Support suggestions and autocompletion in textinput (#407)

* migrate all autocomplete-work from old branch

* added support for multiple suggestions

* fix linter issues

* refactored to only offer matching suggestions for completion

* fix: SetSuggestions + Suggestions

* make: configuration behaviour configurable

* fix for double-width runes

* refactored all suggestions to be rune-arrays

also: accepting suggestions does not overwrite the already given input, rather appends

* fix: make suggestions and OnAcceptSuggestions unexported

* refactor: refreshingMatchingSuggestions -> updateSuggestions

---------

Co-authored-by: Maas Lalani <maas@lalani.dev>

textinput/textinput.go

@@ -1,6 +1,7 @@
 package textinput
 
 import (
+	"reflect"
 	"strings"
 	"time"
 	"unicode"
@@ -32,8 +33,6 @@ const (
 	// EchoNone displays nothing as characters are entered. This is commonly
 	// seen for password fields on the command line.
 	EchoNone
-
-	// EchoOnEdit.
 )
 
 // ValidateFunc is a function that returns an error if the input is invalid.
@@ -54,6 +53,9 @@ type KeyMap struct {
 	LineStart               key.Binding
 	LineEnd                 key.Binding
 	Paste                   key.Binding
+	AcceptSuggestion        key.Binding
+	NextSuggestion          key.Binding
+	PrevSuggestion          key.Binding
 }
 
 // DefaultKeyMap is the default set of key bindings for navigating and acting
@@ -72,6 +74,9 @@ var DefaultKeyMap = KeyMap{
 	LineStart:               key.NewBinding(key.WithKeys("home", "ctrl+a")),
 	LineEnd:                 key.NewBinding(key.WithKeys("end", "ctrl+e")),
 	Paste:                   key.NewBinding(key.WithKeys("ctrl+v")),
+	AcceptSuggestion:        key.NewBinding(key.WithKeys("tab")),
+	NextSuggestion:          key.NewBinding(key.WithKeys("down", "ctrl+n")),
+	PrevSuggestion:          key.NewBinding(key.WithKeys("up", "ctrl+p")),
 }
 
 // Model is the Bubble Tea model for this text input element.
@@ -95,6 +100,7 @@ type Model struct {
 	PromptStyle      lipgloss.Style
 	TextStyle        lipgloss.Style
 	PlaceholderStyle lipgloss.Style
+	CompletionStyle  lipgloss.Style
 
 	// Deprecated: use Cursor.Style instead.
 	CursorStyle lipgloss.Style
@@ -134,6 +140,15 @@ type Model struct {
 
 	// rune sanitizer for input.
 	rsan runeutil.Sanitizer
+
+	// Should the input suggest to complete
+	ShowSuggestions bool
+
+	// suggestions is a list of suggestions that may be used to complete the
+	// input.
+	suggestions            [][]rune
+	matchedSuggestions     [][]rune
+	currentSuggestionIndex int
 }
 
 // New creates a new model with default settings.
@@ -143,12 +158,15 @@ func New() Model {
 		EchoCharacter:    '*',
 		CharLimit:        0,
 		PlaceholderStyle: lipgloss.NewStyle().Foreground(lipgloss.Color("240")),
+		ShowSuggestions:  false,
+		CompletionStyle:  lipgloss.NewStyle().Foreground(lipgloss.Color("240")),
 		Cursor:           cursor.New(),
 		KeyMap:           DefaultKeyMap,
 
-		value: nil,
-		focus: false,
-		pos:   0,
+		suggestions: [][]rune{},
+		value:       nil,
+		focus:       false,
+		pos:         0,
 	}
 }
 
@@ -239,6 +257,17 @@ func (m *Model) Reset() {
 	m.SetCursor(0)
 }
 
+// SetSuggestions sets the suggestions for the input.
+func (m *Model) SetSuggestions(suggestions []string) {
+	m.suggestions = [][]rune{}
+
+	for _, s := range suggestions {
+		m.suggestions = append(m.suggestions, []rune(s))
+	}
+
+	m.updateSuggestions()
+}
+
 // rsan initializes or retrieves the rune sanitizer.
 func (m *Model) san() runeutil.Sanitizer {
 	if m.rsan == nil {
@@ -529,6 +558,15 @@ func (m Model) Update(msg tea.Msg) (Model, tea.Cmd) {
 		return m, nil
 	}
 
