/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.drill.exec.store.http.util;

import com.typesafe.config.Config;
import okhttp3.Cache;
import okhttp3.ConnectionPool;
import okhttp3.Credentials;
import okhttp3.FormBody;
import okhttp3.HttpUrl;
import okhttp3.Interceptor;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.OkHttpClient.Builder;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

import okhttp3.ResponseBody;
import org.apache.commons.lang3.StringUtils;
import org.apache.drill.common.exceptions.EmptyErrorContext;
import org.apache.drill.common.logical.OAuthConfig;
import org.apache.drill.common.logical.StoragePluginConfig.AuthMode;
import org.apache.drill.common.AutoCloseables;
import org.apache.drill.common.exceptions.CustomErrorContext;
import org.apache.drill.common.exceptions.UserException;
import org.apache.drill.exec.ExecConstants;
import org.apache.drill.exec.expr.fn.impl.StringFunctionHelpers;
import org.apache.drill.exec.expr.holders.NullableVarCharHolder;
import org.apache.drill.exec.oauth.PersistentTokenTable;
import org.apache.drill.exec.server.DrillbitContext;
import org.apache.drill.exec.store.StoragePlugin;
import org.apache.drill.exec.store.StoragePluginRegistry;
import org.apache.drill.exec.store.StoragePluginRegistry.PluginException;
import org.apache.drill.exec.store.http.HttpApiConfig;
import org.apache.drill.exec.store.http.HttpApiConfig.HttpMethod;
import org.apache.drill.exec.store.http.HttpApiConfig.PostLocation;
import org.apache.drill.exec.store.http.HttpStoragePlugin;
import org.apache.drill.exec.store.http.HttpStoragePluginConfig;
import org.apache.drill.exec.store.http.HttpSubScan;
import org.apache.drill.exec.store.http.paginator.Paginator;
import org.apache.drill.exec.store.http.oauth.AccessTokenAuthenticator;
import org.apache.drill.exec.store.http.oauth.AccessTokenInterceptor;
import org.apache.drill.exec.store.http.oauth.AccessTokenRepository;
import org.apache.drill.exec.store.http.util.HttpProxyConfig.ProxyBuilder;
import org.apache.drill.exec.store.security.UsernamePasswordWithProxyCredentials;
import org.jetbrains.annotations.NotNull;
import org.json.simple.JSONObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.InetSocketAddress;
import java.net.Proxy;
import java.net.URLDecoder;
import java.nio.charset.StandardCharsets;
import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.concurrent.TimeUnit;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;


/**
 * Performs the actual HTTP requests for the HTTP Storage Plugin. The core
 * method is the getInputStream() method which accepts a url and opens an
 * InputStream with that URL's contents.
 */
public class SimpleHttp implements AutoCloseable {
  private static final Logger logger = LoggerFactory.getLogger(SimpleHttp.class);
  private static final int DEFAULT_TIMEOUT = 1;
  private static final Pattern URL_PARAM_REGEX = Pattern.compile("\\{(\\w+)(?:=(\\w*))?}");
  public static final MediaType JSON_MEDIA_TYPE = MediaType.get("application/json; charset=utf-8");
  public static final MediaType XML_MEDIA_TYPE = MediaType.get("application/xml");
  private static final OkHttpClient SIMPLE_CLIENT = new OkHttpClient.Builder()
    .connectTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS)
    .writeTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS)
    .readTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS)
    .build();


  private final OkHttpClient client;
  private final File tempDir;
  private final HttpProxyConfig proxyConfig;
  private final CustomErrorContext errorContext;
  private final Paginator paginator;
  private final HttpUrl url;
  private final PersistentTokenTable tokenTable;
  private final Map<String, String> filters;
  private final String connection;
  private final HttpStoragePluginConfig pluginConfig;
  private final HttpApiConfig apiConfig;
  private final OAuthConfig oAuthConfig;
  private final int rateLimit;
  private String responseMessage;
  private int responseCode;
  private String responseProtocol;
  private String responseURL;
  private String username;


  public SimpleHttp(HttpSubScan scanDefn, HttpUrl url, File tempDir,
    HttpProxyConfig proxyConfig, CustomErrorContext errorContext, Paginator paginator) {
    this.apiConfig = scanDefn.tableSpec().connectionConfig();
    this.pluginConfig = scanDefn.tableSpec().config();
    this.connection = scanDefn.tableSpec().connection();
    this.oAuthConfig = scanDefn.tableSpec().config().oAuthConfig();
    this.username = scanDefn.getUserName();
    this.filters = scanDefn.filters();
    this.url = url;
    this.tempDir = tempDir;
    this.rateLimit = scanDefn.tableSpec().config().retryDelay();
    this.proxyConfig = proxyConfig;
    this.errorContext = errorContext;
    this.tokenTable = scanDefn.tableSpec().getTokenTable();
    this.paginator = paginator;
    this.client = setupHttpClient();
  }

