feat: frontmatter parse/resolve/serialize

Co-Authored-By: Claude

src/frontmatter.test.ts

@@ -0,0 +1,54 @@
+import { describe, expect, test } from "vitest";
+import { parseNote, resolveFrontmatter, serializeFrontmatter } from "./frontmatter";
+
+describe("parseNote", () => {
+  test("splits frontmatter and body, strips BOM", () => {
+    const { frontmatter, body } = parseNote("---\ntitle: Hi\n---\nHello\n");
+    expect(frontmatter).toEqual({ title: "Hi" });
+    expect(body).toBe("Hello\n");
+  });
+  test("no frontmatter returns empty object and full body", () => {
+    expect(parseNote("Just text")).toEqual({ frontmatter: {}, body: "Just text" });
+  });
+});
+
+describe("resolveFrontmatter", () => {
+  const presets = [{ key: "layout", value: "post" }, { key: "kind", value: "essay" }];
+  test("presets only when mergeDoc is false", () => {
+    expect(resolveFrontmatter(presets, { title: "X" }, [], false)).toEqual(presets);
+  });
+  test("merge appends doc keys and doc overrides preset value", () => {
+    const r = resolveFrontmatter(presets, { kind: "note", title: "X" }, [], true);
+    expect(r).toEqual([
+      { key: "layout", value: "post" },
+      { key: "kind", value: "note" },
+      { key: "title", value: "X" },
+    ]);
+  });
+  test("custom rows come last and override everything", () => {
+    const r = resolveFrontmatter(presets, {}, [{ key: "layout", value: "page" }], false);
+    expect(r[0]).toEqual({ key: "layout", value: "page" });
+    expect(r).toHaveLength(2);
+  });
+  test("date object is rendered as YYYY-MM-DD", () => {
+    const r = resolveFrontmatter([], { date: new Date("2026-06-11T00:00:00Z") }, [], true);
+    expect(r).toEqual([{ key: "date", value: "2026-06-11" }]);
+  });
+});
+
+describe("serializeFrontmatter", () => {
+  test("bare-safe values unquoted, others JSON-quoted", () => {
+    const out = serializeFrontmatter([
+      { key: "layout", value: "post" },
+      { key: "date", value: "2026-06-11" },
+      { key: "title", value: "On making a game" },
+      { key: "description", value: "And how it's different" },
+    ]);
+    expect(out).toBe(
+      `---\nlayout: post\ndate: 2026-06-11\ntitle: On making a game\ndescription: "And how it's different"\n---\n`
+    );
+  });
+  test("empty value becomes quoted empty string", () => {
+    expect(serializeFrontmatter([{ key: "tags", value: "" }])).toBe(`---\ntags: ""\n---\n`);
+  });
+});

src/frontmatter.ts

@@ -0,0 +1,52 @@
+import yaml from "js-yaml";
+
+export interface Pair {
+  key: string;
+  value: string;
+}
+
+export function parseNote(text: string): { frontmatter: Record<string, unknown>; body: string } {
+  const stripped = text.replace(/^/, "");
+  const m = /^---\r?\n([\s\S]*?)\r?\n---\r?\n?/.exec(stripped);
+  if (!m) return { frontmatter: {}, body: stripped };
+  const loaded = yaml.load(m[1]);
+  const frontmatter = loaded && typeof loaded === "object" ? (loaded as Record<string, unknown>) : {};
+  return { frontmatter, body: stripped.slice(m[0].length) };
+}
+
+export function resolveFrontmatter(
+  presets: Pair[],
+  docFrontmatter: Record<string, unknown>,
+  custom: Pair[],
+  mergeDoc: boolean
+): Pair[] {
+  const out: Pair[] = [];
+  const idx = new Map<string, number>();
+  const put = (key: string, value: string) => {
+    const at = idx.get(key);
+    if (at !== undefined) out[at] = { key, value };
+    else { idx.set(key, out.length); out.push({ key, value }); }
+  };
+  for (const p of presets) put(p.key, p.value);
+  if (mergeDoc) for (const [k, v] of Object.entries(docFrontmatter)) put(k, stringifyScalar(v));
+  for (const c of custom) put(c.key, c.value);
+  return out;
+}
+
+function stringifyScalar(v: unknown): string {
+  if (v == null) return "";
+  if (v instanceof Date) return v.toISOString().slice(0, 10);
+  if (typeof v === "object") return yaml.dump(v).trim();
+  return String(v);
+}
+
+export function serializeFrontmatter(pairs: Pair[]): string {
+  const lines = pairs.map((p) => `${p.key}: ${formatValue(p.value)}`);
+  return `---\n${lines.join("\n")}\n---\n`;
+}
+
+function formatValue(v: string): string {
+  if (v === "") return '""';
+  const bareSafe = /^[A-Za-z0-9_./-][A-Za-z0-9_./ -]*$/.test(v) && !/^\s|\s$/.test(v);
+  return bareSafe ? v : JSON.stringify(v);
+}