add tab completion for slash commands

ui.go

@@ -125,8 +125,14 @@ func (b *Barnard) OnScrollOutputBottom(ui *uiterm.Ui, key uiterm.Key) {
 	b.UiOutput.ScrollBottom()
 }
 
+var commands = []string{"/clear", "/deafen", "/exit", "/help", "/quit"}
+
 func (b *Barnard) OnFocusPress(ui *uiterm.Ui, key uiterm.Key) {
 	active := b.Ui.Active()
+	if active == uiViewInput && strings.HasPrefix(b.UiInput.Text, "/") {
+		b.completeCommand()
+		return
+	}
 	if active == uiViewInput {
 		b.Ui.SetActive(uiViewTree)
 	} else if active == uiViewTree {
@@ -134,6 +140,33 @@ func (b *Barnard) OnFocusPress(ui *uiterm.Ui, key uiterm.Key) {
 	}
 }
 
+func (b *Barnard) completeCommand() {
+	text := b.UiInput.Text
+	var matches []string
+	for _, cmd := range commands {
+		if strings.HasPrefix(cmd, text) {
+			matches = append(matches, cmd)
+		}
+	}
+	if len(matches) == 0 {
+		return
+	}
+	if len(matches) == 1 {
+		b.UiInput.Text = matches[0]
+	} else {
+		prefix := matches[0]
+		for _, m := range matches[1:] {
+			for !strings.HasPrefix(m, prefix) {
+				prefix = prefix[:len(prefix)-1]
+			}
+		}
+		if len(prefix) > len(text) {
+			b.UiInput.Text = prefix
+		}
+	}
+	b.Ui.Refresh()
+}
+
 func (b *Barnard) OnTextInput(ui *uiterm.Ui, textbox *uiterm.Textbox, text string) {
 	if text == "" {
 		return