ChatServer.java

import java.io.IOException;
import java.net.URI;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;

class ChatHandler implements URLHandler {
  String chatHistory = "";

  public String handleRequest(URI url) {

    // expect /chat?user=<name>&message=<string>
    if (url.getPath().equals("/chat")) {
      String[] params = url.getQuery().split("&");
      String[] shouldBeUser = params[0].split("=");
      String[] shouldBeMessage = params[1].split("=");
      if (shouldBeUser[0].equals("user") && shouldBeMessage[0].equals("message")) {
        String user = shouldBeUser[1];
        String message = shouldBeMessage[1];
        this.chatHistory += user + ": " + message + "\n\n";
        return this.chatHistory;
      } else {
        return "Invalid parameters: " + String.join("&", params);
      }
    } else if (url.getPath().equals("/")) {
      return this.chatHistory;
    }
    // expect /retrieve-history?file=<name>
    else if (url.getPath().equals("/retrieve-history")) {
      String[] params = url.getQuery().split("&");
      String[] shouldBeFile = params[0].split("=");
      if (shouldBeFile[0].equals("file")) {
        String fileName = shouldBeFile[1];
        // String fileName = shouldBeFileName[0]; // bug4: should be shouldBeFile[1]
        ChatHistoryReader reader = new ChatHistoryReader();
        try {
          String[] contents = reader.readFileAsArray("chathistory/" + fileName);
          for (String line : contents) {
            this.chatHistory += line + "\n\n";
          }
        } catch (IOException e) {
          System.err.println("Error reading file: " + e.getMessage());
        }
      }
      return this.chatHistory;
    }
    // expect /save?name=<name>
    else if (url.getPath().equals("/save")) {
      String[] params = url.getQuery().split("&");
      String[] shouldBeFileName = params[0].split("=");
      if (shouldBeFileName[0].equals("name")) {
        File directory = new File("chathistory");
        File file = new File(directory, shouldBeFileName[1]);

        try (BufferedWriter writer = new BufferedWriter(new FileWriter(file))) {
          writer.write(this.chatHistory);
          return "Data written to " + shouldBeFileName[1] + "in 'chat-history' folder.";
        } catch (IOException e) {
          e.printStackTrace();
          return "Error: Something wrong happen during file save, check StackTrace";
        }
      }
    }

    return "404 Not Found";
  }
}

class ChatServer {
  public static void main(String[] args) throws IOException {
    int port = Integer.parseInt(args[0]);
    Server.start(port, new ChatHandler());
  }
}