package io.jstach.opt.spring.webmvc;

import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Map;

import org.springframework.http.MediaType;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.view.RedirectView;

import io.jstach.jstache.JStache;
import io.jstach.jstache.JStacheInterfaces;
import io.jstach.jstachio.JStachio;
import io.jstach.jstachio.Output.CloseableEncodedOutput;
import io.jstach.opt.spring.web.JStachioHttpMessageConverter;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

/**
 * Another way to use JStachio with Spring MVC is to have models implement Springs
 * {@link View} interface. You can enforce that your models implement this interface with
 * {@link JStacheInterfaces}. Alternatively one can call {@link #of(Object)} on the model
 * and return the result.
 * <p>
 * This view will by default use the static jstachio singleton and if configured correctly
 * that will be the spring version.
 * <p>
 * This approach has pros and cons. It makes your models slightly coupled to Spring MVC
 * but allows you to return different views if say you had to redirect on some inputs
 * ({@link RedirectView}).
 *
 * @author agentgt
 *
 */
public interface JStachioModelView extends View {

        /**
         * The default media type is "<code>text/html; charset=UTF-8</code>".
         */
        @SuppressWarnings("exports")
        static final MediaType DEFAULT_MEDIA_TYPE = JStachioHttpMessageConverter.DEFAULT_MEDIA_TYPE;

        /**
         * The default buffer limit before bailing on trying to set
         * <code>Content-Length</code>. The default is
         * "{@value JStachioHttpMessageConverter#DEFAULT_BUFFER_LIMIT}".
         */
        static final int DEFAULT_BUFFER_LIMIT = JStachioHttpMessageConverter.DEFAULT_BUFFER_LIMIT;

        @SuppressWarnings("exports")
        @Override
        default void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response)
                        throws Exception {

                String contentType = getContentType();
                response.setContentType(contentType);
                Charset charset = getMediaType().getCharset();
                if (charset == null) {
                        charset = StandardCharsets.UTF_8;
                }
                try (var o = createOutput(charset, response)) {
                        jstachio().write(model(), o);
                }
        }

        /**
         * Creates the output from the servlet response to use for rendering.
         * @param charset charset resolved from {@link #getMediaType()}
         * @param response servlet response
         * @return output that should be closed when finished
         */
        @SuppressWarnings("exports")
        default CloseableEncodedOutput<IOException> createOutput(Charset charset, HttpServletResponse response) {
                return new ServletThresholdEncodedOutput(charset, response, DEFAULT_BUFFER_LIMIT);
        }

        /**
         * Returns the jstachio singleton by default.
         * @return stachio singleton by default.
         * @see JStachio#setStatic(java.util.function.Supplier)
         */
        default JStachio jstachio() {
                return JStachio.of();
        }

        /**
         * The model to be rendered by {@link #jstachio()}.
         * @return model defaulting to <code>this</code> instance.
         */
        default Object model() {
                return this;
        }

        @Override
        default String getContentType() {
                return getMediaType().toString();
        }

        /**
         * The media type for this view. The default is
         * "<code>text/html; charset=UTF-8</code>".
         * @return the media type
         */
        @SuppressWarnings("exports")
        default MediaType getMediaType() {
                return DEFAULT_MEDIA_TYPE;
        }

        /**
         * Creates a spring view from a model with content type:
         * "<code>text/html; charset=UTF-8</code>".
         * @param model an instance of a class annotated with {@link JStache}.
         * @return view ready for rendering
         */
        public static JStachioModelView of(Object model) {
                return of(model, MediaType.TEXT_HTML.toString());
        }

        /**
         * Creates a spring view from a model.
         * @param model an instance of a class annotated with {@link JStache}.
         * @param contentType See {@link #getContentType()}
         * @return view ready for rendering
         */
        public static JStachioModelView of(Object model, String contentType) {
                MediaType mediaType = MediaType.parseMediaType(contentType);
                return JStachioModelView.of(model, mediaType);
        }

        /**
         * Creates a spring view from a model.
         * @param model an instance of a class annotated with {@link JStache}.
         * @param mediaType the mediaType
         * @return view ready for rendering
         */
        static JStachioModelView of(Object model, @SuppressWarnings("exports") MediaType mediaType) {
                /*
                 * TODO potentially make this public on the next minor version release.
                 */
                return new JStachioModelView() {
                        @Override
                        public Object model() {
                                return model;
                        }

                        @Override
                        public MediaType getMediaType() {
                                return mediaType;
                        }
                };
        }

}