using UnityEngine;

namespace NightclubArcadia.UI
{
    /// <summary>
    /// Shows and hides a UI panel *without* deactivating its GameObject.
    ///
    /// SetActive(false) is not a safe way to hide this UI. TextMeshProUGUI
    /// resolves its Canvas through Graphic.CacheCanvas, which calls
    /// GetComponentsInParent(includeInactive: false) and then requires
    /// canvas.isActiveAndEnabled. Once the Canvas GameObject has been
    /// deactivated, that lookup yields null, and TMP.GetTextInfo does:
    ///
    ///     if (m_canvas == null) m_canvas = this.canvas;   // still null
    ///     GenerateTextMesh();                             // m_canvas.worldCamera -> NRE
    ///
    /// GenerateTextMesh dereferences m_canvas unguarded, so the very next line
    /// Yarn tries to type throws NullReferenceException. Keeping the hierarchy
    /// active and driving a CanvasGroup instead means the cached Canvas
    /// reference stays valid across any number of enter/exit dialogue cycles.
    /// </summary>
    public static class PanelVisibility
    {
        /// <summary>
        /// Makes the panel visible and interactive. Returns true if the
        /// GameObject had to be re-activated (legacy scene state), in which
        /// case the caller must wait one frame before rendering text so that
        /// TMP's OnEnable can re-cache its Canvas.
        /// </summary>
        public static bool Show(GameObject panel) => SetVisible(panel, true);

        /// <summary>
        /// Hides the panel, leaving the hierarchy active. See class docs.
        /// </summary>
        public static void Hide(GameObject panel) => SetVisible(panel, false);

        static bool SetVisible(GameObject panel, bool visible)
        {
            if (panel == null)
            {
                return false;
            }

            // The UI may still be deactivated by an older saved scene state or
            // by code that predates this helper. Recover from that, and tell
            // the caller a frame of grace is needed.
            var wasReactivated = false;
            if (!panel.activeSelf)
            {
                panel.SetActive(true);
                wasReactivated = true;
            }

            var group = panel.GetComponent<CanvasGroup>();
            if (group == null)
            {
                group = panel.AddComponent<CanvasGroup>();
            }

            group.alpha = visible ? 1f : 0f;
            group.interactable = visible;
            group.blocksRaycasts = visible;

            return wasReactivated;
        }
    }
}