+	// Need to check for completion before, because key is configurable and might be double assigned
+	keyMsg, ok := msg.(tea.KeyMsg)
+	if ok && key.Matches(keyMsg, m.KeyMap.AcceptSuggestion) {
+		if m.canAcceptSuggestion() {
+			m.value = append(m.value, m.matchedSuggestions[m.currentSuggestionIndex][len(m.value):]...)
+			m.CursorEnd()
+		}
+	}
+
 	// Let's remember where the position of the cursor currently is so that if
 	// the cursor position changes, we can reset the blink.
 	oldPos := m.pos //nolint
@@ -577,11 +615,19 @@ func (m Model) Update(msg tea.Msg) (Model, tea.Cmd) {
 			return m, Paste
 		case key.Matches(msg, m.KeyMap.DeleteWordForward):
 			m.deleteWordForward()
+		case key.Matches(msg, m.KeyMap.NextSuggestion):
+			m.nextSuggestion()
+		case key.Matches(msg, m.KeyMap.PrevSuggestion):
+			m.previousSuggestion()
 		default:
 			// Input one or more regular characters.
 			m.insertRunesFromUserInput(msg.Runes)
 		}
 
+		// Check again if can be completed
+		// because value might be something that does not match the completion prefix
+		m.updateSuggestions()
+
 	case pasteMsg:
 		m.insertRunesFromUserInput([]rune(msg))
 
@@ -622,9 +668,23 @@ func (m Model) View() string {
 		m.Cursor.SetChar(char)
 		v += m.Cursor.View()                                   // cursor and text under it
 		v += styleText(m.echoTransform(string(value[pos+1:]))) // text after cursor
+		v += m.completionView(0)                               // suggested completion
 	} else {
-		m.Cursor.SetChar(" ")
-		v += m.Cursor.View()
+		if m.canAcceptSuggestion() {
+			suggestion := m.matchedSuggestions[m.currentSuggestionIndex]
+			if len(value) < len(suggestion) {
+				m.Cursor.TextStyle = m.CompletionStyle
+				m.Cursor.SetChar(m.echoTransform(string(suggestion[pos])))
+				v += m.Cursor.View()
+				v += m.completionView(1)
+			} else {
+				m.Cursor.SetChar(" ")
+				v += m.Cursor.View()
+			}
+		} else {
+			m.Cursor.SetChar(" ")
+			v += m.Cursor.View()
+		}
 	}
 
 	// If a max width and background color were set fill the empty spaces with
@@ -721,3 +781,81 @@ func (m Model) CursorMode() CursorMode {
 func (m *Model) SetCursorMode(mode CursorMode) tea.Cmd {
 	return m.Cursor.SetMode(cursor.Mode(mode))
 }
+
+func (m Model) completionView(offset int) string {
+	var (
+		value = m.value
+		style = m.PlaceholderStyle.Inline(true).Render
+	)
+
+	if m.canAcceptSuggestion() {
+		suggestion := m.matchedSuggestions[m.currentSuggestionIndex]
+		if len(value) < len(suggestion) {
+			return style(string(suggestion[len(value)+offset:]))
+		}
+	}
+	return ""
+}
+
+// AvailableSuggestions returns the list of available suggestions.
+func (m *Model) AvailableSuggestions() []string {
+	suggestions := []string{}
+	for _, s := range m.suggestions {
+		suggestions = append(suggestions, string(s))
+	}
+
+	return suggestions
+}
+
+// CurrentSuggestion returns the currently selected suggestion.
+func (m *Model) CurrentSuggestion() string {
+	return string(m.matchedSuggestions[m.currentSuggestionIndex])
+}
+
+// canAcceptSuggestion returns whether there is an acceptable suggestion to
+// autocomplete the current value.
+func (m *Model) canAcceptSuggestion() bool {
+	return len(m.matchedSuggestions) > 0
+}
+
+// updateSuggestions refreshes the list of matching suggestions.
+func (m *Model) updateSuggestions() {
+	if !m.ShowSuggestions {
+		return
+	}
+
+	if len(m.value) <= 0 || len(m.suggestions) <= 0 {
+		m.matchedSuggestions = [][]rune{}
+		return
+	}
+
+	matches := [][]rune{}
+	for _, s := range m.suggestions {
+		suggestion := string(s)
+
+		if strings.HasPrefix(strings.ToLower(suggestion), strings.ToLower(string(m.value))) {
+			matches = append(matches, []rune(suggestion))
+		}
+	}
+	if !reflect.DeepEqual(matches, m.matchedSuggestions) {
+		m.currentSuggestionIndex = 0
+	}
+
+	m.matchedSuggestions = matches
+}
+
+// nextSuggestion selects the next suggestion.
+func (m *Model) nextSuggestion() {
+	m.currentSuggestionIndex = (m.currentSuggestionIndex + 1)
+	if m.currentSuggestionIndex >= len(m.matchedSuggestions) {
+		m.currentSuggestionIndex = 0
+	}
+}
+
+// previousSuggestion selects the previous suggestion.
+func (m *Model) previousSuggestion() {
+	m.currentSuggestionIndex = (m.currentSuggestionIndex - 1)
+	if m.currentSuggestionIndex < 0 {
+		m.currentSuggestionIndex = len(m.matchedSuggestions) - 1
+	}
+}