feat(model): add card layout block

slack-api-model/src/main/java/com/slack/api/model/block/Blocks.java

@@ -129,4 +129,10 @@ public static ShareShortcutBlock shareShortcut() {
         return ShareShortcutBlock.builder().build();
     }
 
+    // CardBlock
+
+    public static CardBlock card(ModelConfigurator<CardBlock.CardBlockBuilder> configurator) {
+        return configurator.configure(CardBlock.builder()).build();
+    }
+
 }

slack-api-model/src/main/java/com/slack/api/model/block/CardBlock.java

@@ -0,0 +1,74 @@
+package com.slack.api.model.block;
+
+import com.slack.api.model.block.composition.TextObject;
+import com.slack.api.model.block.element.BlockElement;
+import com.slack.api.model.block.element.ImageElement;
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.util.List;
+
+/**
+ * A card is a layout block used to display a compact, structured summary of content. It can be used on
+ * its own or grouped together inside a {@link CarouselBlock carousel}. At least one of {@code heroImage},
+ * {@code title}, {@code actions}, or {@code body} must be provided.
+ *
+ * https://docs.slack.dev/reference/block-kit/blocks/card-block
+ */
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class CardBlock implements LayoutBlock {
+    public static final String TYPE = "card";
+    private final String type = TYPE;
+
+    /**
+     * A top banner image for the card in the form of an image element.
+     * The image URL may be up to 3000 characters and the alt text up to 2000 characters.
+     */
+    private ImageElement heroImage;
+
+    /**
+     * A small icon displayed next to the title and subtitle in the form of an image element.
+     * The image URL may be up to 3000 characters and the alt text up to 2000 characters.
+     * Mutually exclusive with {@code slackIcon}.
+     */
+    private ImageElement icon;
+
+    /**
+     * The name of a built-in Slack icon displayed next to the title and subtitle.
+     * Mutually exclusive with {@code icon}.
+     */
+    private String slackIcon;
+
+    /**
+     * The title of the card. Maximum length for the text in this field is 150 characters.
+     */
+    private TextObject title;
+
+    /**
+     * The subtitle of the card. Maximum length for the text in this field is 150 characters.
+     */
+    private TextObject subtitle;
+
+    /**
+     * The body text of the card. Maximum length for the text in this field is 200 characters.
+     */
+    private TextObject body;
+
+    /**
+     * Secondary text displayed beneath the body of the card. Maximum length for the text in this field
+     * is 200 characters.
+     */
+    private TextObject subtext;
+
+    /**
+     * Interactive elements (such as buttons) displayed at the bottom of the card. Up to 3 buttons.
+     */
+    private List<BlockElement> actions;
+
+    private String blockId;
+}

slack-api-model/src/main/java/com/slack/api/util/json/GsonLayoutBlockFactory.java

@@ -61,6 +61,8 @@ private Class<? extends LayoutBlock> getLayoutClassInstance(String typeName) {
                 return RichTextBlock.class;
             case ShareShortcutBlock.TYPE:
                 return ShareShortcutBlock.class;
+            case CardBlock.TYPE:
+                return CardBlock.class;
             default:
                 if (failOnUnknownProperties) {
                     throw new JsonParseException("Unsupported layout block type: " + typeName);