  /**
   * This constructor does not have an HttpSubScan and can be used outside the context of the HttpStoragePlugin.
   * @param url The URL for an HTTP request
   * @param tempDir Temp directory for caching
   * @param proxyConfig Proxy configuration for making API calls
   * @param errorContext The error context for error messages
   * @param paginator The {@link Paginator} object for pagination.
   * @param tokenTable The OAuth token table
   * @param pluginConfig HttpStoragePlugin configuration.  The plugin obtains OAuth and timeout info from this config.
   * @param endpointConfig The
   * @param connection The name of the connection
   * @param filters A Key/value set of filters and values
   */
  public SimpleHttp(HttpUrl url, File tempDir, HttpProxyConfig proxyConfig, CustomErrorContext errorContext,
                    Paginator paginator, PersistentTokenTable tokenTable, HttpStoragePluginConfig pluginConfig,
                    HttpApiConfig endpointConfig, String connection, Map<String, String> filters, int rateLimit) {
    this.url = url;
    this.tempDir = tempDir;
    this.proxyConfig = proxyConfig;

    if (errorContext == null) {
      this.errorContext = new EmptyErrorContext() {
        @Override
        public void addContext(UserException.Builder builder) {
          super.addContext(builder);
          builder.addContext("URL", url.toString());
        }
      };
    } else {
      this.errorContext = errorContext;
    }

    this.paginator = paginator;
    this.tokenTable = tokenTable;
    this.pluginConfig = pluginConfig;
    this.apiConfig = endpointConfig;
    this.connection = connection;
    this.filters = filters;
    this.rateLimit = rateLimit;
    this.oAuthConfig = pluginConfig.oAuthConfig();
    this.client = setupHttpClient();
  }

  public static SimpleHttpBuilder builder() {
    return new SimpleHttpBuilder();
  }

  /**
   * Configures the OkHTTP3 server object with configuration info from the user.
   *
   * @return OkHttpClient configured server
   */
  protected OkHttpClient setupHttpClient() {
    Builder builder = new OkHttpClient.Builder();

    // Set up the HTTP Cache.   Future possibilities include making the cache size and retention configurable but
    // right now it is on or off.  The writer will write to the Drill temp directory if it is accessible and
    // output a warning if not.
    if (pluginConfig.cacheResults()) {
      setupCache(builder);
    }
    // If OAuth information is provided, we will assume that the user does not want to use
    // basic authentication
    if (oAuthConfig != null) {
      // Add interceptors for OAuth2
      logger.debug("Adding OAuth2 Interceptor");
      AccessTokenRepository repository = new AccessTokenRepository(proxyConfig, pluginConfig, tokenTable);

      builder.authenticator(new AccessTokenAuthenticator(repository));
      builder.addInterceptor(new AccessTokenInterceptor(repository));
    } else if (apiConfig.authType().equalsIgnoreCase("basic")) {
      // If the API uses basic authentication add the authentication code.  Use the global credentials unless there are credentials
      // for the specific endpoint.
      logger.debug("Adding Interceptor");
      Optional<UsernamePasswordWithProxyCredentials> credentials;
      if (pluginConfig.getAuthMode() == AuthMode.USER_TRANSLATION) {
        credentials = getCredentials(username);
        if (!credentials.isPresent() || StringUtils.isEmpty(credentials.get().getUsername()) || StringUtils.isEmpty(credentials.get().getPassword())) {
          throw UserException.connectionError()
            .message("You do not have valid credentials for this API.  Please provide your credentials.")
            .addContext(errorContext)
            .build(logger);
        }
      } else {
        credentials = getCredentials();
      }
      builder.addInterceptor(new BasicAuthInterceptor(credentials.get().getUsername(), credentials.get().getPassword()));
    }

    // Set timeouts
    int timeout = Math.max(1, pluginConfig.timeout());
    builder.connectTimeout(timeout, TimeUnit.SECONDS);
    builder.writeTimeout(timeout, TimeUnit.SECONDS);
    builder.readTimeout(timeout, TimeUnit.SECONDS);
    builder.addInterceptor(new RateLimitInterceptor(rateLimit));
    // OkHttp's connection pooling is disabled because the HTTP plugin creates
    // and discards potentially many OkHttp clients, each leaving lingering
    // CLOSE_WAIT connections around if they have pooling enabled.
    builder.connectionPool(new ConnectionPool(0, 1, TimeUnit.SECONDS));

    // Code to skip SSL Certificate validation
    if (! apiConfig.verifySSLCert()) {
      try {
        TrustManager[] trustAllCerts = getAllTrustingTrustManager();
        SSLContext sslContext = SSLContext.getInstance("SSL");
        sslContext.init(null, trustAllCerts, new java.security.SecureRandom());
        SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();


        builder.sslSocketFactory(sslSocketFactory, (X509TrustManager) trustAllCerts[0]);
        HostnameVerifier verifier = (hostname, session) -> true;
        builder.hostnameVerifier(verifier);

