refactor: AmountInputViewModel to @Observable

Bitkit/Components/NumberPadTextField.swift

@@ -3,7 +3,7 @@ import SwiftUI
 /// NumberPadTextField - Amount view to be used with number pad
 struct NumberPadTextField: View {
     @EnvironmentObject var currency: CurrencyViewModel
-    @ObservedObject var viewModel: AmountInputViewModel
+    var viewModel: AmountInputViewModel
 
     var showConversion: Bool = true
     var showEditButton: Bool = false

Bitkit/ViewModels/AmountInputViewModel.swift

@@ -1,11 +1,16 @@
 import Foundation
 import SwiftUI
 
+@Observable
 @MainActor
-class AmountInputViewModel: ObservableObject {
-    @Published var amountSats: UInt64 = 0
-    @Published var displayText: String = ""
-    @Published var errorKey: String?
+final class AmountInputViewModel {
+    var amountSats: UInt64 = 0
+    var displayText: String = ""
+    var errorKey: String?
+
+    /// Optional per-screen cap (e.g. the max sendable balance in the send flow).
+    /// When set, input is additionally blocked above this value, on top of `maxAmount`.
+    var maxAmountOverride: UInt64?
 
     // MARK: - Constants
 
@@ -15,6 +20,12 @@ class AmountInputViewModel: ObservableObject {
     private let classicBitcoinDecimals = 8
     private let fiatDecimals = 2
 
+    /// The active upper bound for input: the global `maxAmount`, further restricted by `maxAmountOverride` when set.
+    private var effectiveMaxAmount: UInt64 {
+        guard let maxAmountOverride else { return maxAmount }
+        return Swift.min(maxAmount, maxAmountOverride)
+    }
+
     // MARK: - Private Properties
 
     private var rawInputText: String = ""
@@ -38,12 +49,19 @@ class AmountInputViewModel: ObservableObject {
             maxDecimals: maxDecimals
         )
 
+        // Deletions must always apply, even when the amount is above the cap (e.g. a
+        // prefilled invoice amount over the available balance, or a cap that dropped
+        // after input). The cap only blocks growing the amount; without this, each
+        // delete still leaves the amount over the cap and gets rejected, trapping the
+        // user with an invalid amount they can't reduce.
+        let isDeletion = key == "delete"
+
         // For decimal input (classic Bitcoin and fiat), preserve the text as-is
         // For integer input (modern Bitcoin), format the final amount
         if currency.primaryDisplay == .bitcoin && currency.displayUnit == .modern {
             let newAmount = convertToSats(newText, currency: currency)
 
-            if newAmount <= maxAmount {
+            if isDeletion || newAmount <= effectiveMaxAmount {
                 rawInputText = newText
                 displayText = formatDisplayTextFromAmount(newAmount, currency: currency)
                 amountSats = newAmount
@@ -59,7 +77,7 @@ class AmountInputViewModel: ObservableObject {
             // For decimal input, check limits before updating state
             if !newText.isEmpty {
                 let newAmount = convertToSats(newText, currency: currency)
-                if newAmount <= maxAmount {
+                if isDeletion || newAmount <= effectiveMaxAmount {
                     // Update both raw input and display text
                     rawInputText = newText
                     // Format with grouping separators but not decimal formatting

Bitkit/Views/Transfer/FundManualAmountView.swift

@@ -8,13 +8,21 @@ struct FundManualAmountView: View {
 
     let lnPeer: LnPeer
 
-    @StateObject private var amountViewModel = AmountInputViewModel()
+    @State private var amountViewModel = AmountInputViewModel()
     @State private var didAttemptPeerConnection = false
 
     var amountSats: UInt64 {
         amountViewModel.amountSats
     }
 
+    private var fundableBalanceSats: UInt64 {
+        UInt64(max(0, wallet.channelFundableBalanceSats))
+    }
+
+    private var isValidAmount: Bool {
+        amountSats > 0 && amountSats <= fundableBalanceSats
+    }
+
     var body: some View {
         VStack(spacing: 0) {
             NavigationBar(title: t("lightning__external__nav_title"))
@@ -58,7 +66,7 @@ struct FundManualAmountView: View {
                     amountViewModel.handleNumberPadInput(key, currency: currency)
                 }
 
