Beginnings of autocomplete for headers

src-web/components/core/Editor/genericCompletion.ts

@@ -0,0 +1,25 @@
+import type { CompletionContext } from '@codemirror/autocomplete';
+
+export interface GenericCompletionOption {
+  label: string;
+  type: 'constant' | 'variable';
+}
+
+export function genericCompletion({
+  options,
+  minMatch = 1,
+}: {
+  options: GenericCompletionOption[];
+  minMatch?: number;
+}) {
+  return function completions(context: CompletionContext) {
+    const toMatch = context.matchBefore(/^[\w:/]*/);
+    if (toMatch === null) return null;
+
+    const matchedMinimumLength = toMatch.to - toMatch.from >= minMatch;
+    if (!matchedMinimumLength && !context.explicit) return null;
+
+    const optionsWithoutExactMatches = options.filter((o) => o.label !== toMatch.text);
+    return { from: toMatch.from, options: optionsWithoutExactMatches };
+  };
+}