feat: functions

- BigQuery `DATE()`
- `NVL()`

Signed-off-by: Andreas Reichel <andreas@manticore-projects.com>

src/main/java/com/manticore/transpiler/ExpressionTranspiler.java

@@ -1,6 +1,38 @@
 package com.manticore.transpiler;
 
+import net.sf.jsqlparser.expression.CastExpression;
+import net.sf.jsqlparser.expression.Function;
+import net.sf.jsqlparser.expression.operators.relational.ExpressionList;
+import net.sf.jsqlparser.statement.create.table.ColDataType;
 import net.sf.jsqlparser.util.deparser.ExpressionDeParser;
 
 public class ExpressionTranspiler extends ExpressionDeParser {
+  public void visit(Function function) {
+    if (function.getName().equalsIgnoreCase("nvl")) {
+      function.setName("Coalesce");
+    }
+
+    if (function.getName().equalsIgnoreCase("date")) {
+      ExpressionList<?> parameters = function.getParameters();
+      final CastExpression expression;
+      switch (parameters.size()) {
+        // DATE(DATETIME '2016-12-25 23:59:59') AS date_dt
+        case 1:
+        // DATE(TIMESTAMP '2016-12-25 05:30:00+07', 'America/Los_Angeles') AS date_tstz
+        case 2:
+           expression =
+                  new CastExpression("Cast")
+                          .withLeftExpression(parameters.get(0))
+                          .withType(new ColDataType().withDataType("DATE"));
+          super.visit(expression);
+          break;
+        case 3:
+          function.setName("MAKE_DATE");
+          super.visit(function);
+          break;
+      }
+    }
+
+
+  }
 }

src/test/java/com/manticore/transpiler/GoogleBigQueryTranspilerTest.java

@@ -0,0 +1,24 @@
+package com.manticore.transpiler;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.io.File;
+import java.util.Map;
+import java.util.stream.Stream;
+
+public class GoogleBigQueryTranspilerTest extends JSQLTranspilerTest {
+  public final static String TEST_FOLDER_STR =
+      "build/resources/test/com/manticore/transpiler/google_bigquery";
+
+  static Stream<Map.Entry<File, SQLTest>> getSqlTestMap() {
+    return getSqlTestMap(new File(TEST_FOLDER_STR).listFiles(FILENAME_FILTER));
+  }
+
+  @ParameterizedTest(name = "{index} {0}: {1}")
+  @MethodSource("getSqlTestMap")
+  void transpile(Map.Entry<File, SQLTest> entry) throws Exception {
+    super.transpile(entry);
+  }
+
+}

src/test/resources/com/manticore/transpiler/any/nvl_function.sql

@@ -0,0 +1,14 @@
+-- provided
+SELECT Nvl( NULL, 1 ) a
+;
+
+-- expected
+SELECT Coalesce( NULL, 1 ) a
+;
+
+-- count
+1
+
+-- results
+"a"
+"1"

src/test/resources/com/manticore/transpiler/google_bigquery/date_function.sql

@@ -0,0 +1,18 @@
+-- provided
+SELECT
+  DATE(2016, 12, 25) AS date_ymd,
+  DATE(DATETIME '2016-12-25 23:59:59') AS date_dt,
+  DATE(TIMESTAMP '2016-12-25 05:30:00+07', 'America/Los_Angeles') AS date_tstz;
+
+-- expected
+SELECT
+  MAKE_DATE(2016, 12, 25) AS date_ymd,
+  CAST(DATETIME '2016-12-25 23:59:59' AS DATE) AS date_dt,
+  CAST(TIMESTAMP '2016-12-25 05:30:00+07' AS DATE) AS date_tstz;
+
+-- count
+1
+
+-- result
+"date_ymd","date_dt","date_tstz"
+"2016-12-15","2016-12-15","2016-12-15"