prepareSparkMintTransaction i/o validation (WIP)

lib/wallets/wallet/wallet_mixin_interfaces/spark_interface.dart

@@ -563,52 +563,106 @@ mixin SparkInterface on Bip39HDWallet, ElectrumXInterface {
   }
 
   /// Transparent to Spark (mint) transaction creation.
+  ///
+  /// See https://docs.google.com/document/d/1RG52GoYTZDvKlZz_3G4sQu-PpT6JWSZGHLNswWcrE3o
   Future<TxData> prepareSparkMintTransaction({required TxData txData}) async {
-    // https://docs.google.com/document/d/1RG52GoYTZDvKlZz_3G4sQu-PpT6JWSZGHLNswWcrE3o/edit
-
-    // this kind of transaction is generated like a regular transaction, but in
-    // place of regular outputs we put spark outputs, so for that we call
-    // createSparkMintRecipients function, we get spark related data,
-    // everything else we do like for regular transaction, and we put CRecipient
-    // object as a tx outputs, we need to keep the order..
-    // First we pass spark::MintedCoinData>, has following members, Address
-    // which is any spark address, amount (v) how much we want to send, and
-    // memo which can be any string with 32 length (any string we want to send
-    // to receiver), serial_context is a byte array, which should be unique for
-    // each transaction, and for that we serialize and put all inputs into
-    // serial_context vector. So we construct the input part of the transaction
-    // first then we generate spark related data. And we sign like regular
-    // transactions at the end.
+    // "this kind of transaction is generated like a regular transaction, but in
+    // place of [regular] outputs we put spark outputs... we construct the input
+    // part of the transaction first then we generate spark related data [and]
+    // we sign like regular transactions at the end."
 
     // Validate inputs.
 
-    // There should be at least one recipient.
-    if (txData.recipients == null || txData.recipients!.isEmpty) {
-      throw Exception("No recipients provided");
+    // There should be at least one input.
+    if (txData.utxos == null || txData.utxos!.isEmpty) {
+      throw Exception("No inputs provided.");
     }
 
-    // For now let's limit to one recipient.
+    // For now let's limit to one input.
+    if (txData.utxos!.length > 1) {
+      throw Exception("Only one input supported.");
+      // TODO remove and test with multiple inputs.
+    }
+
+    // Validate individual inputs.
+    for (final utxo in txData.utxos!) {
+      // Input amount must be greater than zero.
+      if (utxo.value == 0) {
+        throw Exception("Input value cannot be zero.");
+      }
+
+      // Input value must be greater than dust limit.
+      if (BigInt.from(utxo.value) < cryptoCurrency.dustLimit.raw) {
+        throw Exception("Input value below dust limit.");
+      }
+    }
+
+    // Validate outputs.
+
+    // There should be at least one output.
+    if (txData.recipients == null || txData.recipients!.isEmpty) {
+      throw Exception("No recipients provided.");
+    }
+
+    // For now let's limit to one output.
     if (txData.recipients!.length > 1) {
-      throw Exception("Only one recipient supported");
+      throw Exception("Only one recipient supported.");
+      // TODO remove and test with multiple recipients.
     }
 
     // Limit outputs per tx to 16.
     //
     // See SPARK_OUT_LIMIT_PER_TX at https://github.com/firoorg/sparkmobile/blob/ef2e39aae18ecc49e0ddc63a3183e9764b96012e/include/spark.h#L16
-    // TODO limit outputs to 16.
+    if (txData.recipients!.length > 16) {
+      throw Exception("Too many recipients.");
+    }
 
     // Limit spend value per tx to 1000000000000 satoshis.
     //
     // See SPARK_VALUE_SPEND_LIMIT_PER_TRANSACTION at https://github.com/firoorg/sparkmobile/blob/ef2e39aae18ecc49e0ddc63a3183e9764b96012e/include/spark.h#L17
     // and COIN https://github.com/firoorg/sparkmobile/blob/ef2e39aae18ecc49e0ddc63a3183e9764b96012e/bitcoin/amount.h#L17
     // Note that as MAX_MONEY is greater than this limit, we can ignore it.  See https://github.com/firoorg/sparkmobile/blob/ef2e39aae18ecc49e0ddc63a3183e9764b96012e/bitcoin/amount.h#L31
-    // TODO limit spend value per tx to 1000000000000 satoshis.
+    //
+    // This will be added to and checked as we validate outputs.
+    Amount amountSent = Amount(
+      rawValue: BigInt.zero,
+      fractionDigits: cryptoCurrency.fractionDigits,
+    );
+
+    // Validate individual outputs.
+    for (final recipient in txData.recipients!) {
+      // Output amount must be greater than zero.
+      if (recipient.amount.raw == BigInt.zero) {
+        throw Exception("Output amount cannot be zero.");
+        // Could refactor this for loop to use an index and remove this output.
+      }
+
+      // Output amount must be greater than dust limit.
+      if (recipient.amount < cryptoCurrency.dustLimit) {
+        throw Exception("Output below dust limit.");
+      }
+
+      // Do not add outputs that would exceed the spend limit.
+      amountSent += recipient.amount;
+      if (amountSent.raw > BigInt.from(1000000000000)) {
+        throw Exception(
+          "Spend limit exceeded (10,000 FIRO per tx).",
+        );
+      }
+    }
+
+    // TODO create a transaction builder and add inputs.
 
     // Create the serial context.
+    //
+    // "...serial_context is a byte array, which should be unique for each
+    // transaction, and for that we serialize and put all inputs into
+    // serial_context vector. So we construct the input part of the transaction
+    // first then we generate spark related data."
     List<int> serialContext = [];
     // TODO set serialContext to the serialized inputs.
 
-    // Create outputs.
+    // Create mint recipients.
     final mintRecipients = LibSpark.createSparkMintRecipients(
       outputs: txData.recipients!
           .map((e) => (
@@ -618,9 +672,10 @@ mixin SparkInterface on Bip39HDWallet, ElectrumXInterface {
               ))
           .toList(),
       serialContext: Uint8List.fromList(serialContext),
+      // generate: true // TODO is this needed?
     );
 
-    // TODO Add outputs to txData.
+    // TODO finish.
 
     throw UnimplementedError();
   }