package com.google.sps.servlets;

import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceConfig;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.EmbeddedEntity;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.EntityNotFoundException;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseAuthException;
import com.google.firebase.auth.FirebaseToken;
import com.google.gson.Gson;
import com.google.sps.firebase.FirebaseAppManager;
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/get-student-workspace")
public class GetStudentWorkspace extends HttpServlet {
  private FirebaseAuth authInstance;
  private DatastoreService datastore;
  private Gson gson;

  @Override
  public void init(ServletConfig config) throws ServletException {
    try {
      authInstance = FirebaseAuth.getInstance(FirebaseAppManager.getApp());
      gson = new Gson();
    } catch (IOException e) {
      throw new ServletException(e);
    }
  }

  @Override
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
    datastore = DatastoreServiceFactory.getDatastoreService();
    System.setProperty(
        DatastoreServiceConfig.DATASTORE_EMPTY_LIST_SUPPORT, Boolean.TRUE.toString());

    try {
      // Retrive class entity
      String classCode = request.getParameter("classCode").trim();
      Key classKey = KeyFactory.stringToKey(classCode);
      Entity classEntity = datastore.get(classKey);

      String studentToken = request.getParameter("studentToken");
      FirebaseToken decodedToken = authInstance.verifyIdToken(studentToken);
      String studentID = decodedToken.getUid();

      EmbeddedEntity beingHelped = (EmbeddedEntity) classEntity.getProperty("beingHelped");
      EmbeddedEntity queueInfo = (EmbeddedEntity) beingHelped.getProperty(studentID);

      // if interaction ended
      if (queueInfo == null) {
        response.setContentType("application/json;");
        response.getWriter().print(gson.toJson("null"));

      } else {
        // Get workspace id
        String workspaceID = (String) queueInfo.getProperty("workspaceID");

        // Build workspace link
        String workspaceLink = "/workspace?workspaceID=" + workspaceID;

        response.setContentType("application/json;");
        response.getWriter().print(gson.toJson(workspaceLink));
      }

    } catch (EntityNotFoundException e) {
      response.sendError(HttpServletResponse.SC_NOT_FOUND);
    } catch (IllegalArgumentException e) {
      response.sendError(HttpServletResponse.SC_BAD_REQUEST);
    } catch (FirebaseAuthException e) {
      response.sendError(HttpServletResponse.SC_FORBIDDEN);
    }
  }
}

Create servlet that will return workspace link