Persist exchange rates, selected currencies, and price source via SQLDelight

Adds a SQLDelight-backed AppDatabase (Android, Desktop, iOS/macOS) so the
converter survives restarts: the last-known rates per price source, the
user's selected fiat currencies (with order preserved), and the last-used
price source all reload before the first network fetch completes. Web isn't
a shipped platform and SQLDelight's driver there needs a worker plus a wasm
sqlite binary, so it gets a lighter localStorage-backed implementation of
the same store interfaces instead.

Android needs an app Context for its driver, wired via a new
SatsPriceApplication. iOS/macOS need libsqlite3 linked explicitly (Swift's
autolinking only covers Shared.framework itself, not its C library
dependencies), plus two extension-loading symbols marked optional since
macOS's system sqlite build omits them.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QpjMKWGoiT5aJBzhxvXkwp

shared/src/commonMain/kotlin/xyz/tyiu/satsprice/data/db/ExchangeRateStore.kt

@@ -0,0 +1,11 @@
+package xyz.tyiu.satsprice.data.db
+
+import xyz.tyiu.satsprice.data.ExchangeRates
+
+/** Persists the last known [ExchangeRates] fetched from each price source, keyed by [ExchangeRateSource.id]. */
+interface ExchangeRateStore {
+    suspend fun loadLastKnownRates(sourceId: String): ExchangeRates?
+    suspend fun saveRates(sourceId: String, rates: ExchangeRates)
+}
+
+expect fun createExchangeRateStore(): ExchangeRateStore

shared/src/commonMain/kotlin/xyz/tyiu/satsprice/data/db/SelectedCurrenciesStore.kt

@@ -0,0 +1,9 @@
+package xyz.tyiu.satsprice.data.db
+
+/** Persists the user's selected fiat currency codes, preserving the order they're displayed in. */
+interface SelectedCurrenciesStore {
+    suspend fun loadSelectedCurrencies(): List<String>
+    suspend fun saveSelectedCurrencies(codes: List<String>)
+}
+
+expect fun createSelectedCurrenciesStore(): SelectedCurrenciesStore

shared/src/commonMain/kotlin/xyz/tyiu/satsprice/data/db/SelectedSourceStore.kt

@@ -0,0 +1,9 @@
+package xyz.tyiu.satsprice.data.db
+
+/** Persists the id of the last price source the user selected. */
+interface SelectedSourceStore {
+    suspend fun loadSelectedSourceId(): String?
+    suspend fun saveSelectedSourceId(sourceId: String)
+}
+
+expect fun createSelectedSourceStore(): SelectedSourceStore