      } catch (KeyManagementException | NoSuchAlgorithmException e) {
        logger.error("Error when configuring Drill not to verify SSL certs. {}", e.getMessage());
      }
    }

    // Set the proxy configuration
    addProxyInfo(builder, proxyConfig);

    return builder.build();
  }

  public String url() {
    return url.toString();
  }

  /**
   * Applies the proxy configuration to the OkHttp3 builder.  This ensures that proxy configurations
   * will be consistent across HTTP REST connections.
   * @param builder The input OkHttp3 builder
   * @param proxyConfig The proxy configuration
   */
  public static void addProxyInfo(Builder builder, HttpProxyConfig proxyConfig) {
    if (proxyConfig == null) {
      return;
    }

    Proxy.Type proxyType;
    switch (proxyConfig.type) {
      case SOCKS:
        proxyType = Proxy.Type.SOCKS;
        break;
      case HTTP:
        proxyType = Proxy.Type.HTTP;
        break;
      default:
        proxyType = Proxy.Type.DIRECT;
    }
    if (proxyType != Proxy.Type.DIRECT) {
      builder.proxy(new Proxy(proxyType,
        new InetSocketAddress(proxyConfig.host, proxyConfig.port)));
      if (proxyConfig.username != null) {
        builder.proxyAuthenticator((route, response) -> {
          String credential = Credentials.basic(proxyConfig.username, proxyConfig.password);
          return response.request().newBuilder()
            .header("Proxy-Authorization", credential)
            .build();
        });
      }
    }
  }

  private TrustManager[] getAllTrustingTrustManager() {
    return new TrustManager[] {
      new X509TrustManager() {
        @Override
        public void checkClientTrusted(X509Certificate[] chain, String authType) {
        }

        @Override
        public void checkServerTrusted(X509Certificate[] chain, String authType) {
        }

        @Override
        public X509Certificate[] getAcceptedIssuers() {
          return new X509Certificate[]{};
        }
      }
    };
  }


  /**
   * Returns an InputStream based on the URL and config in the scanSpec. If anything goes wrong
   * the method throws a UserException.
   * @return An Inputstream of the data from the URL call. The caller is responsible for calling
   *         close() on the InputStream.
   */
  public InputStream getInputStream() {

    Request.Builder requestBuilder = new Request.Builder()
      .url(url);

    // The configuration does not allow for any other request types other than POST and GET.
    if (apiConfig.getMethodType() == HttpMethod.POST) {
      // Handle POST requests
      FormBody.Builder formBodyBuilder;

      // If the user wants filters pushed down to the POST body, do so here.
      if (apiConfig.getPostLocation() == PostLocation.POST_BODY) {
        formBodyBuilder = buildPostBody(filters, apiConfig.postBody());
        requestBuilder.post(formBodyBuilder.build());
      } else if (apiConfig.getPostLocation() == PostLocation.JSON_BODY) {
        // Add static parameters from postBody
        JSONObject json = buildJsonPostBody(apiConfig.postBody());
        // Now add filters
        if (filters != null) {
          for (Map.Entry<String, String> filter : filters.entrySet()) {
            json.put(filter.getKey(), filter.getValue());
          }
        }

        RequestBody requestBody = RequestBody.create(json.toJSONString(), JSON_MEDIA_TYPE);
        requestBuilder.post(requestBody);
      } else if (apiConfig.getPostLocation() == PostLocation.XML_BODY) {
        StringBuilder xmlRequest = new StringBuilder();
        xmlRequest.append("<request>");
        if (filters != null) {
          for (Map.Entry<String, String> filter : filters.entrySet()) {
            xmlRequest.append("<").append(filter.getKey()).append(">");
            xmlRequest.append(filter.getValue());
            xmlRequest.append("</").append(filter.getKey()).append(">");
          }
        }
        xmlRequest.append("</request>");
        RequestBody requestBody = RequestBody.create(xmlRequest.toString(), XML_MEDIA_TYPE);
        requestBuilder.post(requestBody);

      } else {
        formBodyBuilder = buildPostBody(apiConfig.postBody());
        requestBuilder.post(formBodyBuilder.build());
      }
    }

    // Log the URL and method to aid in debugging user issues.
    logger.info("Connection: {}, Method {}, URL: {}",
      connection,
      apiConfig.getMethodType().name(), url());

    // Add headers to request
    if (apiConfig.headers() != null) {
      for (Map.Entry<String, String> entry : apiConfig.headers().entrySet()) {
        requestBuilder.addHeader(entry.getKey(), entry.getValue());
      }
    }

    // Build the request object
    Request request = requestBuilder.build();
    Response response = null;

    try {
      logger.debug("Executing request: {}", request);
      logger.debug("Headers: {}", request.headers());

      // Execute the request
      response = client.newCall(request).execute();

      // Preserve the response
      responseMessage = response.message();
      responseCode = response.code();
      responseProtocol = response.protocol().toString();
      responseURL = response.request().url().toString();

