using System;
using System.Runtime.InteropServices;
using UnityEngine;

namespace AOT.UI
{
    /// <summary>Offsets authored edge layouts while keeping full-screen backgrounds unchanged.</summary>
    [DisallowMultipleComponent]
    [RequireComponent(typeof(RectTransform))]
    public sealed class UiSafeArea : MonoBehaviour
    {
        RectTransform _rect;
        Vector2 _position;
        bool _captured;
        static readonly float[] NativeInsets = new float[4];
        static int _frame = -1;
        static Vector4 _insets;
        static float _nextRead;
        static int _width, _height;
#if UNITY_EDITOR
        static Vector4? _preview;
        public static void SetPreviewInsets(Vector4? value) { _preview = value; _frame = -1; }
#endif
#if UNITY_WEBGL && !UNITY_EDITOR
        [DllImport("__Internal")] static extern int AIGame_GetUiSafeInsets([Out] float[] values);
#endif

        void OnEnable()
        {
            _rect = (RectTransform)transform;
            _position = _rect.anchoredPosition;
            _captured = true;
            Apply(CurrentInsets());
        }

        void OnDisable()
        {
            if (_captured && _rect != null) _rect.anchoredPosition = _position;
            _captured = false;
        }

        void LateUpdate() => Apply(CurrentInsets());

        void Apply(Vector4 inset)
        {
            if (!_captured || !(_rect.parent is RectTransform parent)) return;
            Vector2 delta = Vector2.zero;
            if (Mathf.Approximately(_rect.anchorMin.y, 1) && Mathf.Approximately(_rect.anchorMax.y, 1))
                delta.y = -parent.rect.height * inset.w;
            else if (Mathf.Approximately(_rect.anchorMin.y, 0) && Mathf.Approximately(_rect.anchorMax.y, 0))
                delta.y = parent.rect.height * inset.y;
            delta.x = parent.rect.width * (inset.x - inset.z) * .5f;
            _rect.anchoredPosition = _position + delta;
        }

        public static Vector4 NormalizeSafeArea(int width, int height, Rect safe)
        {
            if (width <= 0 || height <= 0 || safe.width <= 0 || safe.height <= 0) return Vector4.zero;
            return Clamp(new Vector4(safe.xMin / width, safe.yMin / height,
                1f - safe.xMax / width, 1f - safe.yMax / height));
        }

        static Vector4 CurrentInsets()
        {
            if (_frame == Time.frameCount) return _insets;
            _frame = Time.frameCount;
#if UNITY_EDITOR
            if (_preview.HasValue) return _insets = Clamp(_preview.Value);
#endif
            if (Time.unscaledTime < _nextRead && _width == Screen.width && _height == Screen.height) return _insets;
            _width = Screen.width; _height = Screen.height;
            _nextRead = Time.unscaledTime + .25f;
            _insets = NormalizeSafeArea(Screen.width, Screen.height, Screen.safeArea);
#if UNITY_WEBGL && !UNITY_EDITOR
            if (AIGame_GetUiSafeInsets(NativeInsets) != 0)
                _insets = Vector4.Max(_insets, Clamp(new Vector4(NativeInsets[0], NativeInsets[1], NativeInsets[2], NativeInsets[3])));
#endif
            return _insets;
        }

        static Vector4 Clamp(Vector4 value) => new Vector4(Valid(value.x), Valid(value.y), Valid(value.z), Valid(value.w));
        static float Valid(float value) => float.IsNaN(value) || float.IsInfinity(value) ? 0 : Mathf.Clamp(value, 0, .35f);
    }
}