import Foundation
#if os(macOS)
import AppKit
#endif

/// SonarDesk's user-visible iCloud Drive document store.
/// Tokens remain in iCloud Keychain and are never written to this folder.
final class ICloudDriveStore {
    static let shared = ICloudDriveStore()
    static let containerIdentifier = "iCloud.net.absdev.SonarDesk"

    enum StoreError: LocalizedError {
        case unavailable
        case notDownloaded

        var errorDescription: String? {
            switch self {
            case .unavailable:
                return "SonarDesk cannot access its iCloud Drive container. Check iCloud Drive and the SonarDesk iCloud capability/signing."
            case .notDownloaded:
                return "The SonarDesk iCloud Drive folder is not currently available on this Mac."
            }
        }
    }

    struct Status {
        let available: Bool
        let containerIdentifier: String
        let documentsURL: URL?
        let message: String
    }

    private let fm = FileManager.default
    private init() {}

    /// Returns the public Documents scope of the SonarDesk ubiquity container.
    /// No local fallback is permitted: persistent SonarDesk files are iCloud-only.
    func root(create: Bool = true) throws -> URL {
        guard let container = fm.url(forUbiquityContainerIdentifier: Self.containerIdentifier) else {
            throw StoreError.unavailable
        }

        let documents = container.appendingPathComponent("Documents", isDirectory: true)
        if create {
            try createHierarchy(at: documents)
            // Touch a harmless marker so the public document scope is materialised immediately.
            let marker = documents.appendingPathComponent(".sonardesk", isDirectory: false)
            if !fm.fileExists(atPath: marker.path) {
                try Data("SonarDesk iCloud Drive data store\n".utf8).write(to: marker, options: .atomic)
            }
        }
        return documents
    }

    func status() -> Status {
        guard let container = fm.url(forUbiquityContainerIdentifier: Self.containerIdentifier) else {
            return Status(available: false,
                          containerIdentifier: Self.containerIdentifier,
                          documentsURL: nil,
                          message: "Unavailable — the signed app has no access to its iCloud Drive container.")
        }
        let documents = container.appendingPathComponent("Documents", isDirectory: true)
        do {
            try createHierarchy(at: documents)
            return Status(available: true,
                          containerIdentifier: Self.containerIdentifier,
                          documentsURL: documents,
                          message: "Connected")
        } catch {
            return Status(available: false,
                          containerIdentifier: Self.containerIdentifier,
                          documentsURL: documents,
                          message: error.localizedDescription)
        }
    }

    func dataDirectory(create: Bool = true) throws -> URL { try directory("Data", create: create) }
    func reportsDirectory(create: Bool = true) throws -> URL { try directory("Reports", create: create) }
    func backupsDirectory(create: Bool = true) throws -> URL { try directory("Backups", create: create) }
    func historyDirectory(create: Bool = true) throws -> URL { try directory("Data/history", create: create) }
    func exportsDirectory(_ name: String, create: Bool = true) throws -> URL { try directory("Reports/\(name)", create: create) }

    private func directory(_ relative: String, create: Bool) throws -> URL {
        let url = try root(create: create).appendingPathComponent(relative, isDirectory: true)
        if create { try fm.createDirectory(at: url, withIntermediateDirectories: true) }
        return url
    }

    func read<T: Decodable>(_ type: T.Type, fileName: String) throws -> T? {
        let url = try dataDirectory().appendingPathComponent(fileName)
        guard fm.fileExists(atPath: url.path) else { return nil }
        try ensureDownloaded(url)
        let coordinator = NSFileCoordinator(filePresenter: nil)
        var coordinationError: NSError?
        var result: Result<T, Error>?
        coordinator.coordinate(readingItemAt: url, options: [], error: &coordinationError) { coordinatedURL in
            result = Result {
                let data = try Data(contentsOf: coordinatedURL, options: [.mappedIfSafe])
                let decoder = JSONDecoder()
                decoder.dateDecodingStrategy = .iso8601
                return try decoder.decode(type, from: data)
            }
        }
        if let coordinationError { throw coordinationError }
        return try result?.get()
    }

    func write<T: Encodable>(_ value: T, fileName: String) throws {
        let url = try dataDirectory().appendingPathComponent(fileName)
        let encoder = JSONEncoder()
        encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
        encoder.dateEncodingStrategy = .iso8601
        let data = try encoder.encode(value)
        try coordinatedAtomicWrite(data, to: url, backupName: fileName)
    }

    func coordinatedAtomicWrite(_ data: Data, to url: URL, backupName: String? = nil) throws {
        let coordinator = NSFileCoordinator(filePresenter: nil)
        var coordinationError: NSError?
        var writeError: Error?
        coordinator.coordinate(writingItemAt: url, options: .forReplacing, error: &coordinationError) { coordinatedURL in
            do {
                if fm.fileExists(atPath: coordinatedURL.path), let backupName {
                    let backupDir = try backupsDirectory()
                    let stamp = ISO8601DateFormatter().string(from: Date()).replacingOccurrences(of: ":", with: "-")
                    let backup = backupDir.appendingPathComponent("\(stamp)-\(backupName)")
                    try? fm.copyItem(at: coordinatedURL, to: backup)
                    pruneBackups(named: backupName, in: backupDir)
                }
                try data.write(to: coordinatedURL, options: [.atomic, .completeFileProtectionUnlessOpen])
            } catch { writeError = error }
        }
        if let coordinationError { throw coordinationError }
        if let writeError { throw writeError }
    }

    private func ensureDownloaded(_ url: URL) throws {
        let values = try url.resourceValues(forKeys: [.isUbiquitousItemKey, .ubiquitousItemDownloadingStatusKey])
        guard values.isUbiquitousItem == true else { return }

        let status = values.ubiquitousItemDownloadingStatus
        if status != .current && status != .downloaded {
            try fm.startDownloadingUbiquitousItem(at: url)
            throw StoreError.notDownloaded
        }
    }

    private func pruneBackups(named fileName: String, in directory: URL) {
        guard let files = try? fm.contentsOfDirectory(at: directory, includingPropertiesForKeys: [.contentModificationDateKey]) else { return }
        let matching = files.filter { $0.lastPathComponent.hasSuffix("-\(fileName)") }.sorted {
            let l = (try? $0.resourceValues(forKeys: [.contentModificationDateKey]).contentModificationDate) ?? .distantPast
            let r = (try? $1.resourceValues(forKeys: [.contentModificationDateKey]).contentModificationDate) ?? .distantPast
            return l > r
        }
        for old in matching.dropFirst(10) { try? fm.removeItem(at: old) }
    }

    func revealRoot() throws {
        #if os(macOS)
        let url = try root()
        NSWorkspace.shared.open(url)
        #endif
    }

    private func createHierarchy(at root: URL) throws {
        try fm.createDirectory(at: root, withIntermediateDirectories: true)
        for relative in ["Data", "Data/history", "Reports", "Reports/PDF", "Reports/CSV", "Reports/JSON", "Backups"] {
            try fm.createDirectory(at: root.appendingPathComponent(relative, isDirectory: true), withIntermediateDirectories: true)
        }
    }
}