feat(monospace): add PdfFontHeader builder for xelatex fontspec

src/main/PdfFontHeader.js

@@ -0,0 +1,43 @@
+'use strict';
+
+// fontspec accepts forward-slash paths on all platforms (TeX normalizes).
+// Normalize Windows backslashes so we can reliably build Path/filename.
+function toPosix(p) {
+  return String(p).replace(/\\/g, '/');
+}
+
+function escape(s) {
+  // fontspec values: braces are the only TeX-significant chars we might emit
+  // from a basename. Backslashes are converted to '/' upstream by toPosix().
+  return String(s).replace(/[{}]/g, '\\$&');
+}
+
+function dirOf(p) {
+  return toPosix(p).replace(/\/[^/]+$/, '') + '/';
+}
+
+function baseName(p) {
+  return toPosix(p).split('/').pop();
+}
+
+// Strip a weight-style suffix from a TTF filename to get the family prefix
+// (e.g. JetBrainsMono-Regular.ttf -> JetBrainsMono). Used as the `\setmonofont`
+// argument so `*-Regular` / `*-Bold` globs resolve to the right files.
+function weightPrefix(p) {
+  return baseName(p).replace(/-(Regular|Bold|Light|Medium|SemiBold|Italic)\.ttf$/i, '');
+}
+
+function build({ fontTtfPath, boldTtfPath, ligatures }) {
+  if (!fontTtfPath) {
+    return '% Monospace font path unavailable; TeX will use its default monospace.\n';
+  }
+
+  const ligValue = ligatures ? 'Ligatures=TeX' : 'Ligatures=NoCommon';
+  const prefix = escape(weightPrefix(fontTtfPath));
+
+  return `\\usepackage{fontspec}
+\\setmonofont[Path=${escape(dirOf(fontTtfPath))},Extension=.ttf,UprightFont=*-Regular,BoldFont=*-Bold,${ligValue}]{${prefix}}
+`;
+}
+
+module.exports = { build };

tests/pdf-font-header.test.js

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+const PdfFontHeader = require('../src/main/PdfFontHeader');
+
+describe('PdfFontHeader.build', () => {
+  test('emits fontspec with Path, family prefix, weight globs, and Ligatures=NoCommon when off', () => {
+    const tex = PdfFontHeader.build({
+      fontTtfPath: '/abs/path/JetBrainsMono-Regular.ttf',
+      boldTtfPath: '/abs/path/JetBrainsMono-Bold.ttf',
+      ligatures: false,
+    });
+    expect(tex).toContain('\\usepackage{fontspec}');
+    // \setmonofont uses the family prefix (weight suffix stripped)
+    expect(tex).toMatch(/\\setmonofont\[[^\]]*\]\{JetBrainsMono\}/);
+    // Path is the directory (no trailing filename)
+    expect(tex).toContain('Path=/abs/path/');
+    // No programming ligatures
+    expect(tex).toContain('Ligatures=NoCommon');
+    // Upright/Bold use the family-prefixed glob
+    expect(tex).toContain('UprightFont=*-Regular');
+    expect(tex).toContain('BoldFont=*-Bold');
+  });
+
+  test('emits Ligatures=TeX when on (preserves --/--- but no programming ligatures)', () => {
+    const tex = PdfFontHeader.build({
+      fontTtfPath: '/abs/JBM-Regular.ttf',
+      boldTtfPath: '/abs/JBM-Bold.ttf',
+      ligatures: true,
+    });
+    expect(tex).toContain('Ligatures=TeX');
+    expect(tex).not.toContain('Ligatures=NoCommon');
+  });
+
+  test('returns a no-op stub when font path is missing', () => {
+    const tex = PdfFontHeader.build({ fontTtfPath: null, boldTtfPath: null, ligatures: false });
+    expect(tex).toContain('% Monospace font path unavailable');
+  });
+
+  test('normalizes Windows backslashes to forward slashes', () => {
+    const tex = PdfFontHeader.build({
+      fontTtfPath: 'C:\\Users\\foo\\JetBrainsMono-Regular.ttf',
+      boldTtfPath: 'C:\\Users\\foo\\JetBrainsMono-Bold.ttf',
+      ligatures: false,
+    });
+    expect(tex).toContain('Path=C:/Users/foo/');
+    expect(tex).toMatch(/\{JetBrainsMono\}/);
+  });
+
+  test('strips the FiraCode weight suffix to derive the family prefix', () => {
+    const tex = PdfFontHeader.build({
+      fontTtfPath: '/abs/FiraCode-Regular.ttf',
+      boldTtfPath: '/abs/FiraCode-Bold.ttf',
+      ligatures: false,
+    });
+    expect(tex).toMatch(/\{FiraCode\}/);
+  });
+});