//
//  NetworkService.swift
//  EmployeeDirectory
//
//  Created by Matt Bruce on 1/20/25.
//

import Foundation

public enum NetworkServiceError: Error {
    /// The response from the server was invalid (e.g., non-200 status code or malformed URL).
    case invalidResponse

    /// The url giving is invalid or malformed
    case invalidURL
    
    /// The data received was invalid or could not be decoded.
    case decodingError(DecodingError)
    
    /// A network-related error occurred.
    case networkError(URLError)
    
    /// An unexpected, uncategorized error occurred.
    case unknownError(Error)
}

public class NetworkService {
    
    // MARK: - Properties

    public static let shared = NetworkService() // Default shared instance

    private let session: URLSession


    // MARK: - Initializer

    /// Public initializer to allow customization
    public init(session: URLSession = .shared) {
        self.session = session
    }

    // MARK: - Public Methods

    /// Fetches data from a URL and decodes it into a generic Decodable type.
    /// - Parameters:
    ///   - endpoint: The url to fetch data from.
    ///   - type: The type to decode the data into.
    /// - Throws: A `ServiceError` for network, decoding, or unexpected errors.
    /// - Returns: The decoded object of the specified type.
    public func fetchData<T: Decodable>(from endpoint: String, as type: T.Type) async throws -> T {
        do {
            //ensure a valid URL
            guard let url = URL(string: endpoint) else {
                throw NetworkServiceError.invalidURL
            }

            // Perform network request
            let (data, response) = try await URLSession.shared.data(for: URLRequest(url: url))
            
            // Validate HTTP response
            guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
                throw NetworkServiceError.invalidResponse
            }
            
            // Decode the response into the specified type
            return try JSONDecoder().decode(T.self, from: data)
            
        } catch let urlError as URLError {
            throw NetworkServiceError.networkError(urlError)
            
        } catch let decodingError as DecodingError {
            throw NetworkServiceError.decodingError(decodingError)
            
        } catch {
            throw NetworkServiceError.unknownError(error)
        }
    }
}