fix(doc-codec): cascade row/table-level borders onto cells with none

packages/doc-codec/src/table/decoration.test.ts

@@ -10,6 +10,8 @@ import {
   readBrc80,
   readShd,
   readShd80,
+  readTableBordersOperand,
+  readTableBordersOperand80,
   writeBrc,
   writeBrc80,
   writeShd,
@@ -282,6 +284,95 @@ describe("Brc", () => {
   });
 });
 
+describe("TableBordersOperand", () => {
+  const GREEN: ContentBorder = { color: { r: 0, g: 1, b: 0 }, widthPt: 1 };
+  const BLUE: ContentBorder = {
+    color: { r: 0, g: 0, b: 1 },
+    widthPt: 0.75,
+    style: "dashed",
+  };
+  const nilBrc = new Array<number>(BRC_SIZE).fill(0xff);
+
+  it("reads all six Brc fields in brcTop/brcLeft/brcBottom/brcRight/brcHorizontalInside/brcVerticalInside order", () => {
+    // [MS-DOC] 2.9.302: cb (MUST be 0x30) then six 8-byte Brc fields back to back, in that declared order.
+    const top: ContentBorder = { color: RED, widthPt: 1 };
+    const left: ContentBorder = { color: BLACK, widthPt: 0.5 };
+    const bottom: ContentBorder = { color: RED, widthPt: 1.5 };
+    const right: ContentBorder = { color: BLACK, widthPt: 2 };
+    const operand = bytes([
+      0x30,
+      ...writeBrc(top),
+      ...writeBrc(left),
+      ...writeBrc(bottom),
+      ...writeBrc(right),
+      ...writeBrc(GREEN),
+      ...writeBrc(BLUE),
+    ]);
+    expect(readTableBordersOperand(operand)).toEqual({
+      top,
+      left,
+      bottom,
+      right,
+      insideHorizontal: GREEN,
+      insideVertical: BLUE,
+    });
+  });
+
+  it("reads a NilBrc field as no border for that side, leaving the others intact", () => {
+    const top: ContentBorder = { color: RED, widthPt: 1 };
+    const operand = bytes([
+      0x30,
+      ...writeBrc(top),
+      ...nilBrc,
+      ...nilBrc,
+      ...nilBrc,
+      ...nilBrc,
+      ...nilBrc,
+    ]);
+    expect(readTableBordersOperand(operand)).toEqual({ top });
+  });
+
+  it("reads a whole-nil operand as a set with no side stated at all", () => {
+    const operand = bytes([
+      0x30,
+      ...nilBrc,
+      ...nilBrc,
+      ...nilBrc,
+      ...nilBrc,
+      ...nilBrc,
+      ...nilBrc,
+    ]);
+    expect(readTableBordersOperand(operand)).toEqual({});
+  });
+});
+
+describe("TableBordersOperand80", () => {
+  const nilBrc80 = new Array<number>(BRC80_SIZE).fill(0xff);
+
+  it("reads all six Brc80 fields in the same order, palette-indexed", () => {
+    // [MS-DOC] 2.9.303: cb (MUST be 0x18) then six 4-byte Brc80MayBeNil fields, same order as TableBordersOperand.
+    const top: ContentBorder = { color: RED, widthPt: 0.5 };
+    const insideVertical: ContentBorder = {
+      color: BLACK,
+      widthPt: 1,
+      style: "dotted",
+    };
+    const operand = bytes([
+      0x18,
+      ...writeBrc80(top),
+      ...nilBrc80,
+      ...nilBrc80,
+      ...nilBrc80,
+      ...nilBrc80,
+      ...writeBrc80(insideVertical),
+    ]);
+    expect(readTableBordersOperand80(operand)).toEqual({
+      top,
+      insideVertical,
+    });
+  });
+});
+
 describe("Shd", () => {
   it("reads ipatAuto's own cvBack as the cell's background", () => {
     // The exact bytes LibreOffice wrote for a #ffff00 cell fill.

packages/doc-codec/src/table/decoration.ts

@@ -171,6 +171,43 @@ export function readBrc(
   );
 }
 
+/** A row's own six-side border cascade, from sprmTTableBorders ([MS-DOC] 2.9.302) or the Word 97-era sprmTTableBorders80 ([MS-DOC] 2.9.303) -- the layer table/tap.ts's own top-of-file note calls "a cascade above the per-cell layer rather than another spelling of it". Both structures always state all six fields (there is no bordersToApply-style subset the way TableBrcOperand has), in the same order: brcTop, brcLeft, brcBottom, brcRight, brcHorizontalInside (the border between this row and its table neighbours), brcVerticalInside (the border between this row's own cells). Left unresolved onto any particular cell here: which of the six reaches a given cell/side depends on that cell's position in the WHOLE table (is this the table's first or last row, this row's first or last physical cell), which only table/read.ts's own cross-row assembly knows -- see its applyRowLevelBorderCascade. */
+export interface TableBordersSet {
+  readonly top?: ContentBorder;
+  readonly left?: ContentBorder;
+  readonly bottom?: ContentBorder;
+  readonly right?: ContentBorder;
+  readonly insideHorizontal?: ContentBorder;
+  readonly insideVertical?: ContentBorder;
+}
+
+function readTableBordersFields(
+  operand: Uint8Array,
+  fieldSize: number,
+  readField: (bytes: Uint8Array, offset: number) => ContentBorder | undefined,
+): TableBordersSet {
+  return {
+    top: readField(operand, 1),
+    left: readField(operand, 1 + fieldSize),
+    bottom: readField(operand, 1 + fieldSize * 2),
+    right: readField(operand, 1 + fieldSize * 3),
+    insideHorizontal: readField(operand, 1 + fieldSize * 4),
+    insideVertical: readField(operand, 1 + fieldSize * 5),
+  };
+}
+
+/** TableBordersOperand's own 49 bytes ([MS-DOC] 2.9.302): cb (1 byte, MUST be 0x30) then six real Brc fields (8 bytes each, 2.9.16) back to back -- brcTop, brcLeft, brcBottom, brcRight, brcHorizontalInside, brcVerticalInside -- each an exact COLORREF exactly like sprmTSetBrc's own per-cell layer. */
+export function readTableBordersOperand(operand: Uint8Array): TableBordersSet {
+  return readTableBordersFields(operand, BRC_SIZE, readBrc);
+}
+
+/** TableBordersOperand80's own 25 bytes ([MS-DOC] 2.9.303): the Word 97-era spelling, cb (1 byte, MUST be 0x18) then the same six fields as Brc80MayBeNil (4 bytes each, 2.9.18), palette-indexed exactly like TC80's own Brc80 fields. */
+export function readTableBordersOperand80(
+  operand: Uint8Array,
+): TableBordersSet {
+  return readTableBordersFields(operand, BRC80_SIZE, readBrc80);
+}
+
 /** Brc80MayBeNil's own no-border value, [MS-DOC] 2.9.18: "When all bits are set (0xFFFFFFFF when interpreted as a 4-byte unsigned integer), this structure specifies that the region in question has no border." */
 const NIL_BRC80: readonly number[] = [0xff, 0xff, 0xff, 0xff];