feat(telemetry): add PostHog client factory with activity state tracking

src/shared/posthog-activity-state.ts

@@ -0,0 +1,89 @@
+import { existsSync, mkdirSync, readFileSync } from "node:fs"
+import { join } from "node:path"
+
+import { getDataDir } from "./data-path"
+import { log } from "./logger"
+import { CACHE_DIR_NAME } from "./plugin-identity"
+import { writeFileAtomically } from "./write-file-atomically"
+
+type PostHogActivityState = {
+  lastActiveDayUTC?: string
+  lastActiveHourUTC?: string
+}
+
+type PostHogActivityCaptureState = {
+  dayUTC: string
+  hourUTC: string
+  captureDaily: boolean
+  captureHourly: boolean
+}
+
+const POSTHOG_ACTIVITY_STATE_FILE = "posthog-activity.json"
+
+function getPostHogActivityStateFilePath(): string {
+  return join(getDataDir(), CACHE_DIR_NAME, POSTHOG_ACTIVITY_STATE_FILE)
+}
+
+function getUtcDayString(date: Date): string {
+  return date.toISOString().slice(0, 10)
+}
+
+function getUtcHourString(date: Date): string {
+  return date.toISOString().slice(0, 13)
+}
+
+function readPostHogActivityState(): PostHogActivityState {
+  const stateFilePath = getPostHogActivityStateFilePath()
+  if (!existsSync(stateFilePath)) {
+    return {}
+  }
+
+  try {
+    const content = readFileSync(stateFilePath, "utf-8")
+    const parsed = JSON.parse(content) as PostHogActivityState
+    return parsed
+  } catch (error) {
+    log("[posthog-activity-state] Failed to read activity state", {
+      error: String(error),
+      stateFilePath,
+    })
+    return {}
+  }
+}
+
+function writePostHogActivityState(nextState: PostHogActivityState): void {
+  const stateFilePath = getPostHogActivityStateFilePath()
+
+  try {
+    mkdirSync(join(getDataDir(), CACHE_DIR_NAME), { recursive: true })
+    writeFileAtomically(stateFilePath, `${JSON.stringify(nextState, null, 2)}\n`)
+  } catch (error) {
+    log("[posthog-activity-state] Failed to write activity state", {
+      error: String(error),
+      stateFilePath,
+    })
+  }
+}
+
+export function getPostHogActivityCaptureState(now: Date = new Date()): PostHogActivityCaptureState {
+  const state = readPostHogActivityState()
+  const dayUTC = getUtcDayString(now)
+  const hourUTC = getUtcHourString(now)
+
+  const captureDaily = state.lastActiveDayUTC !== dayUTC
+  const captureHourly = state.lastActiveHourUTC !== hourUTC
+
+  if (captureDaily || captureHourly) {
+    writePostHogActivityState({
+      lastActiveDayUTC: captureDaily ? dayUTC : state.lastActiveDayUTC,
+      lastActiveHourUTC: captureHourly ? hourUTC : state.lastActiveHourUTC,
+    })
+  }
+
+  return {
+    dayUTC,
+    hourUTC,
+    captureDaily,
+    captureHourly,
+  }
+}