Expected to decode Array<Any> but found a dictionary instead - swift

Question

I was fetching data from an API returning an array but needed to replace it by an API that has "sub levels":
RAW:
ETH:
USD:
TYPE: "5"
MARKET: "CCCAGG"
FROMSYMBOL: "ETH"
TOSYMBOL: "USD"
PRICE: 680.89
CHANGEPCT24HOUR : -9.313816893529749
Here is my struct:
struct Ethereum: Codable {
let percentChange24h: String
let priceUSD: String
private enum CodingKeys: String, CodingKey {
case priceUSD = "PRICE", percentChange24h = "CHANGEPCT24HOUR"
}
}
And the implementation:
func fetchEthereumInfo(completion: #escaping (Ethereum?, Error?) -> Void) {
let url = URL(string: "https://min-api.cryptocompare.com/data/pricemultifull?fsyms=ETH&tsyms=USD")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do {
if let ethereumUSD = try JSONDecoder().decode([Ethereum].self, from: data).first {
print(ethereumUSD)
completion(ethereumUSD, nil)
}
} catch {
print(error)
}
}
task.resume()
}
The console prints typeMismatch(Swift.Array<Any>, Swift.DecodingError.Context(codingPath: [], debugDescription: "Expected to decode Array<Any> but found a dictionary instead.", underlyingError: nil))
I can't really figure out what to update in my code or what this form of API is

Answer 1

First of all the JSON does not contain any array. It's very very easy to read JSON. There are only 2 (two!) collection types, array [] and dictionary {}. As you can see there are no square brackets at all in the JSON string.
Any (sub)dictionary {} has to be decoded to its own type, so it's supposed to be
struct Root : Decodable {
private enum CodingKeys : String, CodingKey { case raw = "RAW" }
let raw : RAW
}
struct RAW : Decodable {
private enum CodingKeys : String, CodingKey { case eth = "ETH" }
let eth : ETH
}
struct ETH : Decodable {
private enum CodingKeys : String, CodingKey { case usd = "USD" }
let usd : USD
}
struct USD : Decodable {
private enum CodingKeys : String, CodingKey {
case type = "TYPE"
case market = "MARKET"
case price = "PRICE"
case percentChange24h = "CHANGEPCT24HOUR"
}
let type : String
let market : String
let price : Double
let percentChange24h : Double
}
To decode the JSON and and print percentChange24h you have to write
let result = try JSONDecoder().decode(Root.self, from: data)
print("percentChange24h", result.raw.eth.usd.percentChange24h)