Refactor "parts" to contain MMS/PDU madness to MMS code paths.

Closes #4248
// FREEBIE

test/androidTest/java/org/thoughtcrime/securesms/database/AttachmentDatabaseTest.java

@@ -0,0 +1,69 @@
+package org.thoughtcrime.securesms.database;
+
+import android.net.Uri;
+
+import org.thoughtcrime.securesms.TextSecureTestCase;
+import org.thoughtcrime.securesms.attachments.AttachmentId;
+import org.thoughtcrime.securesms.attachments.DatabaseAttachment;
+import org.thoughtcrime.securesms.crypto.MasterSecret;
+
+import java.io.FileNotFoundException;
+import java.io.InputStream;
+
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyFloat;
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class AttachmentDatabaseTest extends TextSecureTestCase {
+  private static final long ROW_ID    = 1L;
+  private static final long UNIQUE_ID = 2L;
+
+  private AttachmentDatabase database;
+
+  @Override
+  public void setUp() {
+    database = spy(DatabaseFactory.getAttachmentDatabase(getInstrumentation().getTargetContext()));
+  }
+
+  public void testTaskNotRunWhenThumbnailExists() throws Exception {
+    final AttachmentId attachmentId = new AttachmentId(ROW_ID, UNIQUE_ID);
+
+    when(database.getAttachment(attachmentId)).thenReturn(getMockAttachment("x/x"));
+
+    doReturn(mock(InputStream.class)).when(database).getDataStream(any(MasterSecret.class), any(AttachmentId.class), eq("thumbnail"));
+    database.getThumbnailStream(mock(MasterSecret.class), attachmentId);
+
+    // XXX - I don't think this is testing anything? The thumbnail would be updated asynchronously.
+    verify(database, never()).updateAttachmentThumbnail(any(MasterSecret.class), any(AttachmentId.class), any(InputStream.class), anyFloat());
+  }
+
+  public void testTaskRunWhenThumbnailMissing() throws Exception {
+    final AttachmentId attachmentId = new AttachmentId(ROW_ID, UNIQUE_ID);
+
+    when(database.getAttachment(attachmentId)).thenReturn(getMockAttachment("image/png"));
+    doReturn(null).when(database).getDataStream(any(MasterSecret.class), any(AttachmentId.class), eq("thumbnail"));
+    doNothing().when(database).updateAttachmentThumbnail(any(MasterSecret.class), any(AttachmentId.class), any(InputStream.class), anyFloat());
+
+    try {
+      database.new ThumbnailFetchCallable(mock(MasterSecret.class), attachmentId).call();
+      throw new AssertionError("didn't try to generate thumbnail");
+    } catch (FileNotFoundException fnfe) {
+      // success
+    }
+  }
+
+  private DatabaseAttachment getMockAttachment(String contentType) {
+    DatabaseAttachment attachment = mock(DatabaseAttachment.class);
+    when(attachment.getContentType()).thenReturn(contentType);
+    when(attachment.getDataUri()).thenReturn(Uri.EMPTY);
+
+    return attachment;
+  }
+}