[SPARK-8944][SQL] Support casting between IntervalType and StringType

Author: Wenchen Fan <cloud0fan@outlook.com>

Closes #7355 from cloud-fan/fromString and squashes the following commits:

3bbb9d6 [Wenchen Fan] fix code gen
7dab957 [Wenchen Fan] naming fix
0fbbe19 [Wenchen Fan] address comments
ac1f3d1 [Wenchen Fan] Support casting between IntervalType and StringType

2 files changed, 94 insertions, 0 deletions

diff --git a/unsafe/src/main/java/org/apache/spark/unsafe/types/Interval.java b/unsafe/src/main/java/org/apache/spark/unsafe/types/Interval.java
index 0af982d484..eb7475e9df 100644
--- a/unsafe/src/main/java/org/apache/spark/unsafe/types/Interval.java
+++ b/unsafe/src/main/java/org/apache/spark/unsafe/types/Interval.java
@@ -18,6 +18,8 @@
 package org.apache.spark.unsafe.types;
 
 import java.io.Serializable;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 /**
  * The internal representation of interval type.
@@ -30,6 +32,52 @@ public final class Interval implements Serializable {
   public static final long MICROS_PER_DAY = MICROS_PER_HOUR * 24;
   public static final long MICROS_PER_WEEK = MICROS_PER_DAY * 7;
 
+  /**
+   * A function to generate regex which matches interval string's unit part like "3 years".
+   *
+   * First, we can leave out some units in interval string, and we only care about the value of
+   * unit, so here we use non-capturing group to wrap the actual regex.
+   * At the beginning of the actual regex, we should match spaces before the unit part.
+   * Next is the number part, starts with an optional "-" to represent negative value. We use
+   * capturing group to wrap this part as we need the value later.
+   * Finally is the unit name, ends with an optional "s".
+   */
+  private static String unitRegex(String unit) {
+    return "(?:\\s+(-?\\d+)\\s+" + unit + "s?)?";
+  }
+
+  private static Pattern p = Pattern.compile("interval" + unitRegex("year") + unitRegex("month") +
+    unitRegex("week") + unitRegex("day") + unitRegex("hour") + unitRegex("minute") +
+    unitRegex("second") + unitRegex("millisecond") + unitRegex("microsecond"));
+
+  private static long toLong(String s) {
+    if (s == null) {
+      return 0;
+    } else {
+      return Long.valueOf(s);
+    }
+  }
+
+  public static Interval fromString(String s) {
+    if (s == null) {
+      return null;
+    }
+    Matcher m = p.matcher(s);
+    if (!m.matches() || s.equals("interval")) {
+      return null;
+    } else {
+      long months = toLong(m.group(1)) * 12 + toLong(m.group(2));
+      long microseconds = toLong(m.group(3)) * MICROS_PER_WEEK;
+      microseconds += toLong(m.group(4)) * MICROS_PER_DAY;
+      microseconds += toLong(m.group(5)) * MICROS_PER_HOUR;
+      microseconds += toLong(m.group(6)) * MICROS_PER_MINUTE;
+      microseconds += toLong(m.group(7)) * MICROS_PER_SECOND;
+      microseconds += toLong(m.group(8)) * MICROS_PER_MILLI;
+      microseconds += toLong(m.group(9));
+      return new Interval((int) months, microseconds);
+    }
+  }
+
   public final int months;
   public final long microseconds;
 
diff --git a/unsafe/src/test/java/org/apache/spark/unsafe/types/IntervalSuite.java b/unsafe/src/test/java/org/apache/spark/unsafe/types/IntervalSuite.java
index 0f4f38b2b0..44a949a371 100644
--- a/unsafe/src/test/java/org/apache/spark/unsafe/types/IntervalSuite.java
+++ b/unsafe/src/test/java/org/apache/spark/unsafe/types/IntervalSuite.java
@@ -56,4 +56,50 @@ public class IntervalSuite {
     i = new Interval(34, 3 * MICROS_PER_WEEK + 13 * MICROS_PER_HOUR + 123);
     assertEquals(i.toString(), "interval 2 years 10 months 3 weeks 13 hours 123 microseconds");
   }
+
+  @Test
+  public void fromStringTest() {
+    testSingleUnit("year", 3, 36, 0);
+    testSingleUnit("month", 3, 3, 0);
+    testSingleUnit("week", 3, 0, 3 * MICROS_PER_WEEK);
+    testSingleUnit("day", 3, 0, 3 * MICROS_PER_DAY);
+    testSingleUnit("hour", 3, 0, 3 * MICROS_PER_HOUR);
+    testSingleUnit("minute", 3, 0, 3 * MICROS_PER_MINUTE);
+    testSingleUnit("second", 3, 0, 3 * MICROS_PER_SECOND);
+    testSingleUnit("millisecond", 3, 0, 3 * MICROS_PER_MILLI);
+    testSingleUnit("microsecond", 3, 0, 3);
+
+    String input;
+
+    input = "interval   -5  years  23   month";
+    Interval result = new Interval(-5 * 12 + 23, 0);
+    assertEquals(Interval.fromString(input), result);
+
+    // Error cases
+    input = "interval   3month 1 hour";
+    assertEquals(Interval.fromString(input), null);
+
+    input = "interval 3 moth 1 hour";
+    assertEquals(Interval.fromString(input), null);
+
+    input = "interval";
+    assertEquals(Interval.fromString(input), null);
+
+    input = "int";
+    assertEquals(Interval.fromString(input), null);
+
+    input = "";
+    assertEquals(Interval.fromString(input), null);
+
+    input = null;
+    assertEquals(Interval.fromString(input), null);
+  }
+
+  private void testSingleUnit(String unit, int number, int months, long microseconds) {
+    String input1 = "interval " + number + " " + unit;
+    String input2 = "interval " + number + " " + unit + "s";
+    Interval result = new Interval(months, microseconds);
+    assertEquals(Interval.fromString(input1), result);
+    assertEquals(Interval.fromString(input2), result);
+  }
 }