// The MIT License (MIT)
//
// Copyright (c) 2020-2024 Alexander Grebenyuk (github.com/kean).

import Foundation
import CoreData
import Pulse
import Combine
import SwiftUI

protocol ConsoleDataSourceDelegate: AnyObject {
    /// The data source reloaded the entire dataset.
    func dataSourceDidRefresh(_ dataSource: ConsoleDataSource)

    /// An incremental update. If the diff is nil, it means the app is displaying
    /// a grouped view that doesn't support diffing.
    func dataSource(_ dataSource: ConsoleDataSource, didUpdateWith diff: CollectionDifference<NSManagedObjectID>?)
}

final class ConsoleDataSource: NSObject, NSFetchedResultsControllerDelegate {
    weak var delegate: ConsoleDataSourceDelegate?

    /// - warning: Incompatible with the "group by" option.
    var sortDescriptors: [NSSortDescriptor] = [] {
        didSet { controller.fetchRequest.sortDescriptors = sortDescriptors }
    }

    struct PredicateOptions {
        var filters = ConsoleFilters()
        var isOnlyErrors = false
        var predicate: NSPredicate?
    }

    var predicate: PredicateOptions = .init() {
        didSet { refreshPredicate() }
    }

    var filter: NSPredicate? {
        didSet { refreshPredicate() }
    }

    static let fetchBatchSize = 100

    private let store: LoggerStore
    private let mode: ConsoleMode
    private let options: ConsoleListOptions
    private let controller: NSFetchedResultsController<NSManagedObject>
    private var controllerDelegate: NSFetchedResultsControllerDelegate?
    private var cancellables: [AnyCancellable] = []

    init(store: LoggerStore, mode: ConsoleMode, options: ConsoleListOptions = .init()) {
        self.store = store
        self.mode = mode
        self.options = options

        let entityName: String
        let sortKey: String

        switch mode {
        case .all, .logs:
            entityName = "\(LoggerMessageEntity.self)"
            sortKey = options.messageSortBy.key
        case .network:
            entityName = "\(NetworkTaskEntity.self)"
            sortKey = options.taskSortBy.key
        }

        let request = NSFetchRequest<NSManagedObject>(entityName: entityName)
        request.sortDescriptors = [
            NSSortDescriptor(key: sortKey, ascending: options.order == .ascending)
        ].compactMap { $0 }
        request.fetchBatchSize = ConsoleDataSource.fetchBatchSize
        request.relationshipKeyPathsForPrefetching = ["request"]
        controller = NSFetchedResultsController(
            fetchRequest: request,
            managedObjectContext: store.viewContext,
            sectionNameKeyPath: nil,
            cacheName: nil
        )

        super.init()

        let delegate = ConsoleFetchDelegate()
        delegate.delegate = self
        controllerDelegate = delegate

        controller.delegate = controllerDelegate
    }

    func bind(_ filters: ConsoleFiltersViewModel) {
        cancellables = []
        filters.$options.sink { [weak self] in
            self?.predicate = $0
        }.store(in: &cancellables)
    }

    func refresh() {
        try? controller.performFetch()
        delegate?.dataSourceDidRefresh(self)
    }

    // MARK: Accessing Entities

    var numberOfObjects: Int {
        controller.fetchedObjects?.count ?? 0
    }

    func object(at indexPath: IndexPath) -> NSManagedObject {
        controller.object(at: indexPath)
    }

    var entities: [NSManagedObject] {
        controller.fetchedObjects ?? []
    }

    // MARK: NSFetchedResultsControllerDelegate

    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        delegate?.dataSource(self, didUpdateWith: nil)
    }

    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith diff: CollectionDifference<NSManagedObjectID>) {
        delegate?.dataSource(self, didUpdateWith: diff)
    }

    // MARK: Predicate

    private func refreshPredicate() {
        let predicate = ConsoleDataSource.makePredicate(mode: mode, options: predicate, filter: filter)
        controller.fetchRequest.predicate = predicate
        refresh()
    }

    static func makePredicate(mode: ConsoleMode, options: PredicateOptions, filter: NSPredicate? = nil) -> NSPredicate? {
        let predicates = [
            _makePredicate(mode, options.filters, options.isOnlyErrors),
            options.predicate,
            filter
        ].compactMap { $0 }
        switch predicates.count {
        case 0: return nil
        case 1: return predicates[0]
        default: return NSCompoundPredicate(andPredicateWithSubpredicates: predicates)
        }
    }
}

// MARK: - Predicates

private func _makePredicate(_ mode: ConsoleMode, _ filters: ConsoleFilters, _ isOnlyErrors: Bool) -> NSPredicate? {
    func makeMessagesPredicate(isMessageOnly: Bool) -> NSPredicate? {
        var predicates: [NSPredicate] = []
        if isMessageOnly {
            predicates.append(NSPredicate(format: "task == NULL"))
        }
        if let predicate = ConsoleFilters.makeMessagePredicates(criteria: filters, isOnlyErrors: isOnlyErrors) {
            predicates.append(predicate)
        }
        return predicates.isEmpty ? nil : NSCompoundPredicate(andPredicateWithSubpredicates: predicates)
    }

    switch mode {
    case .all:
        return makeMessagesPredicate(isMessageOnly: false)
    case .logs:
        return makeMessagesPredicate(isMessageOnly: true)
    case .network:
        return ConsoleFilters.makeNetworkPredicates(criteria: filters, isOnlyErrors: isOnlyErrors)
    }
}

// MARK: - Delegates

// Using a separate class because the diff API is not supported for a fetch
// controller with sections, and it prints an error message in logs if the
// delegate implements it, which we want to avoid.

private final class ConsoleFetchDelegate: NSObject, NSFetchedResultsControllerDelegate {
    weak var delegate: NSFetchedResultsControllerDelegate?

    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith diff: CollectionDifference<NSManagedObjectID>) {
        delegate?.controller?(controller, didChangeContentWith: diff)
    }
}

enum ConsoleUpdateEvent {
    /// Full refresh of data.
    case refresh
    /// Incremental update.
    case update(CollectionDifference<NSManagedObjectID>?)
}