[#1367] Send 0 funds only within shielded transaction

- Closes #1367
- Plus slightly refactored SendForm composable to two functions
- Changelog update

CHANGELOG.md

@@ -9,6 +9,9 @@ directly impact users rather than highlighting other key architectural updates.*
 
 ## [Unreleased]
 
+### Fixed
+- Sending zero funds is allowed only for shielded recipient address type
+
 ## [0.2.0 (609)] - 2024-04-18
 
 ### Added

ui-lib/src/androidTest/java/co/electriccoin/zcash/ui/screen/send/SendViewTestSetup.kt

@@ -128,7 +128,7 @@ class SendViewTestSetup(
                     // TODO [#1260]: https://github.com/Electric-Coin-Company/zashi-android/issues/1260
                 },
                 setAmountState = {},
-                amountState = AmountState.new(context, "", monetarySeparators),
+                amountState = AmountState.new(context, monetarySeparators, "", false),
                 setMemoState = {},
                 memoState = MemoState.new(""),
                 walletRestoringState = WalletRestoringState.NONE,

ui-lib/src/main/java/co/electriccoin/zcash/ui/screen/send/AndroidSend.kt

@@ -8,6 +8,7 @@ import androidx.activity.compose.BackHandler
 import androidx.activity.viewModels
 import androidx.annotation.VisibleForTesting
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.saveable.rememberSaveable
@@ -21,6 +22,7 @@ import cash.z.ecc.android.sdk.model.UnifiedSpendingKey
 import cash.z.ecc.android.sdk.model.ZecSend
 import cash.z.ecc.android.sdk.model.proposeSend
 import cash.z.ecc.android.sdk.model.toZecString
+import cash.z.ecc.android.sdk.type.AddressType
 import co.electriccoin.zcash.spackle.Twig
 import co.electriccoin.zcash.ui.common.compose.BalanceState
 import co.electriccoin.zcash.ui.common.model.WalletRestoringState
@@ -95,7 +97,7 @@ internal fun WrapSend(
     )
 }
 
-@Suppress("LongParameterList", "LongMethod")
+@Suppress("LongParameterList", "LongMethod", "CyclomaticComplexMethod")
 @VisibleForTesting
 @Composable
 internal fun WrapSend(
@@ -140,11 +142,25 @@ internal fun WrapSend(
     // Amount computation:
     val (amountState, setAmountState) =
         rememberSaveable(stateSaver = AmountState.Saver) {
+            // Default amount state
             mutableStateOf(
                 AmountState.new(
                     context = context,
                     value = zecSend?.amount?.toZecString() ?: "",
-                    monetarySeparators = monetarySeparators
+                    monetarySeparators = monetarySeparators,
+                    isTransparentRecipient = recipientAddressState.type?.let { it == AddressType.Transparent } ?: false
+                )
+            )
+        }
+    // New amount state based on the recipient address type (e.g. shielded supports zero funds sending and
+    // transparent not)
+    LaunchedEffect(key1 = recipientAddressState) {
+        setAmountState(
+            AmountState.new(
+                context = context,
+                isTransparentRecipient = recipientAddressState.type?.let { it == AddressType.Transparent } ?: false,
+                monetarySeparators = monetarySeparators,
+                value = amountState.value
             )
         )
     }
@@ -155,12 +171,12 @@ internal fun WrapSend(
             mutableStateOf(MemoState.new(zecSend?.memo?.value ?: ""))
         }
 
-    // Clearing form if required form the previous navigation destination
+    // Clearing form from the previous navigation destination if required
     if (sendArguments?.clearForm == true) {
         setSendStage(SendStage.Form)
         setZecSend(null)
         setRecipientAddressState(RecipientAddressState.new("", null))
-        setAmountState(AmountState.new(context, "", monetarySeparators))
+        setAmountState(AmountState.new(context, monetarySeparators, "", false))
         setMemoState(MemoState.new(""))
     }
 

ui-lib/src/main/java/co/electriccoin/zcash/ui/screen/send/model/AmountState.kt

@@ -23,8 +23,9 @@ sealed class AmountState(
     companion object {
         fun new(
             context: Context,
+            monetarySeparators: MonetarySeparators,
             value: String,
-            monetarySeparators: MonetarySeparators
+            isTransparentRecipient: Boolean
         ): AmountState {
             // Validate raw input string
             val validated =
@@ -41,11 +42,11 @@ sealed class AmountState(
             // Convert the input to Zatoshi type-safe amount representation
             val zatoshi = (Zatoshi.fromZecString(context, value, monetarySeparators))
 
