feat: #402 Add Tx Evaluator implementation to return constant cost

core-api/src/main/java/com/bloxbean/cardano/client/api/impl/StaticTransactionEvaluator.java

@@ -0,0 +1,80 @@
+package com.bloxbean.cardano.client.api.impl;
+
+import com.bloxbean.cardano.client.api.TransactionEvaluator;
+import com.bloxbean.cardano.client.api.exception.ApiException;
+import com.bloxbean.cardano.client.api.model.EvaluationResult;
+import com.bloxbean.cardano.client.api.model.Result;
+import com.bloxbean.cardano.client.api.model.Utxo;
+import com.bloxbean.cardano.client.exception.CborDeserializationException;
+import com.bloxbean.cardano.client.plutus.spec.ExUnits;
+import com.bloxbean.cardano.client.transaction.spec.Transaction;
+import com.bloxbean.cardano.client.util.JsonUtil;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * A static implementation of {@link TransactionEvaluator} which returns a static list of {@link EvaluationResult}
+ */
+public class StaticTransactionEvaluator implements TransactionEvaluator {
+    private List<ExUnits> exUnits;
+
+    /**
+     * Constructor
+     * @param exUnits List of {@link ExUnits} to be returned as evaluation result. The number of ExUnits should match the
+     *                number of redeemers in the transaction in the order they appear in the transaction
+     */
+    public StaticTransactionEvaluator(List<ExUnits> exUnits) {
+        this.exUnits = exUnits;
+    }
+
+    @Override
+    public Result<List<EvaluationResult>> evaluateTx(byte[] cbor, Set<Utxo> inputUtxos) throws ApiException {
+        var evaluationResults = getEvaluationResults(cbor);
+        return Result.success(JsonUtil.getPrettyJson(evaluationResults)).withValue(evaluationResults);
+    }
+
+    @Override
+    public Result<List<EvaluationResult>> evaluateTx(byte[] cbor) throws ApiException {
+        var evaluationResults = getEvaluationResults(cbor);
+        return Result.success(JsonUtil.getPrettyJson(evaluationResults)).withValue(evaluationResults);
+    }
+
+    @Override
+    public Result<List<EvaluationResult>> evaluateTx(Transaction transaction, Set<Utxo> inputUtxos) throws ApiException {
+        var evaluationResults = getEvaluationResults(transaction);
+        return Result.success(JsonUtil.getPrettyJson(evaluationResults)).withValue(evaluationResults);
+    }
+
+    private List<EvaluationResult> getEvaluationResults(byte[] txCbor) {
+        Transaction transaction = null;
+        try {
+            transaction = Transaction.deserialize(txCbor);
+        } catch (CborDeserializationException e) {
+            throw new IllegalArgumentException("Invalid transaction cbor. Cost cannot be returned");
+        }
+        return getEvaluationResults(transaction);
+    }
+
+    private List<EvaluationResult> getEvaluationResults(Transaction transaction) {
+        if (transaction.getWitnessSet().getRedeemers() == null)
+            throw new IllegalArgumentException("Transaction doesn't have redeemers. Cost cannot be returned");
+
+        if (transaction.getWitnessSet().getRedeemers().size() != exUnits.size())
+            throw new IllegalArgumentException("Number of redeemers in the transaction doesn't match the number of exUnits provided");
+
+        List<EvaluationResult> evaluationResults = new ArrayList<>();
+        for (int i = 0; i < transaction.getWitnessSet().getRedeemers().size(); i++) {
+            var redeemer = transaction.getWitnessSet().getRedeemers().get(i);
+            var evaluationResult = new EvaluationResult();
+            evaluationResult.setExUnits(exUnits.get(i));
+            evaluationResult.setIndex(redeemer.getIndex().intValue());
+            evaluationResult.setRedeemerTag(redeemer.getTag());
+
+            evaluationResults.add(evaluationResult);
+        }
+
+        return evaluationResults;
+    }
+}