shared/src/commonMain/kotlin/xyz/tyiu/satsprice/data/db/SqlDelightStores.kt

@@ -0,0 +1,68 @@
+package xyz.tyiu.satsprice.data.db
+
+import com.ionspin.kotlin.bignum.decimal.BigDecimal
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import xyz.tyiu.satsprice.data.ExchangeRates
+import xyz.tyiu.satsprice.db.AppDatabase
+import kotlin.time.Instant
+
+/**
+ * Shared by every platform that opens a real [AppDatabase] (Android, Desktop, iOS/macOS) — only
+ * driver construction differs per platform, so that's the only expect/actual boundary needed.
+ * Web isn't a shipped platform (see README's Supported Platforms) and gets an in-memory fallback
+ * instead of a real driver.
+ */
+internal class SqlDelightExchangeRateStore(private val database: AppDatabase) : ExchangeRateStore {
+    override suspend fun loadLastKnownRates(sourceId: String): ExchangeRates? = withContext(Dispatchers.Default) {
+        val rows = database.exchangeRateQueries.selectForSource(sourceId).executeAsList()
+        val first = rows.firstOrNull() ?: return@withContext null
+        ExchangeRates(
+            base = first.base,
+            rates = rows.associate { it.currencyCode to BigDecimal.parseString(it.rate) },
+            fetchedAt = Instant.fromEpochMilliseconds(first.fetchedAt),
+        )
+    }
+
+    override suspend fun saveRates(sourceId: String, rates: ExchangeRates) = withContext(Dispatchers.Default) {
+        database.exchangeRateQueries.transaction {
+            database.exchangeRateQueries.deleteForSource(sourceId)
+            rates.rates.forEach { (currencyCode, rate) ->
+                database.exchangeRateQueries.insertRate(
+                    sourceId = sourceId,
+                    base = rates.base,
+                    currencyCode = currencyCode,
+                    rate = rate.toStringExpanded(),
+                    fetchedAt = rates.fetchedAt.toEpochMilliseconds(),
+                )
+            }
+        }
+    }
+}
+
+internal class SqlDelightSelectedCurrenciesStore(private val database: AppDatabase) : SelectedCurrenciesStore {
+    override suspend fun loadSelectedCurrencies(): List<String> = withContext(Dispatchers.Default) {
+        database.selectedCurrencyQueries.selectAllOrdered().executeAsList().map { it.code }
+    }
+
+    override suspend fun saveSelectedCurrencies(codes: List<String>) = withContext(Dispatchers.Default) {
+        database.selectedCurrencyQueries.transaction {
+            database.selectedCurrencyQueries.deleteAll()
+            codes.forEachIndexed { index, code ->
+                database.selectedCurrencyQueries.insertSelected(code = code, position = index.toLong())
+            }
+        }
+    }
+}
+
+internal class SqlDelightSelectedSourceStore(private val database: AppDatabase) : SelectedSourceStore {
+    override suspend fun loadSelectedSourceId(): String? = withContext(Dispatchers.Default) {
+        database.selectedSourceQueries.select().executeAsOneOrNull()?.sourceId
+    }
+
+    override suspend fun saveSelectedSourceId(sourceId: String) = withContext(Dispatchers.Default) {
+        database.selectedSourceQueries.transaction {
+            database.selectedSourceQueries.upsert(sourceId)
+        }
+    }
+}

shared/src/commonMain/kotlin/xyz/tyiu/satsprice/ui/PriceViewModel.kt

@@ -19,6 +19,12 @@ import xyz.tyiu.satsprice.data.ExchangeRateSource
 import xyz.tyiu.satsprice.data.ExchangeRates
 import xyz.tyiu.satsprice.data.ManualExchangeRateSource
 import xyz.tyiu.satsprice.data.createHttpClient
+import xyz.tyiu.satsprice.data.db.ExchangeRateStore
+import xyz.tyiu.satsprice.data.db.SelectedCurrenciesStore
+import xyz.tyiu.satsprice.data.db.SelectedSourceStore
+import xyz.tyiu.satsprice.data.db.createExchangeRateStore
+import xyz.tyiu.satsprice.data.db.createSelectedCurrenciesStore
+import xyz.tyiu.satsprice.data.db.createSelectedSourceStore
 import xyz.tyiu.satsprice.domain.CurrencyConverter
 import xyz.tyiu.satsprice.domain.formatAmount
 import xyz.tyiu.satsprice.domain.formatAmountFixed
@@ -59,6 +65,9 @@ class PriceViewModel(
     private val manualSource: ManualExchangeRateSource = ManualExchangeRateSource(),
     private val coinbaseSource: ExchangeRateSource = CoinbaseExchangeRateSource(httpClient),
     private val coinGeckoSource: ExchangeRateSource = CoinGeckoExchangeRateSource(httpClient),
+    private val exchangeRateStore: ExchangeRateStore = createExchangeRateStore(),
+    private val selectedCurrenciesStore: SelectedCurrenciesStore = createSelectedCurrenciesStore(),
+    private val selectedSourceStore: SelectedSourceStore = createSelectedSourceStore(),
 ) : ViewModel() {
 
     private val sources: List<ExchangeRateSource> = listOf(coinbaseSource, coinGeckoSource, manualSource)
@@ -84,10 +93,25 @@ class PriceViewModel(
     val uiState: StateFlow<ConverterUiState> = _uiState.asStateFlow()
 
     private var rates: ExchangeRates? = null
+    private var lastPersistedSelection: List<String>? = null
 
