using System;
using Xunit;
using ytLive.Models;
using ytLive.Services;
using ytLive.Services.Encoder;

namespace ytLive.Tests;

/// <summary>
/// TASK 33 slice 2 — the adaptor between the pump's structured stats and the pure policy, plus the two
/// sentences a creator ever sees. The copy is pinned here because "own the mistake" is a product rule,
/// not a wording preference: a mechanism string in a toast is the bug.
/// </summary>
public sealed class StepDownPlannerTests
{
    private static FramePumpStats Strained(double renderMs = 45, int stalls = 12, int dropped = 0) =>
        new(WindowSeconds: 5, FramesSubmitted: 150, FramesRendered: 150,
            AvgRenderMs: renderMs, AvgSubmitMs: 1, AvgWaitMs: 14,
            WorstRenderMs: renderMs * 2, WorstSubmitMs: 2, Dropped: dropped, Stalls: stalls);

    [Fact]
    public void MachineEvidenceAfterThreeWindows_LowersTheFrameRateAndSaysWhoseFaultItWas()
    {
        var now = new DateTime(2026, 11, 9, 12, 0, 0, DateTimeKind.Utc);
        var planner = new StepDownPlanner(
            new StepDownPolicy(vertical: false, startFps: 60, startBitrateMbps: 8.0), now);

        StepDownDecision decision = default;
        for (var i = 0; i < 20 && !(decision.Acted && decision.Action != StepAction.ShedCaptureCadence); i++)
        {
            now = now.AddSeconds(5);
            decision = planner.Observe(Strained(), now);
        }

        Assert.True(decision.Acted);
        Assert.Equal(StepAction.LowerFrameRate, decision.Action);

        var landed = planner.Current;
        Assert.Equal(30, landed.Fps);

        var copy = StepDownPlanner.Describe(decision, landed);
        Assert.Contains("LlamaCasty couldn't keep up", copy);
        Assert.Contains("connection wasn't the problem", copy);
        Assert.DoesNotContain("dropped", copy, StringComparison.OrdinalIgnoreCase);
    }

    [Fact]
    public void EncoderDrops_LowerTheBitrateAndTheCopyBlamesTheUpload()
    {
        var now = new DateTime(2026, 11, 9, 12, 0, 0, DateTimeKind.Utc);
        var planner = new StepDownPlanner(
            new StepDownPolicy(vertical: false, startFps: 60, startBitrateMbps: 8.0), now);

        StepDownDecision decision = default;
        for (var i = 0; i < 4 && !decision.Acted; i++)
        {
            now = now.AddSeconds(5);
            decision = planner.Observe(Strained(renderMs: 1, stalls: 0, dropped: 30), now);
        }

        Assert.Equal(StepAction.LowerBitrate, decision.Action);

        var landed = planner.Current;
        Assert.Equal(60, landed.Fps);
        Assert.Equal(1920, landed.Width);
        Assert.True(landed.BitrateMbps < 8.0);

        var copy = StepDownPlanner.Describe(decision, landed);
        Assert.Contains("upload couldn't hold", copy);
        Assert.DoesNotContain("couldn't keep up", copy);
    }

    [Fact]
    public void TheSessionReportLine_NamesTheCauseInOnePlace()
    {
        var when = new DateTime(2026, 11, 9, 12, 4, 0);
        var machine = new StepDownDecision(StepCause.Machine, StepAction.LowerFrameRate, "frame rate 60 → 30");
        var upload = new StepDownDecision(StepCause.Upload, StepAction.LowerBitrate, "8.0 → 7.2 Mbps on 10% loss");

        Assert.Equal("12:04 quality stepped down — encoder (frame rate 60 → 30)",
            StepDownPlanner.ReportLine(when, machine));
        Assert.Equal("12:04 quality stepped down — upload (8.0 → 7.2 Mbps on 10% loss)",
            StepDownPlanner.ReportLine(when, upload));
        Assert.Equal(string.Empty,
            StepDownPlanner.ReportLine(when, new StepDownDecision(StepCause.None, StepAction.None, null)));
    }

    [Fact]
    public void ShortWindows_AreIgnored_SoAStartupBurstCannotTriggerAStep()
    {
        var now = new DateTime(2026, 11, 9, 12, 0, 0, DateTimeKind.Utc);
        var planner = new StepDownPlanner(
            new StepDownPolicy(vertical: false, startFps: 60, startBitrateMbps: 8.0), now);

        var burst = Strained() with { WindowSeconds = 1 };
        for (var i = 0; i < 20; i++)
        {
            now = now.AddSeconds(1);
            Assert.False(planner.Observe(burst, now).Acted);
        }
    }
}