From 465d3c327fc42f1ae8852948b7215b80da1d60a1 Mon Sep 17 00:00:00 2001
From: Dan Hansen <dan@recidiviz.org>
Date: Thu, 25 Jan 2024 16:57:49 -0800
Subject: [PATCH] [Date] Implement `%y` year without century parser / formatter

---
 internal/function_time_parser.go | 38 ++++++++++++++++++++++++++++++--
 query_test.go                    | 10 +++++++++
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/internal/function_time_parser.go b/internal/function_time_parser.go
index 3802ef4..833918b 100644
--- a/internal/function_time_parser.go
+++ b/internal/function_time_parser.go
@@ -372,8 +372,8 @@ var formatPatternMap = map[rune]*FormatTimeInfo{
 		AvailableTypes: []TimeFormatType{
 			FormatTypeDate, FormatTypeDatetime, FormatTypeTimestamp,
 		},
-		Parse:  centuryParser,
-		Format: centuryFormatter,
+		Parse:  yearWithoutCenturyParser,
+		Format: yearWithoutCenturyFormatter,
 	},
 	'Z': &FormatTimeInfo{
 		AvailableTypes: []TimeFormatType{
@@ -518,6 +518,40 @@ func centuryFormatter(t *time.Time) ([]rune, error) {
 	return []rune(fmt.Sprint(t.Year())[:2]), nil
 }
 
+func yearWithoutCenturyParser(text []rune, t *time.Time) (int, error) {
+	const yearLen = 2
+	if len(text) > yearLen {
+		return 0, fmt.Errorf("unexpected year number")
+	}
+	year, err := strconv.ParseInt(string(text), 10, 64)
+	if err != nil {
+		return 0, fmt.Errorf("unexpected year number")
+	}
+	if year < 0 {
+		return 0, fmt.Errorf("invalid year number %d", year)
+	}
+	century := 2000
+	if year >= 69 {
+		century = 1900
+	}
+	*t = time.Date(
+		century+int(year),
+		t.Month(),
+		int(t.Day()),
+		int(t.Hour()),
+		int(t.Minute()),
+		int(t.Second()),
+		int(t.Nanosecond()),
+		t.Location(),
+	)
+	return len(text), nil
+}
+
+func yearWithoutCenturyFormatter(t *time.Time) ([]rune, error) {
+	year := t.Format("2006")
+	return []rune(year[len(year)-2:]), nil
+}
+
 func ansicParser(text []rune, t *time.Time) (int, error) {
 	v, err := time.Parse("Mon Jan 02 15:04:05 2006", string(text))
 	if err != nil {
diff --git a/query_test.go b/query_test.go
index 31d13f3..7249b3e 100644
--- a/query_test.go
+++ b/query_test.go
@@ -3690,6 +3690,11 @@ SELECT date, EXTRACT(ISOYEAR FROM date), EXTRACT(YEAR FROM date), EXTRACT(MONTH
 			query:        `SELECT FORMAT_DATE("%x", DATE "2008-12-25")`,
 			expectedRows: [][]interface{}{{"12/25/08"}},
 		},
+		{
+			name:         "format_date with %y",
+			query:        `SELECT FORMAT_DATE("%y", DATE "2008-12-25"), FORMAT_DATE("%y", DATE "2012-12-25")`,
+			expectedRows: [][]interface{}{{"08", "12"}},
+		},
 		{
 			name:         "format_date with %b-%d-%Y",
 			query:        `SELECT FORMAT_DATE("%b-%d-%Y", DATE "2008-12-25")`,
@@ -3731,6 +3736,11 @@ SELECT date, EXTRACT(ISOYEAR FROM date), EXTRACT(YEAR FROM date), EXTRACT(MONTH
 			query:        `SELECT LAST_DAY(DATE '2008-11-10', WEEK(MONDAY)) AS last_day`,
 			expectedRows: [][]interface{}{{"2008-11-16"}},
 		},
+		{
+			name:         "parse_date with %y",
+			query:        `SELECT PARSE_DATE("%y", '1'), PARSE_DATE("%y", '67'), PARSE_DATE("%y", '69')`,
+			expectedRows: [][]interface{}{{"2001-01-01", "2067-01-01", "1969-01-01"}},
+		},
 		{
 			name:         "parse date with %A %b %e %Y",
 			query:        `SELECT PARSE_DATE("%A %b %e %Y", "Thursday Dec 25 2008")`,