namespace Sand.ChunkPrototype;

internal sealed class ChunkFieldPage
{
    public ChunkFieldPage(int width, int height)
    {
        Width = width;
        Height = height;
        WindX = new float[width * height];
        WindY = new float[width * height];
        ForceX = new float[width * height];
        ForceY = new float[width * height];
        Pressure = new float[width * height];
    }

    public int Width { get; }
    public int Height { get; }
    public float[] WindX { get; }
    public float[] WindY { get; }
    public float[] ForceX { get; }
    public float[] ForceY { get; }
    public float[] Pressure { get; }
    public int ActiveCellCount { get; private set; }
    public int LastDecayedFrame { get; set; }

    public bool TryGetCell(int localX, int localY, out FieldCellData cell)
    {
        var index = GetIndex(localX, localY);
        cell = new FieldCellData(WindX[index], WindY[index], ForceX[index], ForceY[index], Pressure[index]);
        return !cell.IsEffectivelyZero;
    }

    public FieldCellData GetCell(int localX, int localY)
    {
        var index = GetIndex(localX, localY);
        return new FieldCellData(WindX[index], WindY[index], ForceX[index], ForceY[index], Pressure[index]);
    }

    public void SetCell(int localX, int localY, FieldCellData value)
    {
        var index = GetIndex(localX, localY);
        var wasZero = IsEffectivelyZero(index);
        var nowZero = value.IsEffectivelyZero;
        WindX[index] = value.WindX;
        WindY[index] = value.WindY;
        ForceX[index] = value.ForceX;
        ForceY[index] = value.ForceY;
        Pressure[index] = value.Pressure;
        if (wasZero && !nowZero)
        {
            ActiveCellCount++;
        }
        else if (!wasZero && nowZero)
        {
            ActiveCellCount--;
        }
    }

    public bool IsEmpty() => ActiveCellCount == 0;

    public IEnumerable<(int LocalX, int LocalY, FieldCellData Cell)> EnumerateActiveCells()
    {
        for (var y = 0; y < Height; y++)
        {
            for (var x = 0; x < Width; x++)
            {
                var index = GetIndex(x, y);
                if (IsEffectivelyZero(index))
                {
                    continue;
                }

                yield return (x, y, new FieldCellData(WindX[index], WindY[index], ForceX[index], ForceY[index], Pressure[index]));
            }
        }
    }

    private bool IsEffectivelyZero(int index) =>
        MathF.Abs(WindX[index]) < 0.01f &&
        MathF.Abs(WindY[index]) < 0.01f &&
        MathF.Abs(ForceX[index]) < 0.01f &&
        MathF.Abs(ForceY[index]) < 0.01f &&
        MathF.Abs(Pressure[index]) < 0.01f;

    private int GetIndex(int localX, int localY) => (localY * Width) + localX;
}

internal readonly record struct FieldCellData(float WindX, float WindY, float ForceX, float ForceY, float Pressure)
{
    public bool IsEffectivelyZero =>
        MathF.Abs(WindX) < 0.01f &&
        MathF.Abs(WindY) < 0.01f &&
        MathF.Abs(ForceX) < 0.01f &&
        MathF.Abs(ForceY) < 0.01f &&
        MathF.Abs(Pressure) < 0.01f;
}