add response policy

ken.go

@@ -322,6 +322,10 @@ func (k *Ken) onInteractionCreate(s *discordgo.Session, e *discordgo.Interaction
 	ctx.Command = cmd
 	ctx.Ephemeral = false
 
+	if rpCmd, ok := cmd.(ResponsePolicyCommand); ok {
+		ctx.Ephemeral = rpCmd.ResponsePolicy().Ephemeral
+	}
+
 	if ch.Type == discordgo.ChannelTypeDM || ch.Type == discordgo.ChannelTypeGroupDM {
 		if dmCmd, ok := cmd.(DmCapable); !ok || !dmCmd.IsDmCapable() {
 			k.opt.OnCommandError(ErrNotDMCapable, ctx)

responsepolicy.go

@@ -0,0 +1,36 @@
+package ken
+
+// ResponsePolicy describes rules for context
+// followups and responses.
+type ResponsePolicy struct {
+	// When set to true, the command response will
+	// only be received by the sender of the command.
+	//
+	// This sets the `Ephemeral` flag of the `Context`
+	// to true before any middleware is invoked. So,
+	// you are able to modify the ephemeral flag either
+	// in your middleware or directly in your command
+	// logic, if you desire.
+	Ephemeral bool
+}
+
+// ResponsePolicyCommand defines a command which
+// provides a ResponsePolicy.
+type ResponsePolicyCommand interface {
+	ResponsePolicy() ResponsePolicy
+}
+
+// EphemeralCommand can be added to your command
+// to make all command responses ephemeral.
+// This means, that all responses to the command
+// from the bot will only be received by the sender
+// of the command.
+type EphemeralCommand struct{}
+
+var _ ResponsePolicyCommand = (*EphemeralCommand)(nil)
+
+func (EphemeralCommand) ResponsePolicy() ResponsePolicy {
+	return ResponsePolicy{
+		Ephemeral: true,
+	}
+}