import AppKit
import CryptoKit
import Foundation

public struct DownloadedPackage: Equatable, Sendable {
    public let directory: URL
    /// Apple's own file name, which Installer shows.
    public let name: String
    public var file: URL { directory.appendingPathComponent(name) }

    public init(directory: URL, name: String) {
        self.directory = directory
        self.name = name
    }
}

public enum DownloadError: Error, Equatable, Sendable {
    case failed(String)
    /// Size or SHA-256 differ from the pinned release; the download is already deleted.
    case mismatch
}

@MainActor
public protocol InstallerSession: AnyObject {
    var hasQuit: Bool { get }
}

public enum InstallerOpening {
    case opened(any InstallerSession)
    /// Size or SHA-256 no longer match; the download is already deleted.
    case changed
    case failed(String)
}

public protocol RuntimeInstalling: Sendable {
    func download(_ release: ContainerRuntime.Release,
                  progress: @escaping @Sendable (Int64) -> Void) async throws -> DownloadedPackage
    /// Re-checks the size and hash off the main thread, then opens the package in Installer.
    @MainActor func openInInstaller(_ package: DownloadedPackage, release: ContainerRuntime.Release) async -> InstallerOpening
    func discard(_ package: DownloadedPackage)
}

public struct SystemRuntimeInstaller: RuntimeInstalling {
    static let installerApp = URL(fileURLWithPath: "/System/Library/CoreServices/Installer.app")

    public init() {}

    public func download(_ release: ContainerRuntime.Release,
                         progress: @escaping @Sendable (Int64) -> Void) async throws -> DownloadedPackage {
        Self.removeLeftovers()
        let directory = URL(fileURLWithPath: NSTemporaryDirectory())
            .appendingPathComponent("knotchy-runtime-\(UUID().uuidString)", isDirectory: true)
        do {
            try FileManager.default.createDirectory(at: directory, withIntermediateDirectories: false,
                                                    attributes: [.posixPermissions: 0o700])
        } catch {
            throw DownloadError.failed(error.localizedDescription)
        }
        let package = DownloadedPackage(directory: directory, name: release.url.lastPathComponent)
        do {
            try await FileDownload.fetch(release.url, to: package.file) { written, _ in progress(written) }
        } catch {
            discard(package)
            throw DownloadError.failed(error.localizedDescription)
        }
        guard Self.matches(package.file, release) else {
            discard(package)
            throw DownloadError.mismatch
        }
        return package
    }

    public func discard(_ package: DownloadedPackage) {
        try? FileManager.default.removeItem(at: package.directory)
    }

    /// Folders left by quitting mid-download or a crash.
    public static func removeLeftovers() {
        FileDownload.removeFolders(prefix: "knotchy-runtime-")
    }

    @MainActor
    public func openInInstaller(_ package: DownloadedPackage, release: ContainerRuntime.Release) async -> InstallerOpening {
        let file = package.file
        guard await Task.detached(operation: { Self.matches(file, release) }).value else {
            discard(package)
            return .changed
        }
        let configuration = NSWorkspace.OpenConfiguration()
        configuration.activates = true
        do {
            let app = try await NSWorkspace.shared.open([file], withApplicationAt: Self.installerApp,
                                                        configuration: configuration)
            return .opened(RunningInstaller(app: app))
        } catch {
            return .failed(error.localizedDescription)
        }
    }

    static func matches(_ file: URL, _ release: ContainerRuntime.Release) -> Bool {
        guard let size = (try? FileManager.default.attributesOfItem(atPath: file.path))?[.size] as? NSNumber,
              size.int64Value == release.size,
              let handle = try? FileHandle(forReadingFrom: file) else { return false }
        defer { try? handle.close() }
        var hash = SHA256()
        while let chunk = try? handle.read(upToCount: 1 << 20), !chunk.isEmpty { hash.update(data: chunk) }
        return hash.finalize().map { String(format: "%02x", $0) }.joined() == release.sha256
    }
}

@MainActor
private final class RunningInstaller: InstallerSession {
    let app: NSRunningApplication

    init(app: NSRunningApplication) {
        self.app = app
    }

    var hasQuit: Bool { app.isTerminated }
}