//
//  NetworkRouter.swift
//  Cyberlock
//
//  Created by Jura on 8/21/19.
//  Copyright © 2019 Omicronmedia. All rights reserved.
//

import Foundation

public typealias NetworkResultCompletionClosure = (_ result: Result<Response, Error>) -> Void

public typealias NetworkResultDecodableCompletionClosure<T: Decodable> = (_ result: Result<(T, Response), Error>) -> Void

public enum StubBehavior {
    case never
    case immediate
    case delayed(seconds: TimeInterval)
}

let responseContext = CodingUserInfoKey(rawValue: "response")!

final public class NetworkRouter {
    
    private static var globalPlugins: [NetworkPluginType] = []
    
    public var customHeaders: HTTPHeaders?
    
    private(set) var environment: NetworkEnvironmentSwitchable
    private let plugins: [NetworkPluginType]
    private var requests = [CancellationToken: Cancellable]()
    
    // MARK: - Init
    
    public init(environment: NetworkEnvironmentSwitchable, plugins: [NetworkPluginType] = []) {
        self.environment = environment
        self.plugins = plugins
    }
    
    // MARK: - Plugins
    
    public static func addPlugin(_ plugin: NetworkPluginType) {
        NetworkRouter.globalPlugins.append(plugin)
    }
    
    // MARK: - Interface
    
    @discardableResult
    public func request(_ service: ServiceType, stubBehavior: StubBehavior = .never, completion: @escaping NetworkResultCompletionClosure) -> CancellationToken? {
        let mainThreadCompletion = { result in
            DispatchQueue.main.async { completion(result) }
        }
        return self.sendRequest(service, stubBehavior: stubBehavior, completion: mainThreadCompletion)
    }
    
    @discardableResult
    public func requestDecodable<T: Decodable>(_ decodableType: T.Type, keyPath: String? = nil, service: ServiceType, stubBehavior: StubBehavior = .never, completion: @escaping NetworkResultDecodableCompletionClosure<T>) -> CancellationToken? {
        
        return self.sendRequest(service, stubBehavior: stubBehavior) { result in
            
            result.flatMap { response -> (T, Response) in
                let decoder = JSONDecoder()
                decoder.userInfo[responseContext] = response
                if let keyPath = keyPath, keyPath.count > 0 {
                    decoder.userInfo[decodingContext] = keyPath
                    do {
                        let decoded = try decoder.decode(ResponseResult<T>.self, from: response.data)
                        return (decoded.result, response)
                    } catch {
                        throw NetworkRouterError.decode(native: error, response: response)
                    }
                } else {
                    do {
                        let decoded = try decoder.decode(decodableType, from: response.data)
                        return (decoded, response)
                    } catch {
                        throw NetworkRouterError.decode(native: error, response: response)
                    }
                }
                } >>> { result in
                    DispatchQueue.main.async { completion(result) }
            }
            
        }
        
    }
    
    public func cancel(_ token: CancellationToken) {
        guard let cancellable = self.requests[token] else { return }
        synced(self) {
            self.requests.removeValue(forKey: token)
        }
        cancellable.cancel()
    }

    public func cancelAllRequests() {
        let cancellables = self.requests.values
        synced(self) {
            self.requests.removeAll()
        }
        cancellables.forEach { $0.cancel() }
    }
    
    public func hasNextEnvironment() -> Bool { self.environment.hasNext }
    
    public func switchEnvironment() -> Bool {
        guard self.hasNextEnvironment()
                , let environment = self.environment.nextRecord() else {
                    self.environment = self.environment.reset()
            return false
        }
        self.environment = environment
        return true
    }
    
    // MARK: - Private
    
    // swiftlint:disable function_body_length
    private func sendRequest(_ service: ServiceType, stubBehavior: StubBehavior, completion: @escaping NetworkResultCompletionClosure) -> CancellationToken? {
        
        let request: URLRequest
        do {
            request = try self.buildRequest(service, env: self.environment)
        } catch {
            completion(Result.failure(NetworkRouterError.invalidRequest))
            return nil
        }
        
        let result: Result<URLRequest, NetworkRouterError> = NetworkRouter.networkShouldProcess(priority: NetworkRouter.globalPlugins,
                                                                                                secondary: self.plugins,
                                                                                                service: service,
                                                                                                data: request)
        
        if let error = result.maybeError {
            completion(Result.failure(error))
            return nil
        }
        
        let modified: Result<URLRequest, Error> = NetworkRouter.networkModifyRequest(priority: NetworkRouter.globalPlugins,
                                                                                     secondary: self.plugins,
                                                                                     service: service,
                                                                                     request: request)
        
        guard let netRequest = modified.optional else {
            if let error = modified.maybeError {
                completion(Result.failure(error))
            } else {
                completion(Result.failure(NetworkRouterError.cancelled))
            }
            return nil
        }
        
        let cancellable = NetworkTask(request: netRequest) { [weak self] token, result in
            
            guard let self = self else {
                completion(Result.failure(NetworkRouterError.cancelled))
                return
            }
            
            synced(self) {
                self.requests.removeValue(forKey: token)
            }
            
            guard let modified: Result<Response, Error> = NetworkRouter.networkModifyResponse(priority: self.plugins,
                                                                                              secondary: NetworkRouter.globalPlugins,
                                                                                              service: service,
                                                                                              result: result) else {
                                                                                                completion(Result.failure(NetworkRouterError.cancelled))
                                                                                                return
            }
            
            let processed = NetworkRouter.networkShouldProcess(priority: self.plugins, secondary: NetworkRouter.globalPlugins, service: service, data: modified)
            
            if let error = processed.maybeError {
                completion(Result.failure(error))
                return
            }
            
            guard let netResult = processed.optional else {
                if let error = processed.maybeError {
                    completion(Result.failure(error))
                } else {
                    completion(Result.failure(NetworkRouterError.cancelled))
                }
                return
            }
            
            completion(netResult)
            
        }
        
        synced(self) {
            self.requests[cancellable.token] = cancellable
        }
        
        cancellable.start(with: stubBehavior, sampleResponse: service.sampleResponse)
        
        return cancellable.token
    }
    // swiftlint:enable function_body_length
    
}

// MARK: - Synchronization

private func synced(_ lock: Any?, closure: () -> Void) {
    guard let lock = lock else {
        return
    }
    objc_sync_enter(lock)
    closure()
    objc_sync_exit(lock)
}