PostHog · mariusandra · May 23, 2021 · May 6, 2021 · May 7, 2021 · May 7, 2021
diff --git a/index.ts b/index.ts
@@ -1,72 +1,67 @@
-import { PluginEvent, PluginMeta, PluginAttachment } from '@posthog/plugin-scaffold'
+import { Plugin } from '@posthog/plugin-scaffold'
 
 declare var posthog: {
-    capture: (eventName: string, properties: Record<string,any>) => void
+    capture: (eventName: string, properties: Record<string, any>) => void
 }
 
-async function processEvent(event: PluginEvent, { storage }: PluginMeta) {
-    if (['session_started', 'session_ended'].includes(event.event)) {
-        return event
+type SessionTrackerPlugin = Plugin<{
+    config: {
+        sessionLength: string
+        sessionStartEvent: string
+        sessionEndEvent: string
     }
-
-    const THIRTY_MINUTES = 1000*60*30
-
-    // Last event by the user
-    const userLastSeen = await storage.get(`last_seen_${event.distinct_id}`, 0) as number
-
-    // Last registered session_start by the user 
-    const userLastSessionStarted = await storage.get(`last_session_started_${event.distinct_id}`, 0) as number
-
-    let isFirstEventInSession = false
-
-    if (!event.properties) {
-        event['properties'] = {}
+    global: {
+        sessionLength: number
+        sessionStartEvent: string
+        sessionEndEvent: string
     }
+    jobs: {
+        checkIfSessionIsOver: { distinct_id: string }
+    }
+}>
 
-    const timestamp = event.timestamp
-
-    if (timestamp) {
-        const parsedTimestamp = new Date(timestamp).getTime()
-        const timeSinceLastSeen = parsedTimestamp - userLastSeen
-        isFirstEventInSession = timeSinceLastSeen > THIRTY_MINUTES
-
-        storage.set(`last_seen_${event.distinct_id}`, parsedTimestamp)
-
-        // If it's been over 30min since the user had an event, it's a new session
-        if (isFirstEventInSession) {
-            posthog.capture(
-                'session_started', 
-                { 
-                    distinct_id: event.distinct_id, 
-                    time_since_last_seen: !userLastSeen ? 0 : timeSinceLastSeen,
-                    // backdate to when session _actually_ started
-                    timestamp: new Date(timestamp).toISOString(), 
-                    trigger_event: event.event
-                }
-            )
-            storage.set(`last_session_started_${event.distinct_id}`, parsedTimestamp)
+export const setupPlugin: SessionTrackerPlugin['setupPlugin'] = ({ global, config }) => {
+    global.sessionLength = parseInt(config.sessionLength) || 30
+    global.sessionStartEvent = config.sessionStartEvent || 'Session start'
+    global.sessionEndEvent = config.sessionEndEvent || 'Session end'
+}
 
-            // If we've started a new session, another session must have ended
-            if (userLastSessionStarted) {
-                posthog.capture(
-                    'session_ended',
-                    {
-                        // backdate the session end to the timestamp last event before the new session
-                        timestamp: new Date(userLastSeen).toISOString(), 
-                        distinct_id: event.distinct_id, 
-                        session_duration: userLastSeen - userLastSessionStarted
-                    }
-                )
-            }
-        }
-
+export const onEvent: SessionTrackerPlugin['onEvent'] = async (event, { cache, global, jobs }) => {
+    // skip this for the session start/end events
+    if (event.event === global.sessionStartEvent || event.event === global.sessionEndEvent) {
+        return
+    }
+    // check if we're the first one to increment this key in the last ${global.sessionLength} minutes
+    if ((await cache.incr(`session_${event.distinct_id}`)) === 1) {
+        // if so, dispatch a session start event
+        posthog.capture(global.sessionStartEvent, { distinct_id: event.distinct_id, timestamp: event.timestamp })
+        // and launch a job to check in 30min if the session is still alive
+        await jobs.checkIfSessionIsOver({ distinct_id: event.distinct_id }).runIn(global.sessionLength, 'minutes')
     }
+    // make the key expire in ${global.sessionLength} min
+    await cache.expire(`session_${event.distinct_id}`, global.sessionLength * 60)
+    await cache.set(
+        `last_timestamp_${event.distinct_id}`,
+        event.timestamp || event.now || event.sent_at || new Date().toISOString()
+    )
+}
 
