add Str2Date func to handler date cell

date.go

@@ -0,0 +1,108 @@
+package xlsx
+
+import (
+	"fmt"
+	"math"
+	"strconv"
+)
+
+//# Pre-calculate the datetime epochs for efficiency.
+var (
+	_JDN_delta = []int{2415080 - 61, 2416482 - 1}
+	//epoch_1904         = time.Date(1904, 1, 1, 0, 0, 0, 0, time.Local)
+	//epoch_1900         = time.Date(1899, 12, 31, 0, 0, 0, 0, time.Local)
+	//epoch_1900_minus_1 = time.Date(1899, 12, 30, 0, 0, 0, 0, time.Local)
+	_XLDAYS_TOO_LARGE = []int{2958466, 2958466 - 1462} //# This is equivalent to 10000-01-01
+)
+
+var (
+//ErrXLDateBadTuple = errors.New("XLDate is bad tuple")
+//ErrXLDateError    = errors.New("XLDateError")
+)
+
+func XLDateTooLarge(d float64) error {
+	return fmt.Errorf("XLDate %v is too large", d)
+}
+
+func XLDateAmbiguous(d float64) error {
+	return fmt.Errorf("XLDate %v is ambiguous", d)
+}
+
+func XLDateNegative(d float64) error {
+	return fmt.Errorf("XLDate %v is Negative", d)
+}
+
+func XLDateBadDatemode(datemode int) error {
+	return fmt.Errorf("XLDate is bad datemode %d", datemode)
+}
+
+func divmod(a, b int) (int, int) {
+	c := a % b
+	return (a - c) / b, c
+}
+
+func div(a, b int) int {
+	return (a - a%b) / b
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+// this func provide a method to convert date cell string to
+// a slice []int. the []int means []int{year, month, day, hour, minute, second}
+func StrToDate(data string, datemode int) ([]int, error) {
+	xldate, err := strconv.ParseFloat(data, 64)
+	if err != nil {
+		return nil, err
+	}
+
+	if datemode != 0 && datemode != 1 {
+		return nil, XLDateBadDatemode(datemode)
+	}
+	if xldate == 0.00 {
+		return []int{0, 0, 0, 0, 0, 0}, nil
+	}
+	if xldate < 0.00 {
+		return nil, XLDateNegative(xldate)
+	}
+	xldays := int(xldate)
+	frac := xldate - float64(xldays)
+	seconds := int(math.Floor(frac * 86400.0))
+	hour, minute, second := 0, 0, 0
+	//assert 0 <= seconds <= 86400
+	if seconds == 86400 {
+		xldays += 1
+	} else {
+		//# second = seconds % 60; minutes = seconds // 60
+		var minutes int
+		minutes, second = divmod(seconds, 60)
+		//# minute = minutes % 60; hour    = minutes // 60
+		hour, minute = divmod(minutes, 60)
+	}
+	if xldays >= _XLDAYS_TOO_LARGE[datemode] {
+		return nil, XLDateTooLarge(xldate)
+	}
+
+	if xldays == 0 {
+		return []int{0, 0, 0, hour, minute, second}, nil
+	}
+
+	if xldays < 61 && datemode == 0 {
+		return nil, XLDateAmbiguous(xldate)
+	}
+
+	jdn := xldays + _JDN_delta[datemode]
+	yreg := ((((jdn*4+274277)/146097)*3/4)+jdn+1363)*4 + 3
+	mp := ((yreg%1461)/4)*535 + 333
+	d := ((mp % 16384) / 535) + 1
+	//# mp /= 16384
+	mp >>= 14
+	if mp >= 10 {
+		return []int{(yreg / 1461) - 4715, mp - 9, d, hour, minute, second}, nil
+	}
+	return []int{(yreg / 1461) - 4716, mp + 3, d, hour, minute, second}, nil
+}