#if UNITY_EDITOR
#if UNITY_2019_1_OR_NEWER
#define UI_USE_FOLDOUT_HEADER_2019
#endif

using UnityEditor;
using UnityEngine;
using System.Collections.Generic;
using System;

namespace VLB
{
    public static class FoldableHeader
    {
        public static void OnEnable()
        {
            ms_CurrentFoldableHeader = null;
        }

        public static bool Begin(UnityEngine.Object self, string label)
        {
            return Begin(self, new GUIContent(label));
        }

        public static bool Begin(UnityEngine.Object self, GUIContent label)
        {
            var uniqueString = label.text;
            if(self) uniqueString = self.ToString() + uniqueString;

            if (ms_StyleHeaderFoldable == null)
            {
                ms_StyleHeaderFoldable = new GUIStyle(EditorStyles.foldout);
                ms_StyleHeaderFoldable.fontStyle = FontStyle.Bold;
            }

            ms_CurrentFoldableHeader = uniqueString;

            bool folded = IsFolded(uniqueString);


#if UI_USE_FOLDOUT_HEADER_2019
            folded = !EditorGUILayout.BeginFoldoutHeaderGroup(!folded, label);
#else
            folded = !EditorGUILayout.Foldout(!folded, label, toggleOnLabelClick: true, style: ms_StyleHeaderFoldable);
#endif

            if (folded) ms_FoldedHeaders.Add(uniqueString);
            else ms_FoldedHeaders.Remove(uniqueString);

            return !folded;
        }

        public static void End()
        {
            Debug.Assert(ms_CurrentFoldableHeader != null, "Trying to call FoldableHeader.End() but there is no header opened");
            bool isFolded = IsFolded(ms_CurrentFoldableHeader);
            ms_CurrentFoldableHeader = null;

#if UI_USE_FOLDOUT_HEADER_2019
            EditorGUILayout.EndFoldoutHeaderGroup();
#if UNITY_2019_3_OR_NEWER
            if(!isFolded) EditorGUILayout.Separator();
#endif
#else
            EditorExtensions.DrawLineSeparator();
#endif
        }

        static bool IsFolded(string uniqueString) { return ms_FoldedHeaders.Contains(uniqueString); }

        static string ms_CurrentFoldableHeader = null;
        static HashSet<String> ms_FoldedHeaders = new HashSet<String>();
        static GUIStyle ms_StyleHeaderFoldable = null;
    }
}
#endif // UNITY_EDITOR