      // Case for pagination without limit
      if (paginator != null && (
        response.code() != 200 || response.body() == null ||
        response.body().contentLength() == 0)) {
        paginator.notifyPartialPage();
      }

      // If the request is unsuccessful clean up and throw a UserException
      if (!isSuccessful(responseCode)) {
        AutoCloseables.closeSilently(response);
        throw UserException
          .dataReadError()
          .message("HTTP request failed")
          .addContext("Response code", response.code())
          .addContext("Response message", response.message())
          .addContext(errorContext)
          .build(logger);
      }
      logger.debug("HTTP Request for {} successful.", url());
      logger.debug("Response Headers: {} ", response.headers());

      // Return the InputStream of the response. Note that it is necessary and
      // and sufficient that the caller invokes close() on the returned stream.
      return Objects.requireNonNull(response.body()).byteStream();

    } catch (IOException e) {
      // response can only be null at this location so we do not attempt to close it.
      throw UserException
        .dataReadError(e)
        .message("Failed to read the HTTP response body")
        .addContext("Error message", e.getMessage())
        .addContext(errorContext)
        .build(logger);
    }
  }

  public String getResultsFromApiCall() {
    InputStream inputStream = getInputStream();
    try {
      return new BufferedReader(
        new InputStreamReader(inputStream, StandardCharsets.UTF_8))
        .lines()
        .collect(Collectors.joining("\n"));
    } finally {
      AutoCloseables.closeSilently(inputStream);
    }
  }

  public static HttpProxyConfig getProxySettings(HttpStoragePluginConfig config, Config drillConfig, HttpUrl url) {
    final ProxyBuilder builder = HttpProxyConfig.builder()
      .fromConfigForURL(drillConfig, url.toString());
    final String proxyType = config.proxyType();
    if (proxyType != null && !"direct".equals(proxyType)) {
      builder
        .type(config.proxyType())
        .host(config.proxyHost())
        .port(config.proxyPort());

      Optional<UsernamePasswordWithProxyCredentials> credentials = config.getUsernamePasswordCredentials();

      if (credentials.isPresent()) {
        builder.username(credentials.get().getUsername())
          .password(credentials.get().getPassword());
      }
    }
    return builder.build();
  }

  /**
   * This function is a replacement for the isSuccessful() function which comes
   * with okhttp3.  The issue is that in some cases, a user may not want Drill to throw
   * errors on 400 response codes.  This function will return true/false depending on the
   * configuration for the specific connection.
   *
   * @param responseCode An int of the connection code
   * @return True if the response code is 200-299 and possibly 400-499, false if other
   */
  private boolean isSuccessful(int responseCode) {
    if (apiConfig.errorOn400()) {
      return responseCode >= 200 && responseCode <= 299;
    } else {
      return ((responseCode >= 200 && responseCode <= 299) ||
        (responseCode >= 400 && responseCode <= 499));
    }
  }

  /**
   * If the user has defined username/password for the specific API endpoint, pass the API endpoint credentials.
   * Otherwise, use the global connection credentials.
   * @return A UsernamePasswordCredentials collection with the correct username/password
   */
  private Optional<UsernamePasswordWithProxyCredentials> getCredentials() {
    Optional<UsernamePasswordWithProxyCredentials> apiCreds = apiConfig.getUsernamePasswordCredentials();
    return apiCreds.isPresent() ? apiCreds : pluginConfig.getUsernamePasswordCredentials();
  }

  private Optional<UsernamePasswordWithProxyCredentials> getCredentials(String queryUser) {
    Optional<UsernamePasswordWithProxyCredentials> apiCreds = apiConfig.getUsernamePasswordCredentials();
    return apiCreds.isPresent() ? apiCreds : pluginConfig.getUsernamePasswordCredentials(queryUser);
  }

  /**
   * Gets the HTTP response code from the HTTP call.  Note that this value
   * is only available after the getInputStream() method has been called.
   *
   * @return int value of the HTTP response code
   */
  public int getResponseCode() {
    return responseCode;
  }

  /**
   * Gets the HTTP response code from the HTTP call.  Note that this value
   * is only available after the getInputStream() method has been called.
   *
   * @return int of HTTP response code
   */
  public String getResponseMessage() {
    return responseMessage;
  }

  /**
   * Gets the HTTP response code from the HTTP call.  Note that this value
   * is only available after the getInputStream() method has been called.
   *
   * @return The HTTP response protocol
   */
  public String getResponseProtocol() {
    return responseProtocol;
  }

  /**
   * Gets the HTTP response code from the HTTP call.  Note that this value
   * is only available after the getInputStream() method has been called.
   *
   * @return The HTTP response URL
   */
  public String getResponseURL() {
    return responseURL;
  }