-    event.properties['is_first_event_in_session'] = isFirstEventInSession
+export const jobs: SessionTrackerPlugin['jobs'] = {
+    // a background job to check if a session is still in progress
+    checkIfSessionIsOver: async ({ distinct_id }, { jobs, cache, global }) => {
+        // check if there's a key that has not expired
+        const ping = await cache.get(`session_${distinct_id}`, undefined)
+        if (!ping) {
+            // if it expired, dispatch the session end event
+            const timestamp =
+                (await cache.get(`last_timestamp_${distinct_id}`, undefined)) ||
+                new Date(new Date().valueOf() - global.sessionLength * 60000).toISOString()
 
-    return event
+            await cache.set(`last_timestamp_${distinct_id}`, undefined)
+            posthog.capture(global.sessionEndEvent, { distinct_id, timestamp })
+        } else {
+            // if the key is still there, check again in a minute
+            await jobs.checkIfSessionIsOver({ distinct_id }).runIn(1, 'minute')
+        }
+    },
 }
-
-module.exports = {
-    processEvent,
-}
diff --git a/package.json b/package.json
@@ -25,11 +25,10 @@
         }
     },
     "devDependencies": {
-        "jest": "^26.6.3",
-        "posthog-plugins": "^0.2.2"
+        "jest": "^26.6.3"
     },
     "dependencies": {
-        "@posthog/plugin-scaffold": "^0.5.0",
+        "@posthog/plugin-scaffold": "^0.10.0",
         "@types/jest": "^26.0.22",
         "@types/node": "^14.14.41",
         "ts-jest": "^26.5.5",

diff --git a/plugin.json b/plugin.json
@@ -1,11 +1,30 @@
 {
-  "name": "Session Tracker",
-  "url": "https://github.com/PostHog/session-tracker-plugin",
-  "description": "Advanced session tracking for PostHog.",
-  "main": "index.ts",
-  "config": [
-    {
-      "markdown": "## Important Note For Self-Hosted Users \nThis plugin leverages database storage to work. We estimate that it will use about 3MB of storage for every 10000 users tracked."
-    }
-  ]
+    "name": "Session Tracker",
+    "url": "https://github.com/PostHog/session-tracker-plugin",
+    "description": "Advanced session tracking for PostHog.",
+    "main": "index.ts",
+    "posthogVersion": ">= 1.25.0",
+    "config": [
+        {
+            "key": "sessionLength",
+            "name": "Session length in minutes",
+            "type": "string",
+            "default": "30",
+            "required": true
+        },
+        {
+            "key": "sessionStartEvent",
+            "name": "Session start event",
+            "type": "string",
+            "default": "Session started",
+            "required": true
+        },
+        {
+            "key": "sessionEndEvent",
+            "name": "Session end event",
+            "type": "string",
+            "default": "Session ended",
+            "required": true
+        }
+    ]
 }
diff --git a/yarn.lock b/yarn.lock
@@ -466,22 +466,10 @@
     "@types/yargs" "^15.0.0"
     chalk "^4.0.0"
 
