blog-software-java/src/main/java/eu/m724/blog/TemplateRenderer.java

package eu.m724.blog;

import eu.m724.blog.data.Post;
import eu.m724.blog.data.Site;
import io.pebbletemplates.pebble.PebbleEngine;
import io.pebbletemplates.pebble.extension.AbstractExtension;
import io.pebbletemplates.pebble.extension.Function;
import io.pebbletemplates.pebble.loader.FileLoader;
import io.pebbletemplates.pebble.template.EvaluationContext;
import io.pebbletemplates.pebble.template.PebbleTemplate;

import java.io.IOException;
import java.io.StringWriter;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * The {@code TemplateRenderer} class is responsible for rendering dynamic HTML templates
 * using the Pebble templating engine.
 */
public class TemplateRenderer {
    private final PebbleTemplate indexTemplate, articleTemplate;

    /**
     * Constructs a TemplateRenderer instance for rendering templates from the specified directory.
     *
     * @param templateDirectory the root directory containing the template files
     */
    public TemplateRenderer(Path templateDirectory) {
        var loader = new FileLoader();
        loader.setPrefix(templateDirectory.toString());
        loader.setSuffix(".html");

        var pebbleEngine = new PebbleEngine.Builder()
                .loader(loader)
                .extension(new AbstractExtension() {
                    @Override
                    public Map<String, Function> getFunctions() {
                        return Map.of(
                                "static", new Function() {
                                    @Override
                                    public List<String> getArgumentNames() {
                                        return List.of("path");
                                    }

                                    @Override
                                    public Object execute(Map<String, Object> args, PebbleTemplate self, EvaluationContext context, int lineNumber) {
                                        return "/static/" + args.get("path"); // TODO for more advanced stuff
                                    }
                                },
                                "asset", new Function() {
                                    @Override
                                    public List<String> getArgumentNames() {
                                        return List.of("path");
                                    }

                                    @Override
                                    public Object execute(Map<String, Object> args, PebbleTemplate self, EvaluationContext context, int lineNumber) {
                                        return "/assets/" + args.get("path"); // TODO for more advanced stuff
                                    }
                                }
                        );
                    }
                })
                .build();

        this.indexTemplate = pebbleEngine.getTemplate("index_template");
        this.articleTemplate = pebbleEngine.getTemplate("article_template");
    }

    /**
     * Renders the index page using this template.
     *
     * @param site the {@link Site} this index is for
     * @param posts the {@link Post}s to be included in the index page
     * @return the rendered index HTML page as a string
     * @throws IOException if an error occurs during the template evaluation
     */
    public String renderIndex(Site site, ArrayList<Post> posts) throws IOException {
        Map<String, Object> context = Map.of(
                "site", site,
                "articles", posts
        );

        var writer = new StringWriter();
        indexTemplate.evaluate(writer, context);

        return writer.toString();
    }

    /**
     * Renders the content of a post using this template.
     *
     * @param site the {@link Site} containing the post
     * @param post the {@link Post} to be rendered
     * @return the rendered post HTML page as a string
     * @throws IOException if an error occurs during template evaluation
     */
    public String renderPost(Site site, Post post) throws IOException {
        Map<String, Object> context = Map.of(
                "site", site,
                "article", post
        );

        var writer = new StringWriter();
        articleTemplate.evaluate(writer, context);

        return writer.toString();
    }
}