refactor(ui): Use Render method, drop constructor parameters (#111)

For all UI components defined in the UI package,
make the following changes:

- Instead of a `View() string` method, use a `Render(w io.Writer)`
method.
  This allows reusing the same `strings.Builder` for a render operation,
  reducing unnecessary string concatenation.
- Drop constructor parameters from all `New*` functions.
  The value pointers are placed with an optional `WithValue` method,
  and in case of Select, the list of options with `WithOptions`.

.golangci.yml

@@ -39,6 +39,10 @@ linters-settings:
       - fmt.Fprintf
       - fmt.Fprintln
 
+      # This is always a strings.Builder, and can't fail.
+      - (go.abhg.dev/gs/internal/ui.Writer).WriteString
+      - (go.abhg.dev/gs/internal/ui.Writer).Write
+
   govet:
     enable:
       - niliness

branch.go

@@ -104,13 +104,13 @@ nextBranch:
 		return "", errors.New("no branches available")
 	}
 
-	var result string
-	prompt := ui.NewSelect(&result, branches...).
+	prompt := ui.NewSelect().
+		WithOptions(branches...).
 		WithTitle(p.Title).
 		WithDescription(p.Description)
 	if err := ui.Run(prompt); err != nil {
 		return "", fmt.Errorf("select branch: %w", err)
 	}
 
-	return result, nil
+	return prompt.Value(), nil
 }

branch_checkout.go

@@ -65,7 +65,8 @@ func (cmd *branchCheckoutCmd) Run(ctx context.Context, log *log.Logger, opts *gl
 				} else {
 					log.Warnf("%v: branch not tracked", cmd.Name)
 					track := true
-					prompt := ui.NewConfirm(&track).
+					prompt := ui.NewConfirm().
+						WithValue(&track).
 						WithTitle("Do you want to track this branch now?")
 					if err := ui.Run(prompt); err != nil {
 						return fmt.Errorf("prompt: %w", err)

branch_rename.go

@@ -43,7 +43,8 @@ func (cmd *branchRenameCmd) Run(ctx context.Context, log *log.Logger, opts *glob
 	}
 
 	if cmd.Name == "" {
-		prompt := ui.NewInput(&cmd.Name).
+		prompt := ui.NewInput().
+			WithValue(&cmd.Name).
 			WithTitle("New branch name").
 			WithDescription(fmt.Sprintf("Renaming branch: %v", oldName)).
 			WithValidate(func(s string) error {

branch_submit.go

@@ -170,7 +170,8 @@ func (cmd *branchSubmitCmd) Run(
 		var fields []ui.Field
 		if cmd.Title == "" {
 			cmd.Title = defaultTitle
-			title := ui.NewInput(&cmd.Title).
+			title := ui.NewInput().
+				WithValue(&cmd.Title).
 				WithTitle("Title").
 				WithDescription("Short summary of the pull request").
 				WithValidate(func(s string) error {
@@ -184,7 +185,8 @@ func (cmd *branchSubmitCmd) Run(
 
 		if cmd.Body == "" {
 			cmd.Body = defaultBody
-			body := ui.NewOpenEditor(&cmd.Body).
+			body := ui.NewOpenEditor().
+				WithValue(&cmd.Body).
 				WithTitle("Body").
 				WithDescription("Open your editor to write " +
 					"a detailed description of the pull request")
@@ -196,7 +198,8 @@ func (cmd *branchSubmitCmd) Run(
 
 		if opts.Prompt {
 			// TODO: default to true if subject is "WIP" or similar.
-			draft := ui.NewConfirm(&cmd.Draft).
+			draft := ui.NewConfirm().
+				WithValue(&cmd.Draft).
 				WithTitle("Draft").
 				WithDescription("Mark the pull request as a draft?")
 			fields = append(fields, draft)

internal/ui/confirm.go

@@ -1,8 +1,6 @@
 package ui
 
 import (
-	"strings"
-
 	"github.com/charmbracelet/bubbles/key"
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/lipgloss"
@@ -55,15 +53,13 @@ type Confirm struct {
 
 var _ Field = (*Confirm)(nil)
 