  /**
   * Configures response caching using a provided temp directory.
   *
   * @param builder Builder the Builder object to which the caching is to be
   *                configured
   */
  private void setupCache(Builder builder) {
    int cacheSize = 10 * 1024 * 1024;   // TODO Add cache size in MB to config
    File cacheDirectory = new File(tempDir, "http-cache");
    if (!cacheDirectory.exists()) {
      if (!cacheDirectory.mkdirs()) {
        throw UserException
          .dataWriteError()
          .message("Could not create the HTTP cache directory")
          .addContext("Path", cacheDirectory.getAbsolutePath())
          .addContext("Please check the temp directory or disable HTTP caching.")
          .addContext(errorContext)
          .build(logger);
      }
    }

    try {
      Cache cache = new Cache(cacheDirectory, cacheSize);
      logger.debug("Caching HTTP Query Results at: {}", cacheDirectory);
      builder.cache(cache);
    } catch (Exception e) {
      throw UserException.dataWriteError(e)
        .message("Could not create the HTTP cache")
        .addContext("Path", cacheDirectory.getAbsolutePath())
        .addContext("Please check the temp directory or disable HTTP caching.")
        .addContext(errorContext)
        .build(logger);
    }
  }

  /**
   * Accepts text from a post body in the format:<br>
   * {@code key1=value1}<br>
   * {@code key2=value2}
   * <p>
   * and creates the appropriate headers.
   *
   * @return FormBody.Builder The populated formbody builder
   */
  private FormBody.Builder buildPostBody(String postBody) {
    FormBody.Builder formBodyBuilder = new FormBody.Builder();
    if (StringUtils.isEmpty(postBody)) {
      return formBodyBuilder;
    }
    final Pattern postBodyPattern = Pattern.compile("^.+=.+$");

    String[] lines = postBody.split("\\r?\\n");
    for (String line : lines) {

      // If the string is in the format key=value split it,
      // Otherwise ignore
      if (postBodyPattern.matcher(line).find()) {
        //Split into key/value
        String[] parts = line.split("=");
        formBodyBuilder.add(parts[0], parts[1]);
      }
    }
    return formBodyBuilder;
  }

  private JSONObject buildJsonPostBody(String postBody) {
    JSONObject jsonObject = new JSONObject();
    if (StringUtils.isEmpty(postBody)) {
      return jsonObject;
    }
    final Pattern postBodyPattern = Pattern.compile("^.+=.+$");

    String[] lines = postBody.split("\\r?\\n");
    for (String line : lines) {

      // If the string is in the format key=value split it,
      // Otherwise ignore
      if (postBodyPattern.matcher(line).find()) {
        //Split into key/value
        String[] parts = line.split("=");
        jsonObject.put(parts[0], parts[1]);
      }
    }
    return jsonObject;
  }

  /**
   * This function is used to push filters down to the post body rather than the URL query string.
   * It will also add the static parameters to the post body as well.
   * @param filters A HashMap of the filters and values
   * @param postBody The post body of static parameters.
   * @return The post body builder with the filters and static parameters
   */
  public FormBody.Builder buildPostBody(Map<String, String> filters, String postBody) {
    // Add static parameters
    FormBody.Builder builder = buildPostBody(postBody);

    // Now add the filters
    for (Map.Entry<String, String> filter : filters.entrySet()) {
      builder.add(filter.getKey(), filter.getValue());
    }
    return builder;
  }

  /**
   * Returns the URL-decoded URL. If the URL is invalid, return the original URL.
   *
   * @return Returns the URL-decoded URL
   */
  public static String decodedURL(HttpUrl url) {
    try {
      return URLDecoder.decode(url.toString(), "UTF-8");
    } catch (UnsupportedEncodingException e) {
      return url.toString();
    }
  }

  /**
   * Returns true if the url has url parameters, as indicated by the presence of
   * {param} in a url.
   *
   * @return True if there are URL params, false if not
   */
  public static boolean hasURLParameters(HttpUrl url) {
    String decodedUrl = SimpleHttp.decodedURL(url);
    Matcher matcher = URL_PARAM_REGEX.matcher(decodedUrl);
    return matcher.find();
  }

  /**
   * APIs are sometimes structured with parameters in the URL itself.  For instance, to request a list of
   * an organization's repositories in github, the URL is: https://api.github.com/orgs/{org}/repos, where
   * you can replace the org with the actual organization name.
   *
   * @return A list of URL parameters enclosed by curly braces.
   */
  public static List<String> getURLParameters(HttpUrl url) {
    String decodedURL = decodedURL(url);
    Matcher matcher = URL_PARAM_REGEX.matcher(decodedURL);
    List<String> parameters = new ArrayList<>();
    while (matcher.find()) {
      String param = matcher.group(1);
      parameters.add(param);
    }
    return parameters;
  }

  /**
   * This function is used to extract the default parameter supplied in a URL. For instance,
   * if the supplied URL is http://someapi.com/path/{p1=foo}, the function will return foo. If there
   * is not a matching parameter or no default value, the function will return null.
   * @param url The URL containing a default parameter
   * @param parameter The parameter for which you need the value
   * @return The value for the supplied parameter
   */
  public static String getDefaultParameterValue (HttpUrl url, String parameter) {
    String decodedURL = decodedURL(url);
    Pattern paramRegex = Pattern.compile("\\{" + parameter + "=(\\w+?)}");
    Matcher paramMatcher = paramRegex.matcher(decodedURL);
    if (paramMatcher.find()) {
      return paramMatcher.group(1);
    } else {
      throw UserException
        .validationError()
        .message("Default URL parameters must have a value. The parameter " + parameter + " is not defined in the configuration.")
        .build(logger);
    }
  }

