import Foundation

// MARK: Extension on Formatter to provide ISO8601DateFormatter instances

extension Formatter {

    static let iso8601: ISO8601DateFormatter = {
        let formatter = ISO8601DateFormatter()
        // This options is the default (can be omitted but but I prefer to make it explicit)
        formatter.formatOptions = [.withFractionalSeconds]
        return formatter
    }()

    static let iso8601withFractionalSeconds: ISO8601DateFormatter = {
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
        return formatter
    }()
}

// MARK: Custom date decoding strategy

extension JSONDecoder.DateDecodingStrategy {
    static let customISO8601Cascade = custom {
        let container = try $0.singleValueContainer()
        let string = try container.decode(String.self)
        if let date = Formatter.iso8601withFractionalSeconds.date(from: string) ?? Formatter.iso8601.date(from: string) {
            return date
        }
        throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date: \(string)")
    }
}

// MARK: Data models

struct Event: Decodable {
    let id: Int
    let timestamp: Date
}

struct EventsResponse: Decodable {
    let events: [Event]
}

// MARK: Usage example

let jsonData = """
{
    "events": [
        { "id": 1, "timestamp": "2025-09-05T13:25:41Z" },
        { "id": 2, "timestamp": "2025-09-01T09:53:38.000Z" },
        { "id": 3, "timestamp": "2025-09-18T21:54:22.923456Z" }
    ]
}
""".data(using: .utf8)!

do {
    let decoder = JSONDecoder()
    decoder.dateDecodingStrategy = .customISO8601Cascade

    let response = try decoder.decode(EventsResponse.self, from: jsonData)
    response.events.forEach { print("\($0.id): \($0.timestamp)") }
} catch {
    print("Decoding failed:", error)
}