Hide currency flags shared by more than 3 countries

XCD, XOF, and XAF each have 6-8 issuing countries, which is too many
flags to cram side by side next to a currency code.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FXcrACM5sok3M1KQJ8kByy

shared/src/commonMain/kotlin/xyz/tyiu/satsprice/CurrencyFlag.kt

@@ -12,17 +12,22 @@ private val MULTI_COUNTRY_CURRENCY_REGION_CODES: Map<String, List<String>> = map
     "XPF" to listOf("NC", "PF", "WF"),
 )
 
+/** Above this many issuing countries, showing every flag side by side is too visually noisy. */
+private const val MAX_FLAGS_PER_CURRENCY = 3
+
 /**
  * A country flag emoji for [code], derived from the first two letters of the ISO 4217 code —
  * which double as the issuing country's ISO 3166-1 alpha-2 code for ordinary national
  * currencies — or null when there's no flag to show. [MULTI_COUNTRY_CURRENCY_REGION_CODES]
  * lists every country sharing a currency with no single issuer, so those show all their flags
- * side by side; the remaining "X"-prefixed codes are precious metals, testing codes, and other
+ * side by side, unless there are more than [MAX_FLAGS_PER_CURRENCY] of them; the remaining
- * non-national codes (XAU, XTS, XXX, ...), none of which has a country to show. EUR is a special
+ * "X"-prefixed codes are precious metals, testing codes, and other non-national codes (XAU, XTS,
- * case handled separately, using the EU's own flag.
+ * XXX, ...), none of which has a country to show. EUR is a special case handled separately, using
+ * the EU's own flag.
  */
 fun currencyFlagEmoji(code: String): String? {
     MULTI_COUNTRY_CURRENCY_REGION_CODES[code]?.let { regionCodes ->
+        if (regionCodes.size > MAX_FLAGS_PER_CURRENCY) return null
         return regionCodes.joinToString(" ") { regionFlagEmoji(it) }
     }
     if (code.startsWith("X")) return null

shared/src/commonTest/kotlin/xyz/tyiu/satsprice/CurrencyFlagTest.kt

@@ -19,13 +19,19 @@ class CurrencyFlagTest {
     }
 
     @Test
-    fun currencyFlagEmoji_showsAllFlagsForCurrenciesSharedByMultipleCountries() {
+    fun currencyFlagEmoji_showsAllFlagsForCurrenciesSharedByFewCountries() {
-        assertEquals("🇦🇬 🇦🇮 🇩🇲 🇬🇩 🇰🇳 🇱🇨 🇲🇸 🇻🇨", currencyFlagEmoji("XCD"))
+        assertEquals("🇨🇼 🇸🇽", currencyFlagEmoji("XCG"))
-        assertEquals("🇧🇫 🇧🇯 🇨🇮 🇬🇼 🇲🇱 🇳🇪 🇸🇳 🇹🇬", currencyFlagEmoji("XOF"))
-        assertEquals("🇨🇫 🇨🇬 🇨🇲 🇬🇦 🇬🇶 🇹🇩", currencyFlagEmoji("XAF"))
         assertEquals("🇳🇨 🇵🇫 🇼🇫", currencyFlagEmoji("XPF"))
     }
 
+    @Test
+    fun currencyFlagEmoji_hidesFlagsForCurrenciesSharedByManyCountries() {
+        // Showing every flag side by side gets visually noisy past a few countries.
+        assertNull(currencyFlagEmoji("XCD")) // 8 countries
+        assertNull(currencyFlagEmoji("XOF")) // 8 countries
+        assertNull(currencyFlagEmoji("XAF")) // 6 countries
+    }
+
     @Test
     fun currencyFlagEmoji_returnsNullForNonNationalCodes() {
         // ISO 4217 reserves the remaining "X"-prefixed codes for precious metals, testing codes,