/*
Copyright 2020 The Kubernetes Authors.
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.kubernetes.client.openapi;

import io.kubernetes.client.openapi.auth.ApiKeyAuth;
import io.kubernetes.client.openapi.auth.Authentication;
import io.kubernetes.client.openapi.auth.HttpBasicAuth;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Type;
import java.net.URLConnection;
import java.net.URLEncoder;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.SecureRandom;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.text.DateFormat;
import java.util.*;
import java.util.Map.Entry;
import java.util.concurrent.TimeUnit;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.net.ssl.*;
import okhttp3.*;
import okhttp3.internal.http.HttpMethod;
import okhttp3.internal.tls.OkHostnameVerifier;
import okhttp3.logging.HttpLoggingInterceptor;
import okhttp3.logging.HttpLoggingInterceptor.Level;
import okio.BufferedSink;
import okio.Okio;
import org.joda.time.DateTime;
import org.joda.time.LocalDate;
import org.joda.time.format.DateTimeFormatter;

public class ApiClient {

  private String basePath = "http://localhost";
  private boolean debugging = false;
  private Map<String, String> defaultHeaderMap = new HashMap<String, String>();
  private Map<String, String> defaultCookieMap = new HashMap<String, String>();
  private String tempFolderPath = null;

  private Map<String, Authentication> authentications;

  private DateFormat dateFormat;
  private DateFormat datetimeFormat;
  private boolean lenientDatetimeFormat;
  private int dateLength;

  private InputStream sslCaCert;
  private boolean verifyingSsl;
  private KeyManager[] keyManagers;

  private OkHttpClient httpClient;
  private JSON json;

  private HttpLoggingInterceptor loggingInterceptor;

  /*
   * Basic constructor for ApiClient
   */
  public ApiClient() {
    init();
    initHttpClient();

    // Setup authentications (key: authentication name, value: authentication).
    authentications.put("BearerToken", new ApiKeyAuth("header", "authorization"));
    // Prevent the authentications from being modified.
    authentications = Collections.unmodifiableMap(authentications);
  }

  private void initHttpClient() {
    initHttpClient(Collections.<Interceptor>emptyList());
  }

  private void initHttpClient(List<Interceptor> interceptors) {
    OkHttpClient.Builder builder = new OkHttpClient.Builder();
    builder.addNetworkInterceptor(getProgressInterceptor());
    for (Interceptor interceptor : interceptors) {
      builder.addInterceptor(interceptor);
    }

    httpClient = builder.build();
  }

  private void init() {
    verifyingSsl = true;

    json = new JSON();

    // Set default User-Agent.
    setUserAgent("OpenAPI-Generator/1.0-SNAPSHOT/java");

    authentications = new HashMap<String, Authentication>();
  }

  /**
   * Get base path
   *
   * @return Base path
   */
  public String getBasePath() {
    return basePath;
  }

  /**
   * Set base path
   *
   * @param basePath Base path of the URL (e.g http://localhost
   * @return An instance of OkHttpClient
   */
  public ApiClient setBasePath(String basePath) {
    this.basePath = basePath;
    return this;
  }

  /**
   * Get HTTP client
   *
   * @return An instance of OkHttpClient
   */
  public OkHttpClient getHttpClient() {
    return httpClient;
  }

  /**
   * Set HTTP client, which must never be null.
   *
   * @param newHttpClient An instance of OkHttpClient
   * @return Api Client
   * @throws NullPointerException when newHttpClient is null
   */
  public ApiClient setHttpClient(OkHttpClient newHttpClient) {
    this.httpClient = Objects.requireNonNull(newHttpClient, "HttpClient must not be null!");
    return this;
  }

  /**
   * Get JSON
   *
   * @return JSON object
   */
  public JSON getJSON() {
    return json;
  }

  /**
   * Set JSON
   *
   * @param json JSON object
   * @return Api client
   */
  public ApiClient setJSON(JSON json) {
    this.json = json;
    return this;
  }

  /**
   * True if isVerifyingSsl flag is on
   *
   * @return True if isVerifySsl flag is on
   */
  public boolean isVerifyingSsl() {
    return verifyingSsl;
  }

  /**
   * Configure whether to verify certificate and hostname when making https requests. Default to
   * true. NOTE: Do NOT set to false in production code, otherwise you would face multiple types of
   * cryptographic attacks.
   *
   * @param verifyingSsl True to verify TLS/SSL connection
   * @return ApiClient
   */
  public ApiClient setVerifyingSsl(boolean verifyingSsl) {
    this.verifyingSsl = verifyingSsl;
    applySslSettings();
    return this;
  }

  /**
   * Get SSL CA cert.
   *
   * @return Input stream to the SSL CA cert
   */
  public InputStream getSslCaCert() {
    return sslCaCert;
  }

