GregorianDate.swift

//
//  GregorianDate.swift
//  
//
//  Created by Soroush Khanlou on 12/22/20.
//

import Foundation

public struct GregorianDate: Equatable, Hashable, Comparable, Codable, CustomStringConvertible {

    public let day: Int
    public let month: Int
    public let year: Int

    public var components: DateComponents {
        DateComponents(year: year, month: month, day: day)
    }

    public var description: String {
        [year, month, day]
            .map({ String(format: "%02d", $0) })
            .joined(separator: "-")
    }

    public init?(string: String) {
        guard !string.isEmpty else { return nil }
        let parts = string.split(separator: "-", maxSplits: 3,
                                 omittingEmptySubsequences: true)
        assert(parts.count == 3)
        guard parts.count == 3 else { return nil }
        guard let year  = Int(parts[0]),
              let month = Int(parts[1]),
              let day   = Int(parts[2]),
              month >= 1 && month <= 12, day >= 1 && day <= 31
        else
        {
            return nil
        }

        self.year  = year
        self.month = month
        self.day   = day
    }

    public init(from decoder: Decoder) throws {

        let container = try decoder.singleValueContainer()
        let string = try container.decode(String.self)
        guard let date = GregorianDate(string: string) else {
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "Malformed date")
        }

        self = date
    }

    public func encode(to encoder: Encoder) throws {
        try self.description.encode(to: encoder)
    }

    public init(from date: Date = Date()) {
        let calendar = Calendar(identifier: .gregorian)
        let components = calendar.dateComponents([.day, .month, .year], from: date)
        self.init(year: components.year!, month: components.month!, day: components.day!)
    }

    public init(year: Int, month: Int, day: Int) {
        self.year  = year
        self.month = month
        self.day   = day
    }

    public static func < (lhs: GregorianDate, rhs: GregorianDate) -> Bool {
        return (lhs.year, lhs.month, lhs.day) < (rhs.year, rhs.month, rhs.day)
    }
}