import Foundation
import Observation

/// Whether the signed-in account is an instance admin, from `whoami`. A
/// failed read counts as not: the account menu then leaves Admin out.
enum AdminCheck {

    nonisolated private struct Who: Decodable, Sendable {
        let admin: Bool?
    }

    static func isAdmin(_ client: GitbayClient) async -> Bool {
        ((try? await client.read(["whoami"], as: Who.self))?.admin) ?? false
    }
}

/// The admin screen: `dashboard`'s server build and worker queues, the
/// read the web's /admin page makes.
@Observable
@MainActor
final class AdminOverviewViewModel {

    nonisolated struct Overview: Sendable, Hashable {
        let commit: String?
        let sections: [QueueSection]
    }

    private(set) var state: LoadState<Overview> = .loading

    private let client: GitbayClient

    init(client: GitbayClient) {
        self.client = client
    }

    func load() async {
        do {
            let dashboard = try await client.read(["dashboard"], as: AdminDashboard.self)
            guard let queues = dashboard.queues else {
                state = .empty("Only instance admins can see the worker queues.")
                return
            }
            state = .loaded(Overview(commit: dashboard.server?.commit, sections: queues.sections()))
        } catch {
            state = .from(error)
        }
    }
}

/// `admin user list`, narrowed by the web's five filters, and the four
/// writes /admin/users makes per row.
@Observable
@MainActor
final class AdminUsersViewModel {

    let list: PagedListModel<AdminUser>
    var filter = AdminUserFilter.all {
        didSet {
            guard filter != oldValue else { return }
            list.argv = ["admin", "user", "list"] + filter.flags()
            reloadTask?.cancel()
            reloadTask = Task { await list.reload() }
        }
    }
    private var reloadTask: Task<Void, Never>?
    private(set) var actionError: String?
    private(set) var working = false

    private let client: GitbayClient

    init(client: GitbayClient) {
        self.client = client
        list = PagedListModel(
            client: client,
            argv: ["admin", "user", "list"],
            emptyMessage: "No account matches"
        )
    }

    func load() async {
        reloadTask?.cancel()
        await list.reload()
    }

    /// The list's `.task`: reads only while nothing is shown yet.
    func loadIfNeeded() async {
        guard list.needsLoad else { return }
        await load()
    }

    func perform(_ action: AdminAction, on username: String) async {
        working = true
        actionError = nil
        defer { working = false }
        do {
            try await client.run(action.argv(username))
        } catch let error as GitbayError {
            actionError = error.userFacingMessage
        } catch {
            actionError = GitbayError.transport(error).userFacingMessage
        }
        reloadTask?.cancel()
        reloadTask = Task { await list.reload() }
        await reloadTask?.value
    }
}