-// NewConfirm builds a new confirm field that writes its result
-// to the given boolean pointer.
-//
-// The initial value of the boolean pointer will be used as the default.
-func NewConfirm(value *bool) *Confirm {
+// NewConfirm builds a new confirm field that prompts the user
+// with a yes or no question.
+func NewConfirm() *Confirm {
 	return &Confirm{
 		KeyMap: DefaultConfirmKeyMap,
 		Style:  DefaultConfirmStyle,
-		value:  value,
+		value:  new(bool),
 	}
 }
 
@@ -72,6 +68,19 @@ func (c *Confirm) Err() error {
 	return nil
 }
 
+// WithValue sets the destination for the confirm field.
+// The result of the field will be written to the given boolean pointer.
+// The pointer's current value will be used as the default.
+func (c *Confirm) WithValue(value *bool) *Confirm {
+	c.value = value
+	return c
+}
+
+// Value returns the current value of the confirm field.
+func (c *Confirm) Value() bool {
+	return *c.value
+}
+
 // WithTitle sets the title for the confirm field.
 func (c *Confirm) WithTitle(title string) *Confirm {
 	c.title = title
@@ -116,19 +125,17 @@ func (c *Confirm) Update(msg tea.Msg) tea.Cmd {
 	return tea.Batch(cmds...)
 }
 
-// View renders the confirm field.
-func (c *Confirm) View() string {
-	var s strings.Builder
-	s.WriteString("[")
+// Render renders the confirm field to the given writer.
+func (c *Confirm) Render(w Writer) {
+	w.WriteString("[")
 	if *c.value {
-		s.WriteString(c.Style.DefaultValue.Render("Y"))
-		s.WriteString("/")
-		s.WriteString(c.Style.NonDefaultValue.Render("n"))
+		w.WriteString(c.Style.DefaultValue.Render("Y"))
+		w.WriteString("/")
+		w.WriteString(c.Style.NonDefaultValue.Render("n"))
 	} else {
-		s.WriteString(c.Style.NonDefaultValue.Render("y"))
-		s.WriteString("/")
-		s.WriteString(c.Style.DefaultValue.Render("N"))
+		w.WriteString(c.Style.NonDefaultValue.Render("y"))
+		w.WriteString("/")
+		w.WriteString(c.Style.DefaultValue.Render("N"))
 	}
-	s.WriteString("]")
-	return s.String()
+	w.WriteString("]")
 }

internal/ui/confirm_test.go

@@ -0,0 +1,38 @@
+package ui_test
+
+import (
+	"testing"
+
+	tea "github.com/charmbracelet/bubbletea"
+	"github.com/stretchr/testify/assert"
+	"go.abhg.dev/gs/internal/ui"
+)
+
+func TestConfirm_accept(t *testing.T) {
+	t.Run("default/false", func(t *testing.T) {
+		c := ui.NewConfirm()
+		c.Update(tea.KeyMsg{Type: tea.KeyEnter})
+		assert.False(t, c.Value())
+	})
+
+	t.Run("default/true", func(t *testing.T) {
+		value := true
+		c := ui.NewConfirm().WithValue(&value)
+		c.Update(tea.KeyMsg{Type: tea.KeyEnter})
+
+		assert.True(t, c.Value())
+		assert.True(t, value)
+	})
+
+	t.Run("yes", func(t *testing.T) {
+		c := ui.NewConfirm()
+		c.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("y")})
+		assert.True(t, c.Value())
+	})
+
+	t.Run("no", func(t *testing.T) {
+		c := ui.NewConfirm()
+		c.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("n")})
+		assert.False(t, c.Value())
+	})
+}

internal/ui/form.go

@@ -57,11 +57,16 @@ func AcceptField() tea.Msg {
 	return acceptFieldMsg{}
 }
 
+// Writer receives a rendered view of a [Field].
+type Writer interface {
+	io.Writer
+	io.StringWriter
+}
+
 // Field is a single field in a form.
 type Field interface {
 	Update(msg tea.Msg) tea.Cmd
-	View() string
-	// FIXME: Refactor to View(io.Writer) error
+	Render(Writer)
 
 	// Err reports any errors for the field at render time.
 	// These will be rendered in red below the field.
@@ -187,7 +192,7 @@ func (f *Form) View() string {
 	return s.String()
 }
 
