feat(footer): show last-built timestamp and linked commit SHA

Closes #341

Author: sroertgen

src/components/footer.jsx

@@ -3,9 +3,15 @@ import PropTypes from "prop-types"
 import React from "react"
 
 import { getConfigAndConceptSchemes } from "../hooks/configAndConceptSchemes"
+import { commitUrl, formatBuildTime, shortSha } from "../buildInfo"
 
 const Footer = () => {
-  const { config } = getConfigAndConceptSchemes()
+  const { config, buildTime } = getConfigAndConceptSchemes()
+  const { repositoryUrl, gitCommit } = config
+
+  const formattedTime = formatBuildTime(buildTime)
+  const sha = shortSha(gitCommit)
+  const href = commitUrl(repositoryUrl, gitCommit)
 
   const style = css`
     background: ${config.colors.skoHubMiddleColor};
@@ -54,17 +60,28 @@ const Footer = () => {
     <footer css={style}>
       <div className="footerContent">
         <ul>
-          {process.env.GATSBY_RESPOSITORY_URL && (
+          {repositoryUrl && (
             <li>
-              <a
-                href={process.env.GATSBY_RESPOSITORY_URL}
-                target="_blank"
-                rel="noopener noreferrer"
-              >
+              <a href={repositoryUrl} target="_blank" rel="noopener noreferrer">
                 Source
               </a>
             </li>
           )}
+          {formattedTime && (
+            <li>
+              Last built: {formattedTime}
+              {sha && href && (
+                <>
+                  {" ("}
+                  <a href={href} target="_blank" rel="noopener noreferrer">
+                    {sha}
+                  </a>
+                  {")"}
+                </>
+              )}
+              {sha && !href && ` (${sha})`}
+            </li>
+          )}
           {links.map((link, idx) => (
             <li key={idx} className={idx === 0 ? "push-right" : ""}>
               <a

test/footer.test.jsx

@@ -1,4 +1,4 @@
-import { beforeEach, describe, expect, it, vi } from "vitest"
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest"
 import { render, screen } from "@testing-library/react"
 import React from "react"
 import Footer from "../src/components/footer"
@@ -7,14 +7,102 @@ import { mockConfig } from "./mocks/mockConfig"
 
 const useStaticQuery = vi.spyOn(Gatsby, `useStaticQuery`)
 
+const withMock = (overrides = {}) => ({
+  ...mockConfig,
+  site: {
+    ...mockConfig.site,
+    ...(overrides.site || {}),
+    siteMetadata: {
+      ...mockConfig.site.siteMetadata,
+      ...((overrides.site && overrides.site.siteMetadata) || {}),
+    },
+  },
+})
+
 describe("Footer", () => {
   beforeEach(() => {
-    useStaticQuery.mockImplementation(() => mockConfig)
+    delete process.env.GATSBY_RESPOSITORY_URL
+  })
+
+  afterEach(() => {
+    delete process.env.GATSBY_RESPOSITORY_URL
   })
 
-  it("renders footer", () => {
-    process.env.GATSBY_RESPOSITORY_URL = "http://test.com"
-    render(<Footer></Footer>)
+  it("renders Source link when repositoryUrl is set", () => {
+    useStaticQuery.mockImplementation(() =>
+      withMock({
+        site: {
+          siteMetadata: {
+            repositoryUrl: "https://github.com/skohub-io/skohub-vocabs",
+          },
+        },
+      })
+    )
+    render(<Footer />)
     expect(screen.getByRole("link", { name: "Source" })).toBeInTheDocument()
   })
+
+  it("renders timestamp only when no commit info is available", () => {
+    useStaticQuery.mockImplementation(() =>
+      withMock({
+        site: {
+          buildTime: "2026-04-30T14:30:42.000Z",
+          siteMetadata: { gitCommit: "", repositoryUrl: "" },
+        },
+      })
+    )
+    render(<Footer />)
+    expect(
+      screen.getByText("Last built: 2026-04-30 14:30 UTC")
+    ).toBeInTheDocument()
+    expect(
+      screen.queryByRole("link", { name: /a1b2c3d/ })
+    ).not.toBeInTheDocument()
+  })
+
+  it("renders timestamp + plain short SHA when no repositoryUrl", () => {
+    useStaticQuery.mockImplementation(() =>
+      withMock({
+        site: {
+          buildTime: "2026-04-30T14:30:42.000Z",
+          siteMetadata: {
+            gitCommit: "a1b2c3d4e5f67890abcdef1234567890abcdef12",
+            repositoryUrl: "",
+          },
+        },
+      })
+    )
+    render(<Footer />)
+    expect(
+      screen.getByText("Last built: 2026-04-30 14:30 UTC (a1b2c3d)")
+    ).toBeInTheDocument()
+  })
+
+  it("renders timestamp + linked short SHA when both are set", () => {
+    useStaticQuery.mockImplementation(() =>
+      withMock({
+        site: {
+          buildTime: "2026-04-30T14:30:42.000Z",
+          siteMetadata: {
+            gitCommit: "a1b2c3d4e5f67890abcdef1234567890abcdef12",
+            repositoryUrl: "https://github.com/skohub-io/skohub-vocabs",
+          },
+        },
+      })
+    )
+    render(<Footer />)
+    const link = screen.getByRole("link", { name: "a1b2c3d" })
+    expect(link).toHaveAttribute(
+      "href",
+      "https://github.com/skohub-io/skohub-vocabs/commit/a1b2c3d4e5f67890abcdef1234567890abcdef12"
+    )
+  })
+
+  it("does not render the Last built line when buildTime is missing", () => {
+    useStaticQuery.mockImplementation(() =>
+      withMock({ site: { buildTime: null } })
+    )
+    render(<Footer />)
+    expect(screen.queryByText(/Last built:/)).not.toBeInTheDocument()
+  })
 })