  /**
   * Configure the CA certificate to be trusted when making https requests. Use null to reset to
   * default.
   *
   * @param sslCaCert input stream for SSL CA cert
   * @return ApiClient
   */
  public ApiClient setSslCaCert(InputStream sslCaCert) {
    this.sslCaCert = sslCaCert;
    applySslSettings();
    return this;
  }

  public KeyManager[] getKeyManagers() {
    return keyManagers;
  }

  /**
   * Configure client keys to use for authorization in an SSL session. Use null to reset to default.
   *
   * @param managers The KeyManagers to use
   * @return ApiClient
   */
  public ApiClient setKeyManagers(KeyManager[] managers) {
    this.keyManagers = managers;
    applySslSettings();
    return this;
  }

  public DateFormat getDateFormat() {
    return dateFormat;
  }

  public ApiClient setDateFormat(DateFormat dateFormat) {
    this.json.setDateFormat(dateFormat);
    return this;
  }

  public ApiClient setSqlDateFormat(DateFormat dateFormat) {
    this.json.setSqlDateFormat(dateFormat);
    return this;
  }

  public ApiClient setDateTimeFormat(DateTimeFormatter dateFormat) {
    this.json.setDateTimeFormat(dateFormat);
    return this;
  }

  public ApiClient setLocalDateFormat(DateTimeFormatter dateFormat) {
    this.json.setLocalDateFormat(dateFormat);
    return this;
  }

  public ApiClient setLenientOnJson(boolean lenientOnJson) {
    this.json.setLenientOnJson(lenientOnJson);
    return this;
  }

  /**
   * Get authentications (key: authentication name, value: authentication).
   *
   * @return Map of authentication objects
   */
  public Map<String, Authentication> getAuthentications() {
    return authentications;
  }

  /**
   * Get authentication for the given name.
   *
   * @param authName The authentication name
   * @return The authentication, null if not found
   */
  public Authentication getAuthentication(String authName) {
    return authentications.get(authName);
  }

  /**
   * Helper method to set username for the first HTTP basic authentication.
   *
   * @param username Username
   */
  public void setUsername(String username) {
    for (Authentication auth : authentications.values()) {
      if (auth instanceof HttpBasicAuth) {
        ((HttpBasicAuth) auth).setUsername(username);
        return;
      }
    }
    throw new RuntimeException("No HTTP basic authentication configured!");
  }

  /**
   * Helper method to set password for the first HTTP basic authentication.
   *
   * @param password Password
   */
  public void setPassword(String password) {
    for (Authentication auth : authentications.values()) {
      if (auth instanceof HttpBasicAuth) {
        ((HttpBasicAuth) auth).setPassword(password);
        return;
      }
    }
    throw new RuntimeException("No HTTP basic authentication configured!");
  }

  /**
   * Helper method to set API key value for the first API key authentication.
   *
   * @param apiKey API key
   */
  public void setApiKey(String apiKey) {
    for (Authentication auth : authentications.values()) {
      if (auth instanceof ApiKeyAuth) {
        ((ApiKeyAuth) auth).setApiKey(apiKey);
        return;
      }
    }
    throw new RuntimeException("No API key authentication configured!");
  }

  /**
   * Helper method to set API key prefix for the first API key authentication.
   *
   * @param apiKeyPrefix API key prefix
   */
  public void setApiKeyPrefix(String apiKeyPrefix) {
    for (Authentication auth : authentications.values()) {
      if (auth instanceof ApiKeyAuth) {
        ((ApiKeyAuth) auth).setApiKeyPrefix(apiKeyPrefix);
        return;
      }
    }
    throw new RuntimeException("No API key authentication configured!");
  }

  /**
   * Helper method to set access token for the first OAuth2 authentication.
   *
   * @param accessToken Access token
   */
  public void setAccessToken(String accessToken) {
    throw new RuntimeException("No OAuth2 authentication configured!");
  }

  /**
   * Set the User-Agent header's value (by adding to the default header map).
   *
   * @param userAgent HTTP request's user agent
   * @return ApiClient
   */
  public ApiClient setUserAgent(String userAgent) {
    addDefaultHeader("User-Agent", userAgent);
    return this;
  }

  /**
   * Add a default header.
   *
   * @param key The header's key
   * @param value The header's value
   * @return ApiClient
   */
  public ApiClient addDefaultHeader(String key, String value) {
    defaultHeaderMap.put(key, value);
    return this;
  }

  /**
   * Add a default cookie.
   *
   * @param key The cookie's key
   * @param value The cookie's value
   * @return ApiClient
   */
  public ApiClient addDefaultCookie(String key, String value) {
    defaultCookieMap.put(key, value);
    return this;
  }

  /**
   * Check that whether debugging is enabled for this API client.
   *
   * @return True if debugging is enabled, false otherwise.
   */
  public boolean isDebugging() {
    return debugging;
  }

