//
//  GiphyApiManager.swift
//  LiveLikeGiphyChallenge
//
//  Created by Ljupco Nastevski on 30.1.22.
//

import Foundation

enum GiphyApiError: Error {
    case canceledByUser
    case requestFailed
    case decodingFailed
}

fileprivate struct RequestParamKeys {
    static let ApiKey = "api_key"
    static let QueryKey = "q"
    static let OffsetKey = "offset"
    static let LimitKey = "limit"
}

fileprivate struct Versions {
    static let v1 = "/v1"
}

fileprivate struct Endpoints {
    
    static let Gifs = Versions.v1 + "/gifs"
    
    static let Trending = Gifs + "/trending"
    static let Search = Gifs + "/search"
    
}


class GiphyApiManager {
    
    static let shared = GiphyApiManager()
    
    private var baseUrl = URLComponents(string: Constants.GiphyBaseUrl)!
        
    private let session = URLSession(configuration: .ephemeral, delegate: nil, delegateQueue: nil)
    
    // Last searchable task
    private var lastSearchableTask: URLSessionDataTask?
    
    init() {
        
        // Default query items
        baseUrl.queryItems = [
            URLQueryItem(name: RequestParamKeys.ApiKey, value: Constants.GiphyApiKey),
            URLQueryItem(name: RequestParamKeys.LimitKey, value: String(Constants.GiphyPaginationLimit))
        ]
        
    }
    
    func cancelLastSearchableTask() {
        lastSearchableTask?.cancel()
        lastSearchableTask = nil
    }
    
    func cancelDataTaskForUrl(url: URL) {
        
        session.getAllTasks { tasks in
              tasks.filter { $0.state == .running }.filter { $0.originalRequest?.url == url}.first?.cancel()
            }
        
    }
    
    func getTrendingGifs(offset: Int, completion: @escaping (Result<GiphyListResponse, Error>) -> Void) {
        
        let offset = URLQueryItem(name: RequestParamKeys.OffsetKey, value: String(offset))
        self.lastSearchableTask = self.getCodable(endpoint: Endpoints.Trending, queries: [offset], completion: completion)
    }
    
    func getSearchGifs(offset: Int, query: String, completion: @escaping (Result<GiphyListResponse, Error>) -> Void) {
        
        let offset = URLQueryItem(name: RequestParamKeys.OffsetKey, value: String(offset))
        let query = URLQueryItem(name: RequestParamKeys.QueryKey, value: query)

        self.lastSearchableTask = self.getCodable(endpoint: Endpoints.Search, queries: [offset, query], completion: completion)
    }
    
    func getData(url: URL, completion: @escaping (Data?) -> Void) -> URLSessionDataTask {
        let task = session.dataTask(with: url) { data, _ , _ in
            completion(data)
        }
        task.resume()
        return task
    }


    private func getCodable<U:Codable>(endpoint: String, queries: [URLQueryItem]? = nil, completion: @escaping (Result<U, Error>) -> Void) -> URLSessionDataTask {
        
        var fullUrlComponent = self.baseUrl
        
        if let queries = queries {
            fullUrlComponent.queryItems?.append(contentsOf: queries)
        }

        fullUrlComponent.path = endpoint
        
        
        let task = session.dataTask(with: fullUrlComponent.url!) { d, _, e in
            
            guard let data = d else { completion(.failure(e!)); return }
        
            do {
                let decoded = try JSONDecoder().decode(U.self, from: data)
                completion(.success(decoded))
            } catch {
                completion(.failure(GiphyApiError.decodingFailed))
            }
            
        }
        
        task.resume()
        return task
    }

}