     init {
         manualSource.currencyCode = defaultCurrencyCode
         viewModelScope.launch {
+            selectedCurrenciesStore.loadSelectedCurrencies().takeIf { it.isNotEmpty() }?.let { persisted ->
+                lastPersistedSelection = persisted
+                val selection = if (defaultCurrencyCode in persisted) persisted else listOf(defaultCurrencyCode) + persisted
+                _uiState.update { it.copy(selectedFiatCurrencies = selection) }
+            }
+            selectedSourceStore.loadSelectedSourceId()
+                ?.let { id -> sources.firstOrNull { it.id == id } }
+                ?.let { persisted ->
+                    currentSource = persisted
+                    _uiState.update {
+                        it.copy(sourceName = persisted.displayName, isManualSource = persisted === manualSource)
+                    }
+                }
+            seedFromCache(currentSource)
             while (isActive) {
                 refresh()
                 delay(AUTO_REFRESH_INTERVAL_MILLIS)
@@ -95,6 +119,19 @@ class PriceViewModel(
         }
     }
 
+    /** Shows the last known rates for [source] immediately, before its network fetch completes. */
+    private suspend fun seedFromCache(source: ExchangeRateSource) {
+        val cached = exchangeRateStore.loadLastKnownRates(source.id) ?: return
+        rates = cached
+        _uiState.update { state -> recomputeFromKnownField(state.copy(lastUpdated = cached.fetchedAt), cached) }
+    }
+
+    private fun persistSelectionIfChanged(selection: List<String>) {
+        if (selection == lastPersistedSelection) return
+        lastPersistedSelection = selection
+        viewModelScope.launch { selectedCurrenciesStore.saveSelectedCurrencies(selection) }
+    }
+
     fun refresh() {
         if (currentSource === manualSource && manualSource.rate == null) {
             _uiState.update { it.copy(isLoading = false, errorMessage = null) }
@@ -105,6 +142,8 @@ class PriceViewModel(
             try {
                 val newRates = currentSource.getRates("BTC")
                 rates = newRates
+                exchangeRateStore.saveRates(currentSource.id, newRates)
+                var selectionToPersist: List<String>? = null
                 _uiState.update { state ->
                     val available = systemCurrencyList
                         .filter { newRates.rates.containsKey(it.code) }
@@ -119,6 +158,7 @@ class PriceViewModel(
                     // whatever order the user picked via onFiatCurrenciesReordered.
                     val filtered = state.selectedFiatCurrencies.filter { it == defaultCurrencyCode || it in availableCodes }
                     val selection = if (defaultCurrencyCode in filtered) filtered else listOf(defaultCurrencyCode) + filtered
+                    selectionToPersist = selection
                     recomputeFromKnownField(
                         state.copy(
                             isLoading = false,
@@ -130,6 +170,7 @@ class PriceViewModel(
                         newRates,
                     )
                 }
+                selectionToPersist?.let { persistSelectionIfChanged(it) }
             } catch (e: Exception) {
                 // Not localized: this shared ViewModel has no platform Context to resolve a moko-resources
                 // string on Android, and no locale-aware synchronous resolution path that works everywhere.
@@ -157,6 +198,7 @@ class PriceViewModel(
             val newState = state.copy(selectedFiatCurrencies = newSelection)
             rates?.let { recomputeFromKnownField(newState, it) } ?: newState
         }
+        persistSelectionIfChanged(_uiState.value.selectedFiatCurrencies)
     }
 
     /**
@@ -174,6 +216,7 @@ class PriceViewModel(
             val newState = state.copy(selectedFiatCurrencies = newSelection)
             rates?.let { recomputeFromKnownField(newState, it) } ?: newState
         }
+        persistSelectionIfChanged(_uiState.value.selectedFiatCurrencies)
     }
 
     fun onSourceSelected(displayName: String) {
@@ -187,7 +230,11 @@ class PriceViewModel(
                 rateDisplays = emptyMap(),
             )
         }
-        refresh()
+        viewModelScope.launch {
+            selectedSourceStore.saveSelectedSourceId(selected.id)
+            seedFromCache(selected)
+            refresh()
+        }
     }
 
     fun onManualRateChanged(value: String) {