using System;
using UnityEngine;
using UnityEngine.UI;

/// <summary>
/// Compact runtime HSV colour picker: a saturation/value square, a hue bar and a live
/// swatch. Builds its own UI as children when <see cref="Build"/> is called and raises
/// <see cref="Changed"/> on user interaction. The square is a pure-hue base with two
/// static gradient overlays on top (white-out -> saturation, black-out -> value), so
/// only the base tint changes per hue - no per-frame texture rebuilds. Hue is never
/// lost while dragging the square (the square only edits S/V, the bar only edits H).
/// </summary>
public class HsvColorPicker : MonoBehaviour
{
    /// <summary>Raised with the new colour when the user moves the square or hue bar.</summary>
    public event Action<Color> Changed;

    private float _h, _s, _v, _a = 1f;

    private Image _hueBase;          // pure-hue background of the SV square
    private RectTransform _svHandle;
    private RectTransform _hueHandle;
    private Image _swatch;

    /// <summary>Current colour (HSV -> RGB, with the preserved alpha).</summary>
    public Color Value
    {
        get
        {
            Color c = Color.HSVToRGB(_h, _s, _v);
            c.a = _a;
            return c;
        }
    }

    /// <summary>Shows <paramref name="c"/> without raising <see cref="Changed"/> (external set).</summary>
    public void SetColor(Color c)
    {
        Color.RGBToHSV(c, out _h, out _s, out _v);
        _a = c.a;
        Refresh();
    }

    /// <summary>Builds the picker (square + hue bar + swatch) under this object, top-left aligned.</summary>
    public void Build(float squareSize, float hueHeight)
    {
        // Saturation / value square: base hue + two gradient overlays, top-left of this rect.
        var sv = PaintHud.NewRect("SV", transform);
        TopLeft(sv, new Vector2(0f, 0f), new Vector2(squareSize, squareSize));
        _hueBase = PaintHud.AddImage(sv.gameObject, Color.red); // raycast target for the drag relay

        PaintHud.AddOverlay(sv, PaintHud.SaturationSprite());
        PaintHud.AddOverlay(sv, PaintHud.ValueSprite());

        sv.gameObject.AddComponent<UiPointerSurface>().Picked += OnSvPicked;

        _svHandle = PaintHud.NewRect("Handle", sv);
        _svHandle.sizeDelta = new Vector2(12f, 12f);
        var svHandleImg = PaintHud.AddImage(_svHandle.gameObject, Color.white);
        svHandleImg.raycastTarget = false;

        // Hue bar below the square.
        var hue = PaintHud.NewRect("Hue", transform);
        TopLeft(hue, new Vector2(0f, -(squareSize + 6f)), new Vector2(squareSize, hueHeight));
        var hueImg = hue.gameObject.AddComponent<Image>();
        hueImg.sprite = PaintHud.HueSprite();
        hueImg.type = Image.Type.Simple;

        hue.gameObject.AddComponent<UiPointerSurface>().Picked += OnHuePicked;

        _hueHandle = PaintHud.NewRect("Handle", hue);
        _hueHandle.sizeDelta = new Vector2(4f, hueHeight + 4f);
        var hueHandleImg = PaintHud.AddImage(_hueHandle.gameObject, Color.white);
        hueHandleImg.raycastTarget = false;

        // Swatch, to the right of the square.
        var sw = PaintHud.NewRect("Swatch", transform);
        TopLeft(sw, new Vector2(squareSize + 10f, 0f), new Vector2(34f, 34f));
        _swatch = PaintHud.AddImage(sw.gameObject, Color.white);
        _swatch.raycastTarget = false;

        Refresh();
    }

    private void OnSvPicked(Vector2 p)
    {
        _s = p.x;
        _v = p.y;
        Refresh();
        Changed?.Invoke(Value);
    }

    private void OnHuePicked(Vector2 p)
    {
        _h = p.x;
        Refresh();
        Changed?.Invoke(Value);
    }

    private void Refresh()
    {
        if (_hueBase) _hueBase.color = Color.HSVToRGB(_h, 1f, 1f);
        if (_svHandle)
        {
            _svHandle.anchorMin = _svHandle.anchorMax = new Vector2(_s, _v);
            _svHandle.anchoredPosition = Vector2.zero;
        }
        if (_hueHandle)
        {
            _hueHandle.anchorMin = _hueHandle.anchorMax = new Vector2(_h, 0.5f);
            _hueHandle.anchoredPosition = Vector2.zero;
        }
        if (_swatch) _swatch.color = Color.HSVToRGB(_h, _s, _v);
    }

    /// <summary>Anchors a child to this rect's top-left corner with the given offset and size.</summary>
    private static void TopLeft(RectTransform rt, Vector2 offset, Vector2 size)
    {
        rt.anchorMin = rt.anchorMax = new Vector2(0f, 1f);
        rt.pivot = new Vector2(0f, 1f);
        rt.anchoredPosition = offset;
        rt.sizeDelta = size;
    }
}