feat: implement pagination

completion.go

@@ -28,6 +28,8 @@ type CompletionManager struct {
 	tmp       []Suggest
 	max       uint16
 	completer Completer
+
+	verticalScroll int
 }
 
 // GetSelectedSuggestion returns the selected item.
@@ -50,6 +52,7 @@ func (c *CompletionManager) GetSuggestions() []Suggest {
 // Reset to select nothing.
 func (c *CompletionManager) Reset() {
 	c.selected = -1
+	c.verticalScroll = 0
 	c.Update(*NewDocument())
 	return
 }
@@ -62,6 +65,9 @@ func (c *CompletionManager) Update(in Document) {
 
 // Previous to select the previous suggestion item.
 func (c *CompletionManager) Previous() {
+	if c.verticalScroll == c.selected && c.selected > 0 {
+		c.verticalScroll--
+	}
 	c.selected--
 	c.update()
 	return
@@ -69,6 +75,9 @@ func (c *CompletionManager) Previous() {
 
 // Next to select the next suggestion item.
 func (c *CompletionManager) Next() {
+	if c.verticalScroll+int(c.max)-1 == c.selected {
+		c.verticalScroll++
+	}
 	c.selected++
 	c.update()
 	return
@@ -84,10 +93,12 @@ func (c *CompletionManager) update() {
 	if len(c.tmp) < max {
 		max = len(c.tmp)
 	}
-	if c.selected >= max {
+
+	if c.selected >= len(c.tmp) {
 		c.Reset()
 	} else if c.selected < -1 {
-		c.selected = max - 1
+		c.selected = len(c.tmp) - 1
+		c.verticalScroll = len(c.tmp) - max
 	}
 }
 
@@ -160,5 +171,7 @@ func NewCompletionManager(completer Completer, max uint16) *CompletionManager {
 		selected:  -1,
 		max:       max,
 		completer: completer,
+
+		verticalScroll: 0,
 	}
 }

option.go

@@ -194,6 +194,8 @@ func New(executor Executor, completer Completer, opts ...Option) *Prompt {
 			descriptionBGColor:           Turquoise,
 			selectedDescriptionTextColor: White,
 			selectedDescriptionBGColor:   Cyan,
+			scrollbarThumbColor:          DarkGray,
+			scrollbarBGColor:             Cyan,
 		},
 		buf:         NewBuffer(),
 		executor:    executor,

render.go

@@ -1,5 +1,9 @@
 package prompt
 
+import (
+	"math"
+)
+
 // Render to render prompt information from state of Buffer.
 type Render struct {
 	out    ConsoleWriter
@@ -22,6 +26,8 @@ type Render struct {
 	descriptionBGColor           Color
 	selectedDescriptionTextColor Color
 	selectedDescriptionBGColor   Color
+	scrollbarThumbColor          Color
+	scrollbarBGColor             Color
 }
 
 // Setup to initialize console output.
@@ -72,24 +78,34 @@ func (r *Render) renderWindowTooSmall() {
 }
 
 func (r *Render) renderCompletion(buf *Buffer, completions *CompletionManager) {
-	max := completions.max
+	windowHeight := len(completions.tmp)
-	if max > r.row {
+	if windowHeight > int(completions.max) {
-		max = r.row
+		windowHeight = int(completions.max)
+	}
+	contentHeight := len(completions.tmp)
+
+	fractionVisible := float64(windowHeight) / float64(contentHeight)
+	fractionAbove := float64(completions.verticalScroll) / float64(contentHeight)
+
+	scrollbarHeight := int(math.Min(float64(windowHeight), math.Max(1, float64(windowHeight)*fractionVisible)))
+	scrollbarTop := int(float64(windowHeight) * fractionAbove)
+
+	isScrollThumb := func(row int) bool {
+		return scrollbarTop <= row && row <= scrollbarTop+scrollbarHeight
 	}
 
 	suggestions := completions.GetSuggestions()
 	if l := len(completions.GetSuggestions()); l == 0 {
 		return
-	} else if l > int(max) {
-		suggestions = suggestions[:max]
 	}
 
 	formatted, width := formatSuggestions(
 		suggestions,
-		int(r.col)-len(r.prefix),
+		int(r.col)-len(r.prefix)-1,
 	)
+	formatted = formatted[completions.verticalScroll : completions.verticalScroll+windowHeight]
 	l := len(formatted)
-	r.prepareArea(l)
+	r.prepareArea(windowHeight)
 
 	d := (len(r.prefix) + len(buf.Document().TextBeforeCursor())) % int(r.col)
 	if d == 0 { // the cursor is on right end.
@@ -98,23 +114,32 @@ func (r *Render) renderCompletion(buf *Buffer, completions *CompletionManager) {
 		r.out.CursorBackward(d + width - int(r.col))
 	}
 
+	selected := completions.selected - completions.verticalScroll
+
 	r.out.SetColor(White, Cyan, false)
 	for i := 0; i < l; i++ {
 		r.out.CursorDown(1)
-		if i == completions.selected {
+		if i == selected {
 			r.out.SetColor(r.selectedSuggestionTextColor, r.selectedSuggestionBGColor, true)
 		} else {
 			r.out.SetColor(r.suggestionTextColor, r.suggestionBGColor, false)
 		}
 		r.out.WriteStr(formatted[i].Text)
 
-		if i == completions.selected {
+		if i == selected {
 			r.out.SetColor(r.selectedDescriptionTextColor, r.selectedDescriptionBGColor, false)
 		} else {
 			r.out.SetColor(r.descriptionTextColor, r.descriptionBGColor, false)
 		}
 		r.out.WriteStr(formatted[i].Description)
-		r.out.CursorBackward(width)
+
+		if isScrollThumb(i) {
+			r.out.SetColor(DefaultColor, r.scrollbarThumbColor, false)
+		} else {
+			r.out.SetColor(DefaultColor, r.scrollbarBGColor, false)
+		}
+		r.out.WriteStr(" ")
+		r.out.CursorBackward(width + 1)
 	}
 	if d == 0 { // the cursor is on right end.
 		// DON'T CURSOR DOWN HERE. Because the line doesn't erase properly.