  /**
   * Enable/disable debugging for this API client.
   *
   * @param debugging To enable (true) or disable (false) debugging
   * @return ApiClient
   */
  public ApiClient setDebugging(boolean debugging) {
    if (debugging != this.debugging) {
      if (debugging) {
        loggingInterceptor = new HttpLoggingInterceptor();
        loggingInterceptor.setLevel(Level.BODY);
        httpClient = httpClient.newBuilder().addInterceptor(loggingInterceptor).build();
      } else {
        httpClient.interceptors().remove(loggingInterceptor);
        loggingInterceptor = null;
      }
    }
    this.debugging = debugging;
    return this;
  }

  /**
   * The path of temporary folder used to store downloaded files from endpoints with file response.
   * The default value is <code>null</code>, i.e. using the system's default tempopary folder.
   *
   * @see <a
   *     href="https://docs.oracle.com/javase/7/docs/api/java/io/File.html#createTempFile">createTempFile</a>
   * @return Temporary folder path
   */
  public String getTempFolderPath() {
    return tempFolderPath;
  }

  /**
   * Set the temporary folder path (for downloading files)
   *
   * @param tempFolderPath Temporary folder path
   * @return ApiClient
   */
  public ApiClient setTempFolderPath(String tempFolderPath) {
    this.tempFolderPath = tempFolderPath;
    return this;
  }

  /**
   * Get connection timeout (in milliseconds).
   *
   * @return Timeout in milliseconds
   */
  public int getConnectTimeout() {
    return httpClient.connectTimeoutMillis();
  }

  /**
   * Sets the connect timeout (in milliseconds). A value of 0 means no timeout, otherwise values
   * must be between 1 and {@link Integer#MAX_VALUE}.
   *
   * @param connectionTimeout connection timeout in milliseconds
   * @return Api client
   */
  public ApiClient setConnectTimeout(int connectionTimeout) {
    httpClient =
        httpClient.newBuilder().connectTimeout(connectionTimeout, TimeUnit.MILLISECONDS).build();
    return this;
  }

  /**
   * Get read timeout (in milliseconds).
   *
   * @return Timeout in milliseconds
   */
  public int getReadTimeout() {
    return httpClient.readTimeoutMillis();
  }

  /**
   * Sets the read timeout (in milliseconds). A value of 0 means no timeout, otherwise values must
   * be between 1 and {@link Integer#MAX_VALUE}.
   *
   * @param readTimeout read timeout in milliseconds
   * @return Api client
   */
  public ApiClient setReadTimeout(int readTimeout) {
    httpClient = httpClient.newBuilder().readTimeout(readTimeout, TimeUnit.MILLISECONDS).build();
    return this;
  }

  /**
   * Get write timeout (in milliseconds).
   *
   * @return Timeout in milliseconds
   */
  public int getWriteTimeout() {
    return httpClient.writeTimeoutMillis();
  }

  /**
   * Sets the write timeout (in milliseconds). A value of 0 means no timeout, otherwise values must
   * be between 1 and {@link Integer#MAX_VALUE}.
   *
   * @param writeTimeout connection timeout in milliseconds
   * @return Api client
   */
  public ApiClient setWriteTimeout(int writeTimeout) {
    httpClient = httpClient.newBuilder().writeTimeout(writeTimeout, TimeUnit.MILLISECONDS).build();
    return this;
  }

  /**
   * Format the given parameter object into string.
   *
   * @param param Parameter
   * @return String representation of the parameter
   */
  public String parameterToString(Object param) {
    if (param == null) {
      return "";
    } else if (param instanceof Date || param instanceof DateTime || param instanceof LocalDate) {
      // Serialize to json string and remove the " enclosing characters
      String jsonStr = json.serialize(param);
      return jsonStr.substring(1, jsonStr.length() - 1);
    } else if (param instanceof Collection) {
      StringBuilder b = new StringBuilder();
      for (Object o : (Collection) param) {
        if (b.length() > 0) {
          b.append(",");
        }
        b.append(String.valueOf(o));
      }
      return b.toString();
    } else {
      return String.valueOf(param);
    }
  }

  /**
   * Formats the specified query parameter to a list containing a single {@code Pair} object.
   *
   * <p>Note that {@code value} must not be a collection.
   *
   * @param name The name of the parameter.
   * @param value The value of the parameter.
   * @return A list containing a single {@code Pair} object.
   */
  public List<Pair> parameterToPair(String name, Object value) {
    List<Pair> params = new ArrayList<Pair>();

    // preconditions
    if (name == null || name.isEmpty() || value == null || value instanceof Collection) {
      return params;
    }

    params.add(new Pair(name, parameterToString(value)));
    return params;
  }

  /**
   * Formats the specified collection query parameters to a list of {@code Pair} objects.
   *
   * <p>Note that the values of each of the returned Pair objects are percent-encoded.
   *
   * @param collectionFormat The collection format of the parameter.
   * @param name The name of the parameter.
   * @param value The value of the parameter.
   * @return A list of {@code Pair} objects.
   */
  public List<Pair> parameterToPairs(String collectionFormat, String name, Collection value) {
    List<Pair> params = new ArrayList<Pair>();

