Fix textarea scrolling past end of content

gui.go

@@ -327,8 +327,9 @@ func (g *Gui) SetView(name string, x0, y0, x1, y1 int, overlaps byte) (*View, er
 
 			if v.Editable {
 				cursorX, cursorY := v.TextArea.GetCursorXY()
-				newViewCursorX, newOriginX := updatedCursorAndOrigin(0, v.InnerWidth(), cursorX)
-				newViewCursorY, newOriginY := updatedCursorAndOrigin(0, v.InnerHeight(), cursorY)
+				contentX, contentY := v.TextArea.GetContentDimensions()
+				newViewCursorX, newOriginX := updatedCursorAndOrigin(0, v.InnerWidth(), cursorX, contentX)
+				newViewCursorY, newOriginY := updatedCursorAndOrigin(0, v.InnerHeight(), cursorY, contentY)
 
 				v.SetCursor(newViewCursorX, newViewCursorY)
 				v.SetOrigin(newOriginX, newOriginY)

text_area.go

@@ -36,6 +36,8 @@ type TextArea struct {
 	clipboard     string
 	AutoWrap      bool
 	AutoWrapWidth int
+	maxContentX   int // cached max x coordinate of content (rightmost position)
+	maxContentY   int // cached max y coordinate of content (line count - 1)
 }
 
 func stringToTextAreaCells(str string) []TextAreaCell {
@@ -248,6 +250,29 @@ func (self *TextArea) updateCells() {
 	}
 
 	self.cells, _ = contentToCells(self.content, width)
+	self.computeMaxDimensions()
+}
+
+func (self *TextArea) computeMaxDimensions() {
+	self.maxContentX = 0
+	self.maxContentY = 0
+	for _, cell := range self.cells {
+		if cell.y > self.maxContentY {
+			self.maxContentY = cell.y
+		}
+		rightEdge := cell.x + cell.width
+		if rightEdge > self.maxContentX {
+			self.maxContentX = rightEdge
+		}
+	}
+	// If content ends with a newline, there's a blank line after it
+	if len(self.cells) > 0 && self.cells[len(self.cells)-1].char == "\n" {
+		self.maxContentY++
+	}
+}
+
+func (self *TextArea) GetContentDimensions() (int, int) {
+	return self.maxContentX, self.maxContentY
 }
 
 func (self *TextArea) typeCharacter(ch string) {

view.go

@@ -1730,15 +1730,16 @@ func (v *View) RenderTextArea() {
 	cursorX, cursorY := v.TextArea.GetCursorXY()
 	prevOriginX, prevOriginY := v.Origin()
 	width, height := v.InnerWidth(), v.InnerHeight()
+	contentX, contentY := v.TextArea.GetContentDimensions()
 
-	newViewCursorX, newOriginX := updatedCursorAndOrigin(prevOriginX, width, cursorX)
-	newViewCursorY, newOriginY := updatedCursorAndOrigin(prevOriginY, height, cursorY)
+	newViewCursorX, newOriginX := updatedCursorAndOrigin(prevOriginX, width, cursorX, contentX)
+	newViewCursorY, newOriginY := updatedCursorAndOrigin(prevOriginY, height, cursorY, contentY)
 
 	v.SetCursor(newViewCursorX, newViewCursorY)
 	v.SetOrigin(newOriginX, newOriginY)
 }
 
-func updatedCursorAndOrigin(prevOrigin int, size int, cursor int) (int, int) {
+func updatedCursorAndOrigin(prevOrigin int, size int, cursor int, contentLen int) (int, int) {
 	var newViewCursor int
 	newOrigin := prevOrigin
 	usableSize := size - 1
@@ -1753,6 +1754,15 @@ func updatedCursorAndOrigin(prevOrigin int, size int, cursor int) (int, int) {
 		newViewCursor = cursor - prevOrigin
 	}
 
+	// Prevent scrolling past the end of content
+	maxOrigin := contentLen - usableSize
+	if maxOrigin < 0 {
+		maxOrigin = 0
+	}
+	if newOrigin > maxOrigin {
+		newOrigin = maxOrigin
+	}
+
 	return newViewCursor, newOrigin
 }
 

view_test.go

@@ -101,22 +101,40 @@ func TestUpdatedCursorAndOrigin(t *testing.T) {
 		prevOrigin     int
 		size           int
 		cursor         int
+		contentLen     int
 		expectedCursor int
 		expectedOrigin int
 	}{
-		{0, 10, 0, 0, 0},
-		{0, 10, 9, 9, 0},
-		{0, 10, 10, 9, 1},
-		{0, 10, 19, 9, 10},
-		{0, 10, 20, 9, 11},
-		{20, 10, 19, 0, 19},
-		{20, 10, 25, 5, 20},
+		// Original test cases with very long content (100 chars)
+		{0, 10, 0, 100, 0, 0},
+		{0, 10, 9, 100, 9, 0},
+		{0, 10, 10, 100, 9, 1},
+		{0, 10, 19, 100, 9, 10},
+		{0, 10, 20, 100, 9, 11},
+		{20, 10, 19, 100, 0, 19},
+		{20, 10, 25, 100, 5, 20},
+		// content shorter than view should clamp origin to 0
+		{5, 10, 5, 8, 0, 0},
+		// content equal to usable size should allow origin at most 0
+		{0, 10, 8, 9, 8, 0},
+		// content just longer than usable size (10 content, size 10, usableSize 9)
+		{0, 10, 9, 10, 9, 0},  // cursor at last char, should be visible at origin 0
+		{0, 10, 10, 10, 9, 1}, // cursor past end gets clamped, but so does origin to max 1
+		{1, 10, 8, 10, 7, 1},  // already scrolled, cursor moves left
+		{1, 10, 9, 10, 8, 1},  // cursor at last position of content, origin stays at 1
+		// content exactly fits after some scrolling
+		{5, 10, 5, 14, 0, 5}, // contentLen=14, usableSize=9, maxOrigin=5, cursor at origin
+		{5, 10, 9, 14, 4, 5}, // contentLen=14, cursor at 9, can show 5-13, origin stays at 5
+		// cursor at end of just-longer content should show last chars
+		{0, 10, 20, 20, 9, 11}, // contentLen=20, cursor at 20, maxOrigin=11, shows 11-19
+		// scrolled past middle, content shrinks, should clamp origin
+		{7, 10, 5, 15, 0, 5}, // was scrolled to 7, but contentLen=15 allows maxOrigin=6, cursor at 5 means origin=5
 	}
 
 	for _, test := range tests {
-		cursor, origin := updatedCursorAndOrigin(test.prevOrigin, test.size, test.cursor)
+		cursor, origin := updatedCursorAndOrigin(test.prevOrigin, test.size, test.cursor, test.contentLen)
 		assert.EqualValues(t, test.expectedCursor, cursor, "Cursor is wrong")
-		assert.EqualValues(t, test.expectedOrigin, origin, "Origin in wrong")
+		assert.EqualValues(t, test.expectedOrigin, origin, "Origin is wrong")
 	}
 }