feat(inputfield/autocompletion): Draw selected autocomplete suggestion in `inputfield` without changing it till confirmed with `ENTER`

inputfield.go

@@ -76,6 +76,9 @@ type InputField struct {
 	// The background color of the selected ListItem.
 	autocompleteListSelectedBackgroundColor tcell.Color
 
+	// The text color of the suggestion.
+	autocompleteSuggestionTextColor tcell.Color
+
 	// The screen width of the label area. A value of 0 means use the width of
 	// the label text.
 	labelWidth int
@@ -100,6 +103,9 @@ type InputField struct {
 	// nil, the list's main texts represent the current autocomplete entries.
 	autocompleteList *List
 
+	// The suggested completion of the current autocomplete ListItem.
+	autocompleteListSuggestion string
+
 	// An optional function which may reject the last character that was entered.
 	accept func(text string, ch rune) bool
 
@@ -140,6 +146,7 @@ func NewInputField() *InputField {
 		autocompleteListBackgroundColor:         Styles.MoreContrastBackgroundColor,
 		autocompleteListSelectedTextColor:       Styles.PrimitiveBackgroundColor,
 		autocompleteListSelectedBackgroundColor: Styles.PrimaryTextColor,
+		autocompleteSuggestionTextColor:         Styles.ContrastPrimaryTextColor,
 	}
 }
 
@@ -308,6 +315,12 @@ func (i *InputField) SetAutocompleteListSelectedBackgroundColor(color tcell.Colo
 	return i
 }
 
+// SetAutocompleteSuggestionColor sets the text color of the autocomplete suggestion in the input field.
+func (i *InputField) SetAutocompleteSuggestionTextColor(color tcell.Color) *InputField {
+	i.autocompleteSuggestionTextColor = color
+	return i
+}
+
 // SetFormAttributes sets attributes shared by all form items.
 func (i *InputField) SetFormAttributes(labelWidth int, bgColor, labelColor, labelColorFocused, fieldTextColor, fieldTextColorFocused, fieldBgColor, fieldBgColorFocused tcell.Color) FormItem {
 	i.Lock()
@@ -405,6 +418,7 @@ func (i *InputField) Autocomplete() *InputField {
 		// No entries, no list.
 		i.Lock()
 		i.autocompleteList = nil
+		i.autocompleteListSuggestion = ""
 		i.Unlock()
 		return i
 	}
@@ -415,6 +429,7 @@ func (i *InputField) Autocomplete() *InputField {
 	if i.autocompleteList == nil {
 		i.autocompleteList = NewList()
 		i.autocompleteList.
+			SetChangedFunc(i.autocompleteChanged).
 			ShowSecondaryText(false).
 			SetMainTextColor(i.autocompleteListTextColor).
 			SetSelectedTextColor(i.autocompleteListSelectedTextColor).
@@ -443,6 +458,16 @@ func (i *InputField) Autocomplete() *InputField {
 	return i
 }
 
+// autocompleteChanged gets called when another item in the
+// autocomplete list has been selected.
+func (i *InputField) autocompleteChanged(_ int, item *ListItem) {
+	if referenceVal, isString := item.reference.(string); isString {
+		i.autocompleteListSuggestion = referenceVal[len(i.text):]
+	} else {
+		i.autocompleteListSuggestion = item.mainText[len(i.text):]
+	}
+}
+
 // SetAcceptanceFunc sets a handler which may reject the last character that was
 // entered (by returning false).
 //
@@ -554,9 +579,11 @@ func (i *InputField) Draw(screen tcell.Screen) {
 		if i.maskCharacter > 0 {
 			text = strings.Repeat(string(i.maskCharacter), utf8.RuneCountInString(i.text))
 		}
+		drawnText := ""
 		if fieldWidth >= stringWidth(text) {
 			// We have enough space for the full text.
-			Print(screen, Escape(text), x, y, fieldWidth, AlignLeft, fieldTextColor)
+			drawnText = Escape(text)
+			Print(screen, drawnText, x, y, fieldWidth, AlignLeft, fieldTextColor)
 			i.offset = 0
 			iterateString(text, func(main rune, comb []rune, textPos, textWidth, screenPos, screenWidth int) bool {
 				if textPos >= i.cursorPos {
@@ -594,7 +621,12 @@ func (i *InputField) Draw(screen tcell.Screen) {
 				}
 				return false
 			})
-			Print(screen, Escape(text[i.offset:]), x, y, fieldWidth, AlignLeft, fieldTextColor)
+			drawnText = Escape(text[i.offset:])
+			Print(screen, drawnText, x, y, fieldWidth, AlignLeft, fieldTextColor)
+		}
+		// Draw suggestion
+		if i.maskCharacter == 0 && i.autocompleteListSuggestion != "" {
+			Print(screen, i.autocompleteListSuggestion, x+stringWidth(drawnText), y, fieldWidth-stringWidth(drawnText), AlignLeft, i.autocompleteSuggestionTextColor)
 		}
 	}
 
