import Foundation
import UIKit

class ShareService {
    static let shared = ShareService()

    private init() {}

    func shareTextFile(content: String, fileName: String) {
        guard let viewController = ShareService.topViewController() else { return }

        let tempURL = FileManager.default.temporaryDirectory
            .appendingPathComponent(fileName)

        do {
            try content.write(to: tempURL, atomically: true, encoding: .utf8)

            let activityVC = UIActivityViewController(
                activityItems: [tempURL],
                applicationActivities: nil
            )

            if let popover = activityVC.popoverPresentationController {
                popover.sourceView = viewController.view
                popover.sourceRect = CGRect(
                    x: viewController.view.bounds.midX,
                    y: viewController.view.bounds.midY,
                    width: 0,
                    height: 0
                )
            }

            DispatchQueue.main.async {
                viewController.present(activityVC, animated: true)
            }
        } catch {
            print("Share file error: \(error)")
        }
    }

    func shareCalendarEvent(
        title: String,
        notes: String,
        startDate: Date,
        durationMinutes: Int = 60
    ) {
        let endDate = startDate.addingTimeInterval(TimeInterval(durationMinutes * 60))
        let icsContent = calendarICS(
            title: title,
            notes: notes,
            startDate: startDate,
            endDate: endDate
        )
        shareTextFile(content: icsContent, fileName: "PortfolioJournal-CheckIn.ics")
    }

    private static func topViewController(
        base: UIViewController? = UIApplication.shared.connectedScenes
            .compactMap { $0 as? UIWindowScene }
            .flatMap { $0.windows }
            .first(where: { $0.isKeyWindow })?.rootViewController
    ) -> UIViewController? {
        if let nav = base as? UINavigationController {
            return topViewController(base: nav.visibleViewController)
        }
        if let tab = base as? UITabBarController {
            return topViewController(base: tab.selectedViewController)
        }
        if let presented = base?.presentedViewController {
            return topViewController(base: presented)
        }
        return base
    }

    private func calendarICS(
        title: String,
        notes: String,
        startDate: Date,
        endDate: Date
    ) -> String {
        let uid = UUID().uuidString
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyyMMdd'T'HHmmss'Z'"
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        let stamp = formatter.string(from: Date())
        let start = formatter.string(from: startDate)
        let end = formatter.string(from: endDate)

        return """
        BEGIN:VCALENDAR
        VERSION:2.0
        PRODID:-//PortfolioJournal//MonthlyCheckIn//EN
        BEGIN:VEVENT
        UID:\(uid)
        DTSTAMP:\(stamp)
        DTSTART:\(start)
        DTEND:\(end)
        SUMMARY:\(escapeICS(title))
        DESCRIPTION:\(escapeICS(notes))
        END:VEVENT
        END:VCALENDAR
        """
    }

    private func escapeICS(_ value: String) -> String {
        value
            .replacingOccurrences(of: "\\", with: "\\\\")
            .replacingOccurrences(of: "\n", with: "\\n")
            .replacingOccurrences(of: ";", with: "\\;")
            .replacingOccurrences(of: ",", with: "\\,")
    }
}