@typeparam TNode

@*
 *                                dbMango
 *
 * Copyright 2025 Deutsche Bank AG
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *@

<!-- A very basic hierarchical tree control. Allows the user to expand/contract nodes and select a single node. 
    The control provides callbacks for the user to specify to control how each of these features map to the underlying data model
    The title template is supplied by the user which specifies how to draw each node
-->
<div class="uic-tree">

    @foreach (var node in Nodes.Where(x => x != null ))
    {
        var nodeExpanded = Handler.IsExpanded(node);
        var nodeSelected = ReferenceEquals(Handler.GetSelectedNode(), node) || (node?.Equals(Handler.GetSelectedNode()) ?? false);
        var children          = Handler.ChildSelector(node);
        var hasChildren = children?.Any() ?? false;

        <div class="uic-tree-row">
        @if (hasChildren)
        {
            <span class="uic-tree-icon" @onclick="@(() => OnToggleNode(node, !nodeExpanded))">
                <i class="@(nodeExpanded ? Style.CollapseNodeIconClass : Style.ExpandNodeIconClass)"></i>
            </span>
        }

        <div class="uic-tree-title">
            <span class="@Style.NodeTitleClass @(nodeSelected ? Style.NodeTitleSelectedClass : "")" @onclick="@(() => OnSelectNode(node))">
                @if (TitleTemplate == null)
                {
                    @node?.ToString()
                }
                else
                {
                    @TitleTemplate(node)
                }
            </span>
    </div>

        @if (hasChildren && nodeExpanded)
        {
            <TreeControl 
                Nodes="@children"
                Handler="@Handler"
                TitleTemplate="@TitleTemplate"
                AutoExpandTransientNodes="@AutoExpandTransientNodes" 
                Style="@Style"
                />
        }

    </div>
    }

</div>

@code {

    public class TreeItemHandler
    {
        public Func<TNode?>                            GetSelectedNode { get; init; } = () => default;
        public Action<TNode>                           SetSelectedNode { get; init; } = _ => {};
        public Func<TNode, IReadOnlyCollection<TNode>> ChildSelector   { get; init; } = _ => Array.Empty<TNode>();
        public Func<TNode, bool>                       IsExpanded      { get; init; } = _ => true;
        public Func<TNode, bool>                       IsSelectable    { get; init; } = _ => true;
        public Action<TNode, bool>                     SetIsExpanded   { get; init; } = (_, _) => {/*do nothing*/};

    }

    [Parameter] public IReadOnlyCollection<TNode> Nodes                    { get; set; } = [];
    [Parameter] public TreeItemHandler            Handler                  { get; set; } = new();
    [Parameter] public RenderFragment<TNode>?     TitleTemplate            { get; set; }
    [Parameter] public bool                       AutoExpandTransientNodes { get; set; } = true;
    [Parameter] public TreeStyle                  Style                    { get; set; } = TreeStyle.Bootstrap;

    public class TreeStyle
    {
        public static readonly TreeStyle Bootstrap = new()