  /**
   * Used for APIs which have parameters in the URL.  This function maps the filters pushed down
   * from the query into the URL.  For example the API: github.com/orgs/{org}/repos requires a user to
   * specify an organization and replace {org} with an actual organization.  The filter is passed down from
   * the query.
   *
   * Note that if a URL contains URL parameters and one is not provided in the filters, Drill will throw
   * a UserException.
   *
   * @param url The HttpUrl containing URL Parameters
   * @param filters  A CaseInsensitiveMap of filters
   * @return A string of the URL with the URL parameters replaced by filter values
   */
  public static String mapURLParameters(HttpUrl url, Map<String, String> filters) {
    if (!hasURLParameters(url)) {
      return url.toString();
    }

    if (filters == null) {
      throw UserException
        .parseError()
        .message("API Query with URL Parameters must be populated.")
        .build(logger);
    }

    List<String> params = SimpleHttp.getURLParameters(url);
    String tempUrl = SimpleHttp.decodedURL(url);
    for (String param : params) {

      // The null check here verify that IF the user has configured the API with URL Parameters that:
      // 1.  The filter was pushed down IE: The user put something in the WHERE clause that corresponds to the
      //     parameter
      // 2.  There is a value associated with that parameter.  Strictly speaking, the second check is not
      //     necessary as I don't think Calcite or Drill will push down an empty filter, but for the sake
      //     of providing helpful errors in strange cases, it is there.


      String value = filters.get(param);

      // Check and see if there is a default for this parameter. If not throw an error.
      if (StringUtils.isEmpty(value)) {
        String defaultValue = getDefaultParameterValue(url, param);
        if (! StringUtils.isEmpty(defaultValue)) {
          tempUrl = tempUrl.replace("/{" + param + "=" + defaultValue + "}", "/" + defaultValue);
        } else {
          throw UserException
            .parseError()
            .message("API Query with URL Parameters must be populated. Parameter " + param + " must be included in WHERE clause.")
            .build(logger);
        }
      } else {
        // Note that if the user has a URL with duplicate parameters, both will be replaced.  IE:
        // someapi.com/{p1}/{p1}/something   In this case, both p1 parameters will be replaced with
        // the value.
        tempUrl = tempUrl.replace("{" + param + "}", value);
      }
    }
    return tempUrl;
  }


  public static String mapPositionalParameters(String rawUrl, List<String> params) {
    HttpUrl url = HttpUrl.parse(rawUrl);

    // Validate URL
    if (url == null) {
      throw UserException.functionError()
        .message("URL provided must be a valid URL. " + rawUrl + " is not valid.")
        .build(logger);
    }

    if (!hasURLParameters(url)) {
      return url.toString();
    }

    if (params == null) {
      throw UserException
        .parseError()
        .message("API Query with URL Parameters must be populated.")
        .build(logger);
    }

    String tempUrl = decodedURL(url);
    int startIndex;
    int endIndex;
    int counter = 0;
    while (counter < params.size()) {
      startIndex = tempUrl.indexOf("{");
      endIndex = tempUrl.indexOf("}");

      if (startIndex == -1 || endIndex == -1) {
        break;
      }

      StringBuffer tempUrlBuffer = new StringBuffer(tempUrl);
      tempUrlBuffer.replace(startIndex, endIndex + 1, params.get(counter));
      tempUrl = tempUrlBuffer.toString();
      counter++;
    }
    return tempUrl;
  }

  /**
   * Validates a URL.
   * @param url The input URL.  Should be a string.
   * @return True of the URL is valid, false if not.
   */
  public static boolean validateUrl(String url) {
    return HttpUrl.parse(url) != null;
  }

  /**
   * Accepts a list of input readers and converts that into an ArrayList of Strings
   * @param inputReaders The array of FieldReaders
   * @return A List of Strings containing the values from the FieldReaders or null
   * to indicate that at least one null is present in the arguments.
   */
  public static List<String> buildParameterList(NullableVarCharHolder[] inputReaders) {
    if (inputReaders == null || inputReaders.length == 0) {
      // no args provided
      return Collections.emptyList();
    }

