using System;
using Xunit;
using ytLive.Services;

namespace ytLive.Tests;

/// <summary>
/// TASK 65 slice 1 — the replay ring as pure memory.
///
/// <para>The two rules that matter and are easy to break later: the cap is by <b>bytes</b> (bitrate moves,
/// seconds do not), and a snapshot is always init-segment-first, because an MP4 without its moov is not a
/// video, it is noise.</para>
/// </summary>
public sealed class ClipRingTests
{
    [Fact]
    public void Snapshot_IsInitThenFragmentsInOrder()
    {
        var ring = new ClipRing(1024);
        ring.SetInit(new byte[] { 1, 2 });
        ring.Append(new byte[] { 3 });
        ring.Append(new byte[] { 4, 5 });

        Assert.Equal(new byte[] { 1, 2, 3, 4, 5 }, ring.Snapshot());
        Assert.Equal(5, ring.Bytes);
        Assert.Equal(2, ring.FragmentCount);
    }

    [Fact]
    public void TheCapDropsOldestFragments_SoTheClipEndsAtTheKeypress()
    {
        var ring = new ClipRing(capBytes: 10);
        ring.SetInit(new byte[2]);
        for (var i = 0; i < 5; i++) ring.Append(new byte[3]);   // 2 + 15 = 17 → trims

        Assert.True(ring.Bytes <= 10);
        Assert.Equal(2, ring.FragmentCount);                    // newest two survive

        var snapshot = ring.Snapshot();
        Assert.Equal(2 + 3 + 3, snapshot.Length);
    }

    [Fact]
    public void NothingBuffered_SnapshotsEmpty_SoTheCallerCannotWriteAZeroByteFile()
    {
        var ring = new ClipRing(1024);
        Assert.True(ring.IsEmpty);
        Assert.Empty(ring.Snapshot());

        ring.SetInit(new byte[4]);
        Assert.True(ring.IsEmpty);                              // init alone is not a clip
        Assert.Empty(ring.Snapshot());
    }

    [Fact]
    public void ClearForgetsTheInit_SoTheNextEncoderStartCannotReuseAStaleHeader()
    {
        var ring = new ClipRing(1024);
        ring.SetInit(new byte[] { 9 });
        ring.Append(new byte[] { 8 });
        ring.Clear();

        Assert.True(ring.IsEmpty);
        Assert.Equal(0, ring.Bytes);
        ring.Append(new byte[] { 7 });
        Assert.Empty(ring.Snapshot());                          // still no init → not playable
    }
}