-            // Note that the 0 funds sending is supported for sending a memo-only transaction
+            // Note that the zero funds sending is supported for sending a memo-only shielded transaction
-            return if (zatoshi == null) {
+            return when {
-                Invalid(value)
+                (zatoshi == null) -> Invalid(value)
-            } else {
+                (zatoshi.value == 0L && isTransparentRecipient) -> Invalid(value)
-                Valid(value, zatoshi)
+                else -> Valid(value, zatoshi)
             }
         }
 

ui-lib/src/main/java/co/electriccoin/zcash/ui/screen/send/view/SendView.kt

@@ -264,8 +264,6 @@ private fun SendForm(
     hasCameraFeature: Boolean,
     modifier: Modifier = Modifier,
 ) {
-    val context = LocalContext.current
-
     // TODO [#1171]: Remove default MonetarySeparators locale
     // TODO [#1171]: https://github.com/Electric-Coin-Company/zashi-android/issues/1171
     val monetarySeparators = MonetarySeparators.current(Locale.US)
@@ -305,16 +303,17 @@ private fun SendForm(
 
         SendFormAmountTextField(
             amountSate = amountState,
-            setAmountState = setAmountState,
-            monetarySeparators = monetarySeparators,
             focusManager = focusManager,
-            walletSnapshot = walletSnapshot,
             imeAction =
                 if (recipientAddressState.type == AddressType.Transparent) {
                     ImeAction.Done
                 } else {
                     ImeAction.Next
-                }
+                },
+            isTransparentRecipient = recipientAddressState.type?.let { it == AddressType.Transparent } ?: false,
+            monetarySeparators = monetarySeparators,
+            setAmountState = setAmountState,
+            walletSnapshot = walletSnapshot,
         )
 
         Spacer(Modifier.size(ZcashTheme.dimens.spacingDefault))
@@ -342,6 +341,22 @@ private fun SendForm(
 
         Spacer(modifier = Modifier.height(ZcashTheme.dimens.spacingDefault))
 
+        SendButton(amountState, memoState, monetarySeparators, onCreateZecSend, recipientAddressState, walletSnapshot)
+    }
+}
+
+@Composable
+@Suppress("LongParameterList")
+fun SendButton(
+    amountState: AmountState,
+    memoState: MemoState,
+    monetarySeparators: MonetarySeparators,
+    onCreateZecSend: (ZecSend) -> Unit,
+    recipientAddressState: RecipientAddressState,
+    walletSnapshot: WalletSnapshot,
+) {
+    val context = LocalContext.current
+
     // Common conditions continuously checked for validity
     val sendButtonEnabled =
         recipientAddressState.type !is AddressType.Invalid &&
@@ -404,7 +419,6 @@ private fun SendForm(
             textFontWeight = FontWeight.SemiBold
         )
     }
-    }
 }
 
 @OptIn(ExperimentalFoundationApi::class)
@@ -496,10 +510,11 @@ fun SendFormAddressTextField(
 fun SendFormAmountTextField(
     amountSate: AmountState,
     focusManager: FocusManager,
+    imeAction: ImeAction,
+    isTransparentRecipient: Boolean,
     monetarySeparators: MonetarySeparators,
     setAmountState: (AmountState) -> Unit,
     walletSnapshot: WalletSnapshot,
-    imeAction: ImeAction,
 ) {
     val context = LocalContext.current
 
@@ -540,7 +555,14 @@ fun SendFormAmountTextField(
         FormTextField(
             value = amountSate.value,
             onValueChange = { newValue ->
-                setAmountState(AmountState.new(context, newValue, monetarySeparators))
+                setAmountState(
+                    AmountState.new(
+                        context = context,
+                        value = newValue,
+                        monetarySeparators = monetarySeparators,
+                        isTransparentRecipient = isTransparentRecipient
+                    )
+                )
             },
             modifier = Modifier.fillMaxWidth(),
             error = amountError,