Transaction fee calculation refactoring

xrpl4j-core/src/main/java/org/xrpl/xrpl4j/model/client/fees/FeeParams.java

@@ -0,0 +1,318 @@
+package org.xrpl.xrpl4j.model.client.fees;
+
+/*-
+ * ========================LICENSE_START=================================
+ * xrpl4j :: core
+ * %%
+ * Copyright (C) 2020 - 2026 XRPL Foundation and its contributors
+ * %%
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * =========================LICENSE_END==================================
+ */
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.primitives.UnsignedInteger;
+import org.immutables.value.Value;
+import org.xrpl.xrpl4j.model.transactions.Address;
+import org.xrpl.xrpl4j.model.transactions.Batch;
+import org.xrpl.xrpl4j.model.transactions.RawTransactionWrapper;
+import org.xrpl.xrpl4j.model.transactions.Transaction;
+import org.xrpl.xrpl4j.model.transactions.TransactionType;
+import org.xrpl.xrpl4j.model.transactions.XrpCurrencyAmount;
+
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+
+/**
+ * The inputs to {@link FeeUtils#computeFee(FeeParams)}.
+ *
+ * <p>Everything that can be read from the {@link #transaction()} is read from it — the transaction type and therefore
+ * any per-type surcharge, an {@code EscrowFinish}'s fulfillment, a
+ * {@link org.xrpl.xrpl4j.model.transactions.Batch Batch}'s inner transactions and the accounts
+ * that must sign it. The remaining fields are the things that are not knowable from the transaction: how each party
+ * intends to sign, which cannot be derived because the fee is signed over and the signatures therefore do not exist
+ * yet, plus two values that {@link FeeResult} does not carry.
+ *
+ * <p>Every field other than {@link #feeResult()} and {@link #transaction()} has a default, so the common case is
+ * {@code FeeParams.builder().feeResult(feeResult).transaction(transaction).build()}.
+ */
+@Value.Immutable
+public interface FeeParams {
+
+  /**
+   * The maximum number of entries in an XRPL signer list, and therefore the most signatures any one party can supply.
+   */
+  UnsignedInteger MAX_SIGNER_LIST_SIZE = UnsignedInteger.valueOf(32);
+
+  /**
+   * The largest number of fee increments a {@code LoanPay} transaction can be charged, being
+   * {@code kLoanMaximumPaymentsPerTransaction / kLoanPaymentsPerFeeIncrement}.
+   */
+  UnsignedInteger MAX_LOAN_PAYMENT_FEE_INCREMENTS = UnsignedInteger.valueOf(20);
+
+  /**
+   * The {@link TransactionType}s whose fee is one owner reserve increment rather than a multiple of the base fee.
+   */
+  Set<TransactionType> OWNER_RESERVE_TRANSACTION_TYPES = ImmutableSet.of(
+    TransactionType.ACCOUNT_DELETE,
+    TransactionType.AMM_CREATE
+  );
+
+  /**
+   * The pseudo-transaction {@link TransactionType}s, which are created by consensus rather than submitted, and
+   * therefore carry no fee.
+   */
+  Set<TransactionType> PSEUDO_TRANSACTION_TYPES = ImmutableSet.of(
+    TransactionType.ENABLE_AMENDMENT,
+    TransactionType.SET_FEE,
+    TransactionType.UNL_MODIFY
+  );
+
+  /**
+   * Construct a builder for this class.
+   *
+   * @return An {@link ImmutableFeeParams.Builder}.
+   */
+  static ImmutableFeeParams.Builder builder() {
+    return ImmutableFeeParams.builder();
+  }
+
+  /**
+   * The current network fee levels, obtained by querying the ledger (e.g., via {@code XrplClient#fee()}).
+   *
+   * @return A {@link FeeResult}.
+   */
+  FeeResult feeResult();
+
+  /**
+   * The transaction being priced. It need not be signed, and its {@code Fee} field is ignored; a placeholder of zero
+   * is customary while the real fee is being computed.
+   *
+   * @return The {@link Transaction} to price.
+   */
+  Transaction transaction();
+
+  /**
+   * The number of signatures the transaction's own account will supply in its {@code Signers} array.
+   *
+   * <p>Zero for a single-signed transaction: rippled charges only for the <em>additional</em> signatures of a
+   * multi-signature, since the first is already covered by the base fee.
+   *
+   * @return An {@link UnsignedInteger} number of signatures, defaulting to zero.
+   */
+  @Value.Default
+  default UnsignedInteger signersCount() {
+    return UnsignedInteger.ZERO;
+  }
+
+  /**
+   * The number of signatures the transaction's sponsor will supply in its {@code SponsorSignature.Signers} array.
+   *
+   * <p>Zero when the transaction is unsponsored, and also when the sponsor signs with a single key: rippled counts
+   * only {@code SponsorSignature.Signers} entries, and a lone sponsor signature is carried in
+   * {@code SponsorSignature.TxnSignature} instead.
