feat(textarea) Add multiline placeholder

Add the capability to show a multiline placeholder. Some refactoring was
required to improve readability and improve logic.

End of line buffer character was only shown when line numbers were
displayed which requires some verification whether this is the intended
outcome. This change resolves this issue.

textarea/textarea.go

@@ -3,6 +3,7 @@ package textarea
 import (
 	"crypto/sha256"
 	"fmt"
+	"strconv"
 	"strings"
 	"unicode"
 
@@ -15,6 +16,9 @@ import (
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/lipgloss"
 	rw "github.com/mattn/go-runewidth"
+	"github.com/muesli/reflow/ansi"
+	"github.com/muesli/reflow/wordwrap"
+	rwrap "github.com/muesli/reflow/wrap"
 	"github.com/rivo/uniseg"
 )
 
@@ -1163,36 +1167,80 @@ func (m Model) getPromptString(displayLine int) (prompt string) {
 func (m Model) placeholderView() string {
 	var (
 		s     strings.Builder
-		p     = rw.Truncate(m.Placeholder, m.width, "...")
+		p     = m.Placeholder
 		style = m.style.Placeholder.Inline(true)
 	)
 
-	prompt := m.getPromptString(0)
-	prompt = m.style.Prompt.Render(prompt)
-	s.WriteString(m.style.CursorLine.Render(prompt))
-
+	// maximum width of placeholder text must exclude:
+	// - prompt width
+	// - line number width (or padding)
+	maxWidth := m.MaxWidth - ansi.PrintableRuneWidth(m.Prompt) // remove the prompt width
 	if m.ShowLineNumbers {
-		s.WriteString(m.style.CursorLine.Render(m.style.CursorLineNumber.Render((fmt.Sprintf(m.lineNumberFormat, 1)))))
+		const lnWidth = 4   // up to 3 digits for line number plus 1 margin
+		maxWidth -= lnWidth // remove the line number width (or padding)
 	}
 
-	m.Cursor.TextStyle = m.style.Placeholder
-	m.Cursor.SetChar(string(p[0]))
-	s.WriteString(m.style.CursorLine.Render(m.Cursor.View()))
+	// word wrap lines
+	pwordwrap := wordwrap.String(p, maxWidth)
+	// wrap lines (handles lines that could not be word wrapped)
+	pwrap := rwrap.String(pwordwrap, maxWidth)
+	// split string by new lines
+	plines := strings.Split(strings.TrimSpace(pwrap), "\n")
 
-	// The rest of the placeholder text
-	s.WriteString(m.style.CursorLine.Render(style.Render(p[1:] + strings.Repeat(" ", max(0, m.width-uniseg.StringWidth(p))))))
+	for i := 0; i < m.height; i++ {
+		lineStyle := m.style.Placeholder
+		lineNumberStyle := m.style.LineNumber
+		if len(plines) > i {
+			lineStyle = m.style.CursorLine
+			lineNumberStyle = m.style.CursorLineNumber
+		}
 
-	// The rest of the new lines
-	for i := 1; i < m.height; i++ {
-		s.WriteRune('\n')
+		// render prompt
 		prompt := m.getPromptString(i)
 		prompt = m.style.Prompt.Render(prompt)
-		s.WriteString(prompt)
+		s.WriteString(lineStyle.Render(prompt))
 
+		// when show line numbers enabled:
+		// - render line number for only the cursor line
+		// - indent other placeholder lines
+		// this is consistent with vim with line numbers enabled
 		if m.ShowLineNumbers {
+			var ln string
+
+			switch {
+			case i == 0:
+				ln = strconv.Itoa(i + 1)
+				fallthrough
+			case len(plines) > i:
+				s.WriteString(lineStyle.Render(lineNumberStyle.Render(fmt.Sprintf(m.lineNumberFormat, ln))))
+			default:
+			}
+		}
+
+		switch {
+		// first line
+		case i == 0:
+			// first character of first line as cursor with character
+			m.Cursor.TextStyle = m.style.Placeholder
+			m.Cursor.SetChar(string(plines[0][0]))
+			s.WriteString(lineStyle.Render(m.Cursor.View()))
+
+			// the rest of the first line
+			s.WriteString(lineStyle.Render(style.Render(plines[0][1:] + strings.Repeat(" ", max(0, m.width-uniseg.StringWidth(plines[0]))))))
+		// remaining lines
+		case len(plines) > i:
+			// current line placeholder text
+			if len(plines) > i {
+				s.WriteString(lineStyle.Render(style.Render(plines[i] + strings.Repeat(" ", max(0, m.width-uniseg.StringWidth(plines[i]))))))
+			}
+		default:
+			// end of line buffer character
 			eob := m.style.EndOfBuffer.Render(string(m.EndOfBufferCharacter))
 			s.WriteString(eob)
 		}
+
+		// terminate with new line
+		s.WriteRune('\n')
 	}
 
 	m.viewport.SetContent(s.String())