1 files changed, 42 insertions, 0 deletions
diff --git a/src/math.ts b/src/math.ts
new file mode 100644
index 0000000..71403f4
--- /dev/null
+++ b/src/math.ts
@@ -0,0 +1,42 @@
+import katex from 'katex';
+import 'katex/dist/katex.min.css';
+
+const options = { output: 'htmlAndMathml', throwOnError: false, strict: 'error', trust: false } as const;
+
+/** Render authored TeX with bundled fonts and a MathML equivalent for assistive technology. */
+export function renderEquation(element: HTMLElement, tex: string) {
+  element.classList.add('math-display');
+  element.tabIndex = 0; // Long equations can be scrolled with the keyboard on narrow screens.
+  katex.render(tex, element, { ...options, displayMode: true });
+}
+
+/** Plain prose with explicit $...$ inline math; everything outside delimiters stays text. */
+export function renderProse(element: HTMLElement, text: string) {
+  element.replaceChildren();
+  let offset = 0;
+  for (const match of text.matchAll(/\$([^$\n]+)\$/g)) {
+    element.append(document.createTextNode(text.slice(offset, match.index)));
+    const math = document.createElement('span');
+    katex.render(match[1], math, { ...options, displayMode: false });
+    element.append(math);
+    offset = match.index + match[0].length;
+  }
+  element.append(document.createTextNode(text.slice(offset)));
+}
+
+// Short UI labels retain their plain accessible names while sharing the lesson notation.
+const notation: Record<string, string> = {
+  'log₁₀(N / m⁻³)': String.raw`\log_{10}(N/\mathrm m^{-3})`,
+  'EF − Ei': 'E_F-E_i', 'U₁₂₃': 'U_{123}', 'ΔU₀': String.raw`\Delta U_0`,
+  'K + U': 'K+U', 'q₀': 'q_0', 'q₁': 'q_1', 'q₂': 'q_2', 'q₃': 'q_3',
+  'Uₐ': 'U_a', 'Uᵦ': 'U_b', 'Kₐ': 'K_a', 'rₐ': 'r_a', 'rᵦ': 'r_b',
+  'θₐ': String.raw`\theta_a`, 'θᵦ': String.raw`\theta_b`, 'τz': String.raw`\tau_z`,
+  '|Q|': '|Q|', '|P|': '|P|', '|E|': String.raw`|\vec E|`, 'Ex': 'E_x',
+  'Δx': String.raw`\Delta x`, 'θ': String.raw`\theta`, 'α': String.raw`\alpha`,
+  'κ': String.raw`\kappa`, 'σ': String.raw`\sigma`, '90°': String.raw`90^\circ`,
+};
+const notationPattern = new RegExp(Object.keys(notation).sort((a, b) => b.length - a.length).map(key => key.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')).join('|') + '|\\b[EqdnpUVK]\\b', 'g');
+
+export function renderNotation(element: HTMLElement, text: string) {
+  renderProse(element, text.replace(notationPattern, token => `$${notation[token] ?? token}$`));
+}