improve contact sorting at New Conversation, prefer names starting with letters

app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/NewConversationActivity.kt

@@ -163,11 +163,7 @@ class NewConversationActivity : SimpleActivity() {
         contacts_letter_fastscroller.setupWithRecyclerView(contacts_list, { position ->
             try {
                 val name = contacts[position].name
-                var character = if (name.isNotEmpty()) name.substring(0, 1) else ""
-                if (!character.areLettersOnly()) {
-                    character = "#"
-                }
-
+                val character = if (name.isNotEmpty()) name.substring(0, 1) else ""
                 FastScrollItemIndicator.Text(character.toUpperCase(Locale.getDefault()))
             } catch (e: Exception) {
                 FastScrollItemIndicator.Text("")

app/src/main/kotlin/com/simplemobiletools/smsmessenger/extensions/Context.kt

@@ -403,7 +403,7 @@ fun Context.getAvailableContacts(callback: (ArrayList<Contact>) -> Unit) {
             it.phoneNumber.substring(startIndex)
         }.toMutableList() as ArrayList<Contact>
 
-        allContacts.sortBy { it.name.normalizeString().toLowerCase(Locale.getDefault()) }
+        allContacts.sort()
         callback(allContacts)
     }
 }

app/src/main/kotlin/com/simplemobiletools/smsmessenger/models/Contact.kt

@@ -1,3 +1,24 @@
 package com.simplemobiletools.smsmessenger.models
 
-data class Contact(val id: Int, var name: String, var photoUri: String, var phoneNumber: String)
+import com.simplemobiletools.commons.extensions.normalizeString
+
+data class Contact(val id: Int, var name: String, var photoUri: String, var phoneNumber: String) : Comparable<Contact> {
+    override fun compareTo(other: Contact): Int {
+        val firstString = name.normalizeString()
+        val secondString = other.name.normalizeString()
+
+        return if (firstString.firstOrNull()?.isLetter() == true && secondString.firstOrNull()?.isLetter() == false) {
+            -1
+        } else if (firstString.firstOrNull()?.isLetter() == false && secondString.firstOrNull()?.isLetter() == true) {
+            1
+        } else {
+            if (firstString.isEmpty() && secondString.isNotEmpty()) {
+                1
+            } else if (firstString.isNotEmpty() && secondString.isEmpty()) {
+                -1
+            } else {
+                firstString.compareTo(secondString, true)
+            }
+        }
+    }
+}