CombinePokemonAPI.swift

import Combine
import Foundation

struct NamedURL: Codable {
	let name: String
	let url: URL
}

struct PokeAPIResponse: Codable {
	let results: [NamedURL]
}

struct Pokemon: Codable {
	let id: Int
	let name: String
	let stats: [Stat]
	let weight: Double
}

struct Stat: Codable {
	let baseStat: Int
	let effort: Int
	let stat: NamedURL

	enum CodingKeys: String, CodingKey {
		case baseStat = "base_stat"
		case effort
		case stat
	}
}

class PokemonGetter: ObservableObject {
	@Published var pokemon: [Pokemon] = [] {
		didSet {
			print("Pokémon list updated!")
			for pokemon in pokemon {
				print("Pokémon \(pokemon.id): \(pokemon.name)")
			}
		}
	}

	private let apiURL = URL(string: "https://pokeapi.co/api/v2/pokemon")!
	let jsonDecoder = JSONDecoder()

	private var subscription: AnyCancellable?

	func start() {
		print("Starting...")
		if subscription != nil {
			subscription?.cancel()
		}

		subscription = URLSession.shared.dataTaskPublisher(for: apiURL)
			.map(\.data)
			.decode(type: PokeAPIResponse.self, decoder: jsonDecoder)
			.flatMap { response in
				Publishers.MergeMany(
					response.results.map(self.namedResourceGetter)
				)
				.collect()
			}
			.replaceError(with: [Pokemon(id: 999, name: "Error", stats: [], weight: 100)])
			.sink { pokemon in
				self.pokemon = pokemon.sorted(by: { $0.id < $1.id })
			}
	}

	private func namedResourceGetter(_ namedURL: NamedURL) -> AnyPublisher<Pokemon, Error> {
		URLSession.shared.dataTaskPublisher(for: namedURL.url)
			.map { $0.data }
			.decode(type: Pokemon.self, decoder: jsonDecoder)
			.eraseToAnyPublisher()
	}
}

let pokemonGetter = PokemonGetter()
pokemonGetter.start()