From 9909356eb749b3ba71c4c1c5bc0951a8cc32e81a Mon Sep 17 00:00:00 2001
From: Christian Rocha <christian@rocha.is>
Date: Sat, 18 Jan 2020 00:10:03 -0500
Subject: [PATCH] Left/right arrows move the text input cursor

---
 input/input.go | 64 +++++++++++++++++++++++++++++++++++++-------------
 tea.go         |  5 ++++
 2 files changed, 53 insertions(+), 16 deletions(-)

diff --git a/input/input.go b/input/input.go
index 07f5b48..09f735a 100644
--- a/input/input.go
+++ b/input/input.go
@@ -10,20 +10,22 @@ type Model struct {
 	Value        string
 	Cursor       string
 	HiddenCursor string
-	Blink        bool
 	BlinkSpeed   time.Duration
+
+	blink bool
+	pos   int
 }
 
 type CursorBlinkMsg struct{}
 
 func DefaultModel() Model {
 	return Model{
-		Prompt:       "> ",
-		Value:        "",
-		Cursor:       "█",
-		HiddenCursor: " ",
-		Blink:        false,
-		BlinkSpeed:   time.Second,
+		Prompt:     "> ",
+		Value:      "",
+		BlinkSpeed: time.Millisecond * 600,
+
+		blink: false,
+		pos:   0,
 	}
 }
 
@@ -34,28 +36,58 @@ func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
 		switch msg.Type {
 		case tea.KeyBackspace:
 			if len(m.Value) > 0 {
-				m.Value = m.Value[:len(m.Value)-1]
+				m.Value = m.Value[:m.pos-1] + m.Value[m.pos:]
+				m.pos--
 			}
+			return m, nil
+		case tea.KeyLeft:
+			if m.pos > 0 {
+				m.pos--
+			}
+			return m, nil
+		case tea.KeyRight:
+			if m.pos < len(m.Value) {
+				m.pos++
+			}
+			return m, nil
 		case tea.KeyRune:
-			m.Value = m.Value + msg.String()
+			m.Value = m.Value[:m.pos] + msg.String() + m.Value[m.pos:]
+			m.pos++
+			return m, nil
+		default:
+			return m, nil
 		}
 
 	case CursorBlinkMsg:
-		m.Blink = !m.Blink
-	}
+		m.blink = !m.blink
+		return m, nil
 
-	return m, nil
+	default:
+		return m, nil
+	}
 }
 
 func View(model tea.Model) string {
 	m, _ := model.(Model)
-	cursor := m.Cursor
-	if m.Blink {
-		cursor = m.HiddenCursor
+	v := m.Value[:m.pos]
+	if m.pos < len(m.Value) {
+		v += cursor(string(m.Value[m.pos]), m.blink)
+		v += m.Value[m.pos+1:]
+	} else {
+		v += cursor(" ", m.blink)
 	}
-	return m.Prompt + m.Value + cursor
+	return m.Prompt + v
 }
 
+// Style the cursor
+func cursor(s string, blink bool) string {
+	if blink {
+		return s
+	}
+	return tea.Invert(s)
+}
+
+// Subscription
 func Blink(model tea.Model) tea.Msg {
 	m, _ := model.(Model)
 	time.Sleep(m.BlinkSpeed)
diff --git a/tea.go b/tea.go
index a31acff..326c5a7 100644
--- a/tea.go
+++ b/tea.go
@@ -213,6 +213,11 @@ func ClearScreen() {
 	fmt.Printf(esc + "2J" + esc + "3J" + esc + "1;1H")
 }
 
+// Invert inverts the foreground and background colors of a given string
+func Invert(s string) string {
+	return esc + "7m" + s + esc + "0m"
+}
+
 // UseSysLog logs to the system log. This becomes helpful when debugging since
 // we can't easily print to the terminal since our TUI is occupying it!
 //