package at.gv.egiz.eaaf.core.impl.gui.utils;

import java.util.Locale;

import org.springframework.http.HttpStatusCode;
import org.springframework.util.Assert;
import org.springframework.web.servlet.LocaleResolver;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.ViewResolver;

import at.gv.egiz.eaaf.core.api.gui.IGuiBuilderConfiguration;
import jakarta.annotation.Nullable;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import lombok.NonNull;
import lombok.extern.slf4j.Slf4j;

/**
 * Utils GUI generation by using Spring MVC.

 * @author tlenz
 *
 */
@Slf4j
public class MvcGuiRenderUtils {

  private static final String REQ_ATTR_MODEL_HOLDER = "GUI_MODEL_ASYNCH_RENDERING";
  
  /**
   * Build Spring MVC model from GUI configuration.
   * 
   * @param config GUI configuration
   * @return MVC model
   */
  @NonNull
  public static ModelAndView prepareSpringGuiModel(@NonNull final IGuiBuilderConfiguration config) {
    final ModelAndView mav = new ModelAndView(config.getViewName());
    if (config.getViewParameters() != null) {
      mav.addAllObjects(config.getViewParameters());
      
    }    
    return mav;
    
  }
  
  
  /**
   * Inject GUI-builder configuration into http request to render it asynchronous in Spring intercepter. 
   * 
   * @param request Current HttpServletRequest
   * @param config Configuration for GUI rendering
   */
  public static void setMvcForAsynchRendering(@NonNull final HttpServletRequest request, 
      @NonNull final IGuiBuilderConfiguration config) {
    request.setAttribute(REQ_ATTR_MODEL_HOLDER, prepareSpringGuiModel(config));
        
  }
  
  /**
   * Get GUI model for asynchronous rendering.
   * 
   * @param request Current HttpServletRequest
   * @return GUI model, or <code>null</code> of model was set
   */
  @Nullable
  public static ModelAndView getMvcForAsynchRendering(@NonNull final HttpServletRequest request) {
    return (ModelAndView) request.getAttribute(REQ_ATTR_MODEL_HOLDER);
    
  }
  
  /**
   * Analyze GUI template and HTTP request to evaluate ContentType of HTTP response generated by this builder.
   * 
   * @param httpReq Current HttpServletRequest
   * @param config GUI configuration
   * @param viewResolvers Spring based view-resolvers
   * @param localeResolver Spring based locale-resolvers
   * @return Response content-type, or <code>null</code> if evaluation has no result
   * @throws Exception In case of a GUI rendering error
   */
  @Nullable
  public static String evaluateResponseContentType(HttpServletRequest httpReq,
      IGuiBuilderConfiguration config, @Nullable final ViewResolver[] viewResolvers, 
      @Nullable final LocaleResolver localeResolver) throws Exception {    
    return buildViewFromModel(viewResolvers, 
        getLocaleByRequest(localeResolver, httpReq),
        prepareSpringGuiModel(config)).getContentType();
    
  }
  
  /**
   * Get i18n information from HTTP request.
   * 
   * @param localeResolver Resolver for localization
   * @param request HTTP request
   * @return Current locale
   */
  public static Locale getLocaleByRequest(LocaleResolver localeResolver, @NonNull HttpServletRequest request) {
    return localeResolver != null ? localeResolver.resolveLocale(request) : request.getLocale();
    
  }
  
  /**
   * Render a GUI by using Spring based ModelAndView (MVC) components.
   * 
   * @param mv GUI model
   * @param request Current HttpServletRequest
   * @param response Current HttpServletResponse
   * @param viewResolvers Spring based view-resolvers
   * @param localeResolver Spring based locale-resolvers
   * @throws Exception In case of a GUI rendering error
   */
  public static void render(@NonNull final ModelAndView mv, @NonNull final HttpServletRequest request,
      @NonNull final HttpServletResponse response, @Nullable final ViewResolver[] viewResolvers, 
      @Nullable final LocaleResolver localeResolver) throws Exception {
    Assert.notNull(request, "http request object");
    Assert.notNull(response, "http response object");
    Assert.notNull(mv, "Model and view");

    // Determine locale for request and apply it to the response.
    final Locale locale = getLocaleByRequest(localeResolver, request);
    response.setLocale(locale);

    // Determine view for response
    View view = buildViewFromModel(viewResolvers, locale, mv);

    final HttpStatusCode modelStatus = mv.getStatus();
    if (modelStatus != null) {
      response.setStatus(modelStatus.value());

    } else {
      log.trace("HttpStatus is 'null' Set {} as default", HttpServletResponse.SC_OK);
      response.setStatus(HttpServletResponse.SC_OK);

    }

    // Delegate to the View object for rendering.
    if (log.isTraceEnabled()) {
      log.trace("Rendering view [{}] ", view);
    }

    try {
      view.render(mv.getModelMap(), request, response);
      
    } catch (final Exception ex) {
      if (log.isDebugEnabled()) {
        log.debug("Error rendering view [{}]", view, null, ex);
      }

      throw ex;

    }

  }

  private static View buildViewFromModel(ViewResolver[] viewResolvers, Locale locale, 
      @NonNull ModelAndView mv) throws Exception {

    final String viewName = mv.getViewName();
    View view;
    if (viewName != null) {
      // We need to resolve the view name.
      view = resolveViewName(viewResolvers, viewName, locale);
      
      if (view == null) {
        throw new ServletException("Could not resolve view with name '" + mv.getViewName() + "' ");
      }

    } else {
      // No need to lookup: the ModelAndView object contains the actual View object.
      view = mv.getView();
      if (view == null) {
        throw new ServletException(
            "ModelAndView [" + mv + "] neither contains a view name nor a " + "View object ");
        
      }
    }  
    
    return view;
    
  }


  private static View resolveViewName(@Nullable final ViewResolver[] viewResolvers, 
      final String viewName, final Locale locale) throws Exception {
    if (viewResolvers != null) {      
      for (final ViewResolver viewResolver : viewResolvers) {
        final View view = viewResolver.resolveViewName(viewName, locale);
        if (view != null) {
          return view;
        }

      }
    }

    return null;
  }
  
  private MvcGuiRenderUtils() {
    // private constructor for class with only static methods
  }
  
}