Prevent entering oversized custom donation amounts.

Fixes #14750
Resolves #14854

Co-authored-by: Greyson Parrelli <greyson@signal.org>

app/src/main/java/org/thoughtcrime/securesms/components/settings/app/subscription/boost/Boost.kt

@@ -226,6 +226,10 @@ data class Boost(
   @VisibleForTesting
   class MoneyFilter(val currency: Currency, private val text: AppCompatEditText? = null, private val onCustomAmountChanged: (String) -> Unit = {}) : DigitsKeyListener(false, true), TextWatcher {
 
+    companion object {
+      private const val MAX_INTEGRAL_DIGITS = 10
+    }
+
     val separator = DecimalFormatSymbols.getInstance().decimalSeparator
     val separatorCount = min(1, currency.defaultFractionDigits)
     val symbol: String = currency.getSymbol(Locale.getDefault())
@@ -257,6 +261,12 @@ data class Boost(
       val result = dest.subSequence(0, dstart).toString() + source.toString() + dest.subSequence(dend, dest.length)
       val resultWithoutCurrencyPrefix = BidiUtil.stripBidiIndicator(result.removePrefix(symbol).removeSuffix(symbol).trim())
 
+      val integralDigitCount = resultWithoutCurrencyPrefix.substringBefore(separator).count { it.isDigit() }
+
+      if (integralDigitCount > MAX_INTEGRAL_DIGITS) {
+        return dest.subSequence(dstart, dend)
+      }
+
       if (resultWithoutCurrencyPrefix.length == 1 && !resultWithoutCurrencyPrefix.isDigitsOnly() && resultWithoutCurrencyPrefix != separator.toString()) {
         return dest.subSequence(dstart, dend)
       }

app/src/test/java/org/thoughtcrime/securesms/components/settings/app/subscription/boost/BoostTest__MoneyFilter.kt

@@ -247,4 +247,47 @@ class BoostTest__MoneyFilter {
 
     assertEquals("0.0", result)
   }
+
+  @Test
+  fun `Given USD, when I enter ten integral digits, then I expect successful filter`() {
+    val testSubject = Boost.MoneyFilter(usd)
+    val editable = SpannableStringBuilder("1234567890.12")
+    val dest = SpannableStringBuilder()
+
+    val filterResult = testSubject.filter(editable, 0, editable.length, dest, 0, 0)
+
+    assertNull(filterResult)
+  }
+
+  @Test
+  fun `Given USD, when I enter eleven integral digits, then I expect unsuccessful filter`() {
+    val testSubject = Boost.MoneyFilter(usd)
+    val editable = SpannableStringBuilder("12345678901")
+    val dest = SpannableStringBuilder()
+
+    val filterResult = testSubject.filter(editable, 0, editable.length, dest, 0, 0)
+
+    assertNotNull(filterResult)
+  }
+
+  @Test
+  fun `Given USD and ten integral digits, when I append a digit, then I expect the existing text to be retained`() {
+    val testSubject = Boost.MoneyFilter(usd)
+    val dest = SpannableStringBuilder("$1234567890")
+
+    val filterResult = testSubject.filter("1", 0, 1, dest, dest.length, dest.length)
+
+    assertEquals("", filterResult.toString())
+  }
+
+  @Test
+  fun `Given JPY, when I enter eleven integral digits, then I expect unsuccessful filter`() {
+    val testSubject = Boost.MoneyFilter(yen)
+    val editable = SpannableStringBuilder("12345678901")
+    val dest = SpannableStringBuilder()
+
+    val filterResult = testSubject.filter(editable, 0, editable.length, dest, 0, 0)
+
+    assertNotNull(filterResult)
+  }
 }