This closes #1006, new fn: MONTH ref #65

Co-authored-by: xuri <xuri.me@gmail.com>

2 files changed, 45 insertions, 1 deletions

diff --git a/calc.go b/calc.go
index 9f3e25f..e59d344 100644
--- a/calc.go
+++ b/calc.go
@@ -504,6 +504,7 @@ type formulaFuncs struct {
 //    VAR.P
 //    VARP
 //    VLOOKUP
+//    YEAR
 //
 func (f *File) CalcCellValue(sheet, cell string) (result string, err error) {
 	var (
@@ -6445,6 +6446,36 @@ func (fn *formulaFuncs) MONTH(argsList *list.List) formulaArg {
 	return newNumberFormulaArg(float64(timeFromExcelTime(num.Number, false).Month()))
 }
 
+// YEAR function returns an integer representing the year of a supplied date.
+// The syntax of the function is:
+//
+//    YEAR(serial_number)
+//
+func (fn *formulaFuncs) YEAR(argsList *list.List) formulaArg {
+	if argsList.Len() != 1 {
+		return newErrorFormulaArg(formulaErrorVALUE, "YEAR requires exactly 1 argument")
+	}
+	arg := argsList.Front().Value.(formulaArg)
+	num := arg.ToNumber()
+	if num.Type != ArgNumber {
+		dateString := strings.ToLower(arg.Value())
+		if !isDateOnlyFmt(dateString) {
+			if _, _, _, _, _, err := strToTime(dateString); err.Type == ArgError {
+				return err
+			}
+		}
+		year, _, _, _, err := strToDate(dateString)
+		if err.Type == ArgError {
+			return err
+		}
+		return newNumberFormulaArg(float64(year))
+	}
+	if num.Number < 0 {
+		return newErrorFormulaArg(formulaErrorNUM, "YEAR only accepts positive argument")
+	}
+	return newNumberFormulaArg(float64(timeFromExcelTime(num.Number, false).Year()))
+}
+
 // NOW function returns the current date and time. The function receives no
 // arguments and therefore. The syntax of the function is:
 //
diff --git a/calc_test.go b/calc_test.go
index cea9521..e5a6e1e 100644
--- a/calc_test.go
+++ b/calc_test.go
@@ -965,6 +965,13 @@ func TestCalcCellValue(t *testing.T) {
 		// MONTH
 		"=MONTH(42171)":           "6",
 		"=MONTH(\"31-May-2015\")": "5",
+		// YEAR
+		"=YEAR(15)":              "1900",
+		"=YEAR(\"15\")":          "1900",
+		"=YEAR(2048)":            "1905",
+		"=YEAR(42171)":           "2015",
+		"=YEAR(\"29-May-2015\")": "2015",
+		"=YEAR(\"05/03/1984\")":  "1984",
 		// Text Functions
 		// CHAR
 		"=CHAR(65)": "A",
@@ -1986,10 +1993,16 @@ func TestCalcCellValue(t *testing.T) {
 		"=DAY(\"0-January-1900\")":                                            "#VALUE!",
 		// MONTH
 		"=MONTH()":                    "MONTH requires exactly 1 argument",
-		"=MONTH(43891,43101)":         "MONTH requires exactly 1 argument",
+		"=MONTH(0,0)":                 "MONTH requires exactly 1 argument",
 		"=MONTH(-1)":                  "MONTH only accepts positive argument",
 		"=MONTH(\"text\")":            "#VALUE!",
 		"=MONTH(\"January 25, 100\")": "#VALUE!",
+		// YEAR
+		"=YEAR()":                    "YEAR requires exactly 1 argument",
+		"=YEAR(0,0)":                 "YEAR requires exactly 1 argument",
+		"=YEAR(-1)":                  "YEAR only accepts positive argument",
+		"=YEAR(\"text\")":            "#VALUE!",
+		"=YEAR(\"January 25, 100\")": "#VALUE!",
 		// NOW
 		"=NOW(A1)": "NOW accepts no arguments",
 		// TODAY