feat: slug and date derivation

Co-Authored-By: Claude

src/slug.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, test } from "vitest";
+import { slugify, deriveSlug, deriveDate, postFilename } from "./slug";
+
+describe("slugify", () => {
+  test("lowercases, drops apostrophes, hyphenates", () => {
+    expect(slugify("On Making a Game")).toBe("on-making-a-game");
+    expect(slugify("It's a Test!")).toBe("its-a-test");
+    expect(slugify("  Spaced  out  ")).toBe("spaced-out");
+  });
+});
+
+describe("deriveSlug", () => {
+  test("prefers title, falls back to filename", () => {
+    expect(deriveSlug({ title: "Hello World", filename: "note" })).toBe("hello-world");
+    expect(deriveSlug({ title: "  ", filename: "My Note" })).toBe("my-note");
+  });
+});
+
+describe("deriveDate", () => {
+  const now = new Date("2026-06-19T12:00:00Z");
+  test("uses frontmatter Date or string, else now", () => {
+    expect(deriveDate({ frontmatterDate: new Date("2026-02-06T00:00:00Z"), now })).toBe("2026-02-06");
+    expect(deriveDate({ frontmatterDate: "2026-02-18 09:00", now })).toBe("2026-02-18");
+    expect(deriveDate({ now })).toBe("2026-06-19");
+  });
+});
+
+describe("postFilename", () => {
+  test("joins date and slug", () => {
+    expect(postFilename({ date: "2026-06-19", slug: "hello" })).toBe("2026-06-19-hello.md");
+  });
+});

src/slug.ts

@@ -0,0 +1,29 @@
+export function slugify(s: string): string {
+  return s
+    .toLowerCase()
+    .trim()
+    .replace(/['']/g, "")
+    .replace(/[^a-z0-9]+/g, "-")
+    .replace(/^-+|-+$/g, "");
+}
+
+export function deriveSlug(o: { title?: string; filename: string }): string {
+  const base = o.title && o.title.trim() ? o.title : o.filename;
+  return slugify(base);
+}
+
+export function deriveDate(o: { frontmatterDate?: unknown; now: Date }): string {
+  const d = o.frontmatterDate;
+  if (d instanceof Date && !isNaN(d.getTime())) return fmt(d);
+  if (typeof d === "string" && /^\d{4}-\d{2}-\d{2}/.test(d)) return d.slice(0, 10);
+  return fmt(o.now);
+}
+
+function fmt(d: Date): string {
+  const p = (n: number) => String(n).padStart(2, "0");
+  return `${d.getUTCFullYear()}-${p(d.getUTCMonth() + 1)}-${p(d.getUTCDate())}`;
+}
+
+export function postFilename(o: { date: string; slug: string }): string {
+  return `${o.date}-${o.slug}.md`;
+}