using UnityEngine;
using UnityEngine.UI;

namespace Vanguard.UI
{
    /// <summary>
    /// Фон Lobby: процедурный тёмно-синий градиент с сеткой, центральным
    /// свечением и виньеткой. Кешируется как один спрайт; когда появится
    /// key art, достаточно заменить источник изображения.
    /// </summary>
    public static class LobbyBackdrop
    {
        public const string RootName = "LobbyBackdrop";

        private static Sprite _sprite;

        public static RectTransform Create(Transform parent)
        {
            var go = new GameObject(RootName, typeof(RectTransform), typeof(Image));
            var rect = (RectTransform)go.transform;
            rect.SetParent(parent, false);
            UiKit.Stretch(rect);
            rect.SetAsFirstSibling();

            var image = go.GetComponent<Image>();
            image.sprite = Sprite();
            image.type = Image.Type.Simple;
            image.preserveAspect = false;
            image.raycastTarget = false;

            return rect;
        }

        private static Sprite Sprite()
        {
            if (_sprite != null)
                return _sprite;

            const int width = 512;
            const int height = 288;
            var pixels = new Color32[width * height];

            var top = new Color(0.010f, 0.026f, 0.070f);
            var middle = new Color(0.017f, 0.055f, 0.135f);
            var bottom = new Color(0.006f, 0.016f, 0.045f);
            var glow = new Color(0.06f, 0.26f, 0.62f);
            var grid = new Color(0.16f, 0.46f, 0.92f);

            for (var y = 0; y < height; y++)
            {
                var v = y / (float)(height - 1);
                var baseColor = v < 0.55f
                    ? Color.Lerp(bottom, middle, v / 0.55f)
                    : Color.Lerp(middle, top, (v - 0.55f) / 0.45f);

                for (var x = 0; x < width; x++)
                {
                    var u = x / (float)(width - 1);
                    var color = baseColor;

                    // Мягкое пятно света над центром сцены.
                    var dx = (u - 0.5f) * 2f;
                    var dy = (v - 0.62f) * 2.2f;
                    var distance = Mathf.Sqrt(dx * dx + dy * dy);
                    var light = Mathf.Clamp01(1f - distance / 1.15f);
                    color += glow * (light * light * 0.16f);

                    // Сетка с шагом 32 px по текстуре.
                    if (x % 32 == 0 || y % 32 == 0)
                        color += grid * 0.035f;

                    // Виньетка по краям.
                    var vignette = Mathf.Clamp01(
                        (Mathf.Abs(dx) * 0.55f + Mathf.Abs(v - 0.5f) * 1.1f - 0.35f) / 0.65f);
                    color = Color.Lerp(color, new Color(0f, 0f, 0f), vignette * 0.55f);
                    color.a = 1f;

                    pixels[y * width + x] = color;
                }
            }

            var texture = new Texture2D(width, height, TextureFormat.RGBA32, false)
            {
                hideFlags = HideFlags.DontSave,
                wrapMode = TextureWrapMode.Clamp,
                filterMode = FilterMode.Bilinear,
                name = "LobbyBackdrop",
            };
            texture.SetPixels32(pixels);
            texture.Apply(false, false);

            _sprite = UnityEngine.Sprite.Create(
                texture,
                new Rect(0f, 0f, width, height),
                new Vector2(0.5f, 0.5f),
                100f,
                0,
                SpriteMeshType.FullRect);
            _sprite.name = "LobbyBackdrop";
            _sprite.hideFlags = HideFlags.DontSave;
            return _sprite;
        }
    }
}