feat(monospace): add settings schema with safe defaults

src/main/settings/monospaceSettings.js

@@ -0,0 +1,49 @@
+'use strict';
+
+const FAMILY_BY_KEY = {
+  'jetbrains-mono': 'JetBrains Mono',
+  'fira-code': 'Fira Code',
+};
+
+const ALLOWED_FONTS = Object.keys(FAMILY_BY_KEY);
+
+const DEFAULT_SETTINGS = Object.freeze({
+  monospaceFont: 'jetbrains-mono',
+  monospaceLigatures: false,
+});
+
+function getActiveMonoFont(settings) {
+  const key = settings && settings.monospaceFont;
+  if (typeof key === 'string' && Object.prototype.hasOwnProperty.call(FAMILY_BY_KEY, key)) {
+    return FAMILY_BY_KEY[key];
+  }
+  return FAMILY_BY_KEY[DEFAULT_SETTINGS.monospaceFont];
+}
+
+function isLigaturesEnabled(settings) {
+  return !!(settings && settings.monospaceLigatures === true);
+}
+
+function safeMonospaceSettings(input) {
+  const safe = { ...DEFAULT_SETTINGS };
+  if (input && typeof input === 'object') {
+    if (ALLOWED_FONTS.includes(input.monospaceFont)) {
+      safe.monospaceFont = input.monospaceFont;
+    }
+    if (typeof input.monospaceLigatures === 'boolean') {
+      safe.monospaceLigatures = input.monospaceLigatures;
+    } else if (input.monospaceLigatures === 1 || input.monospaceLigatures === 'true') {
+      safe.monospaceLigatures = true;
+    }
+  }
+  return safe;
+}
+
+module.exports = {
+  FAMILY_BY_KEY,
+  ALLOWED_FONTS,
+  DEFAULT_SETTINGS,
+  getActiveMonoFont,
+  isLigaturesEnabled,
+  safeMonospaceSettings,
+};