Decode date/time from String or TimeInterval in Swift - json

Question

I have a JSON (from a third party) that I need to parse. This JSON returns several nested objects
articles: {
authors: {
birthday: 'DD-MM-YYYY'
}
relevant_until: 'YYYY-MM-DD HH:MM:SS'
publication_date: secondsSince1970,
last_comment: iso8601
}
I'm following this answer to have multiple date formatters and it works, as long as every date extracted from JSON is a string.
But when it comes to the secondsSince1970 (UNIX epoc time) I can't find a way to parse it as a codable object. Everywhere I see the Date(timeIntervalSince1970: timestamp) and I don't know how to use it when decoding it
How do I parse the dates on this object when a date can be passed as a TimeInterval or as a String?
try jsonDecoder.decode(Articles.self, from: jsonData)

Answer 1

extension Formatter {
static let iso8601withFractionalSeconds: DateFormatter = {
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss.SSS"
return formatter
}()
static let iso8601: DateFormatter = {
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
return formatter
}()
static let ddMMyyyy: DateFormatter = {
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "dd-MM-yyyy"
return formatter
}()
}
extension JSONDecoder.DateDecodingStrategy {
static let multiple = custom {
let container = try $0.singleValueContainer()
do {
return try Date(timeIntervalSince1970: container.decode(Double.self))
} catch DecodingError.typeMismatch {
let string = try container.decode(String.self)
if let date = Formatter.iso8601withFractionalSeconds.date(from: string) ??
Formatter.iso8601.date(from: string) ??
Formatter.ddMMyyyy.date(from: string) {
return date
}
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date: \(string)")
}
}
}
Playground testing:
struct Root: Codable {
let articles: Articles
}
struct Articles: Codable {
let authors: Authors
let relevantUntil: Date
let publicationDate: Date
let lastComment: Date
}
struct Authors: Codable {
let birthday: Date
}
let json = """
{"articles": {
"authors": {"birthday": "01-01-1970"},
"relevant_until": "2020-11-19 01:23:45",
"publication_date": 1605705003.0019,
"last_comment": "2020-11-19 01:23:45.678"}
}
"""
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .multiple
decoder.keyDecodingStrategy = .convertFromSnakeCase
do {
let root = try decoder.decode(Root.self, from: .init(json.utf8))
print(root.articles) // Articles(authors: __lldb_expr_107.Authors(birthday: 1970-01-01 03:00:00 +0000), relevantUntil: 2020-11-19 04:23:45 +0000, publicationDate: 2020-11-18 13:10:03 +0000, lastComment: 2020-11-19 04:23:45 +0000)
} catch {
print(error)
}

Answer 2

Following the same logic you can try to decode the JSON property as TimeInterval (or Double) and if that fails, fall back to your String handling:
extension JSONDecoder {
var dateDecodingStrategyFormatters: [DateFormatter]? {
#available(*, unavailable, message: "This variable is meant to be set only")
get { return nil }
set {
guard let formatters = newValue else { return }
self.dateDecodingStrategy = .custom { decoder in
let container = try decoder.singleValueContainer()
do {
let timeInterval = try container.decode(TimeInterval.self)
return Date(timeIntervalSince1970: timeInterval)
} catch DecodingError.typeMismatch {
let dateString = try container.decode(String.self)
for formatter in formatters {
if let date = formatter.date(from: dateString) {
return date
}
}
}
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot decode date")
}
}
}
}