//
//  DownloadManager.swift
//  Zyquo Atlas
//
//  Author: Simon-Pierre Boucher
//  Mail: contact@spboucher.ai
//
//  Handles file downloads via WKDownload: routes new downloads to ~/Downloads,
//  tracks progress, and exposes an observable list for the toolbar downloads
//  popover (reveal / open). One manager per window, set as each web view's
//  download-triggering delegate path through the Tab.
//

import Foundation
import WebKit
import Combine

@MainActor
final class DownloadManager: NSObject, ObservableObject {
    @Published private(set) var items: [DownloadItem] = []

    private var progressObservations: [ObjectIdentifier: NSKeyValueObservation] = [:]

    /// Attaches to a WKDownload (from WKNavigation/UI delegate download hooks).
    func attach(_ download: WKDownload) {
        download.delegate = self
    }

    func reveal(_ item: DownloadItem) {
        guard let url = item.fileURL else { return }
        NSWorkspace.shared.activateFileViewerSelecting([url])
    }

    func open(_ item: DownloadItem) {
        guard let url = item.fileURL, item.state == .finished else { return }
        NSWorkspace.shared.open(url)
    }

    func clearFinished() { items.removeAll { $0.state == .finished } }

    private func index(of download: WKDownload) -> Int? {
        items.firstIndex { $0.downloadID == ObjectIdentifier(download) }
    }
}

// MARK: - Model

struct DownloadItem: Identifiable {
    enum State: Equatable { case inProgress, finished, failed }
    let id = UUID()
    let downloadID: ObjectIdentifier
    var filename: String
    var fileURL: URL?
    var receivedBytes: Int64 = 0
    var totalBytes: Int64 = 0
    var state: State = .inProgress

    var fraction: Double {
        totalBytes > 0 ? Double(receivedBytes) / Double(totalBytes) : 0
    }
}

// MARK: - WKDownloadDelegate

extension DownloadManager: WKDownloadDelegate {
    func download(_ download: WKDownload,
                  decideDestinationUsing response: URLResponse,
                  suggestedFilename: String,
                  completionHandler: @escaping (URL?) -> Void) {
        let downloads = FileManager.default.urls(for: .downloadsDirectory, in: .userDomainMask).first
            ?? FileManager.default.homeDirectoryForCurrentUser.appendingPathComponent("Downloads")
        var dest = downloads.appendingPathComponent(suggestedFilename)
        var n = 1
        while FileManager.default.fileExists(atPath: dest.path) {
            let ext = (suggestedFilename as NSString).pathExtension
            let base = (suggestedFilename as NSString).deletingPathExtension
            dest = downloads.appendingPathComponent(ext.isEmpty ? "\(base) \(n)" : "\(base) \(n).\(ext)")
            n += 1
        }
        let item = DownloadItem(downloadID: ObjectIdentifier(download),
                                filename: dest.lastPathComponent, fileURL: dest,
                                totalBytes: response.expectedContentLength)
        items.insert(item, at: 0)
        progressObservations[ObjectIdentifier(download)] =
            download.progress.observe(\.completedUnitCount) { [weak self] progress, _ in
                Task { @MainActor in
                    guard let self, let i = self.index(of: download) else { return }
                    self.items[i].receivedBytes = progress.completedUnitCount
                    self.items[i].totalBytes = progress.totalUnitCount
                }
            }
        completionHandler(dest)
    }

    func downloadDidFinish(_ download: WKDownload) {
        if let i = index(of: download) { items[i].state = .finished }
        progressObservations[ObjectIdentifier(download)]?.invalidate()
        progressObservations[ObjectIdentifier(download)] = nil
    }

    func download(_ download: WKDownload, didFailWithError error: Error, resumeData: Data?) {
        if let i = index(of: download) { items[i].state = .failed }
        progressObservations[ObjectIdentifier(download)]?.invalidate()
        progressObservations[ObjectIdentifier(download)] = nil
    }
}