using GermanApp.Application.DTOs;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace GermanApp.Application.Interfaces;

/// <summary>
/// Interface for admin services.
/// Part of the Application layer.
/// </summary>
public interface IAdminService
{
    /// <summary>
    /// Gets all users for admin view.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>List of all users</returns>
    Task<IReadOnlyList<AdminUserListItemDto>> GetAllUsersAsync(CancellationToken cancellationToken = default);

    /// <summary>
    /// Gets a specific user by ID.
    /// </summary>
    /// <param name="userId">The user ID</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>The user DTO</returns>
    Task<AdminUserDto?> GetUserByIdAsync(int userId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Updates a user's role.
    /// </summary>
    /// <param name="userId">The user ID</param>
    /// <param name="newRole">The new role</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>The updated user DTO</returns>
    Task<AdminUserDto?> UpdateUserRoleAsync(int userId, string newRole, CancellationToken cancellationToken = default);

    /// <summary>
    /// Deletes a user (admin only, cannot delete self).
    /// </summary>
    /// <param name="userId">The user ID to delete</param>
    /// <param name="adminUserId">The admin user ID making the request</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>True if successful</returns>
    Task<bool> DeleteUserAsync(int userId, int adminUserId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Gets admin dashboard statistics.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Dashboard statistics</returns>
    Task<AdminDashboardStatsDto> GetDashboardStatsAsync(CancellationToken cancellationToken = default);
}