-                CustomButton(title: t("common__continue"), isDisabled: amountSats == 0) {
+                CustomButton(title: t("common__continue"), isDisabled: !isValidAmount) {
                     navigation.navigate(.fundManualConfirm(lnPeer: lnPeer, amountSats: amountSats))
                 }
                 .accessibilityIdentifier("ExternalAmountContinue")
@@ -70,6 +78,14 @@ struct FundManualAmountView: View {
         .task {
             await connectToPeerIfNeeded()
         }
+        .onAppear {
+            updateInputCap()
+        }
+        .onChange(of: wallet.channelFundableBalanceSats) { updateInputCap() }
+    }
+
+    private func updateInputCap() {
+        amountViewModel.maxAmountOverride = fundableBalanceSats > 0 ? fundableBalanceSats : nil
     }
 
     private var numberPadButtons: some View {

Bitkit/Views/Transfer/SpendingAdvancedView.swift

@@ -10,7 +10,7 @@ struct SpendingAdvancedView: View {
     @EnvironmentObject var transfer: TransferViewModel
     @Environment(\.dismiss) var dismiss
 
-    @StateObject private var amountViewModel = AmountInputViewModel()
+    @State private var amountViewModel = AmountInputViewModel()
     @State private var feeEstimate: UInt64?
     @State private var isLoading = false
     @State private var feeEstimateTask: Task<Void, Never>?
@@ -108,6 +108,7 @@ struct SpendingAdvancedView: View {
             )
 
             updateFeeEstimate()
+            updateInputCap()
         }
         .onChange(of: lspBalance) {
             if isValid {
@@ -116,6 +117,12 @@ struct SpendingAdvancedView: View {
                 feeEstimate = nil
             }
         }
+        .onChange(of: transfer.transferValues.maxLspBalance) { updateInputCap() }
+    }
+
+    private func updateInputCap() {
+        let maxLspBalance = transfer.transferValues.maxLspBalance
+        amountViewModel.maxAmountOverride = maxLspBalance > 0 ? maxLspBalance : nil
     }
 
     private var actionButtons: some View {

Bitkit/Views/Transfer/SpendingAmount.swift

@@ -10,7 +10,7 @@ struct SpendingAmount: View {
     @EnvironmentObject var transfer: TransferViewModel
     @EnvironmentObject var wallet: WalletViewModel
 
-    @StateObject private var amountViewModel = AmountInputViewModel()
+    @State private var amountViewModel = AmountInputViewModel()
     @State private var isLoading = false
     @State private var availableAmount: UInt64?
     @State private var maxTransferAmount: UInt64?
@@ -87,6 +87,11 @@ struct SpendingAmount: View {
                 await calculateMaxTransferAmount()
             }
         }
+        .onChange(of: maxTransferAmount) { updateInputCap() }
+    }
+
+    private func updateInputCap() {
+        amountViewModel.maxAmountOverride = (maxTransferAmount ?? 0) > 0 ? maxTransferAmount : nil
     }
 
     private var actionButtons: some View {

Bitkit/Views/Wallets/LnurlWithdraw/LnurlWithdrawAmount.swift

@@ -6,7 +6,7 @@ struct LnurlWithdrawAmount: View {
     @EnvironmentObject var wallet: WalletViewModel
     let onContinue: () -> Void
 
