using System;
using UnityEngine;
using UnityEngine.UIElements;

/// <summary>
///     class to handle the oklch colour picker ui
/// </summary>
public class OklchColourPickerUI : MonoBehaviour
{
    /// <summary>
    ///     perceptual lightness value of the colour (0-100)
    /// </summary>
    public double lightness;

    /// <summary>
    ///     chroma value of the colour (0-0.5)
    /// </summary>
    public double chroma;

    /// <summary>
    ///     hue value of the colour (0-360)
    /// </summary>
    public double hue;

    /// <summary>
    ///     slider for the chroma value
    /// </summary>
    private Slider _chromaSlider;

    /// <summary>
    ///     slider for the hue value
    /// </summary>
    private Slider _hueSlider;

    /// <summary>
    ///     slider for the lightness value
    /// </summary>
    private Slider _lightnessSlider;

    /// <summary>
    ///     visual element for the response colour preview
    /// </summary>
    private VisualElement _responseColour;

    /// <summary>
    ///     function to set the initial values of the sliders
    /// </summary>
    private void Start()
    {
        _lightnessSlider.value = 74.61f;
        _chromaSlider.value = 0.0868f;
        _hueSlider.value = 335.72f;
    }

    /// <summary>
    ///     function to subscribe slider events to their respective functions
    /// </summary>
    public void OnEnable()
    {
        var ui = GetComponent<UIDocument>().rootVisualElement;

        _lightnessSlider = ui.Q<Slider>("ResponseLightnessSlider");
        _lightnessSlider.RegisterCallback<ChangeEvent<float>>(OnLightnessChange);

        _chromaSlider = ui.Q<Slider>("ResponseChromaSlider");
        _chromaSlider.RegisterCallback<ChangeEvent<float>>(OnChromaChange);

        _hueSlider = ui.Q<Slider>("ResponseHueSlider");
        _hueSlider.RegisterCallback<ChangeEvent<float>>(OnHueChange);

        _responseColour = ui.Q<VisualElement>("ResponseColour");
    }

    /// <summary>
    ///     handle lightness slider change
    /// </summary>
    /// <param name="evt">change event</param>
    private void OnLightnessChange(ChangeEvent<float> evt)
    {
        lightness = Math.Clamp(evt.newValue, 0d, 100d);
        _responseColour.style.backgroundColor = ToColor();
    }

    /// <summary>
    ///     handle chroma slider change
    /// </summary>
    /// <param name="evt">change event</param>
    private void OnChromaChange(ChangeEvent<float> evt)
    {
        chroma = Math.Clamp(evt.newValue, 0d, 0.5d);
        _responseColour.style.backgroundColor = ToColor();
    }

    /// <summary>
    ///     handle hue slider change
    /// </summary>
    /// <param name="evt">change event</param>
    private void OnHueChange(ChangeEvent<float> evt)
    {
        hue = Math.Clamp(evt.newValue, 0d, 360d);
        _responseColour.style.backgroundColor = ToColor();
    }

    /// <summary>
    ///     convert the oklch colour to a unity rgba colour object
    /// </summary>
    /// <returns>a unity rgba color object</returns>
    private Color ToColor()
    {
        // clamp values
        var cL = Math.Clamp(lightness / 100.0d, 0d, 1d);
        var cC = Math.Clamp(chroma, 0d, 0.5d);
        var cH = Math.Clamp(hue, 0d, 360d);

        // convert [OKL]Ch to [OKL]ab
        var hueRadians = cH * Math.PI / 180.0d;
        var a = cC * Math.Cos(hueRadians);
        var b = cC * Math.Sin(hueRadians);

        // bring it to linear sRGB, clip it, then bring it back to non-linear sRGB
        var lsrgb = Colorimetry.oklab_to_linear_srgb(new Colorimetry.Lab((float)cL, (float)a, (float)b));
        var clippedLsrgb = Colorimetry.gamut_clip_preserve_chroma(lsrgb);
        var srgb = new Color(
            Math.Clamp((float)Colorimetry.srgb_nonlinear_transform_f(clippedLsrgb.r), 0.0f, 1.0f),
            Math.Clamp((float)Colorimetry.srgb_nonlinear_transform_f(clippedLsrgb.g), 0.0f, 1.0f),
            Math.Clamp((float)Colorimetry.srgb_nonlinear_transform_f(clippedLsrgb.b), 0.0f, 1.0f));

        return srgb;
    }
}