SideStore/SideStoreApp/Sources/SideStoreAppKit/Operations/FetchSourceOperation.swift

//
//  FetchSourceOperation.swift
//  AltStore
//
//  Created by Riley Testut on 7/30/19.
//  Copyright © 2019 Riley Testut. All rights reserved.
//

import CoreData
import Foundation

import SideStoreCore
import RoxasUIKit

@objc(FetchSourceOperation)
final class FetchSourceOperation: ResultOperation<Source> {
    let sourceURL: URL
    let managedObjectContext: NSManagedObjectContext

    private let session: URLSession

    private lazy var dateFormatter: ISO8601DateFormatter = {
        let dateFormatter = ISO8601DateFormatter()
        return dateFormatter
    }()

    init(sourceURL: URL, managedObjectContext: NSManagedObjectContext = DatabaseManager.shared.persistentContainer.newBackgroundContext()) {
        self.sourceURL = sourceURL
        self.managedObjectContext = managedObjectContext

        let configuration = URLSessionConfiguration.default
        configuration.requestCachePolicy = .reloadIgnoringLocalCacheData
        configuration.urlCache = nil

        session = URLSession(configuration: configuration)
    }

    override func main() {
        super.main()

        let dataTask = session.dataTask(with: sourceURL) { data, response, error in

            let childContext = DatabaseManager.shared.persistentContainer.newBackgroundContext(withParent: self.managedObjectContext)
            childContext.mergePolicy = NSOverwriteMergePolicy
            childContext.perform {
                do {
                    let (data, _) = try Result((data, response), error).get()

                    let decoder = SideStoreCore.JSONDecoder()
                    decoder.dateDecodingStrategy = .custom { decoder -> Date in
                        let container = try decoder.singleValueContainer()
                        let text = try container.decode(String.self)

                        // Full ISO8601 Format.
                        self.dateFormatter.formatOptions = [.withFullDate, .withFullTime, .withTimeZone]
                        if let date = self.dateFormatter.date(from: text) {
                            return date
                        }

                        // Just date portion of ISO8601.
                        self.dateFormatter.formatOptions = [.withFullDate]
                        if let date = self.dateFormatter.date(from: text) {
                            return date
                        }

                        throw DecodingError.dataCorruptedError(in: container, debugDescription: "Date is in invalid format.")
                    }

                    decoder.managedObjectContext = childContext
                    decoder.sourceURL = self.sourceURL

                    let source = try decoder.decode(Source.self, from: data)
                    let identifier = source.identifier

                    try childContext.save()

                    self.managedObjectContext.perform {
                        if let source = Source.first(satisfying: NSPredicate(format: "%K == %@", #keyPath(Source.identifier), identifier), in: self.managedObjectContext) {
                            self.finish(.success(source))
                        } else {
                            self.finish(.failure(OperationError.noSources))
                        }
                    }
                } catch {
                    self.managedObjectContext.perform {
                        self.finish(.failure(error))
                    }
                }
            }
        }

        progress.addChild(dataTask.progress, withPendingUnitCount: 1)

        dataTask.resume()
    }
}