package io.vertx.mysqlclient.impl;

import io.vertx.core.json.JsonObject;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.util.HashMap;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import static java.lang.Integer.*;
import static java.lang.String.*;

This is a parser for parsing connection URIs of MySQL.
See Also:
MySQL official documentation: [scheme://][user[:[password]]@]host[:port][/schema][?attribute1=value1&attribute2=value2.../**
 * This is a parser for parsing connection URIs of MySQL.
 * @see <a href="https://dev.mysql.com/doc/refman/8.0/en/connecting-using-uri-or-key-value-pairs.html#connecting-using-uri">MySQL official documentation</a>: [scheme://][user[:[password]]@]host[:port][/schema][?attribute1=value1&attribute2=value2...
 */
public class MySQLConnectionUriParser {
  private static final String SCHEME_DESIGNATOR_REGEX = "mysql://"; // URI scheme designator
  private static final String USER_INFO_REGEX = "((?<userinfo>[a-zA-Z0-9\\-._~%!]+(:[a-zA-Z0-9\\-._~%!]*)?)@)?"; // user name and password
  private static final String NET_LOCATION_REGEX = "(?<host>[0-9.]+|\\[[a-zA-Z0-9:]+]|[a-zA-Z0-9\\-._~%]+)"; // ip v4/v6 address or host name
  private static final String PORT_REGEX = "(:(?<port>\\d+))?"; // port
  private static final String SCHEMA_REGEX = "(/(?<schema>[a-zA-Z0-9\\-._~%!]+))?"; // schema name
  private static final String ATTRIBUTES_REGEX = "(\\?(?<attributes>.*))?"; // attributes

  private static final String FULL_URI_REGEX = "^" // regex start
    + SCHEME_DESIGNATOR_REGEX
    + USER_INFO_REGEX
    + NET_LOCATION_REGEX
    + PORT_REGEX
    + SCHEMA_REGEX
    + ATTRIBUTES_REGEX
    + "$"; // regex end

  public static JsonObject parse(String connectionUri) {
    // if we get any exception during the parsing, then we throw an IllegalArgumentException.
    try {
      JsonObject configuration = new JsonObject();
      doParse(connectionUri, configuration);
      return configuration;
    } catch (Exception e) {
      throw new IllegalArgumentException("Cannot parse invalid connection URI: " + connectionUri, e);
    }
  }

  // execute the parsing process and store options in the configuration
  private static void doParse(String connectionUri, JsonObject configuration) {
    Pattern pattern = Pattern.compile(FULL_URI_REGEX);
    Matcher matcher = pattern.matcher(connectionUri);

    if (matcher.matches()) {
      // parse the user and password
      parseUserAndPassword(matcher.group("userinfo"), configuration);

      // parse the IP address/hostname
      parseHost(matcher.group("host"), configuration);

      // parse the port
      parsePort(matcher.group("port"), configuration);

      // parse the schema name
      parseSchemaName(matcher.group("schema"), configuration);

      // parse the attributes
      parseAttributes(matcher.group("attributes"), configuration);

    } else {
      throw new IllegalArgumentException("Wrong syntax of connection URI");
    }
  }

  private static void parseUserAndPassword(String userInfo, JsonObject configuration) {
    if (userInfo == null || userInfo.isEmpty()) {
      return;
    }
    if (occurExactlyOnce(userInfo, ":")) {
      int index = userInfo.indexOf(":");
      String user = userInfo.substring(0, index);
      if (user.isEmpty()) {
        throw new IllegalArgumentException("Can not only specify the password without a concrete user");
      }
      String password = userInfo.substring(index + 1);
      configuration.put("user", decodeUrl(user));
      configuration.put("password", decodeUrl(password));
    } else if (!userInfo.contains(":")) {
      configuration.put("user", decodeUrl(userInfo));
    } else {
      throw new IllegalArgumentException("Can not use multiple delimiters to delimit user and password");
    }
  }

  private static void parseHost(String hostInfo, JsonObject configuration) {
    if (hostInfo == null || hostInfo.isEmpty()) {
      return;
    }
    parseHostValue(decodeUrl(hostInfo), configuration);
  }

  private static void parsePort(String portInfo, JsonObject configuration) {
    if (portInfo == null || portInfo.isEmpty()) {
      return;
    }
    int port;
    try {
      port = parseInt(decodeUrl(portInfo));
    } catch (NumberFormatException e) {
      throw new IllegalArgumentException("The port must be a valid integer");
    }
    if (port > 65535 || port <= 0) {
      throw new IllegalArgumentException("The port can only range in 1-65535");
    }
    configuration.put("port", port);
  }

  private static void parseSchemaName(String schemaInfo, JsonObject configuration) {
    if (schemaInfo == null || schemaInfo.isEmpty()) {
      return;
    }
    configuration.put("database", decodeUrl(schemaInfo));
  }

  private static void parseAttributes(String attributesInfo, JsonObject configuration) {
    if (attributesInfo == null || attributesInfo.isEmpty()) {
      return;
    }
    Map<String, String> properties = new HashMap<>();
    for (String parameterPair : attributesInfo.split("&")) {
      if (parameterPair.isEmpty()) {
        continue;
      }
      int indexOfDelimiter = parameterPair.indexOf("=");
      if (indexOfDelimiter < 0) {
        throw new IllegalArgumentException(format("Missing delimiter '=' of parameters \"%s\" in the part \"%s\"", attributesInfo, parameterPair));
      } else {
        String key = parameterPair.substring(0, indexOfDelimiter).toLowerCase();
        String value = decodeUrl(parameterPair.substring(indexOfDelimiter + 1).trim());
        switch (key) {
          // Base Connection Parameters
          case "user":
            configuration.put("user", value);
            break;
          case "password":
            configuration.put("password", value);
            break;
          case "host":
            parseHostValue(value, configuration);
            break;
          case "port":
            parsePort(value, configuration);
            break;
          case "socket":
            configuration.put("socket", value);
            break;
          case "schema":
            configuration.put("database", value);
            break;
          //TODO Additional Connection Parameters
          default:
            configuration.put(key, value);
            break;
        }
      }
    }
    if (!properties.isEmpty()) {
      configuration.put("properties", properties);
    }
  }

  private static void parseHostValue(String hostValue, JsonObject configuration) {
    if (isRegardedAsIpv6Address(hostValue)) {
      configuration.put("host", hostValue.substring(1, hostValue.length() - 1));
    } else {
      configuration.put("host", hostValue);
    }
  }

  private static boolean isRegardedAsIpv6Address(String hostAddress) {
    return hostAddress.startsWith("[") && hostAddress.endsWith("]");
  }

  private static String decodeUrl(String url) {
    try {
      return URLDecoder.decode(url, "UTF-8");
    } catch (UnsupportedEncodingException e) {
      throw new IllegalArgumentException("The connection uri contains unknown characters that can not be resolved.");
    }
  }

  private static boolean occurExactlyOnce(String uri, String character) {
    return uri.contains(character) && uri.indexOf(character) == uri.lastIndexOf(character);
  }
}