Add message forwarding (disgoorg#350)

* Add message forwarding

* support multiple snapshots

discord/discord-api-docs@14e1fa7

* fix snapshot structure

* remove Guild from MessageSnapshot

* add fields to PartialMessage

Author: Sebastian

discord/message.go

@@ -102,6 +102,7 @@ type Message struct {
 	Type                 MessageType           `json:"type"`
 	Flags                MessageFlags          `json:"flags"`
 	MessageReference     *MessageReference     `json:"message_reference,omitempty"`
+	MessageSnapshots     []MessageSnapshot     `json:"message_snapshots,omitempty"`
 	Interaction          *MessageInteraction   `json:"interaction,omitempty"`
 	WebhookID            *snowflake.ID         `json:"webhook_id,omitempty"`
 	Activity             *MessageActivity      `json:"activity,omitempty"`
@@ -407,10 +408,34 @@ type MessageApplication struct {
 
 // MessageReference is a reference to another message
 type MessageReference struct {
-	MessageID       *snowflake.ID `json:"message_id"`
-	ChannelID       *snowflake.ID `json:"channel_id,omitempty"`
-	GuildID         *snowflake.ID `json:"guild_id,omitempty"`
-	FailIfNotExists bool          `json:"fail_if_not_exists,omitempty"`
+	Type            MessageReferenceType `json:"type,omitempty"`
+	MessageID       *snowflake.ID        `json:"message_id"`
+	ChannelID       *snowflake.ID        `json:"channel_id,omitempty"`
+	GuildID         *snowflake.ID        `json:"guild_id,omitempty"`
+	FailIfNotExists bool                 `json:"fail_if_not_exists,omitempty"`
+}
+
+type MessageReferenceType int
+
+const (
+	MessageReferenceTypeDefault MessageReferenceType = iota
+	MessageReferenceTypeForward
+)
+
+type MessageSnapshot struct {
+	Message PartialMessage `json:"message"`
+}
+
+type PartialMessage struct {
+	Type            MessageType    `json:"type"`
+	Content         string         `json:"content,omitempty"`
+	Embeds          []Embed        `json:"embeds,omitempty"`
+	Attachments     []Attachment   `json:"attachments"`
+	CreatedAt       time.Time      `json:"timestamp"`
+	EditedTimestamp *time.Time     `json:"edited_timestamp"`
+	Flags           MessageFlags   `json:"flags"`
+	Mentions        []User         `json:"mentions"`
+	MentionRoles    []snowflake.ID `json:"mention_roles"`
 }
 
 // MessageInteraction is sent on the Message object when the message is a response to an interaction