+   *
+   * @return An {@link UnsignedInteger} number of signatures, defaulting to zero.
+   */
+  @Value.Default
+  default UnsignedInteger sponsorSignersCount() {
+    return UnsignedInteger.ZERO;
+  }
+
+  /**
+   * The total number of signatures in a {@code LoanSet}'s {@code CounterpartySignature}.
+   *
+   * <p>Unlike {@link #signersCount()} and {@link #sponsorSignersCount()}, this is a total rather than a count of
+   * additional signatures: rippled charges a base fee even for a single counterparty signature. One is therefore the
+   * correct value for a counterparty signing with a single key, and is the default.
+   *
+   * @return An {@link UnsignedInteger} number of signatures, defaulting to one.
+   */
+  @Value.Default
+  default UnsignedInteger counterpartySignatureCount() {
+    return UnsignedInteger.ONE;
+  }
+
+  /**
+   * The number of fee increments a {@code LoanPay} transaction will be charged, being one increment per
+   * {@code kLoanPaymentsPerFeeIncrement} payments the transaction is estimated to make.
+   *
+   * <p>Deriving this requires the {@code Loan}, {@code LoanBroker} and {@code Vault} ledger objects, so it is supplied
+   * rather than computed. One — a single payment — is the default.
+   *
+   * @return An {@link UnsignedInteger} number of fee increments, defaulting to one.
+   */
+  @Value.Default
+  default UnsignedInteger loanPaymentFeeIncrements() {
+    return UnsignedInteger.ONE;
+  }
+
+  /**
+   * The owner reserve increment, required when pricing an {@code AccountDelete} or {@code AMMCreate} — including one
+   * that is an inner transaction of a {@link org.xrpl.xrpl4j.model.transactions.Batch Batch}.
+   *
+   * <p>Those transactions cost exactly one owner reserve increment rather than a multiple of the base fee, and that
+   * increment is not carried on {@link FeeResult}. It can be read from {@code ServerInfo} (e.g.
+   * {@code serverInfo.validatedLedger().get().reserveIncXrp()}).
+   *
+   * @return An optionally-present {@link XrpCurrencyAmount}.
+   */
+  Optional<XrpCurrencyAmount> ownerReserve();
+
+  /**
+   * How many signatures each {@link org.xrpl.xrpl4j.model.transactions.Batch Batch} participant will supply, for
+   * participants that multi-sign.
+   *
+   * <p>This is needed only when pricing a Batch <em>before</em> its {@code BatchSigners} exist — a wallet displaying
+   * a fee up front, for instance. Once signatures have been collected, the counts are read from
+   * {@link org.xrpl.xrpl4j.model.transactions.Batch#batchSigners() Batch#batchSigners()} and this map is neither
+   * needed nor permitted. Participants absent from the map are
+   * counted as signing with a single key.
+   *
+   * <p>Keys must be members of
+   * {@link org.xrpl.xrpl4j.model.transactions.Batch#requiredSigners() Batch#requiredSigners()} — the accounts that
+   * must sign, derived from the inner
+   * transactions. Note that a required signer is not always an inner's {@code Account}: a delegated inner is signed by
+   * its {@code Delegate}, and a sponsored inner also requires its {@code Sponsor}.
+   *
+   * @return A {@link Map} from a Batch participant's {@link Address} to the number of signatures it will supply,
+   *   defaulting to empty.
+   */
+  Map<Address, UnsignedInteger> signaturesPerBatchSigner();
+
+  /**
+   * Validates that the supplied fields are consistent with the {@link #transaction()} being priced, so that a value
+   * which would be silently ignored is rejected instead.
+   */
+  @Value.Check
+  default void check() {
+    final TransactionType transactionType = this.transaction().transactionType();
+
+    Preconditions.checkArgument(
+      !PSEUDO_TRANSACTION_TYPES.contains(transactionType),
+      "%s is a pseudo-transaction. Pseudo-transactions are created by consensus rather than submitted, and carry " +
+        "no fee.", transactionType
+    );
+    Preconditions.checkArgument(
+      transactionType != TransactionType.UNKNOWN,
+      "The fee of an unknown transaction type cannot be computed, because its fee rules are not known."