@@ -767,14 +799,31 @@ func (i *InputField) InputHandler() func(event *tcell.EventKey, setFocus func(p
 			home()
 		case tcell.KeyEnd, tcell.KeyCtrlE:
 			end()
-		case tcell.KeyEnter, tcell.KeyEscape: // We might be done.
+		case tcell.KeyEnter: // We might be done.
 			if i.autocompleteList != nil {
-				i.autocompleteList = nil
+				currentItem := i.autocompleteList.GetCurrentItem()
 				i.Unlock()
+				if referenceVal, isString := currentItem.reference.(string); isString {
+					i.SetText(referenceVal)
+				} else {
+					i.SetText(currentItem.mainText)
+				}
+				i.Lock()
+				i.autocompleteList = nil
+				i.autocompleteListSuggestion = ""
 			} else {
-				i.Unlock()
 				finish(key)
 			}
+			i.Unlock()
+			return
+		case tcell.KeyEscape:
+			if i.autocompleteList != nil {
+				i.autocompleteList = nil
+				i.autocompleteListSuggestion = ""
+			} else {
+				finish(key)
+			}
+			i.Unlock()
 			return
 		case tcell.KeyDown, tcell.KeyTab: // Autocomplete selection.
 			if i.autocompleteList != nil {
@@ -784,9 +833,7 @@ func (i *InputField) InputHandler() func(event *tcell.EventKey, setFocus func(p
 					newEntry = 0
 				}
 				i.autocompleteList.SetCurrentItem(newEntry)
-				currentText, _ = i.autocompleteList.GetItemText(newEntry) // Don't trigger changed function twice.
 				i.Unlock()
-				i.SetText(currentText)
 			} else {
 				i.Unlock()
 				finish(key)
@@ -799,9 +846,7 @@ func (i *InputField) InputHandler() func(event *tcell.EventKey, setFocus func(p
 					newEntry = i.autocompleteList.GetItemCount() - 1
 				}
 				i.autocompleteList.SetCurrentItem(newEntry)
-				currentText, _ = i.autocompleteList.GetItemText(newEntry) // Don't trigger changed function twice.
 				i.Unlock()
-				i.SetText(currentText)
 			} else {
 				i.Unlock()
 				finish(key)

styles.go

@@ -14,6 +14,7 @@ type Theme struct {
 	SecondaryTextColor         tcell.Color // Secondary text (e.g. labels).
 	TertiaryTextColor          tcell.Color // Tertiary text (e.g. subtitles, notes).
 	InverseTextColor           tcell.Color // Text on primary-colored backgrounds.
+	ContrastPrimaryTextColor   tcell.Color // Primary text for contrasting elements.
 	ContrastSecondaryTextColor tcell.Color // Secondary text on ContrastBackgroundColor-colored backgrounds.
 
 	// Background
@@ -46,6 +47,7 @@ var Styles = Theme{
 	SecondaryTextColor:         tcell.ColorYellow.TrueColor(),
 	TertiaryTextColor:          tcell.ColorGreen.TrueColor(),
 	InverseTextColor:           tcell.ColorBlue.TrueColor(),
+	ContrastPrimaryTextColor:   tcell.ColorBlack.TrueColor(),
 	ContrastSecondaryTextColor: tcell.ColorDarkCyan.TrueColor(),
 
 	PrimitiveBackgroundColor:    tcell.ColorBlack.TrueColor(),