Public initialisers for DayComponent and MonthComponent to support pre-selected date range in the calendar.

Sources/Public/Day.swift

@@ -44,6 +44,16 @@ public struct DayComponents: Hashable {
 
 }
 
+// MARK: Public init from date
+
+extension DayComponents {
+    public init(from date: Date, calendar: Calendar = Calendar.current) {
+        let month = Month(from: date, calendar: calendar)
+        let day = calendar.component(.day, from: date)
+        self = Day(month: month, day: day)
+    }
+}
+
 // MARK: CustomStringConvertible
 
 extension DayComponents: CustomStringConvertible {

Sources/Public/Month.swift

@@ -53,6 +53,14 @@ public struct MonthComponents: Hashable {
 
 }
 
+// MARK: Public init from date
+
+extension MonthComponents {
+    public init(from date: Date, calendar: Calendar = Calendar.current) {
+     self = calendar.month(containing: date)
+  }
+}
+
 // MARK: CustomStringConvertible
 
 extension MonthComponents: CustomStringConvertible {

Tests/DayHelperTests.swift

@@ -138,6 +138,23 @@ final class DayHelperTests: XCTestCase {
       "Expected January 1, 02 - 1 = December 31, 01.")
   }
 
+  func testCreateDayFromDate() {
+    var components = DateComponents()
+    components.era = 1
+    components.year = 2020
+    components.month = 03
+    components.day = 02
+    guard let date = gregorianCalendar.date(from: components) else {
+      XCTFail("Expected a date created from components")
+      return
+    }
+    let day = Day(from: date)
+    XCTAssert(
+      day == Day(month: Month(era: 1, year: 2020, month: 03, isInGregorianCalendar: true), day: 02),
+      "Expected 2020-03."
+    )
+  }
+
   // MARK: Private
 
   private lazy var gregorianCalendar = Calendar(identifier: .gregorian)

Tests/MonthTests.swift

@@ -54,6 +54,19 @@ final class MonthTests: XCTestCase {
       to: Month(era: 1, year: 2020, month: 06, isInGregorianCalendar: true))
     XCTAssert(month2 == Month(era: 1, year: 2018, month: 05, isInGregorianCalendar: true), "Expected 2018-05.")
   }
+
+    func testCreateMonthFromDate() {
+        var components = DateComponents()
+        components.era = 1
+        components.year = 2020
+        components.month = 03
+        guard let date = calendar.date(from: components) else {
+            XCTFail("Expected a date created from components")
+            return
+        }
+        let month = Month(from: date)
+        XCTAssert(month == Month(era: 1, year: 2020, month: 03, isInGregorianCalendar: true), "Expected 2020-03.")
+    }
 
   // MARK: Private