Add Year class

src/year.js

@@ -0,0 +1,109 @@
+'use strict'
+
+const assert = require('assert')
+const { parse } = require('./parser')
+
+const V = new WeakMap()
+const S = new WeakMap()
+
+class Year {
+  static parse(input) {
+    return parse(input, { types: ['Year'] })
+  }
+
+  constructor(input) {
+    V[this] = []
+
+    switch (typeof input) {
+    case 'number':
+      this.year = input
+      break
+
+    case 'string':
+      input = Year.parse(input)
+      // eslint-disable-line no-fallthrough
+
+    case 'object':
+      if (Array.isArray(input))
+        input = { values: input }
+
+      {
+
+        assert(input !== null)
+        if (input.type) assert.equal('Year', input.type)
+
+        assert(input.values)
+        assert(input.values.length)
+
+        this.year = input.values[0]
+        this.significant = input.significant
+      }
+      break
+
+    default:
+      this.year = new Date().getUTCFullYear()
+    }
+  }
+
+  get type() {
+    return 'Year'
+  }
+
+  get year() {
+    return this.values[0]
+  }
+
+  set year(year) {
+    return this.values[0] = Number(year)
+  }
+
+  get significant() {
+    return S[this]
+  }
+
+  set significant(digits) {
+    return S[this] = Number(digits)
+  }
+
+  get values() {
+    return V[this]
+  }
+
+  get edtf() {
+    return this.toEDTF()
+  }
+
+  get min() {
+    return Date.UTC(this.year, 0)
+  }
+
+  get max() {
+    return Date.UTC(this.year, 11, 31, 24, 0, 0)
+  }
+
+  toEDTF() {
+    let abs = Math.abs(this.year)
+    let s = this.significant ? `S${this.significant}` : ''
+
+    if (abs < 9999) return `${pad(this.year, 4)}${s}`
+
+    // TODO exponential form for ending zeroes
+
+    return `Y${pad(this.year)}${s}`
+  }
+}
+
+function pad(year, min = 5) {
+  let abs = Math.abs(year)
+  let sign = (abs === year) ? '' : '-'
+
+  if (abs < 10)    return `${sign}0000${abs}`
+  if (abs < 100)   return `${sign}000${abs}`
+  if (abs < 1000)  return `${sign}00${abs}`
+
+  if (min > 4 && abs < 10000) return `${sign}0${abs}`
+
+  return `${year}`
+}
+
+module.exports = Year