    // preconditions
    if (name == null || name.isEmpty() || value == null || value.isEmpty()) {
      return params;
    }

    // create the params based on the collection format
    if ("multi".equals(collectionFormat)) {
      for (Object item : value) {
        params.add(new Pair(name, escapeString(parameterToString(item))));
      }
      return params;
    }

    // collectionFormat is assumed to be "csv" by default
    String delimiter = ",";

    // escape all delimiters except commas, which are URI reserved
    // characters
    if ("ssv".equals(collectionFormat)) {
      delimiter = escapeString(" ");
    } else if ("tsv".equals(collectionFormat)) {
      delimiter = escapeString("\t");
    } else if ("pipes".equals(collectionFormat)) {
      delimiter = escapeString("|");
    }

    StringBuilder sb = new StringBuilder();
    for (Object item : value) {
      sb.append(delimiter);
      sb.append(escapeString(parameterToString(item)));
    }

    params.add(new Pair(name, sb.substring(delimiter.length())));

    return params;
  }

  /**
   * Formats the specified collection path parameter to a string value.
   *
   * @param collectionFormat The collection format of the parameter.
   * @param value The value of the parameter.
   * @return String representation of the parameter
   */
  public String collectionPathParameterToString(String collectionFormat, Collection value) {
    // create the value based on the collection format
    if ("multi".equals(collectionFormat)) {
      // not valid for path params
      return parameterToString(value);
    }

    // collectionFormat is assumed to be "csv" by default
    String delimiter = ",";

    if ("ssv".equals(collectionFormat)) {
      delimiter = " ";
    } else if ("tsv".equals(collectionFormat)) {
      delimiter = "\t";
    } else if ("pipes".equals(collectionFormat)) {
      delimiter = "|";
    }

    StringBuilder sb = new StringBuilder();
    for (Object item : value) {
      sb.append(delimiter);
      sb.append(parameterToString(item));
    }

    return sb.substring(delimiter.length());
  }

  /**
   * Sanitize filename by removing path. e.g. ../../sun.gif becomes sun.gif
   *
   * @param filename The filename to be sanitized
   * @return The sanitized filename
   */
  public String sanitizeFilename(String filename) {
    return filename.replaceAll(".*[/\\\\]", "");
  }

  /**
   * Check if the given MIME is a JSON MIME. JSON MIME examples: application/json application/json;
   * charset=UTF8 APPLICATION/JSON application/vnd.company+json "* / *" is also default to JSON
   *
   * @param mime MIME (Multipurpose Internet Mail Extensions)
   * @return True if the given MIME is JSON, false otherwise.
   */
  public boolean isJsonMime(String mime) {
    String jsonMime = "(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$";
    return mime != null && (mime.matches(jsonMime) || mime.equals("*/*"));
  }

  /**
   * Select the Accept header's value from the given accepts array: if JSON exists in the given
   * array, use it; otherwise use all of them (joining into a string)
   *
   * @param accepts The accepts array to select from
   * @return The Accept header to use. If the given array is empty, null will be returned (not to
   *     set the Accept header explicitly).
   */
  public String selectHeaderAccept(String[] accepts) {
    if (accepts.length == 0) {
      return null;
    }
    for (String accept : accepts) {
      if (isJsonMime(accept)) {
        return accept;
      }
    }
    return StringUtil.join(accepts, ",");
  }

  /**
   * Select the Content-Type header's value from the given array: if JSON exists in the given array,
   * use it; otherwise use the first one of the array.
   *
   * @param contentTypes The Content-Type array to select from
   * @return The Content-Type header to use. If the given array is empty, or matches "any", JSON
   *     will be used.
   */
  public String selectHeaderContentType(String[] contentTypes) {
    if (contentTypes.length == 0 || contentTypes[0].equals("*/*")) {
      return "application/json";
    }
    for (String contentType : contentTypes) {
      if (isJsonMime(contentType)) {
        return contentType;
      }
    }
    return contentTypes[0];
  }

  /**
   * Escape the given string to be used as URL query value.
   *
   * @param str String to be escaped
   * @return Escaped string
   */
  public String escapeString(String str) {
    try {
      return URLEncoder.encode(str, "utf8").replaceAll("\\+", "%20");
    } catch (UnsupportedEncodingException e) {
      return str;
    }
  }

  /**
   * Deserialize response body to Java object, according to the return type and the Content-Type
   * response header.
   *
   * @param <T> Type
   * @param response HTTP response
   * @param returnType The type of the Java object
   * @return The deserialized Java object
   * @throws ApiException If fail to deserialize response body, i.e. cannot read response body or
   *     the Content-Type of the response is not supported.
   */
  @SuppressWarnings("unchecked")
  public <T> T deserialize(Response response, Type returnType) throws ApiException {
    if (response == null || returnType == null) {
      return null;
    }

    if ("byte[]".equals(returnType.toString())) {
      // Handle binary response (byte array).
      try {
        return (T) response.body().bytes();
      } catch (IOException e) {
        throw new ApiException(e);
      }
    } else if (returnType.equals(File.class)) {
      // Handle file downloading.
      return (T) downloadFileFromResponse(response);
    }

