//
//  DraftsManager.swift
//  ComposeUI
//
//  Created by Shadowfacts on 10/22/18.
//  Copyright © 2018 Shadowfacts. All rights reserved.
//

import Foundation
import Combine
import OSLog

private let logger = Logger(subsystem: Bundle.main.bundleIdentifier!, category: "DraftsManager")
private let encoder = PropertyListEncoder()
private let decoder = PropertyListDecoder()

public class DraftsManager: NSObject, ObservableObject, NSFilePresenter {
    public private(set) static var shared: DraftsManager = {
        let draftsManager = DraftsManager(url: DraftsManager.archiveURL)
        draftsManager.load()
        return draftsManager
    }()
    
    private static var appGroupDirectory = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "group.space.vaccor.Tusker")!
    private static var archiveURL = appGroupDirectory.appendingPathComponent("drafts").appendingPathExtension("plist")
    
    private var url: URL
    
    @Published private var drafts: [UUID: Draft] = [:]
    
    public init(url: URL) {
        self.url = url
        
        super.init()
    }
    
    private func merge(from container: DraftsContainer) {
        for draft in container.drafts.values {
            if let existing = self.drafts[draft.id] {
                existing.merge(from: draft)
            } else {
                self.drafts[draft.id] = draft
            }
        }
        for id in self.drafts.keys where !container.drafts.keys.contains(id) {
            self.drafts.removeValue(forKey: id)
        }
    }
    
    public func load(completion: ((Error?) -> Void)? = nil) {
        NSFileCoordinator(filePresenter: self).coordinate(readingItemAt: self.url, options: [], error: nil) { url in
            do {
                let data = try Data(contentsOf: url)
                let container = try decoder.decode(DraftsContainer.self, from: data)
                DispatchQueue.main.async {
                    self.merge(from: container)
                    completion?(nil)
                }
            } catch {
                logger.error("Error loading: \(String(describing: error))")
                completion?(error)
            }
        }
    }
    
    public func migrate(from url: URL) -> Result<Void, any Error> {
        do {
            let data = try Data(contentsOf: url)
            let container = try decoder.decode(DraftsContainer.self, from: data)
            self.merge(from: container)
            self.save()
        } catch {
            logger.error("Error migrating: \(String(describing: error))")
            return .failure(error)
        }
        return .success(())
    }
    
    public func save(completion: ((Error?) -> Void)? = nil) {
        NSFileCoordinator(filePresenter: self).coordinate(writingItemAt: Self.archiveURL, options: .forReplacing, error: nil) { url in
            do {
                let data = try encoder.encode(DraftsContainer(drafts: self.drafts))
                try data.write(to: url, options: .atomic)
                completion?(nil)
            } catch {
                logger.error("Error saving: \(String(describing: error))")
                completion?(error)
            }
        }
    }
    
    // MARK: Drafts API
    
    var sorted: [Draft] {
        return drafts.values.sorted(by: { $0.lastModified > $1.lastModified })
    }

    public func add(_ draft: Draft) {
        drafts[draft.id] = draft
    }

    public func remove(_ draft: Draft) {
        drafts.removeValue(forKey: draft.id)
    }

    public func getBy(id: UUID) -> Draft? {
        return drafts[id]
    }

    // MARK: NSFilePresenter
    
    public var presentedItemURL: URL? {
        url
    }
    
    public let presentedItemOperationQueue = OperationQueue()
    
    public func presentedItemDidMove(to newURL: URL) {
        self.url = newURL
    }
    
    public func presentedItemDidChange() {
        self.load()
    }
    
    // MARK: Supporting Types
    
    struct DraftsContainer: Codable {
        let drafts: [UUID: Draft]
        
        init(drafts: [UUID: Draft]) {
            self.drafts = drafts
        }
        
        init(from decoder: Decoder) throws {
            let container = try decoder.container(keyedBy: CodingKeys.self)
            self.drafts = try container.decode([UUID: SafeDraft].self, forKey: .drafts).compactMapValues(\.draft)
        }
        
        enum CodingKeys: CodingKey {
            case drafts
        }
    }
    
    // a container that always succeeds at decoding
    // so if a single draft can't be decoded, we don't lose all drafts
    struct SafeDraft: Decodable {
        let draft: Draft?

        init(from decoder: Decoder) throws {
            let container = try decoder.singleValueContainer()
            self.draft = try? container.decode(Draft.self)
        }
    }
}

private extension Draft {
    func merge(from other: Draft) {
        self.lastModified = other.lastModified
        
        self.accountID = other.accountID
        self.text = other.text
        self.contentWarningEnabled = other.contentWarningEnabled
        self.contentWarning = other.contentWarning
        self.attachments = other.attachments
        self.inReplyToID = other.inReplyToID
        self.visibility = other.visibility
        self.poll = other.poll
        self.localOnly = other.localOnly
        
        self.initialText = other.initialText
    }
}