HttpCache.swift

//
//  HttpCache.swift
//  Cache
//
//  Created by Dylan Gyesbreghs on 31/12/2019.
//  Copyright © 2019 Pitch-IT. All rights reserved.
//

import Foundation

public enum HttpCacheStatusCode {
    case disabled
    case notModified
    case modified
}

public enum HttpCacheHeaderFields: String {
    case RequestNoneMatch = "If-None-Match"
    case ResponseNoneMatch = "Etag"
}

public class HttpCache {
    
    private let cache: URLCache = URLCache.shared
    
    public func setup(request: inout URLRequest) {
        
        /// Make sure we have a cached response for that request.
        if let cachedResponse = cache.cachedResponse(for: request),
            let httpResponse = cachedResponse.response as? HTTPURLResponse,
            let value = httpResponse.allHeaderFields[HttpCacheHeaderFields.ResponseNoneMatch.rawValue] as? String {
            request.addValue(value, forHTTPHeaderField: HttpCacheHeaderFields.RequestNoneMatch.rawValue)
        }
        
    }
    
    public func save(response: URLResponse, data: Data, request: URLRequest) -> HttpCacheStatusCode {
        
        if let httpResponse = response as? HTTPURLResponse {
            ///
            /// If Response is not modified, don't do anything.
            ///
            if httpResponse.statusCode == HttpStatusCode.notModified.rawValue {
                return .notModified
            }
            
            ///
            /// Check if a ETag Header is available
            ///
            if let _ = httpResponse.allHeaderFields[HttpCacheHeaderFields.ResponseNoneMatch.rawValue] {
                cache.storeCachedResponse(CachedURLResponse(response: response, data: data), for: request)
                return .modified
            }
        }
        
        return .disabled
        
    }
    
    public func cachedResponse(request: URLRequest) -> CachedURLResponse? {
        return cache.cachedResponse(for: request)
    }
}