using Microsoft.Extensions.Diagnostics.HealthChecks;
using ZB.MOM.WW.OtOpcUa.Commons.Interfaces;

namespace ZB.MOM.WW.OtOpcUa.Host.Health;

/// <summary>
/// Reports Healthy on the admin-role leader, Degraded on a non-leader admin member. Used by
/// the <c>/health/active</c> endpoint so external load balancers can route admin-singleton
/// traffic to the current leader (cookie sessions still work on either node — DataProtection
/// keys are shared).
/// </summary>
public sealed class AdminRoleLeaderHealthCheck : IHealthCheck
{
    private readonly IClusterRoleInfo _roleInfo;

    /// <summary>Initializes a new instance of the AdminRoleLeaderHealthCheck class.</summary>
    /// <param name="roleInfo">The cluster role information provider.</param>
    public AdminRoleLeaderHealthCheck(IClusterRoleInfo roleInfo)
    {
        _roleInfo = roleInfo;
    }

    /// <summary>Checks the health status of the admin role leader.</summary>
    /// <param name="context">The health check context.</param>
    /// <param name="cancellationToken">The cancellation token.</param>
    /// <returns>A task representing the health check operation.</returns>
    public Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default)
    {
        if (!_roleInfo.HasRole("admin"))
            return Task.FromResult(HealthCheckResult.Healthy("Node does not carry admin role"));

        var leader = _roleInfo.RoleLeader("admin");
        var isLeader = leader is not null && leader.Value.Equals(_roleInfo.LocalNode);

        return Task.FromResult(isLeader
            ? HealthCheckResult.Healthy($"Admin leader ({_roleInfo.LocalNode})")
            : HealthCheckResult.Degraded($"Admin member but not leader (leader={leader?.Value ?? "<unknown>"})"));
    }
}