feat(helix): add send chat message endpoint

auth/src/main/java/com/github/twitch4j/auth/domain/TwitchScopes.java

@@ -61,6 +61,7 @@ public enum TwitchScopes {
     HELIX_USER_EDIT_FOLLOWS("user:edit:follows"),
     HELIX_USER_BLOCKS_READ("user:read:blocked_users"),
     HELIX_USER_READ_BROADCAST("user:read:broadcast"),
+    HELIX_USER_CHAT_WRITE("user:write:chat"),
     HELIX_USER_FOLLOWS_READ("user:read:follows"),
     HELIX_USER_SUBSCRIPTIONS_READ("user:read:subscriptions"),
     HELIX_USER_EMAIL("user:read:email"),

rest-helix/src/main/java/com/github/twitch4j/helix/TwitchHelix.java

@@ -540,6 +540,29 @@ HystrixCommand<EmoteList> getEmoteSets(
         @Param("emote_set_id") Collection<String> ids
     );
 
+    /**
+     * Sends a message to the broadcaster’s chat room.
+     * <p>
+     * If an app access token is used, the chatting user must have authorized to the Client ID with the user:bot scope,
+     * and the broadcaster or a moderator must have authorized to the Client ID with the channel:bot scope.
+     *
+     * @param authToken User access token (scope: user:write:chat) or App access token (with Client ID authorized).
+     * @param message   The message to be sent, including the source and target user IDs.
+     * @return metadata about the send message attempt
+     * @see com.github.twitch4j.auth.domain.TwitchScopes#HELIX_USER_CHAT_WRITE
+     * @see com.github.twitch4j.auth.domain.TwitchScopes#CHAT_CHANNEL_BOT
+     * @see com.github.twitch4j.auth.domain.TwitchScopes#CHAT_USER_BOT
+     */
+    @RequestLine("POST /chat/messages")
+    @Headers({
+        "Authorization: Bearer {token}",
+        "Content-Type: application/json"
+    })
+    HystrixCommand<SentChatMessageWrapper> sendChatMessage(
+        @Param("token") String authToken,
+        ChatMessage message
+    );
+
     /**
      * Sends a Shoutout to the specified broadcaster.
      * <p>

rest-helix/src/main/java/com/github/twitch4j/helix/domain/ChatDropReason.java

@@ -0,0 +1,23 @@
+package com.github.twitch4j.helix.domain;
+
+import lombok.AccessLevel;
+import lombok.Data;
+import lombok.Setter;
+
+@Data
+@Setter(AccessLevel.PRIVATE)
+public class ChatDropReason {
+
+    /**
+     * Code for why the message was dropped.
+     * <p>
+     * For example: "channel_settings", "msg_duplicate", "msg_rejected".
+     */
+    private String code;
+
+    /**
+     * Message for why the message was dropped.
+     */
+    private String message;
+
+}

rest-helix/src/main/java/com/github/twitch4j/helix/domain/ChatMessage.java

@@ -0,0 +1,53 @@
+package com.github.twitch4j.helix.domain;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import lombok.AccessLevel;
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+import lombok.With;
+import lombok.extern.jackson.Jacksonized;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+@With
+@Data
+@Setter(AccessLevel.PRIVATE)
+@Builder(toBuilder = true)
+@Jacksonized
+@NoArgsConstructor
+@AllArgsConstructor
+@JsonInclude(JsonInclude.Include.NON_EMPTY)
+public class ChatMessage {
+
+    /**
+     * The ID of the broadcaster whose chat room the message will be sent to.
+     */
+    @NotNull
+    String broadcasterId;
+
+    /**
+     * The ID of the user sending the message.
+     * <p>
+     * This ID must match the user ID in the user access token (if not using an app access token).
+     */
+    @NotNull
+    String senderId;
+
+    /**
+     * The message to send.
+     * <p>
+     * The message is limited to a maximum of 500 characters.
+     */
+    @NotNull
+    String message;
+
+    /**
+     * The ID of the chat message being replied to, if any.
+     */
+    @Nullable
+    String replyParentMessageId;
+
+}

rest-helix/src/main/java/com/github/twitch4j/helix/domain/SentChatMessage.java

@@ -0,0 +1,30 @@
+package com.github.twitch4j.helix.domain;
+
+import lombok.AccessLevel;
+import lombok.Data;
+import lombok.Setter;
+import org.jetbrains.annotations.Nullable;
+
+@Data
+@Setter(AccessLevel.PRIVATE)
+public class SentChatMessage {
+
+    /**
+     * The message id for the message that was sent.
+     * <p>
+     * Can be an empty string when {@link #isSent()} is false.
+     */
+    private String messageId;
+
+    /**
+     * Whether the message passed all checks and was sent.
+     */
+    private boolean isSent;
+
+    /**
+     * The reason the message was dropped, if any.
+     */
+    @Nullable
+    private ChatDropReason dropReason;
+
+}

rest-helix/src/main/java/com/github/twitch4j/helix/domain/SentChatMessageWrapper.java

@@ -0,0 +1,26 @@
+package com.github.twitch4j.helix.domain;
+
+import lombok.AccessLevel;
+import lombok.Data;
+import lombok.Setter;
+
+import java.util.List;
+
+@Data
+@Setter(AccessLevel.PRIVATE)
+public class SentChatMessageWrapper {
+
+    /**
+     * Contains a single object with metadata about the sent message.
+     */
+    private List<SentChatMessage> data;
+
+    /**
+     * @return metadata about the sent message
+     */
+    public SentChatMessage get() {
+        if (data == null || data.isEmpty()) return null; // should never happen
+        return data.get(0);
+    }
+
+}