security: hash question IDs and coarsen categories in Firebase Analytics (SecurityReport #9)

app/src/main/java/app/closer/core/analytics/FirebaseAnalyticsTracker.kt

@@ -3,6 +3,7 @@ package app.closer.core.analytics
 import android.os.Bundle
 import com.google.firebase.analytics.FirebaseAnalytics
 import com.google.firebase.analytics.logEvent
+import java.security.MessageDigest
 import javax.inject.Inject
 import javax.inject.Singleton
 
@@ -11,6 +12,41 @@ class FirebaseAnalyticsTracker @Inject constructor(
     private val analytics: FirebaseAnalytics
 ) : AnalyticsTracker {
 
+    /**
+     * Hashes an identifier for analytics logging.
+     *
+     * Uses SHA-256 and truncates to the first 16 hex characters. This is a one-way,
+     * deterministic transform — enough for aggregate analytics correlation while making
+     * it infeasible to recover the original question content from the logged value.
+     */
+    private fun hashForAnalytics(value: String): String {
+        if (value.isBlank()) return "empty"
+        return try {
+            val digest = MessageDigest.getInstance("SHA-256")
+                .digest(value.toByteArray(Charsets.UTF_8))
+            digest.joinToString("", limit = 8, truncated = "") { "%02x".format(it) }
+        } catch (e: Exception) {
+            "hash_error"
+        }
+    }
+
+    /**
+     * Maps fine-grained category identifiers to a coarse-grained set safe for analytics.
+     *
+     * This preserves useful aggregate behavioral data (e.g. which coarse areas drive
+     * engagement) without leaking the specific, often intimate, category names.
+     */
+    private fun coarseCategory(category: String): String {
+        return when (category.lowercase().trim()) {
+            "communication", "conflict", "trust", "intimacy", "emotional_intimacy",
+            "physical_intimacy", "sex", "desire", "rebuilding_trust" -> "intimacy"
+            "fun", "play", "adventure", "date_night", "travel", "creativity" -> "fun"
+            "money", "future", "goals", "family", "values", "lifestyle" -> "life"
+            "daily_check_in", "app_usage" -> "meta"
+            else -> "other"
+        }
+    }
+
     override fun trackScreenViewed(screenName: String) {
         analytics.logEvent(FirebaseAnalytics.Event.SCREEN_VIEW) {
             param(FirebaseAnalytics.Param.SCREEN_NAME, screenName)
@@ -23,23 +59,23 @@ class FirebaseAnalyticsTracker @Inject constructor(
 
     override fun trackQuestionViewed(questionId: String, category: String) {
         analytics.logEvent("question_viewed") {
-            param("question_id", questionId)
+            param("question_hash", hashForAnalytics(questionId))
-            param("category", category)
+            param("category", coarseCategory(category))
         }
     }
 
     override fun trackAnswerSubmitted(questionId: String, category: String, answerType: String) {
         analytics.logEvent("answer_submitted") {
-            param("question_id", questionId)
+            param("question_hash", hashForAnalytics(questionId))
-            param("category", category)
+            param("category", coarseCategory(category))
             param("answer_type", answerType)
         }
     }
 
     override fun trackAnswerRevealed(questionId: String, category: String) {
         analytics.logEvent("answer_revealed") {
-            param("question_id", questionId)
+            param("question_hash", hashForAnalytics(questionId))
-            param("category", category)
+            param("category", coarseCategory(category))
         }
     }
 
@@ -59,13 +95,13 @@ class FirebaseAnalyticsTracker @Inject constructor(
 
     override fun trackSpinWheelStarted(categoryId: String) {
         analytics.logEvent("spin_wheel_started") {
-            param("category_id", categoryId)
+            param("category_hash", hashForAnalytics(categoryId))
         }
     }
 
     override fun trackSpinWheelCompleted(categoryId: String, answeredCount: Int) {
         analytics.logEvent("spin_wheel_completed") {
-            param("category_id", categoryId)
+            param("category_hash", hashForAnalytics(categoryId))
             param("answered_count", answeredCount.toLong())
         }
     }