-"@maxmind/geoip2-node@^2.3.1":
-  version "2.3.2"
-  resolved "https://registry.yarnpkg.com/@maxmind/geoip2-node/-/geoip2-node-2.3.2.tgz#a0aaf8452693491e815021fe16e692959490ba6d"
-  integrity sha512-a1TSZt3uWe7yrgE2WMdTItK6XuG2Aj125cAXA+JuT2nomv3oqIK8XXg9iJVpzNXAYRV72XO0+zY+3HluOGgF3w==
-  dependencies:
-    camelcase-keys "^6.0.1"
-    ip6addr "^0.2.3"
-    lodash.set "^4.3.2"
-    maxmind "^4.2.0"
-
-"@posthog/plugin-scaffold@^0.5.0":
-  version "0.5.0"
-  resolved "https://registry.yarnpkg.com/@posthog/plugin-scaffold/-/plugin-scaffold-0.5.0.tgz#0d46d0f39700ebf3cf613ba80a2c9a4dc6d13805"
-  integrity sha512-gE12hy/gYdMOYLP/PhbC2XfqvCeoXrdkFeR9HFfSK31RWU+aW+JMK7pi+CATatXfNpMCvjGxIYJk3QBPwm0WDA==
-  dependencies:
-    "@maxmind/geoip2-node" "^2.3.1"
+"@posthog/plugin-scaffold@^0.10.0":
+  version "0.10.0"
+  resolved "https://registry.yarnpkg.com/@posthog/plugin-scaffold/-/plugin-scaffold-0.10.0.tgz#e80f57c5d3833753632607bed3ca71ebf272b12b"
+  integrity sha512-c8lNzQTBMJ0X3SCjcaD+mXZIx2thc+ptf8G4gbfT9YBFFD6TMaxs+/APMUab2aRJRbVwOsCGj9poxwuF4wxPpA==
 
 "@sinonjs/commons@^1.7.0":
   version "1.8.1"
@@ -901,15 +889,6 @@ callsites@^3.0.0:
   resolved "https://registry.yarnpkg.com/callsites/-/callsites-3.1.0.tgz#b3630abd8943432f54b3f0519238e33cd7df2f73"
   integrity sha512-P8BjAsXvZS+VIDUI11hHCQEv74YT67YUi5JJFNWIqL235sBmjX4+qx9Muvls5ivyNENctx46xQLQ3aTuE7ssaQ==
 
-camelcase-keys@^6.0.1:
-  version "6.2.2"
-  resolved "https://registry.yarnpkg.com/camelcase-keys/-/camelcase-keys-6.2.2.tgz#5e755d6ba51aa223ec7d3d52f25778210f9dc3c0"
-  integrity sha512-YrwaA0vEKazPBkn0ipTiMpSajYDSe+KjQfrjhcBMxJt/znbvlHd8Pw/Vamaz5EB4Wfhs3SUR3Z9mwRu/P3s3Yg==
-  dependencies:
-    camelcase "^5.3.1"
-    map-obj "^4.0.0"
-    quick-lru "^4.0.1"
-
 camelcase@^5.0.0, camelcase@^5.3.1:
   version "5.3.1"
   resolved "https://registry.yarnpkg.com/camelcase/-/camelcase-5.3.1.tgz#e3c9b31569e106811df242f715725a1f4c494320"
@@ -1657,14 +1636,6 @@ ip-regex@^2.1.0:
   resolved "https://registry.yarnpkg.com/ip-regex/-/ip-regex-2.1.0.tgz#fa78bf5d2e6913c911ce9f819ee5146bb6d844e9"
   integrity sha1-+ni/XS5pE8kRzp+BnuUUa7bYROk=
 
-ip6addr@^0.2.3:
-  version "0.2.3"
-  resolved "https://registry.yarnpkg.com/ip6addr/-/ip6addr-0.2.3.tgz#660df0d27092434f0aadee025aba8337c6d7d4d4"
-  integrity sha512-qA9DXRAUW+lT47/i/4+Q3GHPwZjGt/atby1FH/THN6GVATA6+Pjp2nztH7k6iKeil7hzYnBwfSsxjthlJ8lJKw==
-  dependencies:
-    assert-plus "^1.0.0"
-    jsprim "^1.4.0"
-
 is-accessor-descriptor@^0.1.6:
   version "0.1.6"
   resolved "https://registry.yarnpkg.com/is-accessor-descriptor/-/is-accessor-descriptor-0.1.6.tgz#a9e12cb3ae8d876727eeef3843f8a0897b5c98d6"
@@ -2343,7 +2314,7 @@ json5@^2.1.2:
   dependencies:
     minimist "^1.2.5"
 
