feat: improve card loading speed (#2124)

* feat: improve card loading times

This commit adds the `stale-while-revalidate` option to speed up the
card loading times.

* mend

api/index.js

@@ -61,7 +61,12 @@ export default async (req, res) => {
       CONSTANTS.ONE_DAY,
     );
 
-    res.setHeader("Cache-Control", `public, max-age=${cacheSeconds}`);
+    res.setHeader(
+      "Cache-Control",
+      `max-age=${
+        cacheSeconds / 2
+      }, s-maxage=${cacheSeconds}, stale-while-revalidate=${CONSTANTS.ONE_DAY}`,
+    );
 
     return res.send(
       renderStatsCard(stats, {

api/pin.js

@@ -58,7 +58,12 @@ export default async (req, res) => {
       cacheSeconds = CONSTANTS.FOUR_HOURS;
     }
 
-    res.setHeader("Cache-Control", `public, max-age=${cacheSeconds}`);
+    res.setHeader(
+      "Cache-Control",
+      `max-age=${
+        cacheSeconds / 2
+      }, s-maxage=${cacheSeconds}, stale-while-revalidate=${CONSTANTS.ONE_DAY}`,
+    );
 
     return res.send(
       renderRepoCard(repoData, {

api/top-langs.js

@@ -52,7 +52,12 @@ export default async (req, res) => {
       CONSTANTS.ONE_DAY,
     );
 
-    res.setHeader("Cache-Control", `public, max-age=${cacheSeconds}`);
+    res.setHeader(
+      "Cache-Control",
+      `max-age=${
+        cacheSeconds / 2
+      }, s-maxage=${cacheSeconds}, stale-while-revalidate=${CONSTANTS.ONE_DAY}`,
+    );
 
     return res.send(
       renderTopLanguages(topLangs, {

api/wakatime.js

@@ -52,7 +52,12 @@ export default async (req, res) => {
       cacheSeconds = CONSTANTS.FOUR_HOURS;
     }
 
-    res.setHeader("Cache-Control", `public, max-age=${cacheSeconds}`);
+    res.setHeader(
+      "Cache-Control",
+      `max-age=${
+        cacheSeconds / 2
+      }, s-maxage=${cacheSeconds}, stale-while-revalidate=${CONSTANTS.ONE_DAY}`,
+    );
 
     return res.send(
       renderWakatimeCard(stats, {