+    );
+
+    checkSignatureCount(this.signersCount(), UnsignedInteger.ZERO, "signersCount");
+    checkSignatureCount(this.sponsorSignersCount(), UnsignedInteger.ZERO, "sponsorSignersCount");
+    checkSignatureCount(this.counterpartySignatureCount(), UnsignedInteger.ONE, "counterpartySignatureCount");
+
+    Preconditions.checkArgument(
+      transactionType == TransactionType.LOAN_SET ||
+        this.counterpartySignatureCount().equals(UnsignedInteger.ONE),
+      "counterpartySignatureCount applies only to a LoanSet, but the transaction is a %s.", transactionType
+    );
+
+    Preconditions.checkArgument(
+      transactionType == TransactionType.LOAN_PAY ||
+        this.loanPaymentFeeIncrements().equals(UnsignedInteger.ONE),
+      "loanPaymentFeeIncrements applies only to a LoanPay, but the transaction is a %s.", transactionType
+    );
+    Preconditions.checkArgument(
+      this.loanPaymentFeeIncrements().compareTo(UnsignedInteger.ONE) >= 0 &&
+        this.loanPaymentFeeIncrements().compareTo(MAX_LOAN_PAYMENT_FEE_INCREMENTS) <= 0,
+      "loanPaymentFeeIncrements must be between 1 and %s, but was %s.",
+      MAX_LOAN_PAYMENT_FEE_INCREMENTS, this.loanPaymentFeeIncrements()
+    );
+
+    Preconditions.checkArgument(
+      this.ownerReserve().isPresent() == this.requiresOwnerReserve(),
+      "ownerReserve must be supplied for %s, and only for those types, whether standalone or as a Batch inner " +
+        "transaction. Transaction was a %s.", OWNER_RESERVE_TRANSACTION_TYPES, transactionType
+    );
+
+    this.checkSignaturesPerBatchSigner(transactionType);
+  }
+
+  /**
+   * Determines whether the transaction being priced costs an owner reserve increment, either because it is one of
+   * {@link #OWNER_RESERVE_TRANSACTION_TYPES} or because it is a {@link org.xrpl.xrpl4j.model.transactions.Batch Batch}
+   * containing one.
+   *
+   * @return {@code true} if {@link #ownerReserve()} is required.
+   */
+  @Value.Derived
+  default boolean requiresOwnerReserve() {
+    if (OWNER_RESERVE_TRANSACTION_TYPES.contains(this.transaction().transactionType())) {
+      return true;
+    }
+
+    return this.transaction() instanceof Batch &&
+      ((Batch) this.transaction()).rawTransactions().stream()
+        .map(RawTransactionWrapper::rawTransaction)
+        .map(Transaction::transactionType)
+        .anyMatch(OWNER_RESERVE_TRANSACTION_TYPES::contains);
+  }
+
+  /**
+   * Validates {@link #signaturesPerBatchSigner()} against the transaction being priced.
+   *
+   * @param transactionType The {@link TransactionType} of {@link #transaction()}.
+   */
+  default void checkSignaturesPerBatchSigner(final TransactionType transactionType) {
+    if (this.signaturesPerBatchSigner().isEmpty()) {
+      return;
+    }
+
+    Preconditions.checkArgument(
+      transactionType == TransactionType.BATCH,
+      "signaturesPerBatchSigner applies only to a Batch, but the transaction is a %s.", transactionType
+    );
+
+    final Batch batch = (Batch) this.transaction();
+    Preconditions.checkArgument(
+      batch.batchSigners().isEmpty(),
+      "signaturesPerBatchSigner is only for pricing a Batch before its signatures exist. This Batch already has " +
+        "BatchSigners, so the counts are read from them instead."
+    );
+
+    final Set<Address> requiredSigners = batch.requiredSigners();
+    this.signaturesPerBatchSigner().forEach((address, count) -> {
+      Preconditions.checkArgument(
+        requiredSigners.contains(address),
+        "%s is not required to sign this Batch, so a signature count for it would be ignored. The accounts that " +
+          "must sign are %s. Note that a required signer is not always an inner transaction's Account: a delegated " +
+          "inner is signed by its Delegate, and a sponsored inner also requires its Sponsor.",
+        address, requiredSigners
+      );
+      checkSignatureCount(count, UnsignedInteger.ONE, "signaturesPerBatchSigner[" + address + "]");
+    });
+  }
+
+  /**
+   * Asserts that a supplied signature count lies within the range a signer list allows: at least {@code minimum} —
+   * zero for a count of additional signatures, one for a total that always includes a first signature — and no more
+   * than the {@link #MAX_SIGNER_LIST_SIZE XRPL signer list limit}.
+   *
+   * @param signatureCount An {@link UnsignedInteger} number of signatures.
+   * @param minimum        The smallest permitted value, either {@link UnsignedInteger#ZERO} or
+   *                       {@link UnsignedInteger#ONE}.
+   * @param fieldName      The name of the field being checked, for use in the failure message.
+   */
+  static void checkSignatureCount(
+    final UnsignedInteger signatureCount, final UnsignedInteger minimum, final String fieldName
+  ) {
+    Preconditions.checkArgument(
+      signatureCount.compareTo(minimum) >= 0 && signatureCount.compareTo(MAX_SIGNER_LIST_SIZE) <= 0,
+      "%s must be between %s and %s (the XRPL signer list limit), but was %s.",
+      fieldName, minimum, MAX_SIGNER_LIST_SIZE, signatureCount
+    );
+  }
+}