#8: created a class for saving the session, added dependencies for Rx…

…Java 3.

app/build.gradle

@@ -33,5 +33,8 @@ dependencies {
     testImplementation 'junit:junit:4.12'
     androidTestImplementation 'androidx.test.ext:junit:1.1.2'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
-
+    // https://mvnrepository.com/artifact/io.reactivex.rxjava3/rxjava
+    implementation group: 'io.reactivex.rxjava3', name: 'rxjava', version: '3.0.7'
+    // https://mvnrepository.com/artifact/io.reactivex.rxjava3/rxandroid
+    implementation group: 'io.reactivex.rxjava3', name: 'rxandroid', version: '3.0.0'
 }

app/src/main/AndroidManifest.xml

@@ -8,7 +8,8 @@
         android:label="@string/app_name"
         android:roundIcon="@mipmap/ic_launcher_round"
         android:supportsRtl="true"
-        android:theme="@style/AppTheme">
+        android:theme="@style/AppTheme"
+        android:name=".HawkApp">
         <activity android:name=".MainActivity">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />

app/src/main/java/so/codex/hawk/HawkApp.kt

@@ -0,0 +1,11 @@
+package so.codex.hawk
+
+import android.app.Application
+
+class HawkApp: Application() {
+
+    override fun onCreate() {
+        super.onCreate()
+        SessionKeeper.init(applicationContext)
+    }
+}

app/src/main/java/so/codex/hawk/SessionKeeper.kt

@@ -0,0 +1,126 @@
+package so.codex.hawk
+
+import android.content.Context
+import android.content.SharedPreferences
+import io.reactivex.rxjava3.core.Observer
+import io.reactivex.rxjava3.subjects.BehaviorSubject
+import so.codex.hawk.entity.Session
+import so.codex.hawk.entity.Token
+
+/**
+ * This class (singleton) is responsible for saving session data (accessToken,refreshToken, time).
+ */
+object SessionKeeper {
+    /**
+     * @property context An instance of the Context class. Used to access [SharedPreferences].
+     */
+    private lateinit var context: Context
+
+    /**
+     * @property KEY_SESSION_PREF Key to get sharedPreferences from context.
+     */
+    private const val KEY_SESSION_PREF = "SESSION_PREF"
+
+    /**
+     * @property KEY_ACCESS_TOKEN The key to get the access token value stored on the device.
+     */
+    const val KEY_ACCESS_TOKEN = "ACCESS_TOKEN"
+
+    /**
+     * @property KEY_REFRESH_TOKEN The key to get the refresh token value stored on the device.
+     */
+    const val KEY_REFRESH_TOKEN = "REFRESH_TOKEN"
+
+    /**
+     * @property KEY_TIME_SESSION A key for getting the value of the start time of
+     *                            the last session stored on the device.
+     */
+    const val KEY_TIME_SESSION = "TIME_SESSION"
+
+    /**
+     * @property session Field for storing the [Session] instance while the application is running.
+     *                   The field is open for reading and closed for direct installation. To save
+     *                   a new instance of the session, use the .saveSession(newSession) methods.
+     */
+    var session: Session = Session(Token("", ""), 0)
+        private set
+
+    /**
+     * @property prefSubject An instance of BehaviorSubject extending the Observable class and
+     *                       capable of sending updates to subscribers. When subscribed, sends
+     *                       the last session update. This instance sends out key-value pairs
+     *                       containing information about updating session elements.
+     */
+    private val prefSubject: BehaviorSubject<Pair<String, String>> = BehaviorSubject.create()
+
+    /**
+     * [SessionKeeper] initialization method.
+     * Must be called 1 time at application start (In [HawkApp] class).
+     *
+     * @param context Must be an applicationContext to avoid memory leaks.
+     */
+    fun init(context: Context) {
+        if(!this::context.isInitialized){
+            this.context = context
+            val preferences = context.getSharedPreferences(KEY_SESSION_PREF, Context.MODE_PRIVATE)
+            restoreSessionFromPref(preferences)
+            preferences.registerOnSharedPreferenceChangeListener { pref, key ->
+                val value = pref.getString(key, "")!!
+                prefSubject.onNext(key to value)
+            }
+        }
+    }
+
+    /**
+     * Method for updating a session instance while the application is running.
+     * The method also stores information about the new session in sharedPreferences.
+     *
+     * @param newSession An instance of the new session. Must be populated with [Token]
+     *                   and last update time.
+     */
+    fun saveSession(newSession: Session) {
+        session = newSession
+        saveToSharedPref(session)
+    }
+
+    /**
+     * Method for adding observer to session update.
+     *
+     * @param observer An observer that will subscribe to the session update and will receive
+     *                 a key-value pair with each update for further use. When subscribing,
+     *                 the observer will receive the last session update and will continue
+     *                 to receive updates until the observable sends an .onComplete().
+     */
+    fun subscribeToSessionUpdate(observer: Observer<Pair<String, String>>) {
+        prefSubject.subscribe(observer)
+    }
+
+    /**
+     * Session recovery method from sharedPreferences saved on the device.
+     *
+     * @param preferences sharedPreferences saved on the device.
+     * @see init
+     */
+    private fun restoreSessionFromPref(preferences: SharedPreferences) {
+        val accessToken = preferences.getString(KEY_ACCESS_TOKEN, "")
+        val refreshToken = preferences.getString(KEY_REFRESH_TOKEN, "")
+        val timeStr = preferences.getString(KEY_TIME_SESSION, "0")
+        val time = timeStr!!.toLong()
+        if (accessToken.isNullOrBlank() or refreshToken.isNullOrBlank()) return
+        session = Session(Token(accessToken!!, refreshToken!!), time)
+    }
+
+    /**
+     * The method of saving the session to sharedPreferences stored on the device.
+     *
+     * @param session Session instance containing information about the new user session.
+     */
+    private fun saveToSharedPref(session: Session) {
+        val editor = context.getSharedPreferences(KEY_SESSION_PREF, Context.MODE_PRIVATE).edit()
+        editor.putString(KEY_ACCESS_TOKEN, session.token.accessToken)
+        editor.putString(KEY_REFRESH_TOKEN, session.token.refreshToken)
+        editor.putString(KEY_TIME_SESSION, "${session.time}")
+        editor.apply()
+    }
+
+}

app/src/main/java/so/codex/hawk/entity/Session.kt

@@ -0,0 +1,4 @@
+package so.codex.hawk.entity
+
+data class Session(val token:Token,val time:Long)
+data class Token(val accessToken: String, val refreshToken: String)