using System;
using System.Runtime.InteropServices;

namespace RobotNet10.Realtime;

/// <summary>
/// Provides real-time scheduling policy management for Linux preempt_rt.
/// </summary>
public static class RealtimeScheduler
{
    /// <summary>
    /// Sets the scheduling policy and priority for the current thread.
    /// </summary>
    /// <param name="policy">Scheduling policy (SCHED_FIFO, SCHED_RR, etc.)</param>
    /// <param name="priority">Priority (1-99 for real-time policies)</param>
    /// <exception cref="InvalidOperationException">Thrown when the operation fails.</exception>
    public static void SetSchedulingPolicy(RealtimeSchedulingPolicy policy, int priority)
    {
        /*if (priority < LinuxNative.MIN_PRIORITY || priority > LinuxNative.MAX_PRIORITY)
        {
            throw new ArgumentOutOfRangeException(nameof(priority), 
                $"Priority must be between {LinuxNative.MIN_PRIORITY} and {LinuxNative.MAX_PRIORITY}");
        }

        var param = new LinuxNative.sched_param
        {
            sched_priority = priority
        };

        int result = LinuxNative.sched_setscheduler(0, (int)policy, ref param);
        if (result != 0)
        {
            LinuxNative.ThrowLastError("sched_setscheduler");
        }*/
    }

    /// <summary>
    /// Gets the current scheduling policy for the current thread.
    /// </summary>
    /// <returns>The current scheduling policy.</returns>
    public static RealtimeSchedulingPolicy GetSchedulingPolicy()
    {
        int policy = LinuxNative.sched_getscheduler(0);
        if (policy < 0)
        {
            LinuxNative.ThrowLastError("sched_getscheduler");
        }
        return (RealtimeSchedulingPolicy)policy;
    }

    /// <summary>
    /// Gets the current priority for the current thread.
    /// </summary>
    /// <returns>The current priority.</returns>
    public static int GetPriority()
    {
        var param = new LinuxNative.sched_param();
        int result = LinuxNative.sched_getparam(0, ref param);
        if (result != 0)
        {
            LinuxNative.ThrowLastError("sched_getparam");
        }
        return param.sched_priority;
    }

    /// <summary>
    /// Sets the priority for the current thread (without changing policy).
    /// </summary>
    /// <param name="priority">Priority (1-99 for real-time policies)</param>
    public static void SetPriority(int priority)
    {
        if (priority < LinuxNative.MIN_PRIORITY || priority > LinuxNative.MAX_PRIORITY)
        {
            throw new ArgumentOutOfRangeException(nameof(priority), 
                $"Priority must be between {LinuxNative.MIN_PRIORITY} and {LinuxNative.MAX_PRIORITY}");
        }

        var param = new LinuxNative.sched_param
        {
            sched_priority = priority
        };

        int result = LinuxNative.sched_setparam(0, ref param);
        if (result != 0)
        {
            LinuxNative.ThrowLastError("sched_setparam");
        }
    }

    /// <summary>
    /// Gets the minimum priority for a scheduling policy.
    /// </summary>
    /// <param name="policy">Scheduling policy</param>
    /// <returns>Minimum priority</returns>
    public static int GetMinPriority(RealtimeSchedulingPolicy policy)
    {
        return LinuxNative.sched_get_priority_min((int)policy);
    }

    /// <summary>
    /// Gets the maximum priority for a scheduling policy.
    /// </summary>
    /// <param name="policy">Scheduling policy</param>
    /// <returns>Maximum priority</returns>
    public static int GetMaxPriority(RealtimeSchedulingPolicy policy)
    {
        return LinuxNative.sched_get_priority_max((int)policy);
    }

    /// <summary>
    /// Yields the CPU to allow other threads to run.
    /// </summary>
    public static void Yield()
    {
        int result = LinuxNative.sched_yield();
        if (result != 0)
        {
            LinuxNative.ThrowLastError("sched_yield");
        }
    }
}

/// <summary>
/// Linux real-time scheduling policies.
/// </summary>
public enum RealtimeSchedulingPolicy
{
    /// <summary>
    /// Normal scheduling policy (default).
    /// </summary>
    Normal = LinuxNative.SCHED_NORMAL,

    /// <summary>
    /// First-In-First-Out real-time scheduling policy.
    /// Threads with higher priority always run before threads with lower priority.
    /// </summary>
    Fifo = LinuxNative.SCHED_FIFO,

    /// <summary>
    /// Round-Robin real-time scheduling policy.
    /// Similar to SCHED_FIFO but threads are time-sliced.
    /// </summary>
    RoundRobin = LinuxNative.SCHED_RR,

    /// <summary>
    /// Batch scheduling policy (for batch jobs).
    /// </summary>
    Batch = LinuxNative.SCHED_BATCH,

    /// <summary>
    /// Idle scheduling policy (lowest priority).
    /// </summary>
    Idle = LinuxNative.SCHED_IDLE,

    /// <summary>
    /// Deadline scheduling policy (for deadline-based scheduling).
    /// </summary>
    Deadline = LinuxNative.SCHED_DEADLINE,
}