feat(presto-clp): Add a plan optimizer to push down supported filters to CLP. (#16)

Author: wraymo

presto-clp/src/main/java/com/facebook/presto/plugin/clp/ClpExpression.java

@@ -0,0 +1,77 @@
+/*
+ * 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 com.facebook.presto.plugin.clp;
+
+import com.facebook.presto.spi.relation.RowExpression;
+
+import java.util.Optional;
+
+/**
+ * Represents the result of converting a Presto RowExpression into a CLP-compatible KQL query. In
+ * every case, `pushDownExpression` represents the part of the RowExpression that could be
+ * converted to a KQL expression, and `remainingExpression` represents the part that could not be
+ * converted.
+ */
+public class ClpExpression
+{
+    // Optional KQL query or column name representing the fully or partially translatable part of the expression.
+    private final Optional<String> pushDownExpression;
+
+    // The remaining (non-translatable) portion of the RowExpression, if any.
+    private final Optional<RowExpression> remainingExpression;
+
+    public ClpExpression(String pushDownExpression, RowExpression remainingExpression)
+    {
+        this.pushDownExpression = Optional.ofNullable(pushDownExpression);
+        this.remainingExpression = Optional.ofNullable(remainingExpression);
+    }
+
+    /**
+     * Creates an empty ClpExpression with neither pushdown nor remaining expressions.
+     */
+    public ClpExpression()
+    {
+        this(null, null);
+    }
+
+    /**
+     * Creates a ClpExpression from a fully translatable KQL query or column name.
+     *
+     * @param pushDownExpression
+     */
+    public ClpExpression(String pushDownExpression)
+    {
+        this(pushDownExpression, null);
+    }
+
+    /**
+     * Creates a ClpExpression from a non-translatable RowExpression.
+     *
+     * @param remainingExpression
+     */
+    public ClpExpression(RowExpression remainingExpression)
+    {
+        this(null, remainingExpression);
+    }
+
+    public Optional<String> getPushDownExpression()
+    {
+        return pushDownExpression;
+    }
+
+    public Optional<RowExpression> getRemainingExpression()
+    {
+        return remainingExpression;
+    }
+}