    String respBody;
    try {
      if (response.body() != null) respBody = response.body().string();
      else respBody = null;
    } catch (IOException e) {
      throw new ApiException(e);
    }

    if (respBody == null || "".equals(respBody)) {
      return null;
    }

    String contentType = response.headers().get("Content-Type");
    if (contentType == null) {
      // ensuring a default content type
      contentType = "application/json";
    }
    if (isJsonMime(contentType)) {
      return json.deserialize(respBody, returnType);
    } else if (returnType.equals(String.class)) {
      // Expecting string, return the raw response body.
      return (T) respBody;
    } else {
      throw new ApiException(
          "Content type \"" + contentType + "\" is not supported for type: " + returnType,
          response.code(),
          response.headers().toMultimap(),
          respBody);
    }
  }

  /**
   * Serialize the given Java object into request body according to the object's class and the
   * request Content-Type.
   *
   * @param obj The Java object
   * @param contentType The request Content-Type
   * @return The serialized request body
   * @throws ApiException If fail to serialize the given object
   */
  public RequestBody serialize(Object obj, String contentType) throws ApiException {
    if (obj instanceof byte[]) {
      // Binary (byte array) body parameter support.
      return RequestBody.create(MediaType.parse(contentType), (byte[]) obj);
    } else if (obj instanceof File) {
      // File body parameter support.
      return RequestBody.create(MediaType.parse(contentType), (File) obj);
    } else if (isJsonMime(contentType)) {
      String content;
      if (obj != null) {
        content = json.serialize(obj);
      } else {
        content = null;
      }
      return RequestBody.create(MediaType.parse(contentType), content);
    } else {
      throw new ApiException("Content type \"" + contentType + "\" is not supported");
    }
  }

  /**
   * Download file from the given response.
   *
   * @param response An instance of the Response object
   * @throws ApiException If fail to read file content from response and write to disk
   * @return Downloaded file
   */
  public File downloadFileFromResponse(Response response) throws ApiException {
    try {
      File file = prepareDownloadFile(response);
      BufferedSink sink = Okio.buffer(Okio.sink(file));
      sink.writeAll(response.body().source());
      sink.close();
      return file;
    } catch (IOException e) {
      throw new ApiException(e);
    }
  }

  /**
   * Prepare file for download
   *
   * @param response An instance of the Response object
   * @return Prepared file for the download
   * @throws IOException If fail to prepare file for download
   */
  public File prepareDownloadFile(Response response) throws IOException {
    String filename = null;
    String contentDisposition = response.header("Content-Disposition");
    if (contentDisposition != null && !"".equals(contentDisposition)) {
      // Get filename from the Content-Disposition header.
      Pattern pattern = Pattern.compile("filename=['\"]?([^'\"\\s]+)['\"]?");
      Matcher matcher = pattern.matcher(contentDisposition);
      if (matcher.find()) {
        filename = sanitizeFilename(matcher.group(1));
      }
    }

    String prefix = null;
    String suffix = null;
    if (filename == null) {
      prefix = "download-";
      suffix = "";
    } else {
      int pos = filename.lastIndexOf(".");
      if (pos == -1) {
        prefix = filename + "-";
      } else {
        prefix = filename.substring(0, pos) + "-";
        suffix = filename.substring(pos);
      }
      // File.createTempFile requires the prefix to be at least three characters long
      if (prefix.length() < 3) prefix = "download-";
    }

    if (tempFolderPath == null) return File.createTempFile(prefix, suffix);
    else return File.createTempFile(prefix, suffix, new File(tempFolderPath));
  }

  /**
   * {@link #execute(Call, Type)}
   *
   * @param <T> Type
   * @param call An instance of the Call object
   * @return ApiResponse&lt;T&gt;
   * @throws ApiException If fail to execute the call
   */
  public <T> ApiResponse<T> execute(Call call) throws ApiException {
    return execute(call, null);
  }

  /**
   * Execute HTTP call and deserialize the HTTP response body into the given return type.
   *
   * @param returnType The return type used to deserialize HTTP response body
   * @param <T> The return type corresponding to (same with) returnType
   * @param call Call
   * @return ApiResponse object containing response status, headers and data, which is a Java object
   *     deserialized from response body and would be null when returnType is null.
   * @throws ApiException If fail to execute the call
   */
  public <T> ApiResponse<T> execute(Call call, Type returnType) throws ApiException {
    try {
      Response response = call.execute();
      T data = handleResponse(response, returnType);
      return new ApiResponse<T>(response.code(), response.headers().toMultimap(), data);
    } catch (IOException e) {
      throw new ApiException(e);
    }
  }

