JSON to Swift Codable Converter

[
  {
    "id": 42,
    "full_name": "Ada Lovelace",
    "avatar_url": "https://example.com/ada.png",
    "joined_at": "2026-03-14T09:26:53Z",
    "roles": [
      "admin"
    ]
  },
  {
    "id": 43,
    "full_name": "Grace Hopper",
    "avatar_url": null,
    "joined_at": "2026-04-01T12:00:00Z",
    "roles": [],
    "team": {
      "id": 7,
      "name": "Compilers"
    }
  }
]

import Foundation

// The JSON root is an array: decode [UserItem].self
// Dates are ISO 8601: set decoder.dateDecodingStrategy = .iso8601Flexible (below; the built-in .iso8601 rejects fractional seconds)

struct UserItem: Codable {
    let id: Int
    let fullName: String
    let avatarUrl: URL?
    let joinedAt: Date
    let roles: [String]
    let team: Team?

    enum CodingKeys: String, CodingKey {
        case id
        case fullName = "full_name"
        case avatarUrl = "avatar_url"
        case joinedAt = "joined_at"
        case roles
        case team
    }
}

struct Team: Codable {
    let id: Int
    let name: String
}

extension JSONDecoder.DateDecodingStrategy {
    /// ISO 8601 date-times with or without seconds and fractional seconds; .iso8601 only reads whole seconds.
    static var iso8601Flexible: Self {
        .custom { decoder in
            let text = try decoder.singleValueContainer().decode(String.self)
            // "2026-01-01T09:00Z" has no seconds, which ISO8601DateFormatter requires.
            let full = text.replacingOccurrences(of: #"T(\d{2}:\d{2})(?=Z|[+-])"#, with: "T$1:00", options: .regularExpression)
            let f = ISO8601DateFormatter()
            for options: ISO8601DateFormatter.Options in [[.withInternetDateTime, .withFractionalSeconds], [.withInternetDateTime]] {
                f.formatOptions = options
                if let date = f.date(from: full) { return date }
            }
            throw DecodingError.dataCorrupted(.init(codingPath: decoder.codingPath, debugDescription: "Not an ISO 8601 date-time: \(text)"))
        }
    }
}

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601

let user = try decoder.decode(User.self, from: data)
print(user.fullName)

// An array at the root decodes the same way
let users = try decoder.decode([User].self, from: data)

let encoded = try JSONEncoder().encode(user)