fix lbl scrolling

pkg/gui/lbl/focus.go

@@ -0,0 +1,52 @@
+package lbl
+
+import "github.com/jesseduffield/lazygit/pkg/utils"
+
+func calculateOrigin(currentOrigin int, bufferHeight int, firstLineIdx int, lastLineIdx int, selectedLineIdx int, mode selectMode) int {
+	needToSeeIdx, wantToSeeIdx := getNeedAndWantLineIdx(firstLineIdx, lastLineIdx, selectedLineIdx, mode)
+
+	return calculateNewOriginWithNeededAndWantedIdx(currentOrigin, bufferHeight, needToSeeIdx, wantToSeeIdx)
+}
+
+// we want to scroll our origin so that the index we need to see is in view
+// and the other index we want to see (e.g. the other side of a line range)
+// is in as close to being in view as possible.
+func calculateNewOriginWithNeededAndWantedIdx(currentOrigin int, bufferHeight int, needToSeeIdx int, wantToSeeIdx int) int {
+	origin := currentOrigin
+	if needToSeeIdx < currentOrigin {
+		origin = needToSeeIdx
+	} else if needToSeeIdx > currentOrigin+bufferHeight {
+		origin = needToSeeIdx - bufferHeight
+	}
+
+	bottom := origin + bufferHeight
+
+	if wantToSeeIdx < origin {
+		requiredChange := origin - wantToSeeIdx
+		allowedChange := bottom - needToSeeIdx
+		return origin - utils.Min(requiredChange, allowedChange)
+	} else if wantToSeeIdx > origin+bufferHeight {
+		requiredChange := wantToSeeIdx - bottom
+		allowedChange := needToSeeIdx - origin
+		return origin + utils.Min(requiredChange, allowedChange)
+	} else {
+		return origin
+	}
+}
+
+func getNeedAndWantLineIdx(firstLineIdx int, lastLineIdx int, selectedLineIdx int, mode selectMode) (int, int) {
+	switch mode {
+	case LINE:
+		return selectedLineIdx, selectedLineIdx
+	case RANGE:
+		if selectedLineIdx == firstLineIdx {
+			return firstLineIdx, lastLineIdx
+		} else {
+			return lastLineIdx, firstLineIdx
+		}
+	case HUNK:
+		return firstLineIdx, lastLineIdx
+	default:
+		panic("unknown mode")
+	}
+}

pkg/gui/lbl/focus_test.go

@@ -0,0 +1,100 @@
+package lbl
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewOrigin(t *testing.T) {
+	type scenario struct {
+		name            string
+		origin          int
+		bufferHeight    int
+		firstLineIdx    int
+		lastLineIdx     int
+		selectedLineIdx int
+		selectMode      selectMode
+		expected        int
+	}
+
+	scenarios := []scenario{
+		{
+			name:            "selection above scroll window",
+			origin:          50,
+			bufferHeight:    100,
+			firstLineIdx:    10,
+			lastLineIdx:     10,
+			selectedLineIdx: 10,
+			selectMode:      LINE,
+			expected:        10,
+		},
+		{
+			name:            "selection below scroll window",
+			origin:          0,
+			bufferHeight:    100,
+			firstLineIdx:    150,
+			lastLineIdx:     150,
+			selectedLineIdx: 150,
+			selectMode:      LINE,
+			expected:        50,
+		},
+		{
+			name:            "selection within scroll window",
+			origin:          0,
+			bufferHeight:    100,
+			firstLineIdx:    50,
+			lastLineIdx:     50,
+			selectedLineIdx: 50,
+			selectMode:      LINE,
+			expected:        0,
+		},
+		{
+			name:            "range ending below scroll window with selection at end of range",
+			origin:          0,
+			bufferHeight:    100,
+			firstLineIdx:    40,
+			lastLineIdx:     150,
+			selectedLineIdx: 150,
+			selectMode:      RANGE,
+			expected:        50,
+		},
+		{
+			name:            "range ending below scroll window with selection at beginning of range",
+			origin:          0,
+			bufferHeight:    100,
+			firstLineIdx:    40,
+			lastLineIdx:     150,
+			selectedLineIdx: 40,
+			selectMode:      RANGE,
+			expected:        40,
+		},
+		{
+			name:            "range starting above scroll window with selection at beginning of range",
+			origin:          50,
+			bufferHeight:    100,
+			firstLineIdx:    40,
+			lastLineIdx:     150,
+			selectedLineIdx: 40,
+			selectMode:      RANGE,
+			expected:        40,
+		},
+		{
+			name:            "hunk extending beyond both bounds of scroll window",
+			origin:          50,
+			bufferHeight:    100,
+			firstLineIdx:    40,
+			lastLineIdx:     200,
+			selectedLineIdx: 70,
+			selectMode:      HUNK,
+			expected:        40,
+		},
+	}
+
+	for _, s := range scenarios {
+		s := s
+		t.Run(s.name, func(t *testing.T) {
+			assert.EqualValues(t, s.expected, calculateOrigin(s.origin, s.bufferHeight, s.firstLineIdx, s.lastLineIdx, s.selectedLineIdx, s.selectMode))
+		})
+	}
+}

pkg/gui/lbl/state.go

@@ -189,3 +189,9 @@ func (s *State) SelectTop() {
 	s.SetLineSelectMode()
 	s.SelectLine(0)
 }
+
+func (s *State) CalculateOrigin(currentOrigin int, bufferHeight int) int {
+	firstLineIdx, lastLineIdx := s.SelectedRange()
+
+	return calculateOrigin(currentOrigin, bufferHeight, firstLineIdx, lastLineIdx, s.GetSelectedLineIdx(), s.selectMode)
+}

pkg/gui/line_by_line_panel.go

@@ -155,25 +155,16 @@ func (gui *Gui) focusSelection(state *LblPanelState) error {
 	bufferHeight := viewHeight - 1
 	_, origin := stagingView.Origin()
 
-	firstLineIdx, lastLineIdx := state.SelectedRange()
+	selectedLineIdx := state.GetSelectedLineIdx()
 
-	margin := 0 // we may want to have a margin in place to show context  but right now I'm thinking we keep this at zero
-
-	var newOrigin int
-	if firstLineIdx-origin < margin {
-		newOrigin = firstLineIdx - margin
-	} else if lastLineIdx-origin > bufferHeight-margin {
-		newOrigin = lastLineIdx - bufferHeight + margin
-	} else {
-		newOrigin = origin
-	}
+	newOrigin := state.CalculateOrigin(origin, bufferHeight)
 
 	gui.g.Update(func(*gocui.Gui) error {
 		if err := stagingView.SetOrigin(0, newOrigin); err != nil {
 			return err
 		}
 
-		return stagingView.SetCursor(0, state.GetSelectedLineIdx()-newOrigin)
+		return stagingView.SetCursor(0, selectedLineIdx-newOrigin)
 	})
 
 	return nil