    List<String> inputArguments = new ArrayList<>();
    for (int i = 0; i < inputReaders.length; i++) {
      if (inputReaders[i].buffer == null) {
        // at least one null arg provided
        return null;
      }

      inputArguments.add(StringFunctionHelpers.getStringFromVarCharHolder(inputReaders[i]));
    }

    return inputArguments;
  }

  /**
   * This function is used to obtain the configuration information for a given API in the HTTP UDF.
   * If aliasing is enabled, this function will resolve aliases for connections.
   * @param endpoint The name of the endpoint.  Should be a {@link String}
   * @param pluginConfig The {@link HttpStoragePluginConfig} the configuration from the plugin
   * @return The {@link HttpApiConfig} corresponding with the endpoint.
   */
  public static HttpApiConfig getEndpointConfig(String endpoint,
                                                HttpStoragePluginConfig pluginConfig) {
    HttpApiConfig endpointConfig = pluginConfig.getConnection(endpoint);
    if (endpointConfig == null) {
      throw UserException.functionError()
        .message("You must call this function with a valid endpoint name.")
        .build(logger);
    } else if (! endpointConfig.inputType().contentEquals("json")) {
      throw UserException.functionError()
        .message("Http_get only supports API endpoints which return json.")
        .build(logger);
    }

    return endpointConfig;
  }

  /**
   * This function will return a {@link HttpStoragePlugin} for use in the HTTP UDFs.  If user or public aliases
   * are used, the function will resolve those aliases.
   * @param context A {@link DrillbitContext} from the current query
   * @param pluginName A {@link String} of the plugin name.  Note that the function will resolve aliases.
   * @return A {@link HttpStoragePlugin} of the plugin.
   */
  public static HttpStoragePlugin getStoragePlugin(String pluginName, DrillbitContext context) {
    StoragePluginRegistry storage = context.getStorage();
    try {
      StoragePlugin pluginInstance = storage.getPlugin(pluginName);
      if (pluginInstance == null) {
        throw UserException.functionError()
          .message(pluginName + " is not a valid plugin.")
          .build(logger);
      }

      if (!(pluginInstance instanceof HttpStoragePlugin)) {
        throw UserException.functionError()
          .message("You can only include HTTP plugins in this function.")
          .build(logger);
      }
      return (HttpStoragePlugin) pluginInstance;
    } catch (PluginException e) {
      throw UserException.functionError()
        .message("Could not access plugin " + pluginName)
        .build(logger);
    }
  }

  /**
   * This function makes an API call and returns a string of the parsed results. It is used in the http_get() UDF
   * and retrieves all the configuration parameters contained in the storage plugin and endpoint configuration. The exception
   * is pagination.  This does not support pagination.
   * @param plugin The HTTP storage plugin upon which the API call is based.
   * @param endpointConfig The configuration of the API endpoint upon which the API call is based.
   * @param context {@link DrillbitContext} The context from the current query
   * @param args An optional list of parameter arguments which will be included in the URL
   * @return A String of the results.
   */
  public static SimpleHttp apiCall(
    HttpStoragePlugin plugin,
    HttpApiConfig endpointConfig,
    DrillbitContext context,
    List<String> args
  ) {
    HttpStoragePluginConfig pluginConfig;
    pluginConfig = plugin.getConfig();

    // Get proxy settings
    HttpProxyConfig proxyConfig = SimpleHttp.getProxySettings(pluginConfig, context.getConfig(), endpointConfig.getHttpUrl());

    // For this use case, we will replace the URL parameters here, rather than doing it in the SimpleHttp client
    // because we are using positional mapping rather than k/v pairs for this.
    String finalUrl;
    if (SimpleHttp.hasURLParameters(endpointConfig.getHttpUrl())) {
      finalUrl = SimpleHttp.mapPositionalParameters(endpointConfig.url(), args);
    } else {
      finalUrl = endpointConfig.url();
    }

    // Now get the client
    return new SimpleHttpBuilder()
      .pluginConfig(pluginConfig)
      .endpointConfig(endpointConfig)
      .tempDir(new File(context.getConfig().getString(ExecConstants.DRILL_TMP_DIR)))
      .url(HttpUrl.parse(finalUrl))
      .proxyConfig(proxyConfig)
      .tokenTable(plugin.getTokenTable())
      .build();
  }

  public static String getRequestAndStringResponse(String url) {
    ResponseBody respBody = null;
    try {
      respBody = makeSimpleGetRequest(url);
      return respBody.string();
    } catch (IOException e) {
      throw UserException
        .dataReadError(e)
        .message("HTTP request failed")
        .build(logger);
    } finally {
      AutoCloseables.closeSilently(respBody);
    }
  }

  /**
   *
   * @param url
   * @return an input stream which the caller is responsible for closing.
   */
  public static InputStream getRequestAndStreamResponse(String url) {
    try {
      return makeSimpleGetRequest(url).byteStream();
    } catch (IOException e) {
      throw UserException
        .dataReadError(e)
        .message("HTTP request failed")
        .build(logger);
    }
  }

  /**
   *
   * @param url
   * @return response body which the caller is responsible for closing.
   * @throws IOException
   */
  public static ResponseBody makeSimpleGetRequest(String url) throws IOException {
    Request.Builder requestBuilder = new Request.Builder()
      .url(url);

    // Build the request object
    Request request = requestBuilder.build();

    // Execute the request
    Response response = SIMPLE_CLIENT.newCall(request).execute();
    return response.body();
  }

