Fix adjustMergeCellsHelper and add some test cases (#1082)

Signed-off-by: Dokiys <dokiychang@gmail.com>

1 files changed, 30 insertions, 12 deletions

diff --git a/adjust.go b/adjust.go
index 9f2176f..243c774 100644
--- a/adjust.go
+++ b/adjust.go
@@ -208,20 +208,23 @@ func (f *File) adjustMergeCells(ws *xlsxWorksheet, dir adjustDirection, num, off
 			if y1 == num && y2 == num && offset < 0 {
 				f.deleteMergeCell(ws, i)
 				i--
+				continue
 			}
-			y1 = f.adjustMergeCellsHelper(y1, num, offset)
-			y2 = f.adjustMergeCellsHelper(y2, num, offset)
+
+			y1, y2 = f.adjustMergeCellsHelper(y1, y2, num, offset)
 		} else {
 			if x1 == num && x2 == num && offset < 0 {
 				f.deleteMergeCell(ws, i)
 				i--
+				continue
 			}
-			x1 = f.adjustMergeCellsHelper(x1, num, offset)
-			x2 = f.adjustMergeCellsHelper(x2, num, offset)
+
+			x1, x2 = f.adjustMergeCellsHelper(x1, x2, num, offset)
 		}
-		if x1 == x2 && y1 == y2 && i >= 0 {
+		if x1 == x2 && y1 == y2 {
 			f.deleteMergeCell(ws, i)
 			i--
+			continue
 		}
 		if areaData.Ref, err = f.coordinatesToAreaRef([]int{x1, y1, x2, y2}); err != nil {
 			return err
@@ -233,19 +236,34 @@ func (f *File) adjustMergeCells(ws *xlsxWorksheet, dir adjustDirection, num, off
 // adjustMergeCellsHelper provides a function for adjusting merge cells to
 // compare and calculate cell axis by the given pivot, operation axis and
 // offset.
-func (f *File) adjustMergeCellsHelper(pivot, num, offset int) int {
-	if pivot > num {
-		pivot += offset
-		if pivot < 1 {
-			return 1
+func (f *File) adjustMergeCellsHelper(p1, p2, num, offset int) (int, int) {
+	if p2 < p1 {
+		p1, p2 = p2, p1
+	}
+
+	if offset >= 0 {
+		if num <= p1 {
+			p1 += offset
+			p2 += offset
+		} else if num <= p2 {
+			p2 += offset
 		}
-		return pivot
+		return p1, p2
+	}
+	if num < p1 || (num == p1 && num == p2) {
+		p1 += offset
+		p2 += offset
+	} else if num <= p2 {
+		p2 += offset
 	}
-	return pivot
+	return p1, p2
 }
 
 // deleteMergeCell provides a function to delete merged cell by given index.
 func (f *File) deleteMergeCell(ws *xlsxWorksheet, idx int) {
+	if idx < 0 {
+		return
+	}
 	if len(ws.MergeCells.Cells) > idx {
 		ws.MergeCells.Cells = append(ws.MergeCells.Cells[:idx], ws.MergeCells.Cells[idx+1:]...)
 		ws.MergeCells.Count = len(ws.MergeCells.Cells)