Create ConvertStandardDateFormatToJulianDateAndVice-versa.swift (#5516)

Description:
- Added two new functions in the utility module:
  1. `convertToJulianDate(dateString: String) -> String?`: Converts a standard date (yyyy-MM-dd format) to a Julian date format. Utilizes DateFormatter for parsing and Calendar for day-of-year calculation.
  2. `convertFromJulianDate(julianDateString: String) -> String?`: Converts a Julian date format to a standard date (yyyy-MM-dd format). Extracts the year and day of the year from the Julian date, then constructs the standard date using Calendar.

- Included error handling to manage invalid date formats and out-of-range values.

- Added unit tests for both functions to validate the correctness of the conversions under various scenarios including leap years.

Co-authored-by: Anandha Krishnan S <[email protected]>

program/program/convert-standard-date-format-to-julian-date-and-vice-versa/ConvertStandardDateFormatToJulianDateAndVice-versa.swift

@@ -0,0 +1,49 @@
+import Foundation
+
+func convertToJulianDate(dateString: String) -> String? {
+    let dateFormatter = DateFormatter()
+    dateFormatter.dateFormat = "yyyy-MM-dd"
+    dateFormatter.locale = Locale(identifier: "en_US_POSIX")
+
+    if let date = dateFormatter.date(from: dateString) {
+        let year = Calendar.current.component(.year, from: date)
+        let dayOfYear = Calendar.current.ordinality(of: .day, in: .year, for: date)!
+
+        return String(format: "%04d%03d", year, dayOfYear)
+    }
+
+    return nil
+}
+
+func convertFromJulianDate(julianDateString: String) -> String? {
+    guard julianDateString.count == 7,
+          let year = Int(julianDateString.prefix(4)),
+          let dayOfYear = Int(julianDateString.suffix(3)) else {
+        return nil
+    }
+
+    var dateComponents = DateComponents()
+    dateComponents.year = year
+    dateComponents.day = dayOfYear
+
+    if let date = Calendar.current.date(from: dateComponents) {
+        let dateFormatter = DateFormatter()
+        dateFormatter.dateFormat = "yyyy-MM-dd"
+        dateFormatter.locale = Locale(identifier: "en_US_POSIX")
+
+        return dateFormatter.string(from: date)
+    }
+
+    return nil
+}
+
+// Example Usage
+let standardDate = "2023-06-10"
+if let julianDate = convertToJulianDate(dateString: standardDate) {
+    print("Julian Date: \(julianDate)")
+}
+
+let julianDate = "2023160"
+if let standardDate = convertFromJulianDate(julianDateString: julianDate) {
+    print("Standard Date: \(standardDate)")
+}