State: Fixed incoming messages being backwards in order

state/state.go

@@ -449,7 +449,9 @@ func (s *State) Messages(channelID discord.Snowflake) ([]discord.Message, error)
 		guildID = c.GuildID
 	}
 
-	for i := range ms {
+	// Iterate in reverse, since the store is expected to prepend the latest
+	// messages.
+	for i := len(ms) - 1; i >= 0; i-- {
 		// Set the guild ID, fine if it's 0 (it's already 0 anyway).
 		ms[i].GuildID = guildID
 

state/store.go

@@ -42,6 +42,7 @@ type StoreGetter interface {
 	Members(guildID discord.Snowflake) ([]discord.Member, error)
 
 	Message(channelID, messageID discord.Snowflake) (*discord.Message, error)
+	// Messages should return messages ordered from latest to earliest.
 	Messages(channelID discord.Snowflake) ([]discord.Message, error)
 	MaxMessages() int // used to know if the state is filled or not.
 
@@ -73,6 +74,8 @@ type StoreModifier interface {
 	MemberSet(guildID discord.Snowflake, member *discord.Member) error
 	MemberRemove(guildID, userID discord.Snowflake) error
 
+	// MessageSet should prepend messages into the slice, the latest being in
+	// front.
 	MessageSet(*discord.Message) error
 	MessageRemove(channelID, messageID discord.Snowflake) error
 

state/store_default.go

@@ -463,19 +463,23 @@ func (s *DefaultStore) MessageSet(message *discord.Message) error {
 		}
 	}
 
-	// Prepend the latest message at the end
-
-	if end := s.MaxMessages(); len(ms) >= end {
-		// Copy hack to prepend. This copies the 0th-(end-1)th entries to
-		// 1st-endth.
-		copy(ms[1:end], ms[0:end-1])
-		// Then, set the 0th entry.
-		ms[0] = *message
+	// Order: latest to earliest, similar to the API.
 
+	var end = len(ms)
+	if max := s.MaxMessages(); end >= max {
+		// If the end (length) is larger than the maximum amount, then cap it.
+		end = max
 	} else {
-		ms = append(ms, *message)
+		// Else, append an empty message to the end.
+		ms = append(ms, discord.Message{})
 	}
 
+	// Copy hack to prepend. This copies the 0th-(end-1)th entries to
+	// 1st-endth.
+	copy(ms[1:end], ms[0:end-1])
+	// Then, set the 0th entry.
+	ms[0] = *message
+
 	s.messages[message.ChannelID] = ms
 	return nil
 }