using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;

namespace BriarQueen.UI.Menus.Components
{
    public class UnderlineButtonGroup : MonoBehaviour
    {
        [Header("Buttons")]
        [SerializeField] private UnderlineButton[] _initialButtons = Array.Empty<UnderlineButton>();

        [SerializeField] private int  _defaultSelectedIndex;
        [SerializeField] private bool _selectDefaultOnEnable    = true;
        [SerializeField] private bool _syncEventSystemSelection = true;

        // Runtime list — combines inspector-assigned and dynamically added buttons
        private readonly List<UnderlineButton> _buttons = new();

        public UnderlineButton Current        { get; private set; }
        public UnderlineButton CurrentHovered { get; private set; }

        private void Reset()
        {
            _initialButtons = GetComponentsInChildren<UnderlineButton>(true);
        }

        private void OnEnable()
        {
            // Register inspector-assigned buttons first
            foreach (var button in _initialButtons)
                AddButton(button);

            if (_selectDefaultOnEnable && _buttons.Count > 0)
                SelectIndex(_defaultSelectedIndex, instant: true);
        }

        private void OnDisable()
        {
            // Remove all — clears both initial and runtime-added buttons
            for (var i = _buttons.Count - 1; i >= 0; i--)
                RemoveButton(_buttons[i]);

            CurrentHovered = null;
            Current        = null;
        }

        // ── Public API ────────────────────────────────────────────────

        /// <summary>
        /// Registers a button with the group at runtime.
        /// Safe to call multiple times — ignores already-registered buttons.
        /// </summary>
        public void AddButton(UnderlineButton button)
        {
            if (button == null || _buttons.Contains(button)) return;

            _buttons.Add(button);
            button.RegisterGroup(this);
            button.SelectionRequested += HandleSelectionRequested;
            button.HoverEntered       += HandleHoverEntered;
            button.HoverExited        += HandleHoverExited;
        }

        /// <summary>
        /// Unregisters a button from the group.
        /// Safe to call on buttons not in the group.
        /// </summary>
        public void RemoveButton(UnderlineButton button)
        {
            if (button == null || !_buttons.Contains(button)) return;

            // If this was the selected or hovered button, clear those references
            if (Current == button)        Current        = null;
            if (CurrentHovered == button) CurrentHovered = null;

            button.UnregisterGroup();
            button.SelectionRequested -= HandleSelectionRequested;
            button.HoverEntered       -= HandleHoverEntered;
            button.HoverExited        -= HandleHoverExited;
            button.SetUnderline(false);
            button.SetSelectedState(false);

            _buttons.Remove(button);

            RefreshAllButtonStates();
        }

        /// <summary>Removes all dynamically added buttons, leaving inspector-assigned ones.</summary>
        public void RemoveAllDynamicButtons()
        {
            for (var i = _buttons.Count - 1; i >= 0; i--)
            {
                var button = _buttons[i];
                if (button == null) continue;

                // Skip buttons that were assigned in the inspector
                var isInitial = System.Array.IndexOf(_initialButtons, button) >= 0;
                if (isInitial) continue;

                RemoveButton(button);
            }
        }

        public void SelectIndex(int index, bool instant = false)
        {
            if (_buttons == null || _buttons.Count == 0) return;
            SelectButton(_buttons[Mathf.Clamp(index, 0, _buttons.Count - 1)], instant);
        }

        public void SelectButton(UnderlineButton button, bool instant = false)
        {
            if (button == null) return;
            if (Current == button && !instant) return;

            Current = button;
            RefreshAllButtonStates();
            SyncEventSystemSelection(button);
        }

        public void ClearSelection()
        {
            Current = null;
            RefreshAllButtonStates();
        }

        // ── Internal ──────────────────────────────────────────────────

        private void RefreshAllButtonStates()
        {
            foreach (var button in _buttons)
            {
                if (button == null) continue;

                var isSelected = button == Current;
                var isHovered  = button == CurrentHovered;

                var showUnderline = isSelected
                    ? CurrentHovered == null || isHovered
                    : isHovered;

                button.SetSelectedState(isSelected);
                button.SetUnderline(showUnderline);
            }
        }

        private void HandleSelectionRequested(UnderlineButton button)
        {
            SelectButton(button);
        }

        private void HandleHoverEntered(UnderlineButton button)
        {
            CurrentHovered = button;
            RefreshAllButtonStates();
        }

        private void HandleHoverExited(UnderlineButton button)
        {
            if (CurrentHovered == button)
                CurrentHovered = null;

            RefreshAllButtonStates();
        }

        private void SyncEventSystemSelection(UnderlineButton button)
        {
            if (!_syncEventSystemSelection || EventSystem.current == null) return;

            var go = button.GetSelectableGameObject();
            if (go == null || EventSystem.current.currentSelectedGameObject == go) return;
            EventSystem.current.SetSelectedGameObject(go);
        }
    }
}