Huge refactorig for consistent col/row numbering (#356)

* Huge refactorig for consistent col/row numbering

Started from simply changing ToALphaString()/TitleToNumber() logic and related fixes.
But have to go deeper, do fixes, after do related fixes and again and again.

Major improvements:

1. Tests made stronger again (But still be weak).
2. "Empty" returns for incorrect input replaces with panic.
3. Check for correct col/row/cell naming & addressing by default.
4. Removed huge amount of duplicated code.
5. Removed ToALphaString(), TitleToNumber() and it helpers functions at all,
and replaced with SplitCellName(), JoinCellName(), ColumnNameToNumber(), ColumnNumberToName(), CellNameToCoordinates(), CoordinatesToCellName().
6. Minor fixes for internal variable naming for code readability (ex. col, row for input params, colIdx, rowIdx for slice indexes etc).

* Formatting fixes

1 files changed, 19 insertions, 16 deletions

diff --git a/picture.go b/picture.go
index 131b15c..f3463aa 100644
--- a/picture.go
+++ b/picture.go
@@ -143,7 +143,7 @@ func (f *File) AddPictureFromBytes(sheet, cell, format, name, extension string,
 	if err != nil {
 		return err
 	}
-	image, _, err := image.DecodeConfig(bytes.NewReader(file))
+	img, _, err := image.DecodeConfig(bytes.NewReader(file))
 	if err != nil {
 		return err
 	}
@@ -162,7 +162,7 @@ func (f *File) AddPictureFromBytes(sheet, cell, format, name, extension string,
 		}
 		drawingHyperlinkRID = f.addDrawingRelationships(drawingID, SourceRelationshipHyperLink, formatSet.Hyperlink, hyperlinkType)
 	}
-	f.addDrawingPicture(sheet, drawingXML, cell, name, image.Width, image.Height, drawingRID, drawingHyperlinkRID, formatSet)
+	f.addDrawingPicture(sheet, drawingXML, cell, name, img.Width, img.Height, drawingRID, drawingHyperlinkRID, formatSet)
 	f.addMedia(file, ext)
 	f.addContentTypePart(drawingID, "drawings")
 	return err
@@ -263,14 +263,11 @@ func (f *File) countDrawings() int {
 // drawingXML, cell, file name, width, height relationship index and format
 // sets.
 func (f *File) addDrawingPicture(sheet, drawingXML, cell, file string, width, height, rID, hyperlinkRID int, formatSet *formatPicture) {
-	cell = strings.ToUpper(cell)
-	fromCol := string(strings.Map(letterOnlyMapF, cell))
-	fromRow, _ := strconv.Atoi(strings.Map(intOnlyMapF, cell))
-	row := fromRow - 1
-	col := TitleToNumber(fromCol)
+	col, row := MustCellNameToCoordinates(cell)
 	width = int(float64(width) * formatSet.XScale)
 	height = int(float64(height) * formatSet.YScale)
-	colStart, rowStart, _, _, colEnd, rowEnd, x2, y2 := f.positionObjectPixels(sheet, col, row, formatSet.OffsetX, formatSet.OffsetY, width, height)
+	colStart, rowStart, _, _, colEnd, rowEnd, x2, y2 :=
+		f.positionObjectPixels(sheet, col, row, formatSet.OffsetX, formatSet.OffsetY, width, height)
 	content, cNvPrID := f.drawingParser(drawingXML)
 	twoCellAnchor := xdrCellAnchor{}
 	twoCellAnchor.EditAs = formatSet.Positioning
@@ -471,30 +468,36 @@ func (f *File) getSheetRelationshipsTargetByID(sheet, rID string) string {
 //    }
 //
 func (f *File) GetPicture(sheet, cell string) (string, []byte) {
+	col, row := MustCellNameToCoordinates(cell)
+
 	xlsx := f.workSheetReader(sheet)
 	if xlsx.Drawing == nil {
 		return "", []byte{}
 	}
+
 	target := f.getSheetRelationshipsTargetByID(sheet, xlsx.Drawing.RID)
 	drawingXML := strings.Replace(target, "..", "xl", -1)
-	cell = strings.ToUpper(cell)
-	fromCol := string(strings.Map(letterOnlyMapF, cell))
-	fromRow, _ := strconv.Atoi(strings.Map(intOnlyMapF, cell))
-	row := fromRow - 1
-	col := TitleToNumber(fromCol)
-	drawingRelationships := strings.Replace(strings.Replace(target, "../drawings", "xl/drawings/_rels", -1), ".xml", ".xml.rels", -1)
+
+	drawingRelationships := strings.Replace(
+		strings.Replace(target, "../drawings", "xl/drawings/_rels", -1), ".xml", ".xml.rels", -1)
+
 	wsDr, _ := f.drawingParser(drawingXML)
+
 	for _, anchor := range wsDr.TwoCellAnchor {
 		if anchor.From != nil && anchor.Pic != nil {
 			if anchor.From.Col == col && anchor.From.Row == row {
-				xlsxWorkbookRelation := f.getDrawingRelationships(drawingRelationships, anchor.Pic.BlipFill.Blip.Embed)
+				xlsxWorkbookRelation := f.getDrawingRelationships(drawingRelationships,
+					anchor.Pic.BlipFill.Blip.Embed)
 				_, ok := supportImageTypes[filepath.Ext(xlsxWorkbookRelation.Target)]
 				if ok {
-					return filepath.Base(xlsxWorkbookRelation.Target), []byte(f.XLSX[strings.Replace(xlsxWorkbookRelation.Target, "..", "xl", -1)])
+					return filepath.Base(xlsxWorkbookRelation.Target),
+						[]byte(f.XLSX[strings.Replace(xlsxWorkbookRelation.Target,
+							"..", "xl", -1)])
 				}
 			}
 		}
 	}
+
 	_, ok := f.XLSX[drawingXML]
 	if !ok {
 		return "", nil