  @Override
  public void close() {
    Cache cache;
    try {
      cache = client.cache();
      if (cache != null) {
        cache.close();
      }
      client.connectionPool().evictAll();
    } catch (IOException e) {
      logger.warn("Error closing cache. {}", e.getMessage());
    }
  }

  /**
   * Intercepts requests and adds authentication headers to the request
   */
  public static class BasicAuthInterceptor implements Interceptor {
    private final String credentials;

    public BasicAuthInterceptor(String user, String password) {
      credentials = Credentials.basic(user, password);
    }

    @NotNull
    @Override
    public Response intercept(Chain chain) throws IOException {
      // Get the existing request
      Request request = chain.request();

      // Replace with new request containing the authorization headers and previous headers
      Request authenticatedRequest = request.newBuilder().header("Authorization", credentials).build();
      return chain.proceed(authenticatedRequest);
    }
  }

  /**
   * This interceptor is used in pagination situations or elsewhere when APIs have burst throttling. The rate limit interceptor
   * will wait a configurable number of milliseconds and retry queries if it encounters a 429
   * response code.
   */
  public static class RateLimitInterceptor implements Interceptor {
    private final int millis;
    public RateLimitInterceptor(int millis) {
      this.millis = millis;
    }

    @NotNull
    @Override
    public Response intercept(Chain chain) throws IOException {

      Response response = chain.proceed(chain.request());
      // 429 is how the api indicates a rate limit error
      if (!response.isSuccessful() && response.code() == 429) {
        logger.info("Received 429 Response.  Throttling API calls: {} ", response.message());
        // Wait and retry request
        try {
          Thread.sleep(millis);
        } catch (InterruptedException e) {
          logger.error("Error retrying HTTP request: {}", e.getMessage());
        }
        response = chain.proceed(chain.request());
      }
      return response;
    }
  }


  public static class SimpleHttpBuilder {
    private HttpSubScan scanDefn;
    private HttpUrl url;
    private File tempDir;
    private HttpProxyConfig proxyConfig;
    private CustomErrorContext errorContext;
    private Paginator paginator;
    private PersistentTokenTable tokenTable;
    private HttpStoragePluginConfig pluginConfig;
    private HttpApiConfig endpointConfig;
    private OAuthConfig oAuthConfig;
    private Map<String,String> filters;
    private String connection;
    private String username;
    private int rateLimit;

    public SimpleHttpBuilder scanDefn(HttpSubScan scanDefn) {
      this.scanDefn = scanDefn;
      this.pluginConfig = scanDefn.tableSpec().config();
      this.endpointConfig = scanDefn.tableSpec().connectionConfig();
      this.oAuthConfig = scanDefn.tableSpec().config().oAuthConfig();
      this.tokenTable = scanDefn.tableSpec().getTokenTable();
      this.filters = scanDefn.filters();
      this.username = scanDefn.getUserName();
      this.rateLimit = scanDefn.tableSpec().config().retryDelay();
      return this;
    }

    public SimpleHttpBuilder url(HttpUrl url) {
      this.url = url;
      return this;
    }

    public SimpleHttpBuilder tempDir(File tempDir) {
      this.tempDir = tempDir;
      return this;
    }

    public SimpleHttpBuilder username(String username) {
      this.username = username;
      return this;
    }

    public SimpleHttpBuilder proxyConfig(HttpProxyConfig proxyConfig) {
      this.proxyConfig = proxyConfig;
      return this;
    }

    public SimpleHttpBuilder errorContext(CustomErrorContext errorContext) {
      this.errorContext = errorContext;
      return this;
    }

    public SimpleHttpBuilder paginator(Paginator paginator) {
      this.paginator = paginator;
      return this;
    }

    public SimpleHttpBuilder rateLimit(int rateLimit) {
      this.rateLimit = rateLimit;
      return this;
    }

    public SimpleHttpBuilder tokenTable(PersistentTokenTable tokenTable) {
      this.tokenTable = tokenTable;
      return this;
    }

    public SimpleHttpBuilder pluginConfig(HttpStoragePluginConfig config) {
      this.pluginConfig = config;
      this.oAuthConfig = config.oAuthConfig();
      return this;
    }

    public SimpleHttpBuilder endpointConfig(HttpApiConfig endpointConfig) {
      this.endpointConfig = endpointConfig;
      return this;
    }

    public SimpleHttpBuilder connection(String connection) {
      this.connection = connection;
      return this;
    }

    public SimpleHttpBuilder filters(Map<String,String> filters) {
      this.filters = filters;
      return this;
    }

    public SimpleHttp build() {
      if (this.scanDefn != null) {
        return new SimpleHttp(scanDefn, url, tempDir, proxyConfig, errorContext, paginator);
      } else {
        return new SimpleHttp(url, tempDir, proxyConfig, errorContext, paginator, tokenTable, pluginConfig, endpointConfig, connection, filters, rateLimit);
      }
    }
  }
}