app/src/main/java/me/zobrist/tichucounter/domain/StringExtensions.kt

@@ -0,0 +1,12 @@
+package me.zobrist.tichucounter.domain
+
+fun String.digitCount(): Int {
+    var count = 0
+    this.forEach {
+        if (it.isDigit()) {
+            count++
+        }
+    }
+    return count
+}
+

app/src/main/java/me/zobrist/tichucounter/ui/counter/CounterViewModel.kt

@@ -10,6 +10,7 @@ import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.launch
 import me.zobrist.tichucounter.data.entity.Round
 import me.zobrist.tichucounter.domain.Tichu
+import me.zobrist.tichucounter.domain.digitCount
 import me.zobrist.tichucounter.domain.getTotalPoints
 import me.zobrist.tichucounter.repository.GameRepository
 import javax.inject.Inject
@@ -202,9 +203,12 @@ class CounterViewModel @Inject constructor(
     override fun digitClicked(digit: String) {
         focusLastInput()
 
-        activeValue += digit
-        updateOtherScore()
-        updateSubmitButton()
+        if(activeValue.digitCount() < 5)
+        {
+            activeValue += digit
+            updateOtherScore()
+            updateSubmitButton()
+        }
     }
 
     override fun negateClicked() {

app/src/test/java/me/zobrist/tichucounter/StringExtensionTest.kt

@@ -0,0 +1,22 @@
+package me.zobrist.tichucounter
+
+import me.zobrist.tichucounter.domain.digitCount
+import org.junit.Assert.*
+import org.junit.Test
+
+/**
+ * Example local unit test, which will execute on the development machine (host).
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+class StringExtensionTest {
+    @Test
+    fun calculation_isCorrect() {
+        assertEquals(0, "-".digitCount())
+        assertEquals(0, "".digitCount())
+        assertEquals(2, "-10".digitCount())
+        assertEquals(2, "10".digitCount())
+        assertEquals(10, "1234567890".digitCount())
+        assertEquals(10, "-1234567890".digitCount())
+    }
+}