add cisa/date.go and cisa/date_test.go

1 files changed, 139 insertions, 0 deletions

diff --git a/cisa/date.go b/cisa/date.go
new file mode 100644
index 0000000..b36b73c
--- /dev/null
+++ b/cisa/date.go
@@ -0,0 +1,139 @@
+package cisa
+
+import (
+  "fmt"
+  "regexp"
+  "strconv"
+)
+
+// YYYY-MM-DD
+type Date uint16
+
+// Returns true if the year is a leap year, and false otherwise.
+//
+// Reference:
+// https://www.timeanddate.com/date/leapyear.html
+func isLeapYear(y uint16) bool {
+  // leap year rules:
+  //   1. year is evenly divisible by 4 and is not evenly divisible by 100
+  //   2. year is evenly divisible by 4 and is evenly divisible by 400
+  return (((y % 4) == 0) && ((y % 100) != 0)) || // rule 1
+         (((y % 4) == 0) && ((y % 400) == 0)) // rule 2
+}
+
+// maximum month days
+var maxMonthDays = []uint16 {
+  31, // jan
+  28, // feb (incorrect for leap years!)
+  31, // mar
+  30, // apr
+  31, // may
+  30, // jun
+  31, // jul
+  31, // aug
+  30, // sep
+  31, // oct
+  30, // nov
+  31, // dec
+}
+
+// Get the maximum day for the given year and month.
+func getMaxMonthDay(y, m uint16) uint16 {
+  if m == 2 && isLeapYear(y) {
+    return 29
+  } else {
+    return maxMonthDays[m - 1]
+  }
+}
+
+// Parse date component and check range.
+func parseDateComponent(name string, s []byte, min, max uint16) (uint16, error) {
+  // parse value
+  vr, err := strconv.ParseUint(string(s), 10, 32)
+  if err != nil {
+    return 0, err
+  }
+
+  v := uint16(vr)
+
+  // check range
+  if v < min || v > max {
+    return 0, fmt.Errorf("%s component out of range [%d, %d]: %d", name, v, min, max)
+  }
+
+  return uint16(v), nil
+}
+
+var dateRe = regexp.MustCompile(`^\d{4}-\d{2}-\d{2}$`)
+
+// Create date from byte slice.
+func NewDate(s []byte) (Date, error) {
+  var r Date
+
+  if !dateRe.Match(s) {
+    return r, fmt.Errorf("invalid date: \"%s\"", s)
+  }
+
+  // parse year
+  y, err := parseDateComponent("year", s[0:4], 1999, 2126)
+  if err != nil {
+    return r, err
+  }
+
+  // parse month
+  m, err := parseDateComponent("month", s[5:7], 1, 12)
+  if err != nil {
+    return r, err
+  }
+
+  // parse day
+  d, err := parseDateComponent("month", s[8:10], 1, getMaxMonthDay(y, m))
+  if err != nil {
+    return r, err
+  }
+
+  // encode return date
+  r = Date((((y - 1999) & 0x3f) << 9) |
+           (((m - 1) & 0xf) << 5) |
+           ((d - 1) & 0x1f))
+
+  // return result
+  return r, nil
+}
+
+// Get year, month, and day components.
+func (me Date) GetComponents() (uint16, uint16, uint16) {
+  // extract components
+  y := uint16((uint16(me) >> 9) + 1999)
+  m := uint16(((uint16(me) >> 5) & 0xf) + 1)
+  d := uint16((uint16(me) & 0x1f) + 1)
+
+  return y, m, d
+}
+
+// Get year component.
+func (me Date) Year() uint16 {
+  y, _, _ := me.GetComponents()
+  return y
+}
+
+// Get month component.
+func (me Date) Month() uint16 {
+  _, m, _ := me.GetComponents()
+  return m
+}
+
+// Get day component.
+func (me Date) Day() uint16 {
+  _, _, d := me.GetComponents()
+  return d
+}
+
+// Convert to string.
+func (me Date) String() string {
+  // extract date components
+  y, m, d := me.GetComponents()
+
+  // return string
+  return fmt.Sprintf("%d-%d-%d", y, m, d)
+}