import DropTwoCore
import Foundation

/// Treibt die Verarbeitung der Dateiliste über `JobQueue` an und hält den
/// UI-Status pro Datei nach. Kennt keine Views — nur `@Published`-Zustand,
/// den SwiftUI beobachtet.
@MainActor
final class ConversionCoordinator: ObservableObject {
    @Published private(set) var items: [DropItem] = []
    @Published private(set) var isRunning = false
    /// Nicht-leer, solange eine Overwrite-Rückfrage aussteht — die View zeigt
    /// dann einen Alert und ruft `resolveConflicts`/`cancelConflictResolution`.
    @Published private(set) var pendingConflicts: [OverwriteConflict] = []

    private var runningTask: Task<Void, Never>?
    private var pendingTargetFolder: URL?

    var overallProgress: Double {
        guard !items.isEmpty else { return 0 }
        let sum = items.reduce(0.0) { partial, item in
            switch item.status {
            case .waiting:
                return partial
            case .running(let progress):
                return partial + progress
            case .skipped, .rejected, .succeeded, .failed, .skippedByUser:
                return partial + 1
            }
        }
        return sum / Double(items.count)
    }

    var problemItems: [DropItem] {
        items.filter { $0.status.needsAttention }
    }

    /// README: "Dateiauswahl vorsortiert nach zuletzt geändert" — neueste zuerst.
    func addFiles(_ urls: [URL]) {
        let existing = Set(items.map(\.sourceURL))
        let newURLs = urls
            .filter { !existing.contains($0) }
            .sorted { modificationDate(for: $0) > modificationDate(for: $1) }
        items.append(contentsOf: newURLs.map(DropItem.init))
    }

    func removeAll() {
        guard !isRunning else { return }
        items.removeAll()
    }

    /// Prüft vor dem eigentlichen Lauf, ob Zieldateien schon existieren, und
    /// stellt bei Konflikten erst eine Rückfrage statt sie mitten im Batch als
    /// Fehler auffliegen zu lassen (README: "überschreiben nur nach Rückfrage").
    func start(targetFolder: URL) {
        guard !isRunning, !items.isEmpty else { return }

        let conflicts = items.compactMap { item -> OverwriteConflict? in
            guard let destination = ConversionPipeline.previewDestination(sourceURL: item.sourceURL, outputRootDirectory: targetFolder),
                  FileManager.default.fileExists(atPath: destination.path) else {
                return nil
            }
            return OverwriteConflict(itemID: item.id, fileName: item.fileName, destination: destination)
        }

        guard conflicts.isEmpty else {
            pendingTargetFolder = targetFolder
            pendingConflicts = conflicts
            return
        }

        runBatch(targetFolder: targetFolder, overwrite: false, skipping: [])
    }

    /// Antwort auf die Overwrite-Rückfrage: `overwrite` gilt für den ganzen
    /// Batch (bewusst keine Datei-für-Datei-Auswahl fürs MVP).
    func resolveConflicts(overwrite: Bool) {
        guard let targetFolder = pendingTargetFolder else { return }
        let skipIDs = overwrite ? Set<UUID>() : Set(pendingConflicts.map(\.itemID))

        for id in skipIDs {
            guard let index = items.firstIndex(where: { $0.id == id }) else { continue }
            items[index].status = .skippedByUser(reason: String(localized: "Zieldatei existiert bereits."))
        }

        pendingConflicts = []
        pendingTargetFolder = nil
        runBatch(targetFolder: targetFolder, overwrite: overwrite, skipping: skipIDs)
    }

    func cancelConflictResolution() {
        pendingConflicts = []
        pendingTargetFolder = nil
    }

    private func runBatch(targetFolder: URL, overwrite: Bool, skipping skipIDs: Set<UUID>) {
        let jobs = items
            .filter { !skipIDs.contains($0.id) }
            .map { JobQueue.Job(id: $0.id, sourceURL: $0.sourceURL) }
        guard !jobs.isEmpty else { return }

        isRunning = true
        for index in items.indices where !skipIDs.contains(items[index].id) {
            items[index].status = .waiting
        }

        var options = ConversionPipeline.Options()
        options.cropOptions.overwrite = overwrite

        runningTask = Task {
            let stream = JobQueue.run(
                jobs: jobs,
                outputRootDirectory: targetFolder,
                options: options,
                progress: { [weak self] job, value in
                    Task { @MainActor in
                        self?.updateProgress(jobID: job.id, value: value)
                    }
                }
            )
            for await result in stream {
                apply(result)
            }
            isRunning = false
        }
    }

    private func updateProgress(jobID: UUID, value: Double) {
        guard let index = items.firstIndex(where: { $0.id == jobID }) else { return }
        items[index].status = .running(progress: value)
    }

    private func apply(_ result: JobQueue.JobResult) {
        guard let index = items.firstIndex(where: { $0.id == result.job.id }) else { return }
        switch result.outcome {
        case .skipped(_, let reason):
            items[index].status = .skipped(reason)
        case .rejected(_, let reason):
            items[index].status = .rejected(reason)
        case .succeeded(let success):
            items[index].status = .succeeded(croppedDestination: success.croppedDestination)
        case .failed(_, let error):
            items[index].status = .failed(message: Self.message(for: error))
        }
    }

    private static func message(for error: Error) -> String {
        if let localizedError = error as? LocalizedError, let description = localizedError.errorDescription {
            return description
        }
        return error.localizedDescription
    }

    private func modificationDate(for url: URL) -> Date {
        (try? url.resourceValues(forKeys: [.contentModificationDateKey]).contentModificationDate) ?? .distantPast
    }
}