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 RelocateEntity_StrandedInPending_MovesToLoadedTarget()
    {
        // Regression: the cold-spawn / run-out "invisible player" bug
        // (2026-07-03). A persistent (server-spawned) entity that spawned into a
        // not-yet-loaded landblock is parked in the pending bucket. The per-frame
        // RelocateEntity is supposed to keep it homed to its current landblock so
        // it draws — but the old implementation scanned ONLY _loaded, so it
        // silently no-op'd on a pending entity and the player stayed hidden
        // forever. Confirmed live: "[ent] APPEND guid=0x5000000A -> PENDING(hidden)"
        // with no later DRAWSET PRESENT, even after the landblock loaded (its
        // sibling NPCs re-hydrated into it fine — the player was excluded).
        var state = new GpuWorldState();

        var player = new WorldEntity
        {
            Id = 1,
            ServerGuid = 0x5000000Au,     // server-spawned + persistent
            SourceGfxObjOrSetupId = 0x01000001u,
            Position = System.Numerics.Vector3.Zero,
            Rotation = System.Numerics.Quaternion.Identity,
            MeshRefs = Array.Empty<MeshRef>(),
        };
        state.MarkPersistent(0x5000000Au);

        // Spawned before its landblock streamed in → parked in pending, hidden.
        state.AppendLiveEntity(0xADAF0011u, player);
        Assert.Empty(state.Entities);
        Assert.Equal(1, state.PendingLiveEntityCount);

        // The player's current landblock IS loaded now (the live log shows the
        // sibling NPCs re-hydrated into it). RelocateEntity — called every frame
        // to keep the player homed to its current landblock — must promote the
        // stranded pending entity into the loaded bucket so it draws.
        state.AddLandblock(MakeStubLandblock(0xBBBBFFFFu));
        state.RelocateEntity(player, 0xBBBB0011u);

        Assert.Single(state.Entities);                 // now drawn
        Assert.Equal(0, state.PendingLiveEntityCount); // no longer stranded
    }

    [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));
    }

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

    [Fact]
    public void RemoveLandblock_RescuesPersistentEntity_FromPendingBucket()
    {
        // #138 (secondary): the player is re-injected via AppendLiveEntity every
        // frame; right after a teleport its landblock hasn't streamed in, so it
        // lands in the pending bucket. If that landblock is then unloaded before
        // it finishes loading, the persistent entity must still be rescued —
        // otherwise the avatar vanishes after a couple round-trips.
        var state = new GpuWorldState();
        const uint playerGuid = 0x50000001u;
        state.MarkPersistent(playerGuid);

        var player = MakeServerEntity(id: 1, serverGuid: playerGuid);
        state.AppendLiveEntity(0xA9B40011u, player);   // landblock not loaded → pending
        Assert.Equal(1, state.PendingLiveEntityCount);

        state.RemoveLandblock(0xA9B4FFFFu);            // unloaded while still pending

        Assert.Contains(player, state.DrainRescued()); // rescued, not dropped
    }

    [Fact]
    public void RemoveLandblock_DoesNotRescue_NonPersistentPendingEntity()
    {
        // A normal server object (door) in the pending bucket is NOT persistent;
        // it must still be dropped (and is recoverable via #138 re-hydrate from
        // _lastSpawnByGuid, not via the rescue path).
        var state = new GpuWorldState();
        var door = MakeServerEntity(id: 2, serverGuid: 0x7A9B4001u);  // not marked persistent
        state.AppendLiveEntity(0xA9B40011u, door);

        state.RemoveLandblock(0xA9B4FFFFu);

        Assert.Empty(state.DrainRescued());
    }
}