Visitor for UpdateClause class hierarchy

versioned/tiered/tiered-impl/src/main/java/org/projectnessie/versioned/impl/condition/AddClause.java

@@ -32,6 +32,11 @@ public static AddClause addToSetOrNumber(ExpressionPath path, Entity value) {
     return ImmutableAddClause.builder().path(path).value(Value.of(value)).build();
   }
 
+  @Override
+  public <T> T accept(UpdateClauseVisitor<T> visitor) {
+    return visitor.visit(this);
+  }
+
   @Override
   public UpdateClause alias(AliasCollector c) {
     return ImmutableAddClause.builder().path(getPath().alias(c)).value(getValue().alias(c)).build();

versioned/tiered/tiered-impl/src/main/java/org/projectnessie/versioned/impl/condition/RemoveClause.java

@@ -21,6 +21,11 @@
 public abstract class RemoveClause implements UpdateClause {
   public abstract ExpressionPath getPath();
 
+  @Override
+  public <T> T accept(UpdateClauseVisitor<T> visitor) {
+    return visitor.visit(this);
+  }
+
   @Override
   public RemoveClause alias(AliasCollector c) {
     return ImmutableRemoveClause.builder().path(getPath().alias(c)).build();

versioned/tiered/tiered-impl/src/main/java/org/projectnessie/versioned/impl/condition/SetClause.java

@@ -24,6 +24,11 @@ public abstract class SetClause implements UpdateClause {
 
   public abstract Value getValue();
 
+  @Override
+  public <T> T accept(UpdateClauseVisitor<T> visitor) {
+    return visitor.visit(this);
+  }
+
   public static SetClause equals(ExpressionPath path, Entity value) {
     return ImmutableSetClause.builder().path(path).value(Value.of(value)).build();
   }

versioned/tiered/tiered-impl/src/main/java/org/projectnessie/versioned/impl/condition/UpdateClause.java

@@ -27,4 +27,11 @@ enum Type {
 
   String toClauseString();
 
+  /**
+   * Entry point for visitation.
+   * @param visitor the visitor that will be invoked.
+   * @param <T> the type of the returned value.
+   * @return the possibly transformed value resulting from the visitation.
+   */
+  abstract  <T> T accept(UpdateClauseVisitor<T> visitor);
 }

versioned/tiered/tiered-impl/src/main/java/org/projectnessie/versioned/impl/condition/UpdateClauseVisitor.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2020 Dremio
+ *
+ * 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.
+ */
+package org.projectnessie.versioned.impl.condition;
+
+/**
+ * Visitor for all classes in the UpdateClause hierarchy.
+ * @param <T> The type to which the UpdateClause will be converted.
+ */
+public interface UpdateClauseVisitor<T> {
+  /**
+   * Visit the passed in AddClause.
+   * @param clause the clause to visit.
+   * @return the possibly transformed value resulting from the visitation.
+   */
+  T visit(AddClause clause);
+
+  /**
+   * Visit the passed in RemoveClause.
+   * @param clause the clause to visit.
+   * @return the possibly transformed value resulting from the visitation.
+   */
+  T visit(RemoveClause clause);
+
+  /**
+   * Visit the passed in SetClause.
+   * @param clause the clause to visit.
+   * @return the possibly transformed value resulting from the visitation.
+   */
+  T visit(SetClause clause);
+}

versioned/tiered/tiered-impl/src/test/java/org/projectnessie/versioned/impl/condition/TestUpdateClauseVisitor.java

