//
//  FetchService.swift
//  Loader
//
//  Created by samara on 14.03.2025.
//

import Foundation

// MARK: - Class
public class NBFetchService {
	
	public enum NBFetchServiceError: Error, LocalizedError {
		case invalidURL
		case networkError(Error)
		case noData
		case parsingError(Error)
		
		public var errorDescription: String? {
			switch self {
			case .invalidURL: "The URL is invalid."
			case .networkError(let error): "Network error: \(error.localizedDescription)"
			case .noData: "No data received."
			case .parsingError(let error): "Failed to parse data: \(error.localizedDescription)"
			}
		}
	}
	
	public init() {}

	/// Identifies the app to its repo backend. The server gates its feed on this, so it
	/// must be deterministic and start with `FTStore`/`FTStore-Manager`. Derived from
	/// the running app's bundle so the same code yields the right value in both apps.
	public static let userAgent: String = {
		let info = Bundle.main.infoDictionary
		let version = (info?["CFBundleShortVersionString"] as? String) ?? "1.0"
		let bundleId = Bundle.main.bundleIdentifier ?? "app.ftstore"
		let product = bundleId == "app.ftstore.manager" ? "FTStore-Manager" : "FTStore"
		return "\(product)/\(version) (\(bundleId))"
	}()
}

// MARK: - Class extension: fetch
extension NBFetchService {
	public func fetch<T: Decodable>(
		from urlString: String,
		completion: @escaping (Result<T, Error>) -> Void
	) {
		guard let url = URL(string: urlString) else {
			completion(.failure(NBFetchServiceError.invalidURL))
			return
		}
		
		fetch(from: url, completion: completion)
	}
	
	public func fetch<T: Decodable>(
		from url: URL,
		completion: @escaping (Result<T, Error>) -> Void
	) {
		DispatchQueue.global(qos: .userInitiated).async {
			// Always pull a fresh copy: source feeds change frequently, and the
			// default protocol cache policy would otherwise serve a stale JSON
			// (showing versions that no longer exist in the live manifest).
			var request = URLRequest(url: url)
			request.cachePolicy = .reloadIgnoringLocalCacheData
			request.setValue(Self.userAgent, forHTTPHeaderField: "User-Agent")
			let task = URLSession.shared.dataTask(with: request) { data, response, error in
				if let error = error {
					completion(.failure(NBFetchServiceError.networkError(error)))
					return
				}
				
				guard let data = data else {
					completion(.failure(NBFetchServiceError.noData))
					return
				}
				
				do {
					let decoder = JSONDecoder()
					let decodedData = try decoder.decode(T.self, from: data)
					completion(.success(decodedData))
				} catch {
					completion(.failure(NBFetchServiceError.parsingError(error)))
				}
			}
			
			task.resume()
		}
	}
}