Calculate SMS characters respecting encoding

Fixes #1171
Closes #5448

// FREEBIE

src/org/thoughtcrime/securesms/ConversationActivity.java

@@ -1222,9 +1222,9 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
   }
 
   private void calculateCharactersRemaining() {
-    int             charactersSpent = composeText.getText().toString().length();
+    String          messageBody     = composeText.getText().toString();
     TransportOption transportOption = sendButton.getSelectedTransport();
-    CharacterState  characterState  = transportOption.calculateCharacters(charactersSpent);
+    CharacterState  characterState  = transportOption.calculateCharacters(messageBody);
 
     if (characterState.charactersRemaining <= 15 || characterState.messagesSpent > 1) {
       charactersLeft.setText(characterState.charactersRemaining + "/" + characterState.maxMessageSize

src/org/thoughtcrime/securesms/TransportOption.java

@@ -66,8 +66,8 @@ public class TransportOption {
     return type == Type.SMS;
   }
 
-  public CharacterState calculateCharacters(int charactersSpent) {
-    return characterCalculator.calculateCharacters(charactersSpent);
+  public CharacterState calculateCharacters(String messageBody) {
+    return characterCalculator.calculateCharacters(messageBody);
   }
 
   public @DrawableRes int getDrawable() {

src/org/thoughtcrime/securesms/util/CharacterCalculator.java

@@ -18,7 +18,7 @@ package org.thoughtcrime.securesms.util;
 
 public abstract class CharacterCalculator {
 
-  public abstract CharacterState calculateCharacters(int charactersSpent);
+  public abstract CharacterState calculateCharacters(String messageBody);
 
   public static class CharacterState {
     public int charactersRemaining;

src/org/thoughtcrime/securesms/util/MmsCharacterCalculator.java

@@ -5,7 +5,7 @@ public class MmsCharacterCalculator extends CharacterCalculator {
   private static final int MAX_SIZE = 5000;
 
   @Override
-  public CharacterState calculateCharacters(int charactersSpent) {
-    return new CharacterState(1, MAX_SIZE - charactersSpent, MAX_SIZE);
+  public CharacterState calculateCharacters(String messageBody) {
+    return new CharacterState(1, MAX_SIZE - messageBody.length(), MAX_SIZE);
   }
 }

src/org/thoughtcrime/securesms/util/PushCharacterCalculator.java

@@ -19,8 +19,8 @@ package org.thoughtcrime.securesms.util;
 public class PushCharacterCalculator extends CharacterCalculator {
   private static final int MAX_SIZE = 2000;
   @Override
-  public CharacterState calculateCharacters(int charactersSpent) {
-    return new CharacterState(1, MAX_SIZE - charactersSpent, MAX_SIZE);
+  public CharacterState calculateCharacters(String messageBody) {
+    return new CharacterState(1, MAX_SIZE - messageBody.length(), MAX_SIZE);
   }
 }
 

src/org/thoughtcrime/securesms/util/SmsCharacterCalculator.java

@@ -16,27 +16,18 @@
  */
 package org.thoughtcrime.securesms.util;
 
+import android.telephony.SmsMessage;
+
 public class SmsCharacterCalculator extends CharacterCalculator {
 
-  public static final int SMS_SIZE           = 160;
-  public static final int MULTIPART_SMS_SIZE = 153;
-
   @Override
-  public CharacterState calculateCharacters(int charactersSpent) {
-    int maxMessageSize;
+  public CharacterState calculateCharacters(String messageBody) {
 
-    if (charactersSpent <= SMS_SIZE) {
-      maxMessageSize = SMS_SIZE;
-    } else {
-      maxMessageSize = MULTIPART_SMS_SIZE;
-    }
-
-    int messagesSpent = charactersSpent / maxMessageSize;
-
-    if (((charactersSpent % maxMessageSize) > 0) || (messagesSpent == 0))
-      messagesSpent++;
-
-    int charactersRemaining = (maxMessageSize * messagesSpent) - charactersSpent;
+    int[] length            = SmsMessage.calculateLength(messageBody, false);
+    int messagesSpent       = length[0];
+    int charactersSpent     = length[1];
+    int charactersRemaining = length[2];
+    int maxMessageSize      = (charactersSpent + charactersRemaining) / messagesSpent;
 
     return new CharacterState(messagesSpent, charactersRemaining, maxMessageSize);
   }