sample of fetching list of pokemon using swift combine

pokemon-fetch-combine.swift

import UIKit
import Combine

struct PokemonResponse: Codable{

    let results: [Pokemon]
}

struct Pokemon: Codable{
    let name: String
    let url: String
}

struct PokemonDetailResponse: Codable{
    let id: Int
    let name: String
    let height: Int
    let weight: Int
    let types: [Types]
}

struct Types: Codable{
    let slot: Int
    let type: Type
}

struct Type: Codable{
    let name: String
}


/// Fetch a pokemon from URL
/// - Parameter urlString: URL of the pokemon
/// - Returns: A publisher with output PokemonDetailResponse
func getPokemon (_ urlString: String) -> AnyPublisher<PokemonDetailResponse, Error> {
    let url = URL(string: urlString)!
    return URLSession.shared.dataTaskPublisher(for: url)
            .map(\.data)
            .decode(type: PokemonDetailResponse.self, decoder: JSONDecoder())
            .receive(on: RunLoop.main)
            .eraseToAnyPublisher()
}


/// Fetch a list of pokemon without details
/// - Parameter urlString: URL of the list of pokemon
/// - Returns: A publisher with output PokemonResponse
func getPokemonList (urlString: String) ->  AnyPublisher<PokemonResponse, Error> {
    let url = URL(string: urlString)!
    return URLSession.shared.dataTaskPublisher(for: url)
        .map(\.data)
        .decode(type: PokemonResponse.self, decoder: JSONDecoder())
        .receive(on: RunLoop.main)
        .eraseToAnyPublisher()
}


/// Fetch a list of pokemon with details
/// - Returns: A publisher with output an array of PokemonDetailResponse
func getPokemonListWithDetails () -> AnyPublisher<[PokemonDetailResponse], Error> {
    return getPokemonList(urlString: "https://pokeapi.co/api/v2/pokemon/")
        .map(\.results)
        .flatMap {
            Publishers
                .MergeMany($0.map { getPokemon($0.url) })
                .collect()
                .eraseToAnyPublisher()
        }
        .eraseToAnyPublisher()
}
 

let cancellable = getPokemonListWithDetails().sink { (completion) in
        print("done")
    } receiveValue: { (pokemons) in
        print(pokemons.map({ "- \($0.name): \($0.types.first?.type.name ?? "")" }).joined(separator: "\n"))
    }