-    @StateObject private var amountViewModel = AmountInputViewModel()
+    @State private var amountViewModel = AmountInputViewModel()
 
     var minAmount: Int {
         Int(max(1, app.lnurlWithdrawData!.minWithdrawableSat))
@@ -77,7 +77,14 @@ struct LnurlWithdrawAmount: View {
             if amountViewModel.amountSats == 0 {
                 amountViewModel.updateFromSats(UInt64(minAmount), currency: currency)
             }
+            updateInputCap()
         }
+        .onChange(of: maxAmount) { updateInputCap() }
+    }
+
+    private func updateInputCap() {
+        let cap = max(minAmount, maxAmount)
+        amountViewModel.maxAmountOverride = cap > 0 ? UInt64(cap) : nil
     }
 
     private func handleContinue() {

Bitkit/Views/Wallets/Receive/ReceiveCjitAmount.swift

@@ -9,7 +9,7 @@ struct ReceiveCjitAmount: View {
 
     @Binding var navigationPath: [ReceiveRoute]
 
-    @StateObject private var amountViewModel = AmountInputViewModel()
+    @State private var amountViewModel = AmountInputViewModel()
 
     var minimumAmount: UInt64 {
         blocktank.minCjitSats ?? 0

Bitkit/Views/Wallets/Receive/ReceiveEdit.swift

@@ -12,7 +12,7 @@ struct ReceiveEdit: View {
 
     @Binding var navigationPath: [ReceiveRoute]
 
-    @StateObject private var amountViewModel = AmountInputViewModel()
+    @State private var amountViewModel = AmountInputViewModel()
     @State private var note = ""
     @State private var isAmountInputFocused: Bool = false
     @FocusState private var isNoteEditorFocused: Bool

Bitkit/Views/Wallets/Send/LnurlPayAmount.swift

@@ -7,7 +7,7 @@ struct LnurlPayAmount: View {
 
     @Binding var navigationPath: [SendRoute]
 
-    @StateObject private var amountViewModel = AmountInputViewModel()
+    @State private var amountViewModel = AmountInputViewModel()
 
     var maxAmount: UInt64 {
         // TODO: subtract fee
@@ -81,6 +81,14 @@ struct LnurlPayAmount: View {
         .navigationBarHidden(true)
         .padding(.horizontal, 16)
         .sheetBackground()
+        .onAppear {
+            updateInputCap()
+        }
+        .onChange(of: maxAmount) { updateInputCap() }
+    }
+
+    private func updateInputCap() {
+        amountViewModel.maxAmountOverride = maxAmount > 0 ? maxAmount : nil
     }
 
     private func onContinue() {

Bitkit/Views/Wallets/Send/SendAmountView.swift

@@ -8,7 +8,7 @@ struct SendAmountView: View {
 
     @Binding var navigationPath: [SendRoute]
 
-    @StateObject private var amountViewModel = AmountInputViewModel()
+    @State private var amountViewModel = AmountInputViewModel()
     @State private var maxSendableAmount: UInt64?
     @State private var routingFee: UInt64 = 0
 
@@ -163,6 +163,8 @@ struct SendAmountView: View {
                     await calculateRoutingFee()
                 }
             }
+
+            updateInputCap()
         }
         .onChange(of: app.selectedWalletToPayFrom) { _, newValue in
             // Recalculate max sendable amount when switching wallet types
@@ -186,6 +188,9 @@ struct SendAmountView: View {
                 }
             }
         }
+        .onChange(of: availableAmount) { _, _ in
+            updateInputCap()
+        }
     }
 
     private func onContinue() async {
@@ -252,6 +257,11 @@ struct SendAmountView: View {
         }
     }
 
+    private func updateInputCap() {
+        // Don't cap when nothing is sendable, so the pad stays usable (Continue stays disabled instead).
+        amountViewModel.maxAmountOverride = availableAmount > 0 ? availableAmount : nil
+    }
+
     private func calculateMaxSendableAmount() async {
         // Make sure we have everything we need to calculate the max sendable amount
         guard app.selectedWalletToPayFrom == .onchain else { return }

BitkitTests/NumberPadTests.swift

@@ -53,6 +53,40 @@ final class NumberPadTests: XCTestCase {
         XCTAssertNotNil(viewModel.errorKey)
     }
 
