Add undo/redo stack

buffer.go

@@ -65,9 +65,12 @@ func (b *Buffer) Insert(idx int, value string) {
 }
 
 // Remove a slice of the rope from start to end (exclusive)
-func (b *Buffer) Remove(start, end int) {
+// Returns the string that was removed
+func (b *Buffer) Remove(start, end int) string {
+	removed := b.text[start:end]
 	b.r.Remove(start, end)
 	b.Update()
+	return removed
 }
 
 // Len gives the length of the buffer

cursor.go

@@ -42,10 +42,10 @@ func (c *Cursor) HasSelection() bool {
 // DeleteSelected deletes the currently selected text
 func (c *Cursor) DeleteSelected() {
 	if c.selectionStart > c.selectionEnd {
-		c.v.buf.Remove(c.selectionEnd, c.selectionStart+1)
+		c.v.eh.Remove(c.selectionEnd, c.selectionStart+1)
 		// Since the cursor is already at the selection start we don't need to move
 	} else {
-		c.v.buf.Remove(c.selectionStart, c.selectionEnd+1)
+		c.v.eh.Remove(c.selectionStart, c.selectionEnd+1)
 		c.loc -= c.selectionEnd - c.selectionStart
 		c.x = c.selectionStartX
 		c.y = c.selectionStartY

eventhandler.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"time"
+)
+
+const (
+	// TextEventInsert repreasents an insertion event
+	TextEventInsert = 1
+	// TextEventRemove represents a deletion event
+	TextEventRemove = -1
+)
+
+// TextEvent holds data for a manipulation on some text that can be undone
+type TextEvent struct {
+	c Cursor
+
+	eventType int
+	text      string
+	start     int
+	end       int
+	buf       *Buffer
+	time      time.Time
+}
+
+// ExecuteTextEvent runs a text event
+func ExecuteTextEvent(t *TextEvent) {
+	if t.eventType == TextEventInsert {
+		t.buf.Insert(t.start, t.text)
+	} else if t.eventType == TextEventRemove {
+		t.text = t.buf.Remove(t.start, t.end)
+	}
+}
+
+// UndoTextEvent undoes a text event
+func UndoTextEvent(t *TextEvent) {
+	t.eventType = -t.eventType
+	ExecuteTextEvent(t)
+}
+
+// EventHandler executes text manipulations and allows undoing and redoing
+type EventHandler struct {
+	v    *View
+	undo *Stack
+	redo *Stack
+}
+
+// NewEventHandler returns a new EventHandler
+func NewEventHandler(v *View) *EventHandler {
+	eh := new(EventHandler)
+	eh.undo = new(Stack)
+	eh.redo = new(Stack)
+	eh.v = v
+	return eh
+}
+
+// Insert creates an insert text event and executes it
+func (eh *EventHandler) Insert(start int, text string) {
+	e := &TextEvent{
+		c:         eh.v.cursor,
+		eventType: TextEventInsert,
+		text:      text,
+		start:     start,
+		end:       start + len(text),
+		buf:       eh.v.buf,
+		time:      time.Now(),
+	}
+	eh.Execute(e)
+}
+
+// Remove creates a remove text event and executes it
+func (eh *EventHandler) Remove(start, end int) {
+	e := &TextEvent{
+		c:         eh.v.cursor,
+		eventType: TextEventRemove,
+		start:     start,
+		end:       end,
+		buf:       eh.v.buf,
+		time:      time.Now(),
+	}
+	eh.Execute(e)
+}
+
+// Execute a textevent and add it to the undo stack
+func (eh *EventHandler) Execute(t *TextEvent) {
+	eh.undo.Push(t)
+	ExecuteTextEvent(t)
+}
+
+// Undo the first event in the undo stack
+func (eh *EventHandler) Undo() {
+	t := eh.undo.Pop()
+	if t == nil {
+		return
+	}
+
+	te := t.(*TextEvent)
+	// Modifies the text event
+	UndoTextEvent(te)
+	eh.redo.Push(t)
+
+	eh.v.cursor = te.c
+}
+
+// Redo the first event in the redo stack
+func (eh *EventHandler) Redo() {
+	t := eh.redo.Pop()
+	if t == nil {
+		return
+	}
+
+	te := t.(*TextEvent)
+	// Modifies the text event
+	UndoTextEvent(te)
+	eh.undo.Push(t)
+	eh.v.cursor = te.c
+}

