using System;
using AcDream.App.Streaming;
using AcDream.Core.World;
using DatReaderWriter.DBObjs;
using Xunit;

namespace AcDream.Core.Tests.Streaming;

/// <summary>
/// Covers <see cref="GpuWorldState"/>'s pending-spawn behavior — the path
/// that survives the race where the server delivers a CreateObject for a
/// landblock that hasn't been streamed in yet. This was the bug that
/// silently dropped 40+ NPCs on the first frame after live login during
/// Phase A.1 visual verification.
/// </summary>
public class GpuWorldStateTests
{
    private static LoadedLandblock MakeStubLandblock(uint canonicalId)
        => new(canonicalId, new LandBlock(), Array.Empty<WorldEntity>());

    private static WorldEntity MakeStubEntity(uint id)
        => new()
        {
            Id = id,
            SourceGfxObjOrSetupId = 0x01000001u,
            Position = System.Numerics.Vector3.Zero,
            Rotation = System.Numerics.Quaternion.Identity,
            MeshRefs = Array.Empty<MeshRef>(),
        };

    [Fact]
    public void AppendLiveEntity_LandblockAlreadyLoaded_AppendsImmediately()
    {
        var state = new GpuWorldState();
        state.AddLandblock(MakeStubLandblock(0xA9B4FFFFu));

        // Server sends a spawn at landblock 0xA9B40011 — same landblock,
        // cell index 0x0011. Canonicalize drops the cell index, lookup
        // succeeds, entity lands in the loaded landblock immediately.
        state.AppendLiveEntity(0xA9B40011u, MakeStubEntity(42));

        Assert.Single(state.Entities);
        Assert.Equal(0u, (uint)state.PendingLiveEntityCount);
    }

    [Fact]
    public void AppendLiveEntity_LandblockNotLoaded_ParksInPending()
    {
        var state = new GpuWorldState();

        // No landblock loaded — the spawn must survive instead of being
        // silently dropped (the bug from Phase A.1's first live run).
        state.AppendLiveEntity(0xA9B40011u, MakeStubEntity(42));

        Assert.Empty(state.Entities);  // not visible yet
        Assert.Equal(1, state.PendingLiveEntityCount);
    }

    [Fact]
    public void AddLandblock_DrainsPendingEntriesForThatLandblock()
    {
        var state = new GpuWorldState();

        // Three spawns arrive before the landblock loads.
        state.AppendLiveEntity(0xA9B40011u, MakeStubEntity(1));
        state.AppendLiveEntity(0xA9B40022u, MakeStubEntity(2));  // same landblock, different cell
        state.AppendLiveEntity(0xA9B40033u, MakeStubEntity(3));
        Assert.Equal(3, state.PendingLiveEntityCount);
        Assert.Empty(state.Entities);

        // Now the landblock streams in.
        state.AddLandblock(MakeStubLandblock(0xA9B4FFFFu));

        // The three pending entities are now visible, and the pending
        // bucket for that landblock is empty.
        Assert.Equal(3, state.Entities.Count);
        Assert.Equal(0, state.PendingLiveEntityCount);
    }

    [Fact]
    public void AddLandblock_DoesNotDrainPendingForADifferentLandblock()
    {
        var state = new GpuWorldState();

        state.AppendLiveEntity(0xA9B40011u, MakeStubEntity(1));   // pending for 0xA9B4FFFF
        state.AppendLiveEntity(0xAAAA0022u, MakeStubEntity(2));   // pending for 0xAAAAFFFF

        // Loading 0xA9B4FFFF only drains its own bucket.
        state.AddLandblock(MakeStubLandblock(0xA9B4FFFFu));

        Assert.Single(state.Entities);
        Assert.Equal(1, state.PendingLiveEntityCount);  // 0xAAAAFFFF entry still parked
    }

    [Fact]
    public void RemoveLandblock_DropsPendingForThatLandblock()
    {
        var state = new GpuWorldState();

        // Spawns for landblock 0xA9B4FFFF arrive while it's pending.
        state.AppendLiveEntity(0xA9B40011u, MakeStubEntity(1));
        state.AppendLiveEntity(0xA9B40022u, MakeStubEntity(2));
        Assert.Equal(2, state.PendingLiveEntityCount);

        // Player moves away — the streamer says "this landblock is no
        // longer in the visible window, drop it." The pending entries
        // for it are dropped too because they came along with that
        // landblock and are no longer relevant.
        state.RemoveLandblock(0xA9B4FFFFu);

        Assert.Equal(0, state.PendingLiveEntityCount);
        Assert.Empty(state.Entities);
    }

    [Fact]
    public void RemoveLandblock_LoadedThenRemoved_DropsItsEntities()
    {
        var state = new GpuWorldState();

        state.AddLandblock(MakeStubLandblock(0xA9B4FFFFu));
        state.AppendLiveEntity(0xA9B40011u, MakeStubEntity(1));
        Assert.Single(state.Entities);

        state.RemoveLandblock(0xA9B4FFFFu);

        Assert.Empty(state.Entities);
    }

    [Fact]
    public void IsLoaded_ReturnsTrueForLoaded_FalseForPendingOnly()
    {
        var state = new GpuWorldState();

        state.AppendLiveEntity(0xA9B40011u, MakeStubEntity(1));
        Assert.False(state.IsLoaded(0xA9B4FFFFu));  // pending doesn't count

        state.AddLandblock(MakeStubLandblock(0xA9B4FFFFu));
        Assert.True(state.IsLoaded(0xA9B4FFFFu));
    }
}