From df22bb5e2f50a8a2023f58169b87bac5cf9e9df5 Mon Sep 17 00:00:00 2001
From: xuri <xuri.me@gmail.com>
Date: Fri, 17 Jun 2022 00:03:31 +0800
Subject: [PATCH] ref #65, new formula function: DAYS360

---
 calc.go      | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 calc_test.go | 15 +++++++++++++++
 2 files changed, 67 insertions(+)

diff --git a/calc.go b/calc.go
index 6da0f6aaad..086c288eb3 100644
--- a/calc.go
+++ b/calc.go
@@ -419,6 +419,7 @@ type formulaFuncs struct {
 //    DATEVALUE
 //    DAY
 //    DAYS
+//    DAYS360
 //    DB
 //    DDB
 //    DEC2BIN
@@ -12330,6 +12331,57 @@ func (fn *formulaFuncs) DAYS(argsList *list.List) formulaArg {
 	return newNumberFormulaArg(end.Number - start.Number)
 }
 
+// DAYS360 function returns the number of days between 2 dates, based on a
+// 360-day year (12 x 30 months). The syntax of the function is:
+//
+//    DAYS360(start_date,end_date,[method])
+//
+func (fn *formulaFuncs) DAYS360(argsList *list.List) formulaArg {
+	if argsList.Len() < 2 {
+		return newErrorFormulaArg(formulaErrorVALUE, "DAYS360 requires at least 2 arguments")
+	}
+	if argsList.Len() > 3 {
+		return newErrorFormulaArg(formulaErrorVALUE, "DAYS360 requires at most 3 arguments")
+	}
+	startDate := toExcelDateArg(argsList.Front().Value.(formulaArg))
+	if startDate.Type != ArgNumber {
+		return startDate
+	}
+	endDate := toExcelDateArg(argsList.Front().Next().Value.(formulaArg))
+	if endDate.Type != ArgNumber {
+		return endDate
+	}
+	start, end := timeFromExcelTime(startDate.Number, false), timeFromExcelTime(endDate.Number, false)
+	sy, sm, sd, ey, em, ed := start.Year(), int(start.Month()), start.Day(), end.Year(), int(end.Month()), end.Day()
+	method := newBoolFormulaArg(false)
+	if argsList.Len() > 2 {
+		if method = argsList.Back().Value.(formulaArg).ToBool(); method.Type != ArgNumber {
+			return method
+		}
+	}
+	if method.Number == 1 {
+		if sd == 31 {
+			sd--
+		}
+		if ed == 31 {
+			ed--
+		}
+	} else {
+		if getDaysInMonth(sy, sm) == sd {
+			sd = 30
+		}
+		if ed > 30 {
+			if sd < 30 {
+				em++
+				ed = 1
+			} else {
+				ed = 30
+			}
+		}
+	}
+	return newNumberFormulaArg(float64(360*(ey-sy) + 30*(em-sm) + (ed - sd)))
+}
+
 // ISOWEEKNUM function returns the ISO week number of a supplied date. The
 // syntax of the function is:
 //
diff --git a/calc_test.go b/calc_test.go
index c7333c56d3..c9891a3893 100644
--- a/calc_test.go
+++ b/calc_test.go
@@ -1476,6 +1476,15 @@ func TestCalcCellValue(t *testing.T) {
 		"=DAYS(2,1)":                           "1",
 		"=DAYS(INT(2),INT(1))":                 "1",
 		"=DAYS(\"02/02/2015\",\"01/01/2015\")": "32",
+		// DAYS360
+		"=DAYS360(\"10/10/2020\", \"10/10/2020\")":       "0",
+		"=DAYS360(\"01/30/1999\", \"02/28/1999\")":       "28",
+		"=DAYS360(\"01/31/1999\", \"02/28/1999\")":       "28",
+		"=DAYS360(\"12/12/1999\", \"08/31/1999\")":       "-101",
+		"=DAYS360(\"12/12/1999\", \"11/30/1999\")":       "-12",
+		"=DAYS360(\"12/12/1999\", \"11/30/1999\",TRUE)":  "-12",
+		"=DAYS360(\"01/31/1999\", \"03/31/1999\",TRUE)":  "60",
+		"=DAYS360(\"01/31/1999\", \"03/31/2000\",FALSE)": "420",
 		// EDATE
 		"=EDATE(\"01/01/2021\",-1)": "44166",
 		"=EDATE(\"01/31/2020\",1)":  "43890",
@@ -3447,6 +3456,12 @@ func TestCalcCellValue(t *testing.T) {
 		"=DAYS(0,\"\")": "#VALUE!",
 		"=DAYS(NA(),0)": "#VALUE!",
 		"=DAYS(0,NA())": "#VALUE!",
+		// DAYS360
+		"=DAYS360(\"12/12/1999\")":                           "DAYS360 requires at least 2 arguments",
+		"=DAYS360(\"12/12/1999\", \"11/30/1999\",TRUE,\"\")": "DAYS360 requires at most 3 arguments",
+		"=DAYS360(\"12/12/1999\", \"11/30/1999\",\"\")":      "strconv.ParseBool: parsing \"\": invalid syntax",
+		"=DAYS360(\"12/12/1999\", \"\")":                     "#VALUE!",
+		"=DAYS360(\"\", \"11/30/1999\")":                     "#VALUE!",
 		// EDATE
 		"=EDATE()":                      "EDATE requires 2 arguments",
 		"=EDATE(0,\"\")":                "strconv.ParseFloat: parsing \"\": invalid syntax",