Link/Image previews for tags

application/build.gradle

@@ -57,6 +57,8 @@ dependencies {
 
     implementation 'io.mikael:urlbuilder:2.0.9'
 
+    implementation 'org.jsoup:jsoup:1.15.3'
+
     implementation 'org.scilab.forge:jlatexmath:1.0.7'
     implementation 'org.scilab.forge:jlatexmath-font-greek:1.0.7'
     implementation 'org.scilab.forge:jlatexmath-font-cyrillic:1.0.7'
@@ -68,6 +70,8 @@ dependencies {
 
 	implementation 'com.github.freva:ascii-table:1.8.0'
 
+    implementation 'io.github.url-detector:url-detector:0.1.23'
+
     implementation 'com.github.ben-manes.caffeine:caffeine:3.1.1'
 
     testImplementation 'org.mockito:mockito-core:4.8.0'

application/src/main/java/org/togetherjava/tjbot/commands/tags/TagCommand.java

@@ -1,21 +1,29 @@
 package org.togetherjava.tjbot.commands.tags;
 
 import net.dv8tion.jda.api.EmbedBuilder;
+import net.dv8tion.jda.api.entities.Message;
+import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.entities.User;
 import net.dv8tion.jda.api.events.interaction.command.CommandAutoCompleteInteractionEvent;
 import net.dv8tion.jda.api.events.interaction.command.SlashCommandInteractionEvent;
 import net.dv8tion.jda.api.interactions.AutoCompleteQuery;
+import net.dv8tion.jda.api.interactions.InteractionHook;
 import net.dv8tion.jda.api.interactions.commands.Command;
 import net.dv8tion.jda.api.interactions.commands.OptionMapping;
 import net.dv8tion.jda.api.interactions.commands.OptionType;
 import net.dv8tion.jda.api.interactions.commands.build.OptionData;
 import net.dv8tion.jda.api.requests.restaction.interactions.ReplyCallbackAction;
+import net.dv8tion.jda.api.utils.FileUpload;
+import net.dv8tion.jda.api.utils.messages.MessageEditBuilder;
 
 import org.togetherjava.tjbot.commands.CommandVisibility;
 import org.togetherjava.tjbot.commands.SlashCommandAdapter;
+import org.togetherjava.tjbot.commands.utils.LinkPreview;
+import org.togetherjava.tjbot.commands.utils.LinkPreviews;
 import org.togetherjava.tjbot.commands.utils.StringDistances;
 
 import java.time.Instant;
-import java.util.Collection;
+import java.util.*;
 
 /**
  * Implements the {@code /tag} command which lets the bot respond content of a tag that has been
@@ -47,28 +55,6 @@ public TagCommand(TagSystem tagSystem) {
                         "Optionally, the user who you want to reply to", false));
     }
 
-    @Override
-    public void onSlashCommand(SlashCommandInteractionEvent event) {
-        String id = event.getOption(ID_OPTION).getAsString();
-        OptionMapping replyToUserOption = event.getOption(REPLY_TO_USER_OPTION);
-
-        if (tagSystem.handleIsUnknownTag(id, event)) {
-            return;
-        }
-
-        ReplyCallbackAction message = event
-            .replyEmbeds(new EmbedBuilder().setDescription(tagSystem.getTag(id).orElseThrow())
-                .setFooter(event.getUser().getName() + " • used " + event.getCommandString())
-                .setTimestamp(Instant.now())
-                .setColor(TagSystem.AMBIENT_COLOR)
-                .build());
-
-        if (replyToUserOption != null) {
-            message = message.setContent(replyToUserOption.getAsUser().getAsMention());
-        }
-        message.queue();
-    }
-
     @Override
     public void onAutoComplete(CommandAutoCompleteInteractionEvent event) {
         AutoCompleteQuery focusedOption = event.getFocusedOption();
@@ -86,4 +72,68 @@ public void onAutoComplete(CommandAutoCompleteInteractionEvent event) {
 
