// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// Copyright (C) LibreHardwareMonitor and Contributors.
// Partial Copyright (C) Michael Möller <mmoeller@openhardwaremonitor.org> and Contributors.
// All Rights Reserved.

using System;
using System.Diagnostics;
using System.Globalization;
using System.Linq;
using System.Text;

namespace LibreHardwareMonitor.Hardware.Cpu;

public class GenericCpu : Hardware
{
    protected readonly int _coreCount;
    protected readonly CpuId[][] _cpuId;
    protected readonly uint _family;
    protected readonly uint _model;
    protected readonly uint _packageType;
    protected readonly uint _stepping;
    protected readonly int _threadCount;

    private readonly CpuLoad _cpuLoad;
    private readonly double _estimatedTimeStampCounterFrequency;
    private readonly double _estimatedTimeStampCounterFrequencyError;
    private readonly bool _isInvariantTimeStampCounter;
    private readonly Sensor[] _threadLoads;

    private readonly Sensor _totalLoad;
    private readonly Sensor _maxLoad;
    private readonly Vendor _vendor;
    private long _lastTime;
    private ulong _lastTimeStampCount;

    public GenericCpu(int processorIndex, CpuId[][] cpuId, ISettings settings) : base(cpuId[0][0].Name, CreateIdentifier(cpuId[0][0].Vendor, processorIndex), settings)
    {
        _cpuId = cpuId;
        _vendor = cpuId[0][0].Vendor;
        _family = cpuId[0][0].Family;
        _model = cpuId[0][0].Model;
        _stepping = cpuId[0][0].Stepping;
        _packageType = cpuId[0][0].PkgType;

        Index = processorIndex;
        _coreCount = cpuId.Length;
        _threadCount = cpuId.Sum(x => x.Length);

        // Check if processor has MSRs.
        HasModelSpecificRegisters = cpuId[0][0].Data.GetLength(0) > 1 && (cpuId[0][0].Data[1, 3] & 0x20) != 0;

        // Check if processor has a TSC.
        HasTimeStampCounter = cpuId[0][0].Data.GetLength(0) > 1 && (cpuId[0][0].Data[1, 3] & 0x10) != 0;

        // Check if processor supports an invariant TSC.
        _isInvariantTimeStampCounter = cpuId[0][0].ExtData.GetLength(0) > 7 && (cpuId[0][0].ExtData[7, 3] & 0x100) != 0;

        _totalLoad = _coreCount > 1 ? new Sensor("CPU Total", 0, SensorType.Load, this, settings) : null;
        _maxLoad = _coreCount > 1 ? new Sensor("CPU Core Max", 1, SensorType.Load, this, settings) : null;

        _cpuLoad = new CpuLoad(cpuId);
        if (_cpuLoad.IsAvailable)
        {
            _threadLoads = new Sensor[_threadCount];
            for (int coreIdx = 0; coreIdx < cpuId.Length; coreIdx++)
            {
                for (int threadIdx = 0; threadIdx < cpuId[coreIdx].Length; threadIdx++)
                {
                    int thread = cpuId[coreIdx][threadIdx].Thread;
                    if (thread < _threadLoads.Length)
                    {
                        // Some cores may have 2 threads while others have only one (e.g. P-cores vs E-cores on Intel 12th gen).
                        string sensorName = CoreString(coreIdx) + (cpuId[coreIdx].Length > 1 ? $" Thread #{threadIdx + 1}" : string.Empty);
                        _threadLoads[thread] = new Sensor(sensorName, thread + 2, SensorType.Load, this, settings);

                        ActivateSensor(_threadLoads[thread]);
                    }
                }
            }

            if (_totalLoad != null)
            {
                ActivateSensor(_totalLoad);
            }

            if (_maxLoad != null)
            {
                ActivateSensor(_maxLoad);
            }
        }

        if (HasTimeStampCounter)
        {
            GroupAffinity previousAffinity = ThreadAffinity.Set(cpuId[0][0].Affinity);
            EstimateTimeStampCounterFrequency(out _estimatedTimeStampCounterFrequency, out _estimatedTimeStampCounterFrequencyError);
            ThreadAffinity.Set(previousAffinity);
        }
        else
        {
            _estimatedTimeStampCounterFrequency = 0;
        }

        TimeStampCounterFrequency = _estimatedTimeStampCounterFrequency;
    }

    /// <summary>
    /// Gets the CPUID.
    /// </summary>
    public CpuId[][] CpuId => _cpuId;

    public override HardwareType HardwareType => HardwareType.Cpu;

    public bool HasModelSpecificRegisters { get; }

    public bool HasTimeStampCounter { get; }

    /// <summary>
    /// Gets the CPU index.
    /// </summary>
    public int Index { get; }

    public double TimeStampCounterFrequency { get; private set; }

    protected string CoreString(int i)
    {
        if (_coreCount == 1)
            return "CPU Core";

        return "CPU Core #" + (i + 1);
    }

    private static Identifier CreateIdentifier(Vendor vendor, int processorIndex)
    {
        string s = vendor switch
        {
            Vendor.AMD => "amdcpu",
            Vendor.Intel => "intelcpu",
            _ => "genericcpu"
        };

        return new Identifier(s, processorIndex.ToString(CultureInfo.InvariantCulture));
    }

    private static void EstimateTimeStampCounterFrequency(out double frequency, out double error)
    {
        // preload the function
        EstimateTimeStampCounterFrequency(0, out double f, out double e);
        EstimateTimeStampCounterFrequency(0, out f, out e);