@@ -0,0 +1,144 @@
+/*
+ * Copyright (C) 2020 Dremio
+ *
+ * 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.
+ */
+
+package org.projectnessie.versioned.impl.condition;
+
+import org.immutables.value.Value.Immutable;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInstance;
+import org.projectnessie.versioned.store.Entity;
+
+/**
+ * Test basic functionality and show usage of the UpdateClauseVisitor as pertains to UpdateExpression and the UpdateClause
+ * hierarchy (ValueOfEntity, ExpressionFunction, ExpressionPath).
+ */
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+public class TestUpdateClauseVisitor {
+
+  private static final Visitor VISITOR = new Visitor();
+  private static final String ID_STR = "id";
+  private static final Entity ENTITY_STR = Entity.ofString(ID_STR);
+  private static final String PATH_STR = "commits";
+  private static final ExpressionPath PATH = ExpressionPath.builder(PATH_STR).build();
+
+  /**
+   * A test visitor which builds up an UpdateCommand representation of the passed in UpdateClause.
+   */
+  static class Visitor implements UpdateClauseVisitor<UpdateCommand> {
+
+    @Override
+    public UpdateCommand visit(final AddClause clause) {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public UpdateCommand visit(final RemoveClause clause) {
+      return ImmutableRemoveCommand.builder()
+          .operator(UpdateCommand.Operator.REMOVE)
+          .path(clause.getPath())
+          .build();
+    }
+
+    @Override
+    public UpdateCommand visit(final SetClause clause) {
+      switch (clause.getValue().getType()) {
+        case VALUE:
+          return ImmutableSetCommand.builder()
+              .operator(UpdateCommand.Operator.SET)
+              .path(clause.getPath())
+              .entity(clause.getValue().getValue())
+              .build();
+        case FUNCTION:
+          return ImmutableSetCommand.builder()
+            .operator(UpdateCommand.Operator.SET)
+            .path(clause.getPath())
+            .entity(handleFunction(clause.getValue().getFunction()))
+            .build();
+        default:
+          throw new UnsupportedOperationException(String.format("Unsupported SetClause type: %s", clause.getValue().getType().name()));
+      }
+    }
+
+    private Entity handleFunction(ExpressionFunction expressionFunction) {
+      if (ExpressionFunction.FunctionName.LIST_APPEND == expressionFunction.getName()) {
+        return expressionFunction.getArguments().get(1).getValue();
+      }
+      throw new UnsupportedOperationException(String.format("Unsupported Set function: %s", expressionFunction.getName()));
+    }
+  }
+
+  @Test
+  void testRemoveClause() {
+    final UpdateClause clause = RemoveClause.of(PATH);
+    testClause(RemoveClause.of(PATH), UpdateCommand.Operator.REMOVE, PATH);
+  }
+
+  @Test
+  void testSetClauseEquals() {
+    final UpdateCommand command = testClause(SetClause.equals(PATH, ENTITY_STR), UpdateCommand.Operator.SET, PATH);
+    Assertions.assertEquals(ENTITY_STR, ((UpdateCommand.SetCommand)command).getEntity());
+  }
+
+  @Test
+  void testSetClauseAppendToList() {
+    final UpdateCommand command = testClause(SetClause.appendToList(PATH, ENTITY_STR), UpdateCommand.Operator.SET, PATH);
+    Assertions.assertEquals(ENTITY_STR, ((UpdateCommand.SetCommand)command).getEntity());
+  }
+
+  UpdateCommand testClause(UpdateClause clause, UpdateCommand.Operator operator, ExpressionPath path) {
+    final UpdateCommand command = clause.accept(VISITOR);
+    Assertions.assertEquals(operator, command.getOperator());
+    Assertions.assertEquals(path, command.getPath());
+    return command;
+  }
+
+  /**
+   * Sample interface or class into which UpdateClauses are converted.
+   */
+  static interface UpdateCommand {
+    /**
+     * An enum encapsulating the type of update.
+     */
+    enum Operator {
+      // An operator to remove some part or all of an entity.
+      REMOVE,
+
+      // An operator to set some part or all of an entity.
+      SET
+    }
+
+    Operator getOperator();
+
+    ExpressionPath getPath();
+
+    /**
+     * Sample of a specific type of update command into which UpdateClauses are converted.
+     */
+    @Immutable
+    abstract class RemoveCommand implements UpdateCommand {
+    }
+
+    /**
+     * Sample of a specific type of update command into which UpdateClauses are converted.
+     */
+    @Immutable
+    abstract class SetCommand implements UpdateCommand {
+
+      abstract Entity getEntity();
+    }
+  }
+}