String metadataFlavorValue = response.getHeaders().getFirstHeaderStringValue("Metadata-Flavor");
    return "Google".equals(metadataFlavorValue);
  }

  protected static String getServiceAccountProjectId() {
    return getServiceAccountProjectId(System.getenv(CREDENTIAL_ENV_NAME));
  }

  @InternalApi("Visible for testing")
  static String getServiceAccountProjectId(String credentialsPath) {
    String project = null;
    if (credentialsPath != null) {
      try (InputStream credentialsStream = new FileInputStream(credentialsPath)) {
        JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();
        JsonObjectParser parser = new JsonObjectParser(jsonFactory);
        GenericJson fileContents = parser.parseAndClose(
            credentialsStream, Charsets.UTF_8, GenericJson.class);
        project = (String) fileContents.get("project_id");
      } catch (IOException e) {
        // ignore
      }
    }
    return project;
  }


  /**
   * Returns a Service object for the current service. For instance, when using Google Cloud
   * Storage, it returns a Storage object.
   */
  @SuppressWarnings("unchecked")
  public ServiceT getService() {
    if (service == null) {
      service = serviceFactory.create((OptionsT) this);
    }
    return service;
  }


  /**
   * Returns a Service RPC object for the current service. For instance, when using Google Cloud
   * Storage, it returns a StorageRpc object.
   */
  @SuppressWarnings("unchecked")
  public ServiceRpc getRpc() {
    if (rpc == null) {
      rpc = serviceRpcFactory.create((OptionsT) this);
    }
    return rpc;
  }


  /**
   * Returns the project ID. Return value can be null (for services that don't require a project
   * ID).
   */
  public String getProjectId() {
    return projectId;
  }


  /**
   * Returns the service host.
   */
  public String getHost() {
    return host;
  }

  /**
   * Returns the authentication credentials.
   */
  public Credentials getCredentials() {
    return credentials;
  }

  /**
   * Returns the authentication credentials. If required, credentials are scoped.
   */
  public Credentials getScopedCredentials() {
    Credentials credentialsToReturn = credentials;
    if (credentials instanceof GoogleCredentials
        && ((GoogleCredentials) credentials).createScopedRequired()) {
      credentialsToReturn = ((GoogleCredentials) credentials).createScoped(getScopes());
    }
    return credentialsToReturn;
  }


  /**
   * Returns configuration parameters for request retries.
   */
  public RetrySettings getRetrySettings() {
    return retrySettings;
  }


  /**
   * Returns the service's clock. Default time source uses {@link System#currentTimeMillis()} to get
   * current time.
   */
  public ApiClock getClock() {
    return clock;
  }

  /**
   * Returns the transport-specific options for this service.
   */
  public TransportOptions getTransportOptions() {
    return transportOptions;
  }

  /**
   * Returns the application's name as a string in the format {@code gcloud-java/[version]},
   * optionally prepended with externally supplied User-Agent header value (via setting custom
   * header provider).
   */
  public String getApplicationName() {
    String libraryVersion = getLibraryVersion();

    // We have to do the following since underlying layers often do not appreciate User-Agent
    // provided as a normal header and override it or treat setting "application name" as the only
    // way to append something to User-Agent header.
    StringBuilder sb = new StringBuilder();
    String customUserAgentValue = getUserAgent();
    if (customUserAgentValue != null) {
      sb.append(customUserAgentValue).append(' ');
    }
    if (libraryVersion == null) {
      sb.append(getLibraryName());
    } else {
      sb.append(getLibraryName()).append('/').append(libraryVersion);
    }

    return sb.toString();
  }

  /**
   * Returns the library's name, {@code gcloud-java}, as a string.
   */
  public static String getLibraryName() {
    return "gcloud-java";
  }

  /**
   * Returns the library's name used by x-goog-api-client header as a string.
   */
  public static String getGoogApiClientLibName() {
    return "gccl";
  }

  /**
   * Returns the library's version as a string.
   */
  public String getLibraryVersion() {
    return GaxProperties.getLibraryVersion(this.getClass());
  }

  @InternalApi
  public final HeaderProvider getMergedHeaderProvider(HeaderProvider internalHeaderProvider) {
    Map<String, String> mergedHeaders =
        ImmutableMap.<String, String>builder()
            .putAll(internalHeaderProvider.getHeaders())
            .putAll(headerProvider.getHeaders())
            .build();
    return FixedHeaderProvider.create(mergedHeaders);
  }

  @InternalApi
  public final String getUserAgent() {
    if (headerProvider != null) {
      for (Map.Entry<String, String> entry : headerProvider.getHeaders().entrySet()) {
        if ("user-agent".equals(entry.getKey().toLowerCase())) {
          return entry.getValue();
        }
      }
    }
    return null;
  }

  protected int baseHashCode() {
    return Objects.hash(projectId, host, credentials, retrySettings, serviceFactoryClassName,
        serviceRpcFactoryClassName, clock);
  }

  protected boolean baseEquals(ServiceOptions<?, ?> other) {
    return Objects.equals(projectId, other.projectId)
        && Objects.equals(host, other.host)
        && Objects.equals(credentials, other.credentials)
        && Objects.equals(retrySettings, other.retrySettings)
        && Objects.equals(serviceFactoryClassName, other.serviceFactoryClassName)
        && Objects.equals(serviceRpcFactoryClassName, other.serviceRpcFactoryClassName)
        && Objects.equals(clock, clock);
  }

  private void readObject(ObjectInputStream input) throws IOException, ClassNotFoundException {
    input.defaultReadObject();
    serviceFactory = newInstance(serviceFactoryClassName);
    serviceRpcFactory = newInstance(serviceRpcFactoryClassName);
  }

  @SuppressWarnings("unchecked")
  @InternalApi
  public static <T> T newInstance(String className) throws IOException, ClassNotFoundException {
    try {
      return (T) Class.forName(className).newInstance();
    } catch (InstantiationException | IllegalAccessException e) {
      throw new IOException(e);
    }
  }

  public static RetrySettings getDefaultRetrySettings() {
    return DEFAULT_RETRY_SETTINGS;
  }

  public static RetrySettings getNoRetrySettings() {
    return NO_RETRY_SETTINGS;
  }

  private static RetrySettings.Builder getDefaultRetrySettingsBuilder() {
    return RetrySettings.newBuilder()
        .setMaxAttempts(6)
        .setInitialRetryDelay(Duration.ofMillis(1000L))
        .setMaxRetryDelay(Duration.ofMillis(32_000L))
        .setRetryDelayMultiplier(2.0)
        .setTotalTimeout(Duration.ofMillis(50_000L))
        .setInitialRpcTimeout(Duration.ofMillis(50_000L))
        .setRpcTimeoutMultiplier(1.0)
        .setMaxRpcTimeout(Duration.ofMillis(50_000L));
  }

  protected abstract Set<String> getScopes();

  public abstract <B extends Builder<ServiceT, OptionsT, B>> B toBuilder();

  /**
   * Some services may have different backoff requirements listed in their SLAs. Be sure to override
   * this method in options subclasses when the service's backoff requirement differs from the
   * default parameters listed in {@link RetrySettings}.
   */
  protected RetrySettings defaultRetrySettings() {
    return getDefaultRetrySettings();
  }

  @InternalApi
  public static <T> T getFromServiceLoader(Class<? extends T> clazz, T defaultInstance) {
    return Iterables.getFirst(ServiceLoader.load(clazz), defaultInstance);
  }
}
