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

/*
 * Copyright (c) 2025  blog-software-java developers
 * blog-software-java is licensed under the GNU General Public License. See the LICENSE.md file
 * in the project root for the full license text.
 */

package eu.m724.blog.template;

import eu.m724.blog.Minifier;
import eu.m724.blog.object.Article;
import eu.m724.blog.object.PageNumbers;
import eu.m724.blog.object.Site;
import io.pebbletemplates.pebble.PebbleEngine;
import io.pebbletemplates.pebble.error.LoaderException;
import io.pebbletemplates.pebble.loader.FileLoader;
import io.pebbletemplates.pebble.template.PebbleTemplate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.io.StringWriter;
import java.nio.file.Path;
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 static final Logger LOGGER = LoggerFactory.getLogger(TemplateRenderer.class);

    private final Site site;
    private final Minifier minifier;

    private final PebbleEngine pebbleEngine;
    private final PebbleTemplate indexTemplate, articleTemplate, pageTemplate;

    /**
     * Constructs a TemplateRenderer instance for rendering templates from the specified directory.

     * @param site the {@link Site} this renderer renders
     * @param templateDirectory the root directory containing the template file
     * @param fileHashes file hashes. currently only applies to assets
     */
    public TemplateRenderer(Site site, Minifier minifier, Path templateDirectory, Map<String, String> fileHashes) {
        this.site = site;
        this.minifier = minifier;


        var loader = new FileLoader();
        loader.setPrefix(templateDirectory.toString());
        loader.setSuffix(".html");

        this.pebbleEngine = new PebbleEngine.Builder()
                .loader(loader)
                .extension(new TemplateExtension(site, fileHashes))
                .build();

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

        var pageTemplate = indexTemplate;

        try {
            pageTemplate = pebbleEngine.getTemplate("page_template");
        } catch (LoaderException e) {
            LOGGER.debug("Template has no page template, using index_template instead");
        }

        this.pageTemplate = pageTemplate;
    }

    /**
     * Renders a page using this template.<br>
     * This is different from index, as this uses page template.
     *
     * @param pageArticles the {@link Article}s to be included in the <strong>CURRENT</strong> page
     * @param pageNumbers a {@link PageNumbers} instance for the current page
     * @return the rendered index HTML page as a string
     * @throws IOException if an error occurs during the template evaluation
     */
    public String renderPage(PageNumbers pageNumbers, List<Article> pageArticles) throws IOException {
        var context = Map.of(
                "page", pageNumbers,
                "articles", pageArticles
        );

        return renderTemplate(pageTemplate, context);
    }

    /**
     * Renders the index page using this template.<br>
     * This is different from rendering page 1, as this uses index template.
     *
     * @param pageArticles the {@link Article}s to be included in the <strong>CURRENT</strong> page
     * @param pageNumbers a {@link PageNumbers} instance for the current page
     * @return the rendered index HTML page as a string
     * @throws IOException if an error occurs during the template evaluation
     */
    public String renderIndex(PageNumbers pageNumbers, List<Article> pageArticles) throws IOException {
        var context = Map.of(
                "page", pageNumbers,
                "articles", pageArticles
        );

        return renderTemplate(indexTemplate, context);
    }

    /**
     * Renders the content of an article using this template.
     *
     * @param article the {@link Article} to be rendered
     * @return the rendered article HTML page as a string
     * @throws IOException if an error occurs during template evaluation
     */
    public String renderArticle(Article article) throws IOException {
        String content = article.rawContent();

        if (site.templateArticles()) {
            var context = Map.of(
                    "article", article
            );

            content = renderTemplate(pebbleEngine.getLiteralTemplate(content), context);
        }

        var context = Map.of(
                "article", article,
                "content", content
        );

        return renderTemplate(articleTemplate, context);
    }

    private String renderTemplate(PebbleTemplate template, Map<String, ?> context) throws IOException {
        var writer = new StringWriter();
        template.evaluate(writer, (Map<String, Object>) context);
        var html = writer.toString();

        if (minifier != null) { // not checking site.minify because the minifier may not be available
            html = minifier.minify(html);
        }

        return html;
    }
}