-jsprim@^1.2.2, jsprim@^1.4.0:
+jsprim@^1.2.2:
   version "1.4.1"
   resolved "https://registry.yarnpkg.com/jsprim/-/jsprim-1.4.1.tgz#313e66bc1e5cc06e438bc1b7499c2e5c56acb6a2"
   integrity sha1-MT5mvB5cwG5Di8G3SZwuXFastqI=
@@ -2407,11 +2378,6 @@ locate-path@^5.0.0:
   dependencies:
     p-locate "^4.1.0"
 
-lodash.set@^4.3.2:
-  version "4.3.2"
-  resolved "https://registry.yarnpkg.com/lodash.set/-/lodash.set-4.3.2.tgz#d8757b1da807dde24816b0d6a84bea1a76230b23"
-  integrity sha1-2HV7HagH3eJIFrDWqEvqGnYjCyM=
-
 lodash.sortby@^4.7.0:
   version "4.7.0"
   resolved "https://registry.yarnpkg.com/lodash.sortby/-/lodash.sortby-4.7.0.tgz#edd14c824e2cc9c1e0b0a1b42bb5210516a42438"
@@ -2458,26 +2424,13 @@ map-cache@^0.2.2:
   resolved "https://registry.yarnpkg.com/map-cache/-/map-cache-0.2.2.tgz#c32abd0bd6525d9b051645bb4f26ac5dc98a0dbf"
   integrity sha1-wyq9C9ZSXZsFFkW7TyasXcmKDb8=
 
-map-obj@^4.0.0:
-  version "4.2.1"
-  resolved "https://registry.yarnpkg.com/map-obj/-/map-obj-4.2.1.tgz#e4ea399dbc979ae735c83c863dd31bdf364277b7"
-  integrity sha512-+WA2/1sPmDj1dlvvJmB5G6JKfY9dpn7EVBUL06+y6PoljPkh+6V1QihwxNkbcGxCRjt2b0F9K0taiCuo7MbdFQ==
-
 map-visit@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/map-visit/-/map-visit-1.0.0.tgz#ecdca8f13144e660f1b5bd41f12f3479d98dfb8f"
   integrity sha1-7Nyo8TFE5mDxtb1B8S80edmN+48=
   dependencies:
     object-visit "^1.0.0"
 
-maxmind@^4.2.0:
-  version "4.3.1"
-  resolved "https://registry.yarnpkg.com/maxmind/-/maxmind-4.3.1.tgz#b20103f19e9fc12e4d1618814380d89a00f65770"
-  integrity sha512-0CxAgwWIwQy4zF1/qCMOeUPleMTYgfnsuIsZ4Otzx6hzON4PCqivPiH6Kz7iWrC++KOGCbSB3nxkJMvDEdWt6g==
-  dependencies:
-    mmdb-lib "1.2.0"
-    tiny-lru "7.0.6"
-
 merge-stream@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/merge-stream/-/merge-stream-2.0.0.tgz#52823629a14dd00c9770fb6ad47dc6310f2c1f60"
@@ -2552,11 +2505,6 @@ mkdirp@1.x:
   resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-1.0.4.tgz#3eb5ed62622756d79a5f0e2a221dfebad75c2f7e"
   integrity sha512-vVqVZQyf3WLx2Shd0qJ9xuvqgAyKPLAiqITEtqW0oIUjzo3PePDd6fW9iFz30ef7Ysp/oiWqbhszeGWW2T6Gzw==
 
