Add initial storage manager (#14)

* Add initial storage manager

Signed-off-by: Tiago Nascimento <tiago.nascimento@spruceid.com>

* Addressing review comments

Signed-off-by: Tiago Nascimento <tiago.nascimento@spruceid.com>

* Fix reference to wallet.sdk.KeyManager

---------

Signed-off-by: Tiago Nascimento <tiago.nascimento@spruceid.com>
Co-authored-by: Ross Schulman <ross@rbs.io>

MobileSdk/build.gradle.kts

@@ -131,6 +131,7 @@ dependencies {
     implementation("androidx.camera:camera-mlkit-vision:1.3.0-alpha06")
     implementation("com.google.android.gms:play-services-mlkit-text-recognition:19.0.0")
     /* End UI dependencies */
+    implementation("androidx.datastore:datastore-preferences:1.1.1")
     testImplementation("junit:junit:4.13.2")
     androidTestImplementation("com.android.support.test:runner:1.0.2")
     androidTestImplementation("com.android.support.test.espresso:espresso-core:3.0.2")

MobileSdk/src/main/java/com/spruceid/mobile/sdk/StorageManager.kt

@@ -0,0 +1,158 @@
+import android.content.Context
+import android.util.Base64
+import androidx.datastore.core.DataStore
+import androidx.datastore.preferences.core.*
+import androidx.datastore.preferences.preferencesDataStoreFile
+import com.spruceid.mobile.sdk.KeyManager
+import kotlinx.coroutines.flow.catch
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.map
+
+private class DataStoreSingleton private constructor(context: Context) {
+    val dataStore: DataStore<Preferences> = store(context, "default")
+
+    companion object {
+        private const val FILENAME_PREFIX = "sprucekit/datastore/"
+
+        private fun location(context: Context, file: String) =
+            context.preferencesDataStoreFile(FILENAME_PREFIX + file.lowercase())
+
+        private fun store(context: Context, file: String): DataStore<Preferences> =
+            PreferenceDataStoreFactory.create(produceFile = { location(context, file) })
+
+        @Volatile
+        private var instance: DataStoreSingleton? = null
+
+        fun getInstance(context: Context) =
+            instance
+                ?: synchronized(this) {
+                    instance ?: DataStoreSingleton(context).also {
+                        instance = it
+                    }
+                }
+    }
+}
+
+object StorageManager {
+    private const val B64_FLAGS = Base64.URL_SAFE or Base64.NO_PADDING or Base64.NO_WRAP
+    private const val KEY_NAME = "sprucekit/datastore"
+
+    /// Function: encrypt
+    ///
+    /// Encrypts the given string.
+    ///
+    /// Arguments:
+    /// value - The string value to be encrypted
+    private fun encrypt(value: String): Result<ByteArray> {
+        val keyManager = KeyManager()
+        try {
+            if (!keyManager.keyExists(KEY_NAME)) {
+                keyManager.generateEncryptionKey(KEY_NAME)
+            }
+            val encrypted = keyManager.encryptPayload(KEY_NAME, value.toByteArray())
+            val iv = Base64.encodeToString(encrypted.first, B64_FLAGS)
+            val bytes = Base64.encodeToString(encrypted.second, B64_FLAGS)
+            val res = "$iv;$bytes".toByteArray()
+            return Result.success(res)
+        } catch (e: Exception) {
+            return Result.failure(e)
+        }
+    }
+
+    /// Function: decrypt
+    ///
+    /// Decrypts the given byte array.
+    ///
+    /// Arguments:
+    /// value - The byte array to be decrypted
+    private fun decrypt(value: ByteArray): Result<String> {
+        val keyManager = KeyManager()
+        try {
+            if (!keyManager.keyExists(KEY_NAME)) {
+                return Result.failure(Exception("Cannot retrieve values before creating encryption keys"))
+            }
+            val decoded = value.decodeToString().split(";")
+            assert(decoded.size == 2)
+            val iv = Base64.decode(decoded.first(), B64_FLAGS)
+            val encrypted = Base64.decode(decoded.last(), B64_FLAGS)
+            val decrypted =
+                keyManager.decryptPayload(KEY_NAME, iv, encrypted)
+                    ?: return Result.failure(Exception("Failed to decrypt value"))
+            return Result.success(decrypted.decodeToString())
+        } catch (e: Exception) {
+            return Result.failure(e)
+        }
+    }
+
+    /// Function: add
+    ///
+    /// Adds a key-value pair to storage.  Should the key already exist, the value will be
+    /// replaced.
+    ///
+    /// Arguments:
+    /// context - The application context to be able to access the DataStore
+    /// key - The key to add
+    /// value - The value to add under the key
+    suspend fun add(context: Context, key: String, value: String): Result<Unit> {
+        val storeKey = byteArrayPreferencesKey(key)
+        val storeValue = encrypt(value)
+
+        if (storeValue.isFailure) {
+            return Result.failure(Exception("Failed to encrypt value for storage"))
+        }
+
+        DataStoreSingleton.getInstance(context).dataStore.edit { store ->
+            store[storeKey] = storeValue.getOrThrow()
+        }
+
+        return Result.success(Unit)
+    }
+
+    /// Function: get
+    ///
+    /// Retrieves the value from storage identified by key.
+    ///
+    /// Arguments:
+    /// context - The application context to be able to access the DataStore
+    /// key - The key to retrieve
+    suspend fun get(context: Context, key: String): Result<String?> {
+        val storeKey = byteArrayPreferencesKey(key)
+        return DataStoreSingleton.getInstance(context)
+            .dataStore
+            .data
+            .map { store ->
+                try {
+                    store[storeKey]?.let { v ->
+                        val storeValue = decrypt(v)
+                        when {
+                            storeValue.isSuccess -> Result.success(storeValue.getOrThrow())
+                            storeValue.isFailure -> Result.failure(storeValue.exceptionOrNull()!!)
+                            else -> Result.failure(Exception("Failed to decrypt value for storage"))
+                        }
+                    }
+                        ?: Result.success(null)
+                } catch (e: Exception) {
+                    Result.failure(e)
+                }
+            }
+            .catch { exception -> emit(Result.failure(exception)) }
+            .first()
+    }
+
+    /// Function: remove
+    ///
+    /// Removes a key-value pair from storage by key.
+    ///
+    /// Arguments:
+    /// context - The application context to be able to access the DataStore
+    /// key - The key to remove
+    suspend fun remove(context: Context, key: String): Result<Unit> {
+        val storeKey = stringPreferencesKey(key)
+        DataStoreSingleton.getInstance(context).dataStore.edit { store ->
+            if (store.contains(storeKey)) {
+                store.remove(storeKey)
+            }
+        }
+        return Result.success(Unit)
+    }
+}