+    func testMaxAmountOverrideBlocksInputAboveBalance() {
+        let viewModel = AmountInputViewModel()
+        let currency = mockCurrency(primaryDisplay: .bitcoin, displayUnit: .modern)
+        viewModel.maxAmountOverride = 50000
+
+        // Up to the cap is allowed
+        for digit in "50000" {
+            viewModel.handleNumberPadInput(String(digit), currency: currency)
+        }
+        XCTAssertEqual(viewModel.amountSats, 50000)
+
+        // Next keystroke would make 500_000 > 50_000 and is blocked
+        viewModel.handleNumberPadInput("0", currency: currency)
+        XCTAssertEqual(viewModel.amountSats, 50000) // Should not change
+        XCTAssertNotNil(viewModel.errorKey)
+    }
+
+    func testClearingMaxAmountOverrideRestoresGlobalCap() {
+        let viewModel = AmountInputViewModel()
+        let currency = mockCurrency(primaryDisplay: .bitcoin, displayUnit: .modern)
+
+        // With a low override, input is blocked above it
+        viewModel.maxAmountOverride = 100
+        viewModel.handleNumberPadInput("9", currency: currency)
+        viewModel.handleNumberPadInput("9", currency: currency)
+        viewModel.handleNumberPadInput("9", currency: currency) // 999 > 100 -> blocked
+        XCTAssertEqual(viewModel.amountSats, 99)
+
+        // Clearing the override lets input grow again, up to the global cap
+        viewModel.maxAmountOverride = nil
+        viewModel.handleNumberPadInput("9", currency: currency)
+        XCTAssertEqual(viewModel.amountSats, 999)
+    }
+
     // MARK: - Classic Bitcoin Tests
 
     func testClassicBitcoinDecimalInput() {
@@ -206,6 +240,35 @@ final class NumberPadTests: XCTestCase {
         XCTAssertEqual(viewModel.amountSats, 100_000)
     }
 
+    func testDeleteAllowedWhenAmountAboveCap() {
+        let viewModel = AmountInputViewModel()
+        let currency = mockCurrency(primaryDisplay: .bitcoin, displayUnit: .modern)
+
+        // A prefilled amount lands above a low cap (e.g. an invoice that exceeds the
+        // available balance, set via updateFromSats which does not enforce the cap).
+        viewModel.maxAmountOverride = 1000
+        viewModel.updateFromSats(123_456, currency: currency)
+        XCTAssertEqual(viewModel.amountSats, 123_456)
+
+        // Adding a digit is still blocked: it would grow the amount further above the cap.
+        viewModel.handleNumberPadInput("7", currency: currency)
+        XCTAssertEqual(viewModel.amountSats, 123_456) // unchanged
+        XCTAssertNotNil(viewModel.errorKey)
+
+        // Deleting is allowed even though the result is still above the cap, so the user
+        // can reduce an over-cap amount instead of being stuck.
+        viewModel.handleNumberPadInput("delete", currency: currency)
+        XCTAssertEqual(viewModel.displayText, "12 345")
+        XCTAssertEqual(viewModel.amountSats, 12345)
+        XCTAssertNil(viewModel.errorKey)
+
+        // Keep deleting down below the cap.
+        viewModel.handleNumberPadInput("delete", currency: currency) // 1 234
+        viewModel.handleNumberPadInput("delete", currency: currency) // 123
+        XCTAssertEqual(viewModel.amountSats, 123)
+        XCTAssertNil(viewModel.errorKey)
+    }
+
     // MARK: - Leading Zero Tests
 
     func testLeadingZeroBehavior() {

changelog.d/next/346.fixed.md

@@ -0,0 +1 @@
+The send amount number pad now caps entry at your available balance, so you can no longer enter more than you can send.

changelog.d/next/585.fixed.md

@@ -0,0 +1 @@
+Number-pad entry on the spending, LNURL, and channel-funding amount screens now caps at the available maximum, and manual channel funding can no longer exceed your available balance.