using System.Runtime.CompilerServices;

namespace Uwaa.PNG;

internal class Palette
{
    public bool HasAlphaValues { get; private set; }

    public byte[] Data { get; }

    /// <summary>
    /// Creates a palette object. Input palette data length from PLTE chunk must be a multiple of 3.
    /// </summary>
    public Palette(byte[] data)
    {
        Data = new byte[data.Length * 4 / 3];
        var dataIndex = 0;
        for (var i = 0; i < data.Length; i += 3)
        {
            Data[dataIndex++] = data[i];
            Data[dataIndex++] = data[i + 1];
            Data[dataIndex++] = data[i + 2];
            Data[dataIndex++] = 255;
        }
    }

    /// <summary>
    /// Adds transparency values from tRNS chunk.
    /// </summary>
    public void SetAlphaValues(byte[] bytes)
    {
        HasAlphaValues = true;

        for (var i = 0; i < bytes.Length; i++)
            Data[(i * 4) + 3] = bytes[i];
    }

    public Pixel GetPixel(int index)
    {
        return Unsafe.As<byte, Pixel>(ref Data[index * 4]);
    }
}