stack.go

@@ -0,0 +1,43 @@
+package main
+
+// Stack is a simple implementation of a LIFO stack
+type Stack struct {
+	top  *Element
+	size int
+}
+
+// An Element which is stored in the Stack
+type Element struct {
+	value interface{} // All types satisfy the empty interface, so we can store anything here.
+	next  *Element
+}
+
+// Len returns the stack's length
+func (s *Stack) Len() int {
+	return s.size
+}
+
+// Push a new element onto the stack
+func (s *Stack) Push(value interface{}) {
+	s.top = &Element{value, s.top}
+	s.size++
+}
+
+// Pop removes the top element from the stack and returns its value
+// If the stack is empty, return nil
+func (s *Stack) Pop() (value interface{}) {
+	if s.size > 0 {
+		value, s.top = s.top.value, s.top.next
+		s.size--
+		return
+	}
+	return nil
+}
+
+// Peek lets you see and edit the top value of the stack without popping it
+func (s *Stack) Peek() *interface{} {
+	if s.size > 0 {
+		return &s.top.value
+	}
+	return nil
+}

todolist.md

@@ -22,7 +22,7 @@
     - [ ] Opened with Ctrl-h
 
 - [ ] Undo/redo
-    - [ ] Undo/redo stack
+    - [x] Undo/redo stack
     - [ ] Functionality similar to nano
 
 - [ ] Command execution

view.go

@@ -15,6 +15,8 @@ type View struct {
 	width         int
 	lineNumOffset int
 
+	eh *EventHandler
+
 	buf *Buffer
 	sl  Statusline
 
@@ -46,6 +48,8 @@ func NewViewWidthHeight(buf *Buffer, s tcell.Screen, w, h int) *View {
 		v:   v,
 	}
 
+	v.eh = NewEventHandler(v)
+
 	v.sl = Statusline{
 		v: v,
 	}
@@ -132,11 +136,11 @@ func (v *View) HandleEvent(event tcell.Event) int {
 			v.cursor.Right()
 			ret = 1
 		case tcell.KeyEnter:
-			v.buf.Insert(v.cursor.loc, "\n")
+			v.eh.Insert(v.cursor.loc, "\n")
 			v.cursor.Right()
 			ret = 2
 		case tcell.KeySpace:
-			v.buf.Insert(v.cursor.loc, " ")
+			v.eh.Insert(v.cursor.loc, " ")
 			v.cursor.Right()
 			ret = 2
 		case tcell.KeyBackspace2:
@@ -145,12 +149,20 @@ func (v *View) HandleEvent(event tcell.Event) int {
 				v.cursor.ResetSelection()
 				ret = 2
 			} else if v.cursor.loc > 0 {
+				// We have to do something a bit hacky here because we want to
+				// delete the line by first moving left and then deleting backwards
+				// but the undo redo would place the cursor in the wrong place
+				// So instead we move left, save the position, move back, delete
+				// and restore the position
 				v.cursor.Left()
-				v.buf.Remove(v.cursor.loc, v.cursor.loc+1)
+				cx, cy, cloc := v.cursor.x, v.cursor.y, v.cursor.loc
+				v.cursor.Right()
+				v.eh.Remove(v.cursor.loc-1, v.cursor.loc)
+				v.cursor.x, v.cursor.y, v.cursor.loc = cx, cy, cloc
 				ret = 2
 			}
 		case tcell.KeyTab:
-			v.buf.Insert(v.cursor.loc, "\t")
+			v.eh.Insert(v.cursor.loc, "\t")
 			v.cursor.Right()
 			ret = 2
 		case tcell.KeyCtrlS:
@@ -160,6 +172,12 @@ func (v *View) HandleEvent(event tcell.Event) int {
 			}
 			// Need to redraw the status line
 			ret = 1
+		case tcell.KeyCtrlZ:
+			v.eh.Undo()
+			ret = 2
+		case tcell.KeyCtrlY:
+			v.eh.Redo()
+			ret = 2
 		case tcell.KeyPgUp:
 			v.PageUp()
 			return 2
@@ -177,7 +195,7 @@ func (v *View) HandleEvent(event tcell.Event) int {
 				v.cursor.DeleteSelected()
 				v.cursor.ResetSelection()
 			}
-			v.buf.Insert(v.cursor.loc, string(e.Rune()))
+			v.eh.Insert(v.cursor.loc, string(e.Rune()))
 			v.cursor.Right()
 			ret = 2
 		}