[IMP] XLSX: Faulty default styles

Due to some mismatch between the style in the default exported construct
and the default values computed for a cell style, we were creating
useless style entries at export.

By setting a style index on a worksheet cell entry, our import code would
then apply this style to the cell even though that same cell, when
exported, had no style whatsoever.

Furthermore, we did not process Excel default color properly.
In Xlsx file, the color is sometimes set specifically to
"FF000000" in the style sheet. However, that color (black) is not
applied as a user-defined color in Excel (i.e. it's importance is lower
than the color applied by a table[^1]). Instead, a user-defined
"black" will be referred to via a theme property[^2].

Since we did not detect this "default color" pattern, we would consider
the attribute `rgb=FF000000` as a user-defined color an ultimately set
it in the plugin structure at import.

This revision detects the "default color" situation and discards the
given color to let the library (and specifically the CellPlugin as that
issue affects the cell font color in particular) use its own default
behaviour.

[^1]: To test this out:
      - Go to Excel and create a sheet on which you put
        a table.
      - Apply a style such that the text turns white
      - On the cells with white text, manually apply an italic format
      - Import the xlsx file inside o-spreadsheet
      ==> the text turned black in o-spreadsheet

[^2]: This situation seems to only concern that specific color and might
encompass a broader scope but I haven't been able to find proper
documentation about this.

closes #3799

Signed-off-by: Rémi Rahir (rar) <[email protected]>

src/xlsx/conversion/color_conversion.ts

@@ -86,3 +86,11 @@ export function hexaToInt(hex: Color) {
   }
   return parseInt(hex.replace("#", ""), 16);
 }
+
+/**
+ * When defining style (fontColor, borderColor for instance)
+ * Excel will specify rgb="FF000000"
+ * In that case, We should not consider this value as user-defined but
+ * rather like an instruction: "Use your system default"
+ */
+export const DEFAULT_SYSTEM_COLOR = "FF000000";

src/xlsx/extraction/base_extractor.ts

@@ -8,6 +8,7 @@ import {
   XLSXTheme,
   XMLFile,
 } from "../../types/xlsx";
+import { DEFAULT_SYSTEM_COLOR } from "../conversion";
 import { fixXlsxUnicode } from "../helpers/misc";
 import { XLSXImportWarningManager } from "../helpers/xlsx_parser_error_manager";
 import { escapeQueryNameSpaces } from "../helpers/xml_helpers";
@@ -327,9 +328,10 @@ export class XlsxBaseExtractor {
       rgb = this.getThemeColor(themeIndex, theme.clrScheme);
     } else {
       rgb = this.extractAttr(colorElement, "rgb")?.asString();
+      rgb = rgb === DEFAULT_SYSTEM_COLOR ? undefined : rgb;
     }
     const color = {
-      rgb,
+      rgb: rgb || defaultColor,
       auto: this.extractAttr(colorElement, "auto")?.asBool(),
       indexed: this.extractAttr(colorElement, "indexed")?.asNum(),
       tint: this.extractAttr(colorElement, "tint")?.asNum(),

src/xlsx/functions/worksheet.ts

@@ -86,7 +86,10 @@ export function addRows(
 
         // style
         const id = normalizeStyle(construct, extractStyle(cell, data));
-        attributes.push(["s", id]);
+        // don't add style if default
+        if (id) {
+          attributes.push(["s", id]);
+        }
 
         let additionalAttrs: XMLAttributes = [];
         let cellNode = escapeXml``;

src/xlsx/helpers/content_helpers.ts

@@ -96,7 +96,7 @@ export function extractStyle(cell: ExcelCellData, data: WorkbookData): Extracted
       vertical: style.verticalAlign
         ? V_ALIGNMENT_EXPORT_CONVERSION_MAP[style.verticalAlign]
         : undefined,
-      wrapText: style.wrapping === "wrap",
+      wrapText: style.wrapping === "wrap" || undefined,
     },
   };
 

src/xlsx/helpers/xml_helpers.ts

@@ -93,15 +93,15 @@ export function getDefaultXLSXStructure(data: ExcelWorkbookData): XLSXStructure
         fillId: 0,
         numFmtId: 0,
         borderId: 0,
-        alignment: { vertical: "bottom" },
+        alignment: {},
       },
     ],
     fonts: [
       {
         size: DEFAULT_FONT_SIZE,
         family: 2,
         color: { rgb: "000000" },
-        name: "Calibri",
+        name: "Arial",
       },
     ],
     fills: [{ reservedAttribute: "none" }, { reservedAttribute: "gray125" }],