using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using UnityEngine;

namespace CultMath.Unity;

[StructLayout(LayoutKind.Sequential)]
public readonly struct PlanetaryPageInputGpu
{
    public PlanetaryPageInputGpu(Vector4 directionRadius, Vector4 sampling)
    {
        DirectionRadius = directionRadius;
        Sampling = sampling;
    }

    public readonly Vector4 DirectionRadius;
    public readonly Vector4 Sampling;
}

[StructLayout(LayoutKind.Sequential)]
public readonly struct PlanetaryPageMetadataGpu
{
    public PlanetaryPageMetadataGpu(Vector4 address, Vector4 layout, Vector4 bounds, Vector4 state)
    {
        Address = address;
        Layout = layout;
        Bounds = bounds;
        State = state;
    }

    public readonly Vector4 Address;
    public readonly Vector4 Layout;
    public readonly Vector4 Bounds;
    public readonly Vector4 State;
}

public readonly struct PlanetaryPageUpload
{
    public PlanetaryPageUpload(
        PlanetaryPageInputGpu[] inputs,
        PlanetaryPageMetadataGpu[] metadata,
        int outputSampleCount,
        ulong contentVersion,
        ulong presentationVersion)
    {
        Inputs = inputs;
        Metadata = metadata;
        OutputSampleCount = outputSampleCount;
        ContentVersion = contentVersion;
        PresentationVersion = presentationVersion;
    }

    public PlanetaryPageInputGpu[] Inputs { get; }
    public PlanetaryPageMetadataGpu[] Metadata { get; }
    public int OutputSampleCount { get; }
    public ulong ContentVersion { get; }
    public ulong PresentationVersion { get; }
}

public static class PlanetaryPageUploadBuilder
{
    public static PlanetaryPageUpload Build(
        in PlanetaryResidencySnapshot snapshot,
        int interiorSize,
        int borderSize,
        float radius)
    {
        if (!float.IsFinite(radius) || radius <= 0) throw new ArgumentOutOfRangeException(nameof(radius));
        var inputs = new List<PlanetaryPageInputGpu>();
        var metadata = new PlanetaryPageMetadataGpu[snapshot.Tiles.Length];
        foreach (var (resident, pageIndex) in snapshot.Tiles.Select((resident, index) => (resident, index)))
        {
            var layout = new PlanetaryPageLayout(resident.Tile, interiorSize, borderSize).Validate();
            var content = PlanetaryGpuPageBuilder.BuildContent(layout, radius);
            var outputOffset = inputs.Count;
            foreach (var input in content.Inputs)
            {
                inputs.Add(new(
                    ToUnity(input.DirectionRadius),
                    ToUnity(input.Sampling)));
            }
            var commonMetadata = PlanetaryGpuPageBuilder.Metadata(content, outputOffset, resident.Blend);
            metadata[pageIndex] = new(
                ToUnity(commonMetadata.Address),
                ToUnity(commonMetadata.Layout),
                ToUnity(commonMetadata.Bounds),
                ToUnity(commonMetadata.State));
        }
        return new(inputs.ToArray(), metadata, inputs.Count, snapshot.ContentVersion, snapshot.PresentationVersion);
    }

    private static Vector4 ToUnity(float4 value) => new(value.x, value.y, value.z, value.w);
}