Add foundation for determining funding transaction inputs and change

Author: MatthewLM

coinlib/lib/src/dlc/funding_collector.dart

@@ -0,0 +1,22 @@
+part of "library.dart";
+
+/// Collects the inputs and change outputs for each participant for the
+/// construction of a Funding Transaction.
+///
+/// This can only be created through a [DLCReady] object to remind consumers of
+/// the library to create DLCs in the correct order as the Refund Transaction
+/// and Contract Execution Transactions must first be created through a
+/// [DLCStatefulBuilder].
+class DLCFundingCollector {
+
+  final DLCTerms terms;
+  final Map<ECPublicKey, DLCParticipantFundingCommitment> fundingCommitments;
+
+  DLCFundingCollector._(this.terms) : fundingCommitments = {};
+
+  // TODO: Create funding transaction without inputs and change, determine total
+  // contribution requirements for each participant.
+  // TODO: Allow adding DLCParticipantFundingCommitment and verify contribution
+  // meets requirement including fee
+
+}

coinlib/lib/src/dlc/library.dart

@@ -28,6 +28,8 @@ import 'package:collection/collection.dart';
 part "builder.dart";
 part "create_apo_transaction.dart";
 part "errors.dart";
+part "funding_collector.dart";
 part "outcome.dart";
+part "participant_funding_commitment.dart";
 part "ready.dart";
 part "terms.dart";

coinlib/lib/src/dlc/participant_funding_commitment.dart

@@ -0,0 +1,30 @@
+part of "library.dart";
+
+/// The proposed inputs and change for a DLC funding participant. Their net
+/// contribution must reach their amount in [DLCTerms.fundAmounts] plus a share
+/// of the fee that includes the fee specific to their inputs and change input
+/// and a fraction of all other transaction data.
+/// TODO: The required commitment should probably be determined by
+/// [DLCFundingCollector] and this docstring updated accordingly.
+class DLCParticipantFundingCommitment {
+
+  /// The change output to include in the outputs
+  final Output change;
+  /// The inputs provided by the participant. The [InputCandidate] contains the
+  /// input value but this must be validated against the actual output value to
+  /// be correct.
+  final List<InputCandidate> inputs;
+
+  DLCParticipantFundingCommitment({
+    required this.change,
+    required this.inputs,
+  });
+
+  // TODO: Add coin selector to meet required contribution and fee, making this
+  // easier for consumers of the library to fund their contribution.
+
+  /// Amount contributed after subtracting change from inputs
+  BigInt get netAmount
+    => addBigInts(inputs.map((input) => input.value)) - change.value;
+
+}

coinlib/lib/src/dlc/ready.dart

@@ -41,4 +41,10 @@ class DLCReady with Writable {
     writer.writeOrderedXPubkeyMap(cets, (cet) => cet.write(writer));
   }
 
+  /// Create the [DLCFundingCollector] class to start construction of the
+  /// Funding Transaction. The [terms] must correspond to this [DLCReady] object
+  /// though this is not validated.
+  DLCFundingCollector beginFunding(DLCTerms terms)
+    => DLCFundingCollector._(terms);
+
 }