From 29028cb601cdd39dfe4306be5f3920f7995f06f1 Mon Sep 17 00:00:00 2001
From: Mustafa Senoglu <mmustafasenoglu0@gmail.com>
Date: Sat, 5 Sep 2026 15:08:56 +0300
Subject: [PATCH] ui: truncate long text to terminal width in Select/Prompt
 templates

screenbuf assumes each Write() is exactly one terminal line, but when
text is wider than the terminal it wraps, causing stale content to
remain on screen (issue #466).

Add a truncFunc template helper that measures the terminal width via
golang.org/x/term and truncates the string so the rendered line stays
within bounds. The function is registered in promptui.FuncMap and
applied to the default Select and NamedSelect templates (Label,
Active, Inactive) with a prefixLen of 4 to account for the page
arrow, spacing, and icon characters.
---
 go.mod          |  1 +
 ui/templates.go | 48 ++++++++++++++++++++++++++++++++++++++++++------
 ui/terminal.go  | 18 ++++++++++++++++++
 3 files changed, 61 insertions(+), 6 deletions(-)
 create mode 100644 ui/terminal.go

diff --git a/go.mod b/go.mod
index 5ded2a8..c360aa6 100644
--- a/go.mod
+++ b/go.mod
@@ -14,6 +14,7 @@ require (
 	go.step.sm/crypto v0.89.0
 	golang.org/x/net v0.58.0
 	golang.org/x/sys v0.47.0
+	golang.org/x/term v0.45.0
 )
 
 require (
diff --git a/ui/templates.go b/ui/templates.go
index cc37891..9c317c6 100644
--- a/ui/templates.go
+++ b/ui/templates.go
@@ -3,6 +3,7 @@ package ui
 import (
 	"fmt"
 	"runtime"
+	"unicode/utf8"
 
 	"github.com/chzyer/readline"
 	"github.com/manifoldco/promptui"
@@ -40,6 +41,34 @@ func init() {
 		promptui.KeyForward = readline.CharForward
 		promptui.KeyForwardDisplay = "→"
 	}
+
+	// Register trunc template function in promptui's FuncMap so all
+	// templates (label, active, inactive, selected, help) can use it.
+	promptui.FuncMap["trunc"] = truncFunc
+}
+
+// truncFunc truncates s so that the rendered line does not exceed the
+// terminal width. prefixLen is the visible character count of everything
+// that appears before the template content on the same line (icons,
+// arrows, indentation). An ellipsis "..." is appended when truncation
+// occurs.
+func truncFunc(s string, prefixLen int) string {
+	w := getTerminalWidth()
+	if w <= 0 {
+		return s
+	}
+	max := w - prefixLen
+	if max <= 0 {
+		return ""
+	}
+	n := utf8.RuneCountInString(s)
+	if n <= max {
+		return s
+	}
+	if max <= 3 {
+		return string([]rune(s)[:max])
+	}
+	return string([]rune(s)[:max-3]) + "..."
 }
 
 // PrintSelectedTemplate returns the default template used in PrintSelected.
@@ -71,11 +100,18 @@ func SimplePromptTemplates() *promptui.PromptTemplates {
 
 // SelectTemplates returns the default promptui.SelectTemplate for string
 // slices. The given name is the prompt of the selected option.
+//
+// The prefixLen values account for the visible characters before the
+// item text on each line:
+//
+//	Label:   "?" + " " + ... + ": "  → 4
+//	Active:  "▸" + " "               → 4 (incl. page arrow + space)
+//	Inactive: "  "                   → 4
 func SelectTemplates(name string) *promptui.SelectTemplates {
 	return &promptui.SelectTemplates{
-		Label:    fmt.Sprintf("%s {{ . }}: ", IconInitial),
-		Active:   fmt.Sprintf("%s {{ . | underline }}", IconSelect),
-		Inactive: "  {{ . }}",
+		Label:    fmt.Sprintf("%s {{ . | trunc 4 }}: ", IconInitial),
+		Active:   fmt.Sprintf("%s {{ . | trunc 4 | underline }}", IconSelect),
+		Inactive: "  {{ . | trunc 4 }}",
 		Selected: fmt.Sprintf(`{{ %q | green }} {{ "%s:" | bold }} {{ .Name }}`, IconGood, name),
 	}
 }
@@ -85,9 +121,9 @@ func SelectTemplates(name string) *promptui.SelectTemplates {
 // option.
 func NamedSelectTemplates(name string) *promptui.SelectTemplates {
 	return &promptui.SelectTemplates{
-		Label:    fmt.Sprintf("%s {{.Name}}: ", IconInitial),
-		Active:   fmt.Sprintf("%s {{ .Name | underline }}", IconSelect),
-		Inactive: "  {{.Name}}",
+		Label:    fmt.Sprintf("%s {{ .Name | trunc 4 }}: ", IconInitial),
+		Active:   fmt.Sprintf("%s {{ .Name | trunc 4 | underline }}", IconSelect),
+		Inactive: "  {{ .Name | trunc 4 }}",
 		Selected: fmt.Sprintf(`{{ %q | green }} {{ "%s:" | bold }} {{ .Name }}`, IconGood, name),
 	}
 }
diff --git a/ui/terminal.go b/ui/terminal.go
new file mode 100644
index 0000000..b180580
--- /dev/null
+++ b/ui/terminal.go
@@ -0,0 +1,18 @@
+package ui
+
+import (
+	"os"
+
+	"golang.org/x/term"
+)
+
+// getTerminalWidth returns the width of the terminal in columns.
+// Returns 0 if the width cannot be determined.
+func getTerminalWidth() int {
+	fd := int(os.Stderr.Fd())
+	w, _, err := term.GetSize(fd)
+	if err != nil {
+		return 0
+	}
+	return w
+}