Persist referral parameters for seven days

src/analytics/misc/refParams.ts

@@ -2,16 +2,80 @@
  * This is used for our own Bluesky post embeds, and maybe other things.
  *
  * In the case of our embeds, `ref_src=embed`. Not sure if `ref_url` is used.
+ *
+ * Referral parameters are captured on page load and retained for seven days so
+ * return visits can be attributed to the same source.
  */
 
 import * as env from '#/env'
 
+const STORAGE_KEY = 'bsky.analytics.refParams'
+const TTL = 7 * 24 * 60 * 60 * 1000
+
+type RefParams = {
+  src: string
+  url: string
+  timestamp: number
+}
+
+function getStoredRefParams(now: number): RefParams | undefined {
+  const value = window.localStorage.getItem(STORAGE_KEY)
+  if (!value) return
+
+  let parsed: unknown
+  try {
+    parsed = JSON.parse(value)
+  } catch {
+    window.localStorage.removeItem(STORAGE_KEY)
+    return
+  }
+
+  if (
+    !parsed ||
+    typeof parsed !== 'object' ||
+    !('src' in parsed) ||
+    typeof parsed.src !== 'string' ||
+    !('url' in parsed) ||
+    typeof parsed.url !== 'string' ||
+    (!parsed.src && !parsed.url) ||
+    !('timestamp' in parsed) ||
+    typeof parsed.timestamp !== 'number' ||
+    !Number.isFinite(parsed.timestamp) ||
+    parsed.timestamp <= 0 ||
+    parsed.timestamp > now ||
+    now - parsed.timestamp >= TTL
+  ) {
+    window.localStorage.removeItem(STORAGE_KEY)
+    return
+  }
+
+  return {src: parsed.src, url: parsed.url, timestamp: parsed.timestamp}
+}
+
 let refSrc = ''
 let refUrl = ''
 if (env.IS_WEB) {
   const params = new URLSearchParams(window.location.search)
   refSrc = params.get('ref_src') ?? ''
   refUrl = decodeURIComponent(params.get('ref_url') ?? '')
+
+  try {
+    const now = Date.now()
+    const stored = getStoredRefParams(now)
+    if (refSrc || refUrl) {
+      if (stored?.src !== refSrc || stored?.url !== refUrl) {
+        window.localStorage.setItem(
+          STORAGE_KEY,
+          JSON.stringify({src: refSrc, url: refUrl, timestamp: now}),
+        )
+      }
+    } else if (stored) {
+      refSrc = stored.src
+      refUrl = stored.url
+    }
+  } catch {
+    /* localStorage may be unavailable; keep the current URL's attribution. */
+  }
 }
 
 export const src = refSrc