Implement structured Android entry viewer (#99)

android/platform/src/main/kotlin/de/rfc1437/ironstorage/platform/AndroidSecretClipboard.kt

@@ -0,0 +1,29 @@
+package de.rfc1437.ironstorage.platform
+
+import android.content.ClipData
+import android.content.ClipboardManager
+import android.content.Context
+import android.os.Build
+import android.os.PersistableBundle
+import de.rfc1437.ironstorage.core.SecretClipboard
+
+class AndroidSecretClipboard(context: Context) : SecretClipboard {
+    private val manager = context.getSystemService(ClipboardManager::class.java)
+    override fun read(): ByteArray? = manager.primaryClip?.let { clip ->
+        if (clip.itemCount == 1) clip.getItemAt(0).text?.toString()?.toByteArray() else null
+    }
+    override fun write(value: ByteArray) {
+        val clip = ClipData.newPlainText("IronStorage", value.toString(Charsets.UTF_8))
+        clip.description.extras = PersistableBundle().apply {
+            putBoolean("android.content.extra.IS_SENSITIVE", true)
+        }
+        manager.setPrimaryClip(clip)
+    }
+    override fun clear() {
+        if (Build.VERSION.SDK_INT >= 28) {
+            manager.clearPrimaryClip()
+        } else {
+            manager.setPrimaryClip(ClipData.newPlainText("", ""))
+        }
+    }
+}