Fetching Ratings

RatingsFetcher.swift

import Foundation
import Combine

public struct RatingsFetcher {
    
    /// Asynchronously gets the number of ratings for the current version of the given app.
    /// - Parameter appId: App ID to look up
    /// - Returns: Count of ratings for the current version
    public static func ratingsForCurrentVersion(appId: Int) async throws -> Int {
        guard let url = URL(string: "https://itunes.apple.com/lookup?id=\(appId)") else {
            return 0
        }
        
        let (data, _) = try await URLSession.shared.data(from: url)
        let ratingsInfo = try JSONDecoder().decode(RatingsInfo.self, from: data)
        return ratingsInfo.results.first?.userRatingCountForCurrentVersion ?? 0
    }
    
    /// Gets a `Publisher` which in turn gets the number of ratings for
    /// the current version of the given app.
    /// - Parameter appId: App ID to look up
    /// - Returns: Publisher which signals with the count of ratings for the current version
    static func ratingsPublisherForCurrentVersion(appId: Int) -> AnyPublisher<Int, Error> {
        guard let url = URL(string: "https://itunes.apple.com/lookup?id=\(appId)") else {
            return Just(0).setFailureType(to: Error.self).eraseToAnyPublisher()
        }
        
        return URLSession.shared.dataTaskPublisher(for: url)
            .tryMap { (data, _) -> Int in
                let ratingsInfo = try JSONDecoder().decode(RatingsInfo.self, from: data)
                return ratingsInfo.results.first?.userRatingCountForCurrentVersion ?? 0
            }
            .eraseToAnyPublisher()
    }
    
    private struct RatingsInfo: Decodable {
        let resultCount: Int
        let results: [RatingsInfoResult]
    }
    
    private struct RatingsInfoResult: Decodable {
        let userRatingCountForCurrentVersion: Int
    }
}