using System;
using JetBrains.Annotations;
using Robust.Shared.IoC;

namespace Robust.Shared.Timing
{
    /// <summary>
    ///     This holds main loop timing information and helper functions.
    /// </summary>
    public interface IGameTiming
    {
        /// <summary>
        /// Is program execution inside of the simulation, or rendering?
        /// </summary>
        bool InSimulation { get; set; }

        /// <summary>
        ///     Is the simulation currently paused?
        /// </summary>
        bool Paused { get; set; }

        /// <summary>
        ///     The current synchronized uptime of the simulation. Use this for in-game timing. This can be rewound for
        ///     prediction, and is affected by Paused and TimeScale.
        /// </summary>
        TimeSpan CurTime { get; }

        /// <summary>
        ///     The current real uptime of the simulation. Use this for UI and out of game timing.
        /// </summary>
        TimeSpan RealTime { get; }

        /// <summary>
        ///     The <see cref="RealTime"/> of the server.
        /// </summary>
        /// <remarks>
        ///     0 if we are the client and we are not connected to a server.
        ///     <see cref="RealTime"/> if we are the server.
        /// </remarks>
        TimeSpan ServerTime { get; }

        /// <summary>
        ///     The simulated time it took to render the last frame.
        /// </summary>
        TimeSpan FrameTime { get; }

        /// <summary>
        ///     The real time it took to render the last frame.
        /// </summary>
        TimeSpan RealFrameTime { get; }

        /// <summary>
        ///     Average real frame time over the last 50 frames.
        /// </summary>
        TimeSpan RealFrameTimeAvg { get; }

        /// <summary>
        ///     Standard Deviation of the frame time over the last 50 frames.
        /// </summary>
        TimeSpan RealFrameTimeStdDev { get; }

        /// <summary>
        ///     Current graphics frame since init OpenGL which is taken as frame 1. Useful to set a conditional breakpoint on specific frames, and
        ///     synchronize with OGL debugging tools that capture frames. Depending on the tools used, this frame
        ///     number will vary between 1 frame more or less due to how that tool is counting frames,
        ///     i.e. starting from 0 or 1, having a separate counter, etc. Available in timing debug panel.
        /// </summary>
        uint CurFrame { get; set; }

        /// <summary>
        ///     Average real FPS over the last 50 frames.
        /// </summary>
        double FramesPerSecondAvg { get; }

        /// <summary>
        ///     The current simulation tick being processed.
        /// </summary>
        GameTick CurTick { get; set; }

        /// <summary>
        ///     Time, relative to <see cref="RealTime"/>, the last tick started at.
        ///     If we're currently in simulation, that's THIS tick.
        /// </summary>
        TimeSpan LastTick { get; set; }

        /// <summary>
        ///     The target ticks/second of the simulation.
        /// </summary>
        byte TickRate { get; set; }

        /// <summary>
        /// The baseline time value that CurTime is calculated relatively to.
        /// </summary>
        (TimeSpan, GameTick) TimeBase { get; set; }

        /// <summary>
        ///     The length of a tick at the current TickRate. 1/TickRate.
        /// </summary>
        TimeSpan TickPeriod { get; }

        /// <summary>
        /// The remaining time left over after the last tick was ran.
        /// </summary>
        TimeSpan TickRemainder { get; set; }

        TimeSpan CalcAdjustedTickPeriod();

        /// <summary>
        ///     Fraction of how far into the tick we are. <c>0</c> is 0% and <see cref="ushort.MaxValue"/> is 100%.
        /// </summary>
        ushort TickFraction
        {
            get
            {
                if (InSimulation)
                {
                    return ushort.MaxValue;
                }

                return (ushort)(ushort.MaxValue * TickRemainder.TotalSeconds / TickPeriod.TotalSeconds);
            }
        }

        /// <summary>
        ///     If the client clock is a little behind or ahead of the server, you can
        ///     use the to adjust the timing of the clock speed. The default value is 0,
        ///     and you can run the clock from -1 (almost stopped) to 1 (almost no delay).
        ///     This has no effect on in-simulation timing, and only changes the speed at which
        ///     the simulation progresses in relation to Real time. Don't mess with this unless
        ///     you know what you are doing. DO NOT TOUCH THIS ON SERVER.
        /// </summary>
        float TickTimingAdjustment { get; set; }

        /// <summary>
        ///     Ends the 'lap' of the timer, updating frame time info.
        /// </summary>
        void StartFrame();

        /// <summary>
        /// Is this the first time CurTick has been predicted?
        /// </summary>
        bool IsFirstTimePredicted { get; }

        /// <summary>
        /// True if CurTick is ahead of LastRealTick, and <see cref="ApplyingState"/> is false.
        /// </summary>
        bool InPrediction { get; }

        /// <summary>
        /// If true, the game is currently in the process of applying a game server-state.
        /// </summary>
        bool ApplyingState { get; }

        string TickStamp => $"{CurTick}, predFirst: {IsFirstTimePredicted}, tickRem: {TickRemainder.TotalSeconds}, sim: {InSimulation}";

        /// <summary>
        /// Statically-accessible version of <see cref="TickStamp"/>.
        /// </summary>
        /// <remarks>
        /// This is intended as a debugging aid, and should not be used in regular committed code.
        /// </remarks>
        static string TickStampStatic => IoCManager.Resolve<IGameTiming>().TickStamp;

        /// <summary>
        /// Resets the simulation time. This should be called on round restarts.
        /// </summary>
        void ResetSimTime();
        void ResetSimTime((TimeSpan, GameTick) timeBase);

        void SetTickRateAt( byte tickRate, GameTick atTick);

        TimeSpan RealLocalToServer(TimeSpan local);
        TimeSpan RealServerToLocal(TimeSpan server);
    }
}