         event.replyChoices(choices).queue();
     }
+
+    @Override
+    public void onSlashCommand(SlashCommandInteractionEvent event) {
+        String id = event.getOption(ID_OPTION).getAsString();
+        OptionMapping replyToUserOption = event.getOption(REPLY_TO_USER_OPTION);
+
+        if (tagSystem.handleIsUnknownTag(id, event)) {
+            return;
+        }
+
+        String tagContent = tagSystem.getTag(id).orElseThrow();
+        MessageEmbed contentEmbed = new EmbedBuilder().setDescription(tagContent)
+            .setFooter(event.getUser().getName() + " • used " + event.getCommandString())
+            .setTimestamp(Instant.now())
+            .setColor(TagSystem.AMBIENT_COLOR)
+            .build();
+
+        Optional<String> replyToUserMention = Optional.ofNullable(replyToUserOption)
+            .map(OptionMapping::getAsUser)
+            .map(User::getAsMention);
+
+        List<String> links = LinkPreviews.extractLinks(tagContent)
+            .stream()
+            .limit(Message.MAX_EMBED_COUNT - 1L)
+            .toList();
+        if (links.isEmpty()) {
+            // No link previews
+            ReplyCallbackAction message = event.replyEmbeds(contentEmbed);
+            replyToUserMention.ifPresent(message::setContent);
+            message.queue();
+            return;
+        }
+
+        event.deferReply().queue();
+
+        respondWithLinkPreviews(event.getHook(), links, contentEmbed, replyToUserMention);
+    }
+
+    private void respondWithLinkPreviews(InteractionHook eventHook, List<String> links,
+            MessageEmbed contentEmbed, Optional<String> replyToUserMention) {
+        LinkPreviews.createLinkPreviews(links).thenAccept(linkPreviews -> {
+            if (linkPreviews.isEmpty()) {
+                // Did not find any previews
+                MessageEditBuilder message = new MessageEditBuilder().setEmbeds(contentEmbed);
+                replyToUserMention.ifPresent(message::setContent);
+                eventHook.editOriginal(message.build()).queue();
+                return;
+            }
+
+            Collection<MessageEmbed> embeds = new ArrayList<>();
+            embeds.add(contentEmbed);
+            embeds.addAll(linkPreviews.stream().map(LinkPreview::embed).toList());
+
+            List<FileUpload> attachments = linkPreviews.stream()
+                .map(LinkPreview::attachment)
+                .filter(Objects::nonNull)
+                .toList();
+
+            MessageEditBuilder message =
+                    new MessageEditBuilder().setEmbeds(embeds).setFiles(attachments);
+            replyToUserMention.ifPresent(message::setContent);
+            eventHook.editOriginal(message.build()).queue();
+        });
+    }
 }

application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreview.java

@@ -0,0 +1,73 @@
+package org.togetherjava.tjbot.commands.utils;
+
+import net.dv8tion.jda.api.EmbedBuilder;
+import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.utils.FileUpload;
+
+import javax.annotation.Nullable;
+
+import java.io.InputStream;
+
+/**
+ * Preview of a URL for display as embed in Discord.
+ * <p>
+ * If the attachment is not {@code null}, it has to be made available to the message as well, for
+ * example
+ * {@code new MessageCreateBuilder().addEmbeds(linkPreview.embed).addFiles(linkPreview.attachment)}.
+ *
+ * @param attachment the thumbnail image of the link, referenced within the embed, if present
+ * @param embed the embed representing the preview of the link
+ */
+public record LinkPreview(@Nullable FileUpload attachment, MessageEmbed embed) {
+    /**
+     * Creates a new instance of this link preview, but with the given thumbnail.
+     * <p>
+     * Any previous thumbnail is overridden and replaced.
+     *
+     * @param thumbnailName the name of the thumbnail, with extension, e.g. {@code foo.png}
+     * @param thumbnail the thumbnails data as raw data stream
+     * @return this preview, but with a thumbnail
+     */
+    LinkPreview withThumbnail(String thumbnailName, InputStream thumbnail) {
+        return createWithThumbnail(embed, thumbnailName, thumbnail);
+    }
+
+    /**
+     * Creates a link preview that only has a thumbnail and no other text.
+     * 
+     * @param thumbnailName the name of the thumbnail, with extension, e.g. {@code foo.png}
+     * @param thumbnail the thumbnails data as raw data stream
+     * @return the thumbnail as link preview
+     */
+    static LinkPreview ofThumbnail(String thumbnailName, InputStream thumbnail) {
+        return createWithThumbnail(null, thumbnailName, thumbnail);
+    }
+
+    /**
+     * Creates a link preview that consists of the given text.
+     * <p>
+     * Use {@link #withThumbnail(String, InputStream)} to decorate the preview also with a thumbnail
+     * image.
+     *
+     * @param title the title of the preview, if present
+     * @param url the link to the resource this preview represents
+     * @param description the description of the preview, if present
+     * @return the text as link preview
+     */
+    static LinkPreview ofText(@Nullable String title, String url, @Nullable String description) {
+        MessageEmbed embed =
+                new EmbedBuilder().setTitle(title, url).setDescription(description).build();
+
+        return new LinkPreview(null, embed);
+    }
+
+    private static LinkPreview createWithThumbnail(@Nullable MessageEmbed embedToDecorate,
+            String thumbnailName, InputStream thumbnail) {
+        FileUpload attachment = FileUpload.fromData(thumbnail, thumbnailName);
+        MessageEmbed embed =
+                new EmbedBuilder(embedToDecorate).setThumbnail("attachment://" + thumbnailName)
+                    .build();
+
+        return new LinkPreview(attachment, embed);
+    }
+}