  /**
   * {@link #executeAsync(Call, Type, ApiCallback)}
   *
   * @param <T> Type
   * @param call An instance of the Call object
   * @param callback ApiCallback&lt;T&gt;
   */
  public <T> void executeAsync(Call call, ApiCallback<T> callback) {
    executeAsync(call, null, callback);
  }

  /**
   * Execute HTTP call asynchronously.
   *
   * @param <T> Type
   * @param call The callback to be executed when the API call finishes
   * @param returnType Return type
   * @param callback ApiCallback
   * @see #execute(Call, Type)
   */
  @SuppressWarnings("unchecked")
  public <T> void executeAsync(Call call, final Type returnType, final ApiCallback<T> callback) {
    call.enqueue(
        new Callback() {
          @Override
          public void onFailure(Call call, IOException e) {
            callback.onFailure(new ApiException(e), 0, null);
          }

          @Override
          public void onResponse(Call call, Response response) throws IOException {
            T result;
            try {
              result = (T) handleResponse(response, returnType);
            } catch (ApiException e) {
              callback.onFailure(e, response.code(), response.headers().toMultimap());
              return;
            }
            callback.onSuccess(result, response.code(), response.headers().toMultimap());
          }
        });
  }

  /**
   * Handle the given response, return the deserialized object when the response is successful.
   *
   * @param <T> Type
   * @param response Response
   * @param returnType Return type
   * @return Type
   * @throws ApiException If the response has an unsuccessful status code or fail to deserialize the
   *     response body
   */
  public <T> T handleResponse(Response response, Type returnType) throws ApiException {
    if (response.isSuccessful()) {
      if (returnType == null || response.code() == 204) {
        // returning null if the returnType is not defined,
        // or the status code is 204 (No Content)
        if (response.body() != null) {
          try {
            response.body().close();
          } catch (Exception e) {
            throw new ApiException(
                response.message(), e, response.code(), response.headers().toMultimap());
          }
        }
        return null;
      } else {
        return deserialize(response, returnType);
      }
    } else {
      String respBody = null;
      if (response.body() != null) {
        try {
          respBody = response.body().string();
        } catch (IOException e) {
          throw new ApiException(
              response.message(), e, response.code(), response.headers().toMultimap());
        }
      }
      throw new ApiException(
          response.message(), response.code(), response.headers().toMultimap(), respBody);
    }
  }

  /**
   * Build HTTP call with the given options.
   *
   * @param path The sub-path of the HTTP URL
   * @param method The request method, one of "GET", "HEAD", "OPTIONS", "POST", "PUT", "PATCH" and
   *     "DELETE"
   * @param queryParams The query parameters
   * @param collectionQueryParams The collection query parameters
   * @param body The request body object
   * @param headerParams The header parameters
   * @param cookieParams The cookie parameters
   * @param formParams The form parameters
   * @param authNames The authentications to apply
   * @param callback Callback for upload/download progress
   * @return The HTTP call
   * @throws ApiException If fail to serialize the request body object
   */
  public Call buildCall(
      String path,
      String method,
      List<Pair> queryParams,
      List<Pair> collectionQueryParams,
      Object body,
      Map<String, String> headerParams,
      Map<String, String> cookieParams,
      Map<String, Object> formParams,
      String[] authNames,
      ApiCallback callback)
      throws ApiException {
    Request request =
        buildRequest(
            path,
            method,
            queryParams,
            collectionQueryParams,
            body,
            headerParams,
            cookieParams,
            formParams,
            authNames,
            callback);

    return httpClient.newCall(request);
  }

  /**
   * Build an HTTP request with the given options.
   *
   * @param path The sub-path of the HTTP URL
   * @param method The request method, one of "GET", "HEAD", "OPTIONS", "POST", "PUT", "PATCH" and
   *     "DELETE"
   * @param queryParams The query parameters
   * @param collectionQueryParams The collection query parameters
   * @param body The request body object
   * @param headerParams The header parameters
   * @param cookieParams The cookie parameters
   * @param formParams The form parameters
   * @param authNames The authentications to apply
   * @param callback Callback for upload/download progress
   * @return The HTTP request
   * @throws ApiException If fail to serialize the request body object
   */
  public Request buildRequest(
      String path,
      String method,
      List<Pair> queryParams,
      List<Pair> collectionQueryParams,
      Object body,
      Map<String, String> headerParams,
      Map<String, String> cookieParams,
      Map<String, Object> formParams,
      String[] authNames,
      ApiCallback callback)
      throws ApiException {
    updateParamsForAuth(authNames, queryParams, headerParams, cookieParams);

    final String url = buildUrl(path, queryParams, collectionQueryParams);
    final Request.Builder reqBuilder = new Request.Builder().url(url);
    processHeaderParams(headerParams, reqBuilder);
    processCookieParams(cookieParams, reqBuilder);

    String contentType = (String) headerParams.get("Content-Type");
    // ensuring a default content type
    if (contentType == null) {
      contentType = "application/json";
    }

