using MoShiro.Measurement;

namespace MoShiro.Measurement.Tests;

public sealed class AdaptiveRateTests
{
    private const long Second = 1_000_000;

    /// <summary>按当前频率发包、按 <paramref name="lost"/> 决定回不回，每秒评估一次；返回结束时的秒数。</summary>
    private static long Run(AdaptiveRate rate, long fromSecond, int seconds, Func<long, bool> lost, double rttMs = 20, List<ProbeTransition>? log = null, bool stopAtDead = false)
    {
        long second = fromSecond;
        for (int i = 0; i < seconds; i++, second++)
        {
            int probes = Math.Max(1, (int)Math.Round(rate.Hz));
            if (rate.State == ProbeState.Dead)
            {
                probes = i % 4 == 0 ? 1 : 0; // 退避：几秒才发一个
            }

            for (int k = 0; k < probes; k++)
            {
                long sent = second * Second + k * Second / probes;
                rate.OnSend(sent);
                if (!lost(second))
                {
                    rate.OnReply(sent, sent + (long)(rttMs * 1000), rttMs);
                }
            }

            if (rate.Evaluate((second + 1) * Second) is { } change)
            {
                log?.Add(change);
                if (stopAtDead && change.To == ProbeState.Dead)
                {
                    return second + 1;
                }
            }
        }

        return second;
    }

    [Fact]
    public void QuietLine_AfterWarmUp_ProbesJustEnoughToProveTheLossBound()
    {
        var rate = new AdaptiveRate(new AdaptiveRateOptions());
        long at = Run(rate, 0, 600, _ => false);
        Assert.Equal(ProbeState.Quiet, rate.State);
        Assert.Equal(5, rate.Hz, 0.01); // 3 / (0.2% × 300 s)
        Assert.True(at > 0);
    }

    [Fact]
    public void SustainedLoss_RaisesToTheMaximum_AndComesBackOnlyAfterTheHoldTimes()
    {
        var rate = new AdaptiveRate(new AdaptiveRateOptions());
        long at = Run(rate, 0, 600, _ => false);
        at = Run(rate, at, 60, second => second % 10 == 0); // 每 10 秒丢一整秒的包
        Assert.Equal(ProbeState.Active, rate.State);
        Assert.Equal(10, rate.Hz);

        at = Run(rate, at, 800, _ => false); // 不到 15 分钟：还在 Active
        Assert.Equal(ProbeState.Active, rate.State);
        at = Run(rate, at, 400, _ => false); // 超过 15 分钟：降到 Watch
        Assert.Equal(ProbeState.Watch, rate.State);
        Run(rate, at, 1900, _ => false); // 最后一次丢包 30 分钟之后：回到 Quiet
        Assert.Equal(ProbeState.Quiet, rate.State);
    }

    [Fact]
    public void AnIsolatedLoss_OnlyRaisesToWatch()
    {
        var rate = new AdaptiveRate(new AdaptiveRateOptions());
        long at = Run(rate, 0, 600, _ => false);
        var log = new List<ProbeTransition>();
        Run(rate, at, 120, second => second == at + 10, log: log);
        Assert.Equal(ProbeState.Watch, rate.State);
        Assert.DoesNotContain(log, change => change.To == ProbeState.Active);
    }

    [Fact]
    public void Unreachable_BacksOffExponentially_AndRecoversOnTheFirstReply()
    {
        var rate = new AdaptiveRate(new AdaptiveRateOptions(), new Random(1));
        long at = Run(rate, 0, 600, _ => false);
        at = Run(rate, at, 60, _ => true, stopAtDead: true);
        Assert.Equal(ProbeState.Dead, rate.State);

        var delays = new List<double>();
        long now = at * Second;
        for (int i = 0; i < 8; i++)
        {
            double delay = rate.NextDelay().TotalSeconds;
            delays.Add(delay);
            now += (long)(delay * Second);
            rate.OnSend(now);
        }

        Assert.InRange(delays[0], 0.8, 1.2); // 从 1 秒开始
        Assert.True(delays[3] > delays[0] * 4, string.Join(",", delays)); // 翻倍增长（有抖动）
        Assert.All(delays, delay => Assert.InRange(delay, 0.8, 36.0)); // 最长 30 秒，抖动 ±20%

        rate.OnReply(now, now + 30_000, 30);
        Assert.Equal(ProbeState.Watch, rate.Evaluate(now + 2 * Second)!.To);
    }

    [Fact]
    public void QuietLineWithTightRtt_MayDropBelowTheGrid_ButAJitteryOneStaysAtTheMaximum()
    {
        var tight = new AdaptiveRate(new AdaptiveRateOptions());
        Run(tight, 0, 1200, _ => false, rttMs: 20); // RTT 恒定：p99 的置信区间几乎为零，降到丢包下界 5 Hz
        Assert.Equal(ProbeState.Quiet, tight.State);
        Assert.Equal(5, tight.Hz, 0.01);

        var jittery = new AdaptiveRate(new AdaptiveRateOptions());
        var random = new Random(7);
        long second = 0;
        for (int i = 0; i < 1200; i++, second++)
        {
            int probes = Math.Max(1, (int)Math.Round(jittery.Hz));
            for (int k = 0; k < probes; k++)
            {
                long sent = second * Second + k * Second / probes;
                double rtt = 20 + random.NextDouble() * random.NextDouble() * 60; // 长尾 20 到 80 ms
                jittery.OnSend(sent);
                jittery.OnReply(sent, sent + (long)(rtt * 1000), rtt);
            }

            jittery.Evaluate((second + 1) * Second);
        }

        Assert.Equal(10, jittery.Hz, 0.01); // 分位数精度保护：抖动大，样本不能少
    }

    [Fact]
    public void Weight_IsTheTimeAProbeStandsFor_InUnitsOfTheGrid()
    {
        var rate = new AdaptiveRate(new AdaptiveRateOptions());
        Run(rate, 0, 1200, _ => false);
        Assert.Equal(5, rate.Hz, 0.01);
        rate.NextDelay();
        Assert.Equal(2, rate.Weight); // 5 Hz 的一个包代表 2 个 10 Hz 网格间隔
    }

    [Fact]
    public void RttWellAboveTheBaseline_RaisesToWatch()
    {
        var rate = new AdaptiveRate(new AdaptiveRateOptions());
        long at = Run(rate, 0, 900, _ => false, rttMs: 20);
        Assert.Equal(ProbeState.Quiet, rate.State);
        Run(rate, at, 30, _ => false, rttMs: 120);
        Assert.Equal(ProbeState.Watch, rate.State);
    }

    [Fact]
    public void Prior_WarmsUpBeforeTheEveningPeak_AndLetsHistoricallyQuietHoursUseTheLowestRate()
    {
        const long peakStart = 1_000 * 3600; // 秒
        double? Prior(long us)
        {
            long second = us / Second;
            return second >= peakStart && second < peakStart + 4 * 3600 ? 0.8 : 0.0;
        }

        var rate = new AdaptiveRate(new AdaptiveRateOptions { Prior = Prior });
        long at = Run(rate, 100_000, 1200, _ => false); // 远离高峰，历史平稳：证明窗口拉长，2 Hz
        Assert.Equal(ProbeState.Quiet, rate.State);
        Assert.Equal(2, rate.Hz, 0.01);

        Run(rate, peakStart - 1500, 120, _ => false); // 距离高峰不到半小时：提前升到 Active
        Assert.Equal(ProbeState.Active, rate.State);
        Assert.True(at > 0);
    }
}