using System.Collections.Generic;
using AcDream.Core.Terrain;
using AcDream.Core.World;

namespace AcDream.App.Streaming;

/// <summary>
/// A job posted to <see cref="LandblockStreamer"/>'s inbox. Either a load
/// (fetch this landblock from the dats and build its CPU-side mesh data)
/// or an unload (release any state tied to this landblock on the render
/// thread's next Tick drain).
/// </summary>
public abstract record LandblockStreamJob(uint LandblockId)
{
    public sealed record Load(uint LandblockId, LandblockStreamJobKind Kind) : LandblockStreamJob(LandblockId);
    public sealed record Unload(uint LandblockId) : LandblockStreamJob(LandblockId);
}

/// <summary>
/// Outbox record the render thread drains. Either a successful load, a
/// failed load (logged and ignored until region recenters off/back), or
/// an unload notification (tells the render thread to release GPU state
/// for this landblock id).
/// </summary>
public abstract record LandblockStreamResult(uint LandblockId)
{
    /// <summary>
    /// A landblock load completed. <see cref="Tier"/> distinguishes Far
    /// (terrain only) from Near (terrain + entities). <see cref="MeshData"/>
    /// is built off the render thread on the streaming worker.
    /// </summary>
    public sealed record Loaded(
        uint LandblockId,
        LandblockStreamTier Tier,
        LoadedLandblock Landblock,
        LandblockMeshData MeshData
    ) : LandblockStreamResult(LandblockId);

    /// <summary>
    /// A previously-Far-resident landblock was promoted to Near. The result
    /// carries the full near landblock plus mesh data so the render thread can
    /// run the same near-tier side effects as a fresh LoadNear: cell visibility,
    /// building registries, EnvCell finalization, lighting, and static collision.
    /// GpuWorldState still merges only the entity layer so live entities already
    /// attached to the landblock are preserved.
    /// </summary>
    public sealed record Promoted(
        uint LandblockId,
        LoadedLandblock Landblock,
        LandblockMeshData MeshData
    ) : LandblockStreamResult(LandblockId)
    {
        public IReadOnlyList<WorldEntity> Entities => Landblock.Entities;
    }

    public sealed record Failed(uint LandblockId, string Error) : LandblockStreamResult(LandblockId);
    public sealed record Unloaded(uint LandblockId) : LandblockStreamResult(LandblockId);

    /// <summary>
    /// The worker loop itself crashed with an unhandled exception. Not tied
    /// to a specific landblock — distinguished from <see cref="Failed"/>
    /// because consumers typically route this to a fatal-log path rather
    /// than retrying a single landblock later. LandblockId is 0 by
    /// convention; readers should pattern-match on the type, not the id.
    /// </summary>
    public sealed record WorkerCrashed(string Error) : LandblockStreamResult(0);
}