-func (f *Form) renderField(w io.Writer, field Field, accepted bool) {
+func (f *Form) renderField(w Writer, field Field, accepted bool) {
 	if title := field.Title(); title != "" {
 		titleStyle := f.Style.Title
 		if accepted {
@@ -196,7 +201,7 @@ func (f *Form) renderField(w io.Writer, field Field, accepted bool) {
 
 		fmt.Fprintf(w, "%s: ", titleStyle.Render(title))
 	}
-	fmt.Fprint(w, field.View())
+	field.Render(w)
 	if err := field.Err(); err != nil {
 		fmt.Fprintf(w, "\n%s", f.Style.Error.Render(err.Error()))
 	}

internal/ui/input.go

@@ -40,23 +40,27 @@ type Input struct {
 
 var _ Field = (*Input)(nil)
 
-// NewInput builds a new input field that writes its result
-// to the given string pointer.
-//
-// If the value is non-empty, it will be used as the initial value.
-func NewInput(value *string) *Input {
+// NewInput builds a new input field.
+func NewInput() *Input {
 	m := textinput.New()
 	m.Prompt = "" // we have our own prompt
-	m.SetValue(*value)
 	m.Focus()
 	return &Input{
 		KeyMap: DefaultInputKeyMap,
 		Style:  DefaultInputStyle,
 		model:  &m,
-		value:  value,
+		value:  new(string),
 	}
 }
 
+// WithValue sets the destination for the input field.
+// If the value is non-empty, it will be used as the initial value.
+func (i *Input) WithValue(value *string) *Input {
+	i.value = value
+	i.model.SetValue(*value)
+	return i
+}
+
 // WithTitle sets the title of the input field.
 func (i *Input) WithTitle(title string) *Input {
 	i.title = title
@@ -116,7 +120,7 @@ func (i *Input) Update(msg tea.Msg) tea.Cmd {
 	return tea.Batch(cmds...)
 }
 
-// View renders the input field.
-func (i *Input) View() string {
-	return i.model.View()
+// Render renders the input field.
+func (i *Input) Render(w Writer) {
+	w.WriteString(i.model.View())
 }

internal/ui/editor_prompt.go → internal/ui/open_editor.go

@@ -85,16 +85,15 @@ type OpenEditor struct {
 
 var _ Field = (*OpenEditor)(nil)
 
-// NewOpenEditor builds an [OpenEditor] field with default values.
-// It will feed the value pointer with the content of the editor.
-//
-// If the value is non-empty, the editor will be pre-filled with its content.
-func NewOpenEditor(value *string) *OpenEditor {
+// NewOpenEditor builds an [OpenEditor] field.
+// It will prompt the user to open an editor and write a message,
+// or accept the current value.
+func NewOpenEditor() *OpenEditor {
 	ed := &OpenEditor{
 		KeyMap: DefaultOpenEditorKeyMap,
 		Style:  DefaultOpenEditorStyle,
 		Editor: DefaultEditor(),
-		value:  value,
+		value:  new(string),
 	}
 	if ed.Editor.Command == "" {
 		ed.err = errors.New("no editor found: please set $EDITOR")
@@ -107,6 +106,15 @@ func (a *OpenEditor) Err() error {
 	return a.err
 }
 
+// WithValue specifies the value to edit.
+// The current value will be used as the initial content of the editor.
+// The value will be updated when the editor is closed,
+// or left unchanged if the user skips the editor.
+func (a *OpenEditor) WithValue(value *string) *OpenEditor {
+	a.value = value
+	return a
+}
+
 // WithTitle sets the title for the field.
 func (a *OpenEditor) WithTitle(title string) *OpenEditor {
 	a.title = title
@@ -191,14 +199,11 @@ func (a *OpenEditor) Update(msg tea.Msg) tea.Cmd {
 	return nil
 }
 
-// View renders the field to the screen.
-func (a *OpenEditor) View() string {
-	var s strings.Builder
-	fmt.Fprintf(&s, "Press [%v] to open %v or [%v] to skip",
+// Render renders the field to the screen.
+func (a *OpenEditor) Render(w Writer) {
+	fmt.Fprintf(w, "Press [%v] to open %v or [%v] to skip",
 		a.Style.Key.Render(a.KeyMap.Edit.Help().Key),
 		a.Style.Editor.Render(a.Editor.Command),
 		a.Style.Key.Render(a.KeyMap.Accept.Help().Key),
 	)
-
-	return s.String()
 }