Unspecified leap years

src/bitmask.js

@@ -9,7 +9,7 @@ const PATTERN = /^[0-9xXdDmMyY]{8}$/
 const YYYYMMDD = 'YYYYMMDD'.split('')
 const MAXDAYS = [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
 
-const { floor, pow, max, min } = Math
+const { floor, pow, max, min, abs } = Math
 
 
 /**
@@ -173,6 +173,9 @@ class Bitmask {
       }
 
       break
+    default:
+      if (!this.test(Bitmask.MONTH) && month === 1 && day === 29)
+        year = this.lastLeapYear(year)
     }
 
     if (month === 1 && day > 28 && !leap(year)) {
@@ -263,6 +266,24 @@ class Bitmask {
   toString(symbol = 'X') {
     return this.masks(['YYYY', 'MM', 'DD'], symbol).join('-')
   }
+
+  lastLeapYear(year) {
+    if (leap(year))
+      return year
+    const values = [pad(year)]
+    const [minYear] = this.min(values)
+    const yearReg = this.masks(values, '.')
+    let [newYear] = this.max(values)
+
+    while (!(leap(newYear) &&
+            pad(newYear).match(yearReg)) &&
+            newYear >= minYear) {
+      newYear--
+    }
+    if (newYear < minYear)
+      return year
+    return newYear
+  }
 }
 
 Bitmask.prototype.is = Bitmask.prototype.test
@@ -274,6 +295,16 @@ function leap(year) {
   return true
 }
 
+function pad(number) {
+  let k = abs(number)
+
+  if (k < 10)   return `000${k}`
+  if (k < 100)  return `00${k}`
+  if (k < 1000) return `0${k}`
+
+  return `${k}`
+}
+
 Bitmask.DAY   = Bitmask.D = Bitmask.compute('yyyymmxx')
 Bitmask.MONTH = Bitmask.M = Bitmask.compute('yyyyxxdd')
 Bitmask.YEAR  = Bitmask.Y = Bitmask.compute('xxxxmmdd')

src/date.js

@@ -61,7 +61,26 @@ class Date extends global.Date {
               args[4] = args[4] + obj.offset
             }
 
-            args = [ExtDateTime.UTC(...args)]
+            let UTCDateTime = ExtDateTime.UTC(...args)
+
+            const mask = new Bitmask(obj.unspecified)
+            if (mask.test(Bitmask.YEAR) > 0 &&
+            !mask.test(Bitmask.MONTH) &&
+            !mask.test(Bitmask.DAY)) {
+              let date = new global.Date(UTCDateTime),
+                year = date.getUTCFullYear(),
+                day = date.getUTCDate()
+              const leapYear = mask.lastLeapYear(abs(year))
+              if (leapYear !== abs(year)) {
+                args[0] = leapYear * (year < 0 ? -1 : 1)
+                let newUTCDateTime = ExtDateTime.UTC(...args),
+                  newDate = new global.Date(newUTCDateTime),
+                  newDay = newDate.getUTCDate()
+                if (newDay !== day) UTCDateTime = newUTCDateTime
+              }
+            }
+
+            args = [UTCDateTime]
           }
 
           ({ uncertain, approximate, unspecified } = obj)

test/date.js

@@ -588,3 +588,28 @@ describe('Date', () => {
       expect(new Date([2014, 3, 1]).format('en-US')).to.eql('4/1/2014'))
   })
 })
+
+describe('Leap year', () => {
+  it('YYXX-02-29', () => {
+    let date = new Date({
+      values: [2100, 1, 29],
+      unspecified: 12
+    })
+
+    expect(date.edtf).to.eql('21XX-02-29')
+
+    date = new Date('21XX-02-29')
+
+    expect(date.edtf).to.eql('21XX-02-29')
+  })
+
+  it('.next()', () => {
+    let date = new Date('201X-02-28')
+    expect(date.next().edtf).to.eql('201X-02-29')
+  })
+
+  it('.prev()', () => {
+    let date = new Date('201X-03-01')
+    expect(date.prev().edtf).to.eql('201X-02-29')
+  })
+})