ScrumData.swift

//
//  ScrumData.swift
//  Scrumdinger
//
//  Created by Jamie Pinkham on 12/15/20.
//

import SwiftUI
import Combine

//whatever
enum ScrumDataProviderError: Error {
    case underlying(Error)
}

protocol ScrumDataProvider {
    func load() -> AnyPublisher<[DailyScrum], ScrumDataProviderError>
    func save(_ scrums: [DailyScrum]) -> AnyPublisher<Void, ScrumDataProviderError>
}

//here's the logic from the Apple sample, expressed as a ScrumDataProvider
final class DocumentsProvider: ScrumDataProvider {
    func load() -> AnyPublisher<[DailyScrum], ScrumDataProviderError> {
        return AnyPublisher(Future { promise in
            guard let data = try? Data(contentsOf: Self.fileURL) else {
                #if DEBUG
                promise(.success(DailyScrum.data))
                #endif
                return
            }
            do {
                let dailyScrums = try JSONDecoder().decode([DailyScrum].self, from: data)
                promise(.success(dailyScrums))
            } catch let error {
                promise(.failure(ScrumDataProviderError.underlying(error)))
            }
        })
    }
    
    func save(_ scrums: [DailyScrum]) -> AnyPublisher<Void, ScrumDataProviderError> {
        return AnyPublisher(
            Future { promise in
                do {
                    let data = try JSONEncoder().encode(scrums)
                    let outfile = Self.fileURL
                    promise(.success(try data.write(to: outfile)))
                } catch let error {
                    promise(.failure(.underlying(error)))
                }
            }
        )
    }
    
    private static var documentsFolder: URL {
        do {
            return try FileManager.default.url(for: .documentDirectory,
                                               in: .userDomainMask,
                                               appropriateFor: nil,
                                               create: false)
        } catch {
            //oops, seems unrecoverable to me.
            fatalError("Can't find documents directory.")
        }
    }
    private static var fileURL: URL {
        return documentsFolder.appendingPathComponent("scrums.data")
    }
}

class ScrumData: ObservableObject {
    @Published var scrums: [DailyScrum] = []
    let provider: ScrumDataProvider
    init(provider: ScrumDataProvider = DocumentsProvider()) {
        self.provider = provider
    }
    func load() {
        provider.load().replaceError(with: []).assign(to: &$scrums)
    }
    func save() {
        provider.save(scrums) //uh-oh what do we do with all those fatal errors we had!?
    }
}