using System;
using static System.Buffers.Binary.BinaryPrimitives;

namespace NHSE.Core;

/// <summary>
/// Advanced design pattern with 4 sheets arranged in a square.
/// </summary>
public sealed class DesignPatternPRO(Memory<byte> Raw) : IVillagerOrigin
{
    public const int Width = 32;
    public const int Height = 32;

    public const int SIZE = 0x8A8; // 3 bytes unused at end
    public const int SheetCount = 4;
    private const int PersonalOffset = 0x38;
    private const int UsageCompatibilityOffset = 0x70;
    private const int PaletteDataStart = 0x78;
    public const int PaletteColorCount = 15; // y not 16???
    private const int PaletteColorSize = 3; // R, G, B
    private const int PixelDataOffset = PaletteDataStart + (PaletteColorCount * PaletteColorSize); // 0xA5
    private const int PixelCount = 0x400; // Width * Height
    private const int SheetDataSize = PixelCount / 2; // 4bit|4bit pixel packing

    public Span<byte> Data => Raw.Span;

    public uint Hash
    {
        get => ReadUInt32LittleEndian(Data);
        set => WriteUInt32LittleEndian(Data, value);
    }

    public uint Version
    {
        get => ReadUInt32LittleEndian(Data[0x04..]);
        set => WriteUInt32LittleEndian(Data[0x04..], value);
    }

    public string DesignName
    {
        get => StringUtil.GetString(Data, 0x10, 20);
        set => StringUtil.GetBytes(value, 20).CopyTo(Data[0x10..]);
    }

    public uint TownID
    {
        get => ReadUInt32LittleEndian(Data[PersonalOffset..]);
        set => WriteUInt32LittleEndian(Data[PersonalOffset..], value);
    }

    public string TownName
    {
        get => StringUtil.GetString(Data, PersonalOffset + 0x04, 10);
        set => StringUtil.GetBytes(value, 10).CopyTo(Data[(PersonalOffset + 0x04)..]);
    }

    public Span<byte> GetTownIdentity() => Data.Slice(PersonalOffset + 0x00, 4 + 20);

    public uint PlayerID
    {
        get => ReadUInt32LittleEndian(Data[(PersonalOffset + 0x1C)..]);
        set => WriteUInt32LittleEndian(Data[(PersonalOffset + 0x1C)..], value);
    }

    public string PlayerName
    {
        get => StringUtil.GetString(Data, PersonalOffset + 0x20, 10);
        set => StringUtil.GetBytes(value, 10).CopyTo(Data[(PersonalOffset + 0x20)..]);
    }

    public uint UsageCompatibility
    {
        get => ReadUInt32LittleEndian(Data[UsageCompatibilityOffset..]);
        set => WriteUInt32LittleEndian(Data[UsageCompatibilityOffset..], value);
    }

    public Span<byte> GetPlayerIdentity() => Data.Slice(PersonalOffset + 0x1C, 4 + 20);

    public void SetPixelAtIndex(int sheet, int index, int value)
    {
        var ofs = PixelDataOffset + (index / 2) + (sheet * SheetDataSize);
        var val = Data[ofs];
        var update = ((index & 1) == 0)
            ? (val & 0xF0) | (value & 0xF)
            : (value & 0xF) << 4 | (val & 0xF);
        Data[ofs] = (byte) update;
    }

    private int GetPixelAtIndex(int sheet, int index)
    {
        var ofs = PixelDataOffset + (index / 2) + (sheet * SheetDataSize);
        var val = Data[ofs];
        return (index & 1) == 0 ? (val & 0x0F) : (val >> 4);
    }

    public static int GetPixelIndex(int sheet, int x, int y) => (sheet * SheetDataSize) + (y * Height) + x;

    public int GetPixel(int sheet, int x, int y)
    {
        if ((uint)x >= Width)
            throw new ArgumentException($"Argument out of range (0-{Width})", nameof(x));
        if ((uint)y >= Height)
            throw new ArgumentException($"Argument out of range (0-{Height})", nameof(y));

        var index = GetPixelIndex(sheet, x, y);
        return GetPixelAtIndex(sheet, index);
    }

    public static int GetColorOffset(int index)
    {
        if ((uint)index >= PaletteColorCount)
            throw new ArgumentException($"Argument out of range (0-{PaletteColorCount})", nameof(index));
        return PaletteDataStart + (index * PaletteColorSize);
    }

    /// <summary>
    /// Builds a new array with unpacked 32bit pixel data.
    /// </summary>
    public byte[] GetBitmap(int sheet)
    {
        var result = new byte[4 * Width * Height];
        LoadBitmap(sheet, result);
        return result;
    }

    private void LoadBitmap(int sheet, Span<byte> data)
    {
        for (int i = 0; i < PixelCount; i++)
        {
            var choice = GetPixelAtIndex(sheet, i);
            if (choice == PaletteColorCount)
                continue; // transparent?
            var palette = GetColorOffset(choice);
            var ofs = i * 4;
            data[ofs + 2] = Data[palette + 0];
            data[ofs + 1] = Data[palette + 1];
            data[ofs + 0] = Data[palette + 2];
            data[ofs + 3] = 0xFF; // opaque
        }
    }

    /// <summary>
    /// Returns a raw slice of data containing the 24bit color pixels.
    /// </summary>
    public byte[] GetPaletteBitmap()
    {
        var result = new byte[3 * PaletteColorCount];
        LoadPaletteBitmap(result);
        return result;
    }

    private void LoadPaletteBitmap(Span<byte> result)
    {
        for (int i = 0; i < PaletteColorCount; i++)
        {
            var ofs = PaletteDataStart + (i * 3);
            result[(i * 3) + 2] = Data[ofs + 0];
            result[(i * 3) + 1] = Data[ofs + 1];
            result[(i * 3) + 0] = Data[ofs + 2];
        }
    }
}