Vernissage/CoreData/ViewedStatusHandler.swift

//
//  https://mczachurski.dev
//  Copyright © 2023 Marcin Czachurski and the repository contributors.
//  Licensed under the Apache License 2.0.
//

import Foundation
import SwiftData
import PixelfedKit

class ViewedStatusHandler {
    public static let shared = ViewedStatusHandler()
    private init() { }
    
    /// Append new visible statuses to database.
    func append(contentsOf statuses: [Status], accountId: String, modelContext: ModelContext) throws {
        guard let accountDataFromDb = AccountDataHandler.shared.getAccountData(accountId: accountId, modelContext: modelContext) else {
            return
        }
        
        for status in statuses {
            guard self.getViewedStatus(accountId: accountId, statusId: status.id, modelContext: modelContext) == nil else {
                continue
            }
            
            let viewedStatus = ViewedStatus(id: status.id, reblogId: status.reblog?.id, date: Date())
            modelContext.insert(viewedStatus)

            viewedStatus.pixelfedAccount = accountDataFromDb
            accountDataFromDb.viewedStatuses.append(viewedStatus)
        }
        
        try modelContext.save()
    }
    
    /// Check if given status (real picture) has been already visible on the timeline (during last month).
    func hasBeenAlreadyOnTimeline(accountId: String, status: Status, modelContext: ModelContext) -> Bool {
        guard let reblog = status.reblog else {
            return false
        }

        do {
            let reblogId = reblog.id
            let statusId = status.id

            var fetchDescriptor = FetchDescriptor<ViewedStatus>(
                // Here we are finding status which is older then checked status AND orginal status has been visible OR same reblogged by different user status has been visible.
                predicate: #Predicate { $0.pixelfedAccount?.id == accountId && $0.id < statusId && ($0.id == reblogId || $0.reblogId == reblogId) }
            )
            fetchDescriptor.fetchLimit = 1
            fetchDescriptor.includePendingChanges = true
            
            guard try modelContext.fetch(fetchDescriptor).first != nil else {
                return false
            }
                        
            return true
        } catch {
            CoreDataError.shared.handle(error, message: "Error during fetching viewed statuses (hasBeenAlreadyOnTimeline).")
            return false
        }
    }
    
    /// Mark to delete statuses older then one month.
    func deleteOldViewedStatuses(modelContext: ModelContext) throws {
        let oldViewedStatuses = self.getOldViewedStatuses(modelContext: modelContext)
        for status in oldViewedStatuses {
            modelContext.delete(status)
        }
        
        try modelContext.save()
    }
    
    private func getViewedStatus(accountId: String, statusId: String, modelContext: ModelContext) -> ViewedStatus? {
        do {
            var fetchDescriptor = FetchDescriptor<ViewedStatus>(
                predicate: #Predicate { $0.id == statusId && $0.pixelfedAccount?.id == accountId }
            )
            fetchDescriptor.fetchLimit = 1
            fetchDescriptor.includePendingChanges = true
            
            return try modelContext.fetch(fetchDescriptor).first
        } catch {
            CoreDataError.shared.handle(error, message: "Error during fetching viewed statuses (getOldViewedStatuses).")
            return nil
        }
    }
    
    private func getOldViewedStatuses(modelContext: ModelContext) -> [ViewedStatus] {
        guard let date = Calendar.current.date(byAdding: .month, value: -1, to: Date()) else {
            return []
        }
        
        do {
            var fetchDescriptor = FetchDescriptor<ViewedStatus>(
                predicate: #Predicate { $0.date < date }
            )
            fetchDescriptor.includePendingChanges = true
            
            return try modelContext.fetch(fetchDescriptor)
        } catch {
            CoreDataError.shared.handle(error, message: "Error during fetching viewed statuses (getOldViewedStatuses).")
            return []
        }
    }
}