    RequestBody reqBody;
    if (!HttpMethod.permitsRequestBody(method)) {
      reqBody = null;
    } else if ("application/x-www-form-urlencoded".equals(contentType)) {
      reqBody = buildRequestBodyFormEncoding(formParams);
    } else if ("multipart/form-data".equals(contentType)) {
      reqBody = buildRequestBodyMultipart(formParams);
    } else if (body == null) {
      if ("DELETE".equals(method)) {
        // allow calling DELETE without sending a request body
        reqBody = null;
      } else {
        // use an empty request body (for POST, PUT and PATCH)
        reqBody = RequestBody.create(MediaType.parse(contentType), "");
      }
    } else {
      reqBody = serialize(body, contentType);
    }

    // Associate callback with request (if not null) so interceptor can
    // access it when creating ProgressResponseBody
    reqBuilder.tag(callback);

    Request request = null;

    if (callback != null && reqBody != null) {
      ProgressRequestBody progressRequestBody = new ProgressRequestBody(reqBody, callback);
      request = reqBuilder.method(method, progressRequestBody).build();
    } else {
      request = reqBuilder.method(method, reqBody).build();
    }

    return request;
  }

  /**
   * Build full URL by concatenating base path, the given sub path and query parameters.
   *
   * @param path The sub path
   * @param queryParams The query parameters
   * @param collectionQueryParams The collection query parameters
   * @return The full URL
   */
  public String buildUrl(String path, List<Pair> queryParams, List<Pair> collectionQueryParams) {
    final StringBuilder url = new StringBuilder();
    url.append(basePath).append(path);

    if (queryParams != null && !queryParams.isEmpty()) {
      // support (constant) query string in `path`, e.g. "/posts?draft=1"
      String prefix = path.contains("?") ? "&" : "?";
      for (Pair param : queryParams) {
        if (param.getValue() != null) {
          if (prefix != null) {
            url.append(prefix);
            prefix = null;
          } else {
            url.append("&");
          }
          String value = parameterToString(param.getValue());
          url.append(escapeString(param.getName())).append("=").append(escapeString(value));
        }
      }
    }

    if (collectionQueryParams != null && !collectionQueryParams.isEmpty()) {
      String prefix = url.toString().contains("?") ? "&" : "?";
      for (Pair param : collectionQueryParams) {
        if (param.getValue() != null) {
          if (prefix != null) {
            url.append(prefix);
            prefix = null;
          } else {
            url.append("&");
          }
          String value = parameterToString(param.getValue());
          // collection query parameter value already escaped as part of parameterToPairs
          url.append(escapeString(param.getName())).append("=").append(value);
        }
      }
    }

    return url.toString();
  }

  /**
   * Set header parameters to the request builder, including default headers.
   *
   * @param headerParams Header parameters in the form of Map
   * @param reqBuilder Request.Builder
   */
  public void processHeaderParams(Map<String, String> headerParams, Request.Builder reqBuilder) {
    for (Entry<String, String> param : headerParams.entrySet()) {
      reqBuilder.header(param.getKey(), parameterToString(param.getValue()));
    }
    for (Entry<String, String> header : defaultHeaderMap.entrySet()) {
      if (!headerParams.containsKey(header.getKey())) {
        reqBuilder.header(header.getKey(), parameterToString(header.getValue()));
      }
    }
  }

  /**
   * Set cookie parameters to the request builder, including default cookies.
   *
   * @param cookieParams Cookie parameters in the form of Map
   * @param reqBuilder Request.Builder
   */
  public void processCookieParams(Map<String, String> cookieParams, Request.Builder reqBuilder) {
    for (Entry<String, String> param : cookieParams.entrySet()) {
      reqBuilder.addHeader("Cookie", String.format("%s=%s", param.getKey(), param.getValue()));
    }
    for (Entry<String, String> param : defaultCookieMap.entrySet()) {
      if (!cookieParams.containsKey(param.getKey())) {
        reqBuilder.addHeader("Cookie", String.format("%s=%s", param.getKey(), param.getValue()));
      }
    }
  }

  /**
   * Update query and header parameters based on authentication settings.
   *
   * @param authNames The authentications to apply
   * @param queryParams List of query parameters
   * @param headerParams Map of header parameters
   * @param cookieParams Map of cookie parameters
   */
  public void updateParamsForAuth(
      String[] authNames,
      List<Pair> queryParams,
      Map<String, String> headerParams,
      Map<String, String> cookieParams) {
    for (String authName : authNames) {
      Authentication auth = authentications.get(authName);
      if (auth == null) {
        throw new RuntimeException("Authentication undefined: " + authName);
      }
      auth.applyToParams(queryParams, headerParams, cookieParams);
    }
  }

  /**
   * Build a form-encoding request body with the given form parameters.
   *
   * @param formParams Form parameters in the form of Map
   * @return RequestBody
   */
  public RequestBody buildRequestBodyFormEncoding(Map<String, Object> formParams) {
    okhttp3.FormBody.Builder formBuilder = new okhttp3.FormBody.Builder();
    for (Entry<String, Object> param : formParams.entrySet()) {
      formBuilder.add(param.getKey(), parameterToString(param.getValue()));
    }
    return formBuilder.build();
  }

