using System;
using System.Runtime.InteropServices;

namespace RobotNet10.Realtime;

/// <summary>
/// Provides high-resolution clock access for real-time applications.
/// </summary>
public class RealtimeClock
{
    private readonly RealtimeClockType _clockType;

    /// <summary>
    /// Initializes a new instance of RealtimeClock.
    /// </summary>
    /// <param name="clockType">Type of clock to use</param>
    public RealtimeClock(RealtimeClockType clockType)
    {
        _clockType = clockType;
    }

    /// <summary>
    /// Gets the current time from the clock.
    /// </summary>
    /// <returns>Current time</returns>
    public DateTime GetTime()
    {
        var tp = new LinuxNative.timespec();
        int result = LinuxNative.clock_gettime((int)_clockType, ref tp);
        if (result != 0)
        {
            LinuxNative.ThrowLastError("clock_gettime");
        }

        if (_clockType == RealtimeClockType.Realtime)
        {
            return DateTimeOffset.FromUnixTimeSeconds(tp.tv_sec)
                .AddTicks(tp.tv_nsec / 100)
                .DateTime;
        }
        else
        {
            // For monotonic clocks, return time since boot
            return DateTime.UtcNow; // Note: This is approximate for monotonic clocks
        }
    }

    /// <summary>
    /// Gets the time as a TimeSpan (for monotonic clocks, represents time since boot).
    /// </summary>
    /// <returns>TimeSpan representing the clock time</returns>
    public TimeSpan GetTimeSpan()
    {
        var tp = new LinuxNative.timespec();
        int result = LinuxNative.clock_gettime((int)_clockType, ref tp);
        if (result != 0)
        {
            LinuxNative.ThrowLastError("clock_gettime");
        }

        return TimeSpan.FromSeconds(tp.tv_sec) + TimeSpan.FromTicks(tp.tv_nsec / 100);
    }

    /// <summary>
    /// Gets the resolution of the clock.
    /// </summary>
    /// <returns>Clock resolution</returns>
    public TimeSpan GetResolution()
    {
        var res = new LinuxNative.timespec();
        int result = LinuxNative.clock_getres((int)_clockType, ref res);
        if (result != 0)
        {
            LinuxNative.ThrowLastError("clock_getres");
        }

        return TimeSpan.FromSeconds(res.tv_sec) + TimeSpan.FromTicks(res.tv_nsec / 100);
    }

    /// <summary>
    /// Sets the clock time (only for CLOCK_REALTIME).
    /// </summary>
    /// <param name="time">Time to set</param>
    public void SetTime(DateTime time)
    {
        if (_clockType != RealtimeClockType.Realtime)
        {
            throw new InvalidOperationException("Only CLOCK_REALTIME can be set");
        }

        var tp = new LinuxNative.timespec
        {
            tv_sec = ((DateTimeOffset)time.ToUniversalTime()).ToUnixTimeSeconds(),
            tv_nsec = (time.Millisecond % 1000) * 1000000
        };

        int result = LinuxNative.clock_settime((int)_clockType, ref tp);
        if (result != 0)
        {
            LinuxNative.ThrowLastError("clock_settime");
        }
    }
}

/// <summary>
/// Linux clock types.
/// </summary>
public enum RealtimeClockType
{
    /// <summary>
    /// System-wide real-time clock (wall clock time).
    /// Can be set by root.
    /// </summary>
    Realtime = LinuxNative.CLOCK_REALTIME,

    /// <summary>
    /// Monotonic clock that cannot be set and represents monotonic time since some unspecified starting point.
    /// Best for measuring elapsed time.
    /// </summary>
    Monotonic = LinuxNative.CLOCK_MONOTONIC,

    /// <summary>
    /// Monotonic raw clock (not subject to NTP adjustments).
    /// </summary>
    MonotonicRaw = LinuxNative.CLOCK_MONOTONIC_RAW,

    /// <summary>
    /// Clock that measures CPU time consumed by the calling process.
    /// </summary>
    ProcessCpuTime = LinuxNative.CLOCK_PROCESS_CPUTIME_ID,

    /// <summary>
    /// Clock that measures CPU time consumed by the calling thread.
    /// </summary>
    ThreadCpuTime = LinuxNative.CLOCK_THREAD_CPUTIME_ID,

    /// <summary>
    /// Boot time clock (monotonic clock that includes time spent in suspend).
    /// </summary>
    BootTime = LinuxNative.CLOCK_BOOTTIME,
}