Massive refactoring of modules handling SQL functions to allow for ne…

…sting

legacy/src/main/java/com/amazon/opendistroforelasticsearch/sql/legacy/utils/SQLDefinitionExpr.java

@@ -0,0 +1,73 @@
+package com.amazon.opendistroforelasticsearch.sql.legacy.utils;
+
+import com.alibaba.druid.sql.ast.SQLExprImpl;
+import com.alibaba.druid.sql.ast.expr.SQLValuableExpr;
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+
+public class SQLDefinitionExpr extends SQLExprImpl implements SQLValuableExpr {
+
+    private final String name;
+
+    private final String definition;
+
+    public SQLDefinitionExpr(String name, String definition) {
+        this.name = name;
+        this.definition = definition;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getDefinition() {
+        return definition;
+    }
+
+    @Override
+    public Object getValue() {
+        return this.getName();
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null) {
+            return false;
+        }
+        if (getClass() != obj.getClass()) {
+            return false;
+        }
+        SQLDefinitionExpr other = (SQLDefinitionExpr) obj;
+        if (name == null) {
+            if (other.name != null) {
+                return false;
+            }
+        } else if (!name.equals(other.name)) {
+            return false;
+        }
+        if (definition == null) {
+            if (other.definition != null) {
+                return false;
+            }
+        } else if (!definition.equals(other.definition)) {
+            return false;
+        }
+        return true;
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + ((name == null) ? 0 : name.hashCode());
+        result = prime * result + ((definition == null) ? 0 : definition.hashCode());
+        return result;
+    }
+
+    @Override
+    protected void accept0(SQLASTVisitor visitor) {
+
+    }
+}