  /**
   * Build a multipart (file uploading) request body with the given form parameters, which could
   * contain text fields and file fields.
   *
   * @param formParams Form parameters in the form of Map
   * @return RequestBody
   */
  public RequestBody buildRequestBodyMultipart(Map<String, Object> formParams) {
    MultipartBody.Builder mpBuilder = new MultipartBody.Builder().setType(MultipartBody.FORM);
    for (Entry<String, Object> param : formParams.entrySet()) {
      if (param.getValue() instanceof File) {
        File file = (File) param.getValue();
        Headers partHeaders =
            Headers.of(
                "Content-Disposition",
                "form-data; name=\"" + param.getKey() + "\"; filename=\"" + file.getName() + "\"");
        MediaType mediaType = MediaType.parse(guessContentTypeFromFile(file));
        mpBuilder.addPart(partHeaders, RequestBody.create(mediaType, file));
      } else {
        Headers partHeaders =
            Headers.of("Content-Disposition", "form-data; name=\"" + param.getKey() + "\"");
        mpBuilder.addPart(
            partHeaders, RequestBody.create(null, parameterToString(param.getValue())));
      }
    }
    return mpBuilder.build();
  }

  /**
   * Guess Content-Type header from the given file (defaults to "application/octet-stream").
   *
   * @param file The given file
   * @return The guessed Content-Type
   */
  public String guessContentTypeFromFile(File file) {
    String contentType = URLConnection.guessContentTypeFromName(file.getName());
    if (contentType == null) {
      return "application/octet-stream";
    } else {
      return contentType;
    }
  }

  /**
   * Get network interceptor to add it to the httpClient to track download progress for async
   * requests.
   */
  private Interceptor getProgressInterceptor() {
    return new Interceptor() {
      @Override
      public Response intercept(Interceptor.Chain chain) throws IOException {
        final Request request = chain.request();
        final Response originalResponse = chain.proceed(request);
        if (request.tag() instanceof ApiCallback) {
          final ApiCallback callback = (ApiCallback) request.tag();
          return originalResponse
              .newBuilder()
              .body(new ProgressResponseBody(originalResponse.body(), callback))
              .build();
        }
        return originalResponse;
      }
    };
  }

  /**
   * Apply SSL related settings to httpClient according to the current values of verifyingSsl and
   * sslCaCert.
   */
  private void applySslSettings() {
    try {
      TrustManager[] trustManagers;
      HostnameVerifier hostnameVerifier;
      if (!verifyingSsl) {
        trustManagers =
            new TrustManager[] {
              new X509TrustManager() {
                @Override
                public void checkClientTrusted(
                    java.security.cert.X509Certificate[] chain, String authType)
                    throws CertificateException {}

                @Override
                public void checkServerTrusted(
                    java.security.cert.X509Certificate[] chain, String authType)
                    throws CertificateException {}

                @Override
                public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                  return new java.security.cert.X509Certificate[] {};
                }
              }
            };
        hostnameVerifier =
            new HostnameVerifier() {
              @Override
              public boolean verify(String hostname, SSLSession session) {
                return true;
              }
            };
      } else {
        TrustManagerFactory trustManagerFactory =
            TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());

        if (sslCaCert == null) {
          trustManagerFactory.init((KeyStore) null);
        } else {
          char[] password = null; // Any password will work.
          CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
          Collection<? extends Certificate> certificates =
              certificateFactory.generateCertificates(sslCaCert);
          if (certificates.isEmpty()) {
            throw new IllegalArgumentException("expected non-empty set of trusted certificates");
          }
          KeyStore caKeyStore = newEmptyKeyStore(password);
          int index = 0;
          for (Certificate certificate : certificates) {
            String certificateAlias = "ca" + Integer.toString(index++);
            caKeyStore.setCertificateEntry(certificateAlias, certificate);
          }
          trustManagerFactory.init(caKeyStore);
        }
        trustManagers = trustManagerFactory.getTrustManagers();
        hostnameVerifier = OkHostnameVerifier.INSTANCE;
      }

      SSLContext sslContext = SSLContext.getInstance("TLS");
      sslContext.init(keyManagers, trustManagers, new SecureRandom());
      httpClient =
          httpClient
              .newBuilder()
              .sslSocketFactory(sslContext.getSocketFactory(), (X509TrustManager) trustManagers[0])
              .hostnameVerifier(hostnameVerifier)
              .build();
    } catch (GeneralSecurityException e) {
      throw new RuntimeException(e);
    }
  }

  private KeyStore newEmptyKeyStore(char[] password) throws GeneralSecurityException {
    try {
      KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
      keyStore.load(null, password);
      return keyStore;
    } catch (IOException e) {
      throw new AssertionError(e);
    }
  }
}