-mmdb-lib@1.2.0:
-  version "1.2.0"
-  resolved "https://registry.yarnpkg.com/mmdb-lib/-/mmdb-lib-1.2.0.tgz#0ecd93f4942f65a2d09be0502fa9126939606727"
-  integrity sha512-3XYebkStxqCgWJjsmT9FCaE19Yi4Tvs2SBPKhUks3rJJh52oF1AKAd9kei+LTutud3a6RCZ0o2Um96Fn7o3zVA==
-
 ms@2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/ms/-/ms-2.0.0.tgz#5608aeadfc00be6c2901df5f9861788de0d597c8"
@@ -2814,11 +2762,6 @@ posix-character-classes@^0.1.0:
   resolved "https://registry.yarnpkg.com/posix-character-classes/-/posix-character-classes-0.1.1.tgz#01eac0fe3b5af71a2a6c02feabb8c1fef7e00eab"
   integrity sha1-AerA/jta9xoqbAL+q7jB/vfgDqs=
 
-posthog-plugins@^0.2.2:
-  version "0.2.2"
-  resolved "https://registry.yarnpkg.com/posthog-plugins/-/posthog-plugins-0.2.2.tgz#84bf2c7c50a3fea7a585187c9febda59ab774dd9"
-  integrity sha512-AFOKFexaCwKQ7+zjpM7g6Cj/75YF3QMx513xFahCHGAZrqrZuIPyY+xPvg1U4TA0J4P5OfzPz5tQYmPYcuppyw==
-
 prelude-ls@~1.1.2:
   version "1.1.2"
   resolved "https://registry.yarnpkg.com/prelude-ls/-/prelude-ls-1.1.2.tgz#21932a549f5e52ffd9a827f570e04be62a97da54"
@@ -2865,11 +2808,6 @@ qs@~6.5.2:
   resolved "https://registry.yarnpkg.com/qs/-/qs-6.5.2.tgz#cb3ae806e8740444584ef154ce8ee98d403f3e36"
   integrity sha512-N5ZAX4/LxJmF+7wN74pUD6qAh9/wnvdQcjq9TZjevvXzSUo7bfmw91saqMjzGS2xq91/odN2dW/WOl7qQHNDGA==
 
-quick-lru@^4.0.1:
-  version "4.0.1"
-  resolved "https://registry.yarnpkg.com/quick-lru/-/quick-lru-4.0.1.tgz#5b8878f113a58217848c6482026c73e1ba57727f"
-  integrity sha512-ARhCpm70fzdcvNQfPoy49IaanKkTlRWF2JMzqhcJbhSFRZv7nPTvZJdcY7301IPmvW+/p0RgIWnQDLJxifsQ7g==
-
 react-is@^17.0.1:
   version "17.0.1"
   resolved "https://registry.yarnpkg.com/react-is/-/react-is-17.0.1.tgz#5b3531bd76a645a4c9fb6e693ed36419e3301339"
@@ -3366,11 +3304,6 @@ throat@^5.0.0:
   resolved "https://registry.yarnpkg.com/throat/-/throat-5.0.0.tgz#c5199235803aad18754a667d659b5e72ce16764b"
   integrity sha512-fcwX4mndzpLQKBS1DVYhGAcYaYt7vsHNIvQV+WXMvnow5cgjPphq5CaayLaGsjRdSCKZFNGt7/GYAuXaNOiYCA==
 
-tiny-lru@7.0.6:
-  version "7.0.6"
-  resolved "https://registry.yarnpkg.com/tiny-lru/-/tiny-lru-7.0.6.tgz#b0c3cdede1e5882aa2d1ae21cb2ceccf2a331f24"
-  integrity sha512-zNYO0Kvgn5rXzWpL0y3RS09sMK67eGaQj9805jlK9G6pSadfriTczzLHFXa/xcW4mIRfmlB9HyQ/+SgL0V1uow==
-
 tmpl@1.0.x:
   version "1.0.4"
   resolved "https://registry.yarnpkg.com/tmpl/-/tmpl-1.0.4.tgz#23640dd7b42d00433911140820e5cf440e521dd1"