using UnityEngine;
using UnityEngine.UIElements;

namespace Uigenx
{
    /// <summary>
    /// Keeps its content inside <see cref="Screen.safeArea"/> by padding itself. Screen space is
    /// bottom left origin and UI Toolkit is top left, so the vertical insets are swapped here.
    /// </summary>
    [UxmlElement]
    public partial class SafeAreaRoot : VisualElement
    {
        public const string UssClassName = "ugx-safe-area-root";

        /// <summary>How often the safe area is re-read, in milliseconds. Rotation has no event.</summary>
        public const long PollIntervalMs = 500;

        [UxmlAttribute("apply-safe-area")]
        public bool ApplySafeArea
        {
            get => _applySafeArea;
            set
            {
                if (_applySafeArea == value) return;
                _applySafeArea = value;
                if (!_applySafeArea) ClearPadding();
                else Apply();
            }
        }

        bool _applySafeArea = true;
        Rect _lastSafeArea;
        int _lastScreenWidth;
        int _lastScreenHeight;
        float _lastWidth;
        float _lastHeight;
        IVisualElementScheduledItem _poll;

        public SafeAreaRoot()
        {
            AddToClassList(UssClassName);
            style.flexGrow = 1f;
            RegisterCallback<GeometryChangedEvent>(OnGeometryChanged);
            RegisterCallback<AttachToPanelEvent>(OnAttach);
            RegisterCallback<DetachFromPanelEvent>(OnDetach);
        }

        void OnAttach(AttachToPanelEvent evt)
        {
            _poll = schedule.Execute(Apply).Every(PollIntervalMs);
            Apply();
        }

        void OnDetach(DetachFromPanelEvent evt)
        {
            _poll?.Pause();
            _poll = null;
        }

        void OnGeometryChanged(GeometryChangedEvent evt) => Apply();

        void Apply()
        {
            if (!_applySafeArea) return;

            int screenWidth = Screen.width;
            int screenHeight = Screen.height;
            if (screenWidth <= 0 || screenHeight <= 0) return;

            float width = resolvedStyle.width;
            float height = resolvedStyle.height;
            if (float.IsNaN(width) || float.IsNaN(height) || width <= 0f || height <= 0f) return;

            var safe = Screen.safeArea;
            // Re-applying padding triggers another geometry pass, so nothing is written when the
            // inputs are unchanged.
            if (safe == _lastSafeArea && screenWidth == _lastScreenWidth && screenHeight == _lastScreenHeight &&
                Mathf.Approximately(width, _lastWidth) && Mathf.Approximately(height, _lastHeight)) return;

            _lastSafeArea = safe;
            _lastScreenWidth = screenWidth;
            _lastScreenHeight = screenHeight;
            _lastWidth = width;
            _lastHeight = height;

            style.paddingLeft = width * Mathf.Clamp01(safe.xMin / screenWidth);
            style.paddingRight = width * Mathf.Clamp01((screenWidth - safe.xMax) / screenWidth);
            style.paddingTop = height * Mathf.Clamp01((screenHeight - safe.yMax) / screenHeight);
            style.paddingBottom = height * Mathf.Clamp01(safe.yMin / screenHeight);
        }

        void ClearPadding()
        {
            _lastSafeArea = default;
            _lastScreenWidth = 0;
            _lastScreenHeight = 0;
            style.paddingLeft = 0f;
            style.paddingRight = 0f;
            style.paddingTop = 0f;
            style.paddingBottom = 0f;
        }
    }
}