feat: auto-load wallet transactions on scroll

Add infinite scroll pagination to the wallet transactions screen.
When the user scrolls within 5 items of the bottom, the next page of
transactions is automatically fetched and appended. Uses the existing
NWC list_transactions limit/offset support and total_count to know
when all transactions have been loaded.

https://claude.ai/code/session_01CdNY7qYDRHJr1jhAFvVgzj

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/wallet/WalletTransactionsScreen.kt

@@ -32,6 +32,7 @@ import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.filled.ArrowBack
 import androidx.compose.material.icons.filled.ArrowDownward
@@ -49,6 +50,7 @@ import androidx.compose.material3.TopAppBar
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
@@ -86,6 +88,24 @@ fun WalletTransactionsScreen(
 
     val transactions by walletViewModel.transactions.collectAsState()
     val isLoading by walletViewModel.isLoading.collectAsState()
+    val isLoadingMore by walletViewModel.isLoadingMore.collectAsState()
+    val hasMore by walletViewModel.hasMoreTransactions.collectAsState()
+
+    val listState = rememberLazyListState()
+
+    val shouldLoadMore by remember {
+        derivedStateOf {
+            val lastVisibleIndex = listState.layoutInfo.visibleItemsInfo.lastOrNull()?.index ?: 0
+            val totalItems = listState.layoutInfo.totalItemsCount
+            lastVisibleIndex >= totalItems - 5 && !isLoadingMore && hasMore && transactions.isNotEmpty()
+        }
+    }
+
+    LaunchedEffect(shouldLoadMore) {
+        if (shouldLoadMore) {
+            walletViewModel.loadMoreTransactions()
+        }
+    }
 
     Scaffold(
         topBar = {
@@ -144,11 +164,25 @@ fun WalletTransactionsScreen(
         } else {
             LazyColumn(
                 modifier = Modifier.padding(padding),
+                state = listState,
             ) {
                 items(transactions) { tx ->
                     TransactionItem(tx, accountViewModel, nav)
                     HorizontalDivider()
                 }
+                if (isLoadingMore) {
+                    item {
+                        Column(
+                            modifier =
+                                Modifier
+                                    .fillMaxWidth()
+                                    .padding(16.dp),
+                            horizontalAlignment = Alignment.CenterHorizontally,
+                        ) {
+                            CircularProgressIndicator(modifier = Modifier.size(24.dp))
+                        }
+                    }
+                }
             }
         }
     }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/wallet/WalletViewModel.kt

@@ -88,6 +88,14 @@ class WalletViewModel : ViewModel() {
     private val _isLoading = MutableStateFlow(false)
     val isLoading = _isLoading.asStateFlow()
 
+    private val _isLoadingMore = MutableStateFlow(false)
+    val isLoadingMore = _isLoadingMore.asStateFlow()
+
+    private val _hasMoreTransactions = MutableStateFlow(true)
+    val hasMoreTransactions = _hasMoreTransactions.asStateFlow()
+
+    private val pageSize = 20
+
     private val _error = MutableStateFlow<String?>(null)
     val error = _error.asStateFlow()
 
@@ -153,24 +161,30 @@ class WalletViewModel : ViewModel() {
         }
     }
 
-    fun fetchTransactions(
+    fun fetchTransactions() {
-        limit: Int = 20,
-        offset: Int = 0,
-    ) {
         val acc = account ?: return
         viewModelScope.launch(Dispatchers.IO) {
             _isLoading.value = true
+            _hasMoreTransactions.value = true
             try {
                 acc.sendNwcRequest(
                     ListTransactionsMethod.create(
-                        limit = limit,
+                        limit = pageSize,
-                        offset = offset,
+                        offset = 0,
                         unpaid = false,
                     ),
                 ) { response ->
                     when (response) {
                         is ListTransactionsSuccessResponse -> {
-                            _transactions.value = response.result?.transactions ?: emptyList()
+                            val txs = response.result?.transactions ?: emptyList()
+                            _transactions.value = txs
+                            val totalCount = response.result?.total_count
+                            _hasMoreTransactions.value =
+                                if (totalCount != null) {
+                                    txs.size < totalCount
+                                } else {
+                                    txs.size >= pageSize
+                                }
                         }
 
                         is NwcErrorResponse -> {
@@ -188,6 +202,48 @@ class WalletViewModel : ViewModel() {
         }
     }
 
+    fun loadMoreTransactions() {
+        if (_isLoadingMore.value || !_hasMoreTransactions.value) return
+        val acc = account ?: return
+        val currentOffset = _transactions.value.size
+        viewModelScope.launch(Dispatchers.IO) {
+            _isLoadingMore.value = true
+            try {
+                acc.sendNwcRequest(
+                    ListTransactionsMethod.create(
+                        limit = pageSize,
+                        offset = currentOffset,
+                        unpaid = false,
+                    ),
+                ) { response ->
+                    when (response) {
+                        is ListTransactionsSuccessResponse -> {
+                            val newTxs = response.result?.transactions ?: emptyList()
+                            _transactions.value = _transactions.value + newTxs
+                            val totalCount = response.result?.total_count
+                            _hasMoreTransactions.value =
+                                if (totalCount != null) {
+                                    _transactions.value.size < totalCount
+                                } else {
+                                    newTxs.size >= pageSize
+                                }
+                        }
+
+                        is NwcErrorResponse -> {
+                            _error.value = response.error?.message ?: "Failed to load more transactions"
+                        }
+
+                        else -> {}
+                    }
+                    _isLoadingMore.value = false
+                }
+            } catch (e: Exception) {
+                _error.value = e.message
+                _isLoadingMore.value = false
+            }
+        }
+    }
+
     fun sendPayment(bolt11: String) {
         val acc = account ?: return
         viewModelScope.launch(Dispatchers.IO) {