slack-api-model/src/test/java/test_locally/api/model/block/BlockKitTest.java

@@ -1940,4 +1940,98 @@ public void parseRichTextElements() {
         RichTextSectionElement section = (RichTextSectionElement) ((RichTextBlock) message.getBlocks().get(0)).getElements().get(0);
         assertThat(section.getElements().size(), is(10));
     }
+
+    @Test
+    public void parseCardBlock() {
+        // https://docs.slack.dev/reference/block-kit/blocks/card-block
+        String json = "{\"blocks\":[\n" +
+                "  {\n" +
+                "    \"type\": \"card\",\n" +
+                "    \"block_id\": \"card1\",\n" +
+                "    \"icon\": {\n" +
+                "      \"type\": \"image\",\n" +
+                "      \"image_url\": \"https://picsum.photos/36/36\",\n" +
+                "      \"alt_text\": \"Icon\"\n" +
+                "    },\n" +
+                "    \"hero_image\": {\n" +
+                "      \"type\": \"image\",\n" +
+                "      \"image_url\": \"https://picsum.photos/400/300\",\n" +
+                "      \"alt_text\": \"Sample hero image\"\n" +
+                "    },\n" +
+                "    \"title\": {\n" +
+                "      \"type\": \"mrkdwn\",\n" +
+                "      \"text\": \"Lumon Industries\"\n" +
+                "    },\n" +
+                "    \"subtitle\": {\n" +
+                "      \"type\": \"mrkdwn\",\n" +
+                "      \"text\": \"Committed to work-life balance\"\n" +
+                "    },\n" +
+                "    \"body\": {\n" +
+                "      \"type\": \"mrkdwn\",\n" +
+                "      \"text\": \"Please enjoy each card equally.\"\n" +
+                "    },\n" +
+                "    \"actions\": [\n" +
+                "      {\n" +
+                "        \"type\": \"button\",\n" +
+                "        \"text\": {\n" +
+                "          \"type\": \"plain_text\",\n" +
+                "          \"text\": \"Action Button\"\n" +
+                "        },\n" +
+                "        \"action_id\": \"button_action\"\n" +
+                "      }\n" +
+                "    ]\n" +
+                "  }\n" +
+                "]}";
+        Gson gson = GsonFactory.createSnakeCase();
+        Message message = gson.fromJson(json, Message.class);
+        assertThat(message, is(notNullValue()));
+        assertThat(message.getBlocks().size(), is(1));
+
+        CardBlock card = (CardBlock) message.getBlocks().get(0);
+        assertThat(card.getType(), is("card"));
+        assertThat(card.getBlockId(), is("card1"));
+        assertThat(card.getIcon().getImageUrl(), is("https://picsum.photos/36/36"));
+        assertThat(card.getIcon().getAltText(), is("Icon"));
+        assertThat(card.getHeroImage().getImageUrl(), is("https://picsum.photos/400/300"));
+        assertThat(card.getHeroImage().getAltText(), is("Sample hero image"));
+        assertThat(card.getTitle().getType(), is("mrkdwn"));
+        assertThat(((com.slack.api.model.block.composition.MarkdownTextObject) card.getTitle()).getText(), is("Lumon Industries"));
+        assertThat(((com.slack.api.model.block.composition.MarkdownTextObject) card.getSubtitle()).getText(), is("Committed to work-life balance"));
+        assertThat(((com.slack.api.model.block.composition.MarkdownTextObject) card.getBody()).getText(), is("Please enjoy each card equally."));
+        assertThat(card.getActions().size(), is(1));
+        ButtonElement button = (ButtonElement) card.getActions().get(0);
+        assertThat(button.getActionId(), is("button_action"));
+        assertThat(button.getText().getText(), is("Action Button"));
+
+        // Round-trip back to JSON and ensure the card survives serialization.
+        Message roundTrip = gson.fromJson(gson.toJson(message), Message.class);
+        CardBlock reparsed = (CardBlock) roundTrip.getBlocks().get(0);
+        assertThat(reparsed.getBlockId(), is("card1"));
+        assertThat(reparsed.getActions().size(), is(1));
+        assertThat(((ButtonElement) reparsed.getActions().get(0)).getActionId(), is("button_action"));
+    }
+
+    @Test
+    public void buildCardBlock() {
+        CardBlock card = card(c -> c
+                .blockId("card2")
+                .title(com.slack.api.model.block.composition.MarkdownTextObject.builder().text("Title").build())
+                .body(com.slack.api.model.block.composition.PlainTextObject.builder().text("Body").build())
+                .actions(Arrays.asList(
+                        ButtonElement.builder()
+                                .actionId("a")
+                                .text(plainText("Click"))
+                                .build()
+                ))
+        );
+        assertThat(card.getType(), is("card"));
+        assertThat(card.getBlockId(), is("card2"));
+        Gson gson = GsonFactory.createSnakeCase();
+        Message message = new Message();
+        message.setBlocks(asBlocks(card));
+        Message reparsed = gson.fromJson(gson.toJson(message), Message.class);
+        CardBlock parsedCard = (CardBlock) reparsed.getBlocks().get(0);
+        assertThat(parsedCard.getBlockId(), is("card2"));
+        assertThat(parsedCard.getActions().size(), is(1));
+    }
 }