Add SessionGenerator to generate the Session ID

firebase-sessions/src/main/kotlin/com/google/firebase/sessions/FirebaseSessions.kt

@@ -24,6 +24,9 @@ import com.google.firebase.ktx.Firebase
 import com.google.firebase.ktx.app
 
 class FirebaseSessions internal constructor(firebaseApp: FirebaseApp) {
+
+  private val sessionGenerator = SessionGenerator(collectEvents = true)
+
   init {
     val sessionInitiator = SessionInitiator(WallClock::elapsedRealtime, this::initiateSessionStart)
     val context = firebaseApp.applicationContext.applicationContext
@@ -40,6 +43,8 @@ class FirebaseSessions internal constructor(firebaseApp: FirebaseApp) {
   private fun initiateSessionStart() {
     // TODO(mrober): Generate a session
     Log.i(TAG, "Initiate session start")
+
+    sessionGenerator.generateNewSession()
   }
 
   companion object {

firebase-sessions/src/main/kotlin/com/google/firebase/sessions/SessionGenerator.kt

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.sessions
+
+import java.util.UUID
+
+/**
+ * [SessionInfo] is a data class responsible for storing information about the current Session.
+ *
+ * @hide
+ */
+internal data class SessionInfo(
+  val sessionId: String,
+  val firstSessionId: String,
+  val collectEvents: Boolean,
+  val sessionIndex: Int,
+)
+
+/**
+ * The [SessionGenerator] is responsible for generating the Session ID, and keeping the
+ * [SessionInfo] up to date with the latest values.
+ *
+ * @hide
+ */
+internal class SessionGenerator(collectEvents: Boolean) {
+  private var firstSessionId = ""
+  private var sessionIndex: Int = -1
+  private var collectEvents = collectEvents
+
+  private var thisSession: SessionInfo =
+    SessionInfo(
+      sessionId = "",
+      firstSessionId = "",
+      collectEvents = collectEvents,
+      sessionIndex = sessionIndex
+    )
+
+  // Generates a new Session ID. If there was already a generated Session ID
+  // from the last session during the app's lifecycle, it will also set the last Session ID
+  fun generateNewSession() {
+    val newSessionId = UUID.randomUUID().toString().replace("-", "").lowercase()
+
+    // If firstSessionId is set, use it. Otherwise set it to the
+    // first generated Session ID
+    firstSessionId = if (firstSessionId.isEmpty()) newSessionId else firstSessionId
+
+    sessionIndex += 1
+
+    thisSession =
+      SessionInfo(
+        sessionId = newSessionId,
+        firstSessionId = firstSessionId,
+        collectEvents = collectEvents,
+        sessionIndex = sessionIndex
+      )
+  }
+
+  val currentSession: SessionInfo
+    get() = thisSession
+}

firebase-sessions/src/test/kotlin/com/google/firebase/sessions/SessionGeneratorTest.kt

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.sessions
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.Test
+
+class SessionGeneratorTest {
+  fun isValidSessionId(sessionId: String): Boolean {
+    if (sessionId.length != 32) {
+      return false
+    }
+    if (sessionId.contains("-")) {
+      return false
+    }
+    if (sessionId.lowercase() != sessionId) {
+      return false
+    }
+    return true
+  }
+
+  // This test case isn't important behavior. Nothing should access
+  // currentSession before generateNewSession has been called. This test just
+  // ensures it has consistent behavior.
+  @Test
+  fun currentSession_beforeGenerateReturnsDefault() {
+    val sessionGenerator = SessionGenerator(collectEvents = false)
+
+    assertThat(sessionGenerator.currentSession.sessionId).isEqualTo("")
+    assertThat(sessionGenerator.currentSession.firstSessionId).isEqualTo("")
+    assertThat(sessionGenerator.currentSession.collectEvents).isEqualTo(false)
+    assertThat(sessionGenerator.currentSession.sessionIndex).isEqualTo(-1)
+  }
+
+  @Test
+  fun generateNewSessionID_generatesValidSessionInfo() {
+    val sessionGenerator = SessionGenerator(collectEvents = true)
+
+    sessionGenerator.generateNewSession()
+
+    assertThat(isValidSessionId(sessionGenerator.currentSession.sessionId)).isEqualTo(true)
+    assertThat(isValidSessionId(sessionGenerator.currentSession.firstSessionId)).isEqualTo(true)
+    assertThat(sessionGenerator.currentSession.firstSessionId)
+      .isEqualTo(sessionGenerator.currentSession.sessionId)
+    assertThat(sessionGenerator.currentSession.collectEvents).isEqualTo(true)
+    assertThat(sessionGenerator.currentSession.sessionIndex).isEqualTo(0)
+  }
+
+  // Ensures that generating a Session ID multiple times results in the fist
+  // Session ID being set in the firstSessionId field
+  @Test
+  fun generateNewSessionID_incrementsSessionIndex_keepsFirstSessionId() {
+    val sessionGenerator = SessionGenerator(collectEvents = true)
+
+    sessionGenerator.generateNewSession()
+
+    val firstSessionInfo = sessionGenerator.currentSession
+
+    assertThat(isValidSessionId(firstSessionInfo.sessionId)).isEqualTo(true)
+    assertThat(isValidSessionId(firstSessionInfo.firstSessionId)).isEqualTo(true)
+    assertThat(firstSessionInfo.firstSessionId).isEqualTo(firstSessionInfo.sessionId)
+    assertThat(firstSessionInfo.sessionIndex).isEqualTo(0)
+
+    sessionGenerator.generateNewSession()
+    val secondSessionInfo = sessionGenerator.currentSession
+
+    assertThat(isValidSessionId(secondSessionInfo.sessionId)).isEqualTo(true)
+    assertThat(isValidSessionId(secondSessionInfo.firstSessionId)).isEqualTo(true)
+    // Ensure the new firstSessionId is equal to the first Session ID from earlier
+    assertThat(secondSessionInfo.firstSessionId).isEqualTo(firstSessionInfo.sessionId)
+    // Session Index should increase
+    assertThat(secondSessionInfo.sessionIndex).isEqualTo(1)
+
+    // Do a third round just in case
+    sessionGenerator.generateNewSession()
+    val thirdSessionInfo = sessionGenerator.currentSession
+
+    assertThat(isValidSessionId(thirdSessionInfo.sessionId)).isEqualTo(true)
+    assertThat(isValidSessionId(thirdSessionInfo.firstSessionId)).isEqualTo(true)
+    // Ensure the new firstSessionId is equal to the first Session ID from earlier
+    assertThat(thirdSessionInfo.firstSessionId).isEqualTo(firstSessionInfo.sessionId)
+    // Session Index should increase
+    assertThat(thirdSessionInfo.sessionIndex).isEqualTo(2)
+  }
+}