        // estimate the frequency
        error = double.MaxValue;
        frequency = 0;
        for (int i = 0; i < 5; i++)
        {
            EstimateTimeStampCounterFrequency(0.025, out f, out e);
            if (e < error)
            {
                error = e;
                frequency = f;
            }

            if (error < 1e-4)
                break;
        }
    }

    private static void EstimateTimeStampCounterFrequency(double timeWindow, out double frequency, out double error)
    {
        long ticks = (long)(timeWindow * Stopwatch.Frequency);

        long timeBegin = Stopwatch.GetTimestamp() + (long)Math.Ceiling(0.001 * ticks);
        long timeEnd = timeBegin + ticks;

        while (Stopwatch.GetTimestamp() < timeBegin)
        { }

        ulong countBegin = OpCode.Rdtsc();
        long afterBegin = Stopwatch.GetTimestamp();

        while (Stopwatch.GetTimestamp() < timeEnd)
        { }

        ulong countEnd = OpCode.Rdtsc();
        long afterEnd = Stopwatch.GetTimestamp();

        double delta = timeEnd - timeBegin;
        frequency = 1e-6 * ((double)(countEnd - countBegin) * Stopwatch.Frequency) / delta;

        double beginError = (afterBegin - timeBegin) / delta;
        double endError = (afterEnd - timeEnd) / delta;
        error = beginError + endError;
    }


    public override string GetReport()
    {
        StringBuilder r = new();

        switch (_vendor)
        {
            case Vendor.AMD:
                r.AppendLine("AMD CPU");
                break;
            case Vendor.Intel:
                r.AppendLine("Intel CPU");
                break;
            default:
                r.AppendLine("Generic CPU");
                break;
        }

        r.AppendLine();
        r.AppendFormat("Name: {0}{1}", _name, Environment.NewLine);
        r.AppendFormat("Number of Cores: {0}{1}", _coreCount, Environment.NewLine);
        r.AppendFormat("Threads per Core: {0}{1}", _cpuId[0].Length, Environment.NewLine);
        r.AppendLine(string.Format(CultureInfo.InvariantCulture, "Timer Frequency: {0} MHz", Stopwatch.Frequency * 1e-6));
        r.AppendLine("Time Stamp Counter: " + (HasTimeStampCounter ? _isInvariantTimeStampCounter ? "Invariant" : "Not Invariant" : "None"));
        r.AppendLine(string.Format(CultureInfo.InvariantCulture, "Estimated Time Stamp Counter Frequency: {0} MHz", Math.Round(_estimatedTimeStampCounterFrequency * 100) * 0.01));
        r.AppendLine(string.Format(CultureInfo.InvariantCulture,
                                   "Estimated Time Stamp Counter Frequency Error: {0} Mhz",
                                   Math.Round(_estimatedTimeStampCounterFrequency * _estimatedTimeStampCounterFrequencyError * 1e5) * 1e-5));

        r.AppendLine(string.Format(CultureInfo.InvariantCulture, "Time Stamp Counter Frequency: {0} MHz", Math.Round(TimeStampCounterFrequency * 100) * 0.01));
        r.AppendLine();

        return r.ToString();
    }

    public override void Update()
    {
        if (HasTimeStampCounter && _isInvariantTimeStampCounter)
        {
            // make sure always the same thread is used
            GroupAffinity previousAffinity = ThreadAffinity.Set(_cpuId[0][0].Affinity);

            // read time before and after getting the TSC to estimate the error
            long firstTime = Stopwatch.GetTimestamp();
            ulong timeStampCount = OpCode.Rdtsc();
            long time = Stopwatch.GetTimestamp();

            // restore the thread affinity mask
            ThreadAffinity.Set(previousAffinity);

            double delta = (double)(time - _lastTime) / Stopwatch.Frequency;
            double error = (double)(time - firstTime) / Stopwatch.Frequency;

            // only use data if they are measured accurate enough (max 0.1ms delay)
            if (error < 0.0001)
            {
                // ignore the first reading because there are no initial values
                // ignore readings with too large or too small time window
                if (_lastTime != 0 && delta is > 0.5 and < 2)
                {
                    // update the TSC frequency with the new value
                    TimeStampCounterFrequency = (timeStampCount - _lastTimeStampCount) / (1e6 * delta);
                }

                _lastTimeStampCount = timeStampCount;
                _lastTime = time;
            }
        }

        if (_cpuLoad.IsAvailable)
        {
            _cpuLoad.Update();

            float maxLoad = 0;
            if (_threadLoads != null)
            {
                for (int i = 0; i < _threadLoads.Length; i++)
                {
                    if (_threadLoads[i] != null)
                    {
                        _threadLoads[i].Value = (float)_cpuLoad.GetThreadLoad(i);
                        maxLoad = Math.Max(maxLoad, _threadLoads[i].Value ?? 0);
                    }
                }
            }

            if (_totalLoad != null)
                _totalLoad.Value = (float)_cpuLoad.GetTotalLoad();

            if (_maxLoad != null)
                _maxLoad.Value = maxLoad;
        }
    }
}
