add forumMessage/notForumMessage extensions

tgbotapi.utils/src/commonMain/kotlin/dev/inmo/tgbotapi/extensions/utils/updates/MessageFilters.kt

@@ -2,8 +2,10 @@ package dev.inmo.tgbotapi.extensions.utils.updates
 
 import dev.inmo.tgbotapi.extensions.utils.*
 import dev.inmo.tgbotapi.types.message.abstracts.CommonMessage
+import dev.inmo.tgbotapi.types.message.abstracts.Message
 import dev.inmo.tgbotapi.types.message.content.TextContent
 import dev.inmo.tgbotapi.types.message.textsources.BotCommandTextSource
+import dev.inmo.tgbotapi.utils.extensions.threadIdOrNull
 
 /**
  * A predicate to test whether a message contains any commands in its body.
@@ -42,3 +44,39 @@ fun CommonMessage<*>.hasCommands(): Boolean = withContentOrNull<TextContent>() ?
  * @see hasCommands
  */
 fun CommonMessage<*>.hasNoCommands(): Boolean = !this.hasCommands()
+
+/**
+ * A predicate to test that message has been sent in the forum.
+ * Use it as the `initialFilter` parameter in behaviour builder triggers.
+ * E.g.
+ *
+ * ```kotlin
+ * onContentMessage(
+ *     initialFilter = Message::forumMessage
+ * ) {
+ *     // The message here will be from forum
+ * }
+ * ```
+ *
+ * @return true if this [Message] is from forum ([threadIdOrNull] is not null). False otherwise.
+ * @see notForumMessage
+ */
+fun Message.forumMessage(): Boolean = threadIdOrNull != null
+
+/**
+ * A predicate to test that message has not been sent in the forum.
+ * Use it as the `initialFilter` parameter in behaviour builder triggers.
+ * E.g.
+ *
+ * ```kotlin
+ * onContentMessage(
+ *     initialFilter = Message::notForumMessage
+ * ) {
+ *     // The message here will not be from forum
+ * }
+ * ```
+ *
+ * @return true if this [Message] is not from forum ([threadIdOrNull] is not null). False otherwise.
+ * @see forumMessage
+ */
+fun Message.notForumMessage(): Boolean = !forumMessage()