allow to set subject in email threads

src/main/java/org/thoughtcrime/securesms/ConversationActivity.java

@@ -786,6 +786,8 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
       return future;
     }
 
+    inputPanel.setSubject(draft.getSubject());
+
     final String text = TextUtils.isEmpty(sharedText)? draft.getText() : sharedText;
     if(!text.isEmpty()) {
       composeText.setText(text);
@@ -977,10 +979,12 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
     if (dcChat.canSend()) {
       composePanel.setVisibility(View.VISIBLE);
       attachmentManager.setHidden(false);
+      inputPanel.setSubjectVisible(!dcChat.isEncrypted());
     } else {
       composePanel.setVisibility(View.GONE);
       attachmentManager.setHidden(true);
       hideSoftKeyboard();
+      inputPanel.setSubjectVisible(false);
     }
   }
 
@@ -1063,12 +1067,14 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
 
     Optional<QuoteModel> quote = inputPanel.getQuote();
     boolean editing = isEditing;
+    final String subject = inputPanel.getSubject();
 
     // for a quick ui feedback, we clear the related controls immediately on sending messages.
     // for drafts, however, we do not change the controls, the activity may be resumed.
     if (action==ACTION_SEND_OUT) {
       composeText.setText("");
       inputPanel.clearQuote();
+      inputPanel.clearSubject();
     }
 
     Util.runOnAnyBackgroundThread(() -> {
@@ -1133,6 +1139,10 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
         msg.setQuote(quote.get().getQuotedMsg());
       }
 
+      if (!subject.isEmpty() && msg != null) {
+        msg.setSubject(subject);
+      }
+
       if (action==ACTION_SEND_OUT) {
 
         // for WEBXDC, drafts are just sent out as is.

src/main/java/org/thoughtcrime/securesms/ConversationItem.java

@@ -411,8 +411,11 @@ public class ConversationItem extends BaseConversationItem
     bodyText.setClickable(false);
     bodyText.setFocusable(false);
 
+    String subject = messageRecord.getSubject();
     String text = messageRecord.getText();
 
+    if (!subject.isEmpty() && messageRecord.isOutgoing() && !messageRecord.isSecure()) text = subject + "\n\n" + text;
+
     if (messageRecord.getType() == DcMsg.DC_MSG_CALL || text.isEmpty()) {
       bodyText.setVisibility(View.GONE);
     }

src/main/java/org/thoughtcrime/securesms/components/InputPanel.java

@@ -56,6 +56,7 @@ public class InputPanel extends ConstraintLayout
   private QuoteView       quoteView;
   private EmojiToggle     emojiToggle;
   private ComposeText     composeText;
+  private android.widget.EditText subjectText;
   private View            quickCameraToggle;
   private View            quickAudioToggle;
   private View            buttonToggle;
@@ -91,6 +92,7 @@ public class InputPanel extends ConstraintLayout
     this.quoteView              = findViewById(R.id.quote_view);
     this.emojiToggle            = findViewById(R.id.emoji_toggle);
     this.composeText            = findViewById(R.id.embedded_text_editor);
+    this.subjectText            = findViewById(R.id.subject_text);
     this.quickCameraToggle      = findViewById(R.id.quick_camera_toggle);
     this.quickAudioToggle       = findViewById(R.id.quick_audio_toggle);
     this.buttonToggle           = findViewById(R.id.button_toggle);
@@ -198,6 +200,30 @@ public class InputPanel extends ConstraintLayout
     composeText.performClick();
   }
 
+  public void setSubjectVisible(boolean visible) {
+    subjectText.setVisibility(visible ? View.VISIBLE : View.GONE);
+    emojiToggle.setVisibility(!visible ? View.VISIBLE : View.GONE);
+  }
+
+  public String getSubject() {
+    if (subjectText != null && subjectText.getVisibility() == View.VISIBLE) {
+      return subjectText.getText().toString().trim();
+    }
+    return "";
+  }
+
+  public void clearSubject() {
+    if (subjectText != null) {
+      subjectText.setText("");
+    }
+  }
+
+  public void setSubject(String subject) {
+    if (subjectText != null && subject != null) {
+      subjectText.setText(subject);
+    }
+  }
+
   public void setMediaKeyboard(@NonNull MediaKeyboard mediaKeyboard) {
     mediaKeyboard.setKeyboardListener(this);
   }

src/main/res/layout/conversation_input_panel.xml

@@ -25,11 +25,28 @@
         app:message_type="preview"
         tools:visibility="visible" />
 
+    <EditText
+        android:id="@+id/subject_text"
+        style="@style/ComposeEditText"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="8dp"
+        android:layout_marginEnd="8dp"
+        android:layout_marginBottom="6dp"
+        android:hint="@string/subject"
+        android:inputType="text"
+        android:maxLines="1"
+        android:visibility="gone"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/quote_view"
+        tools:visibility="visible" />
+
     <FrameLayout
         android:id="@+id/input_field_frame_layout"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintEnd_toStartOf="@+id/button_toggle"
-        app:layout_constraintTop_toBottomOf="@id/quote_view"
+        app:layout_constraintTop_toBottomOf="@id/subject_text"
         app:layout_constraintBottom_toBottomOf="parent"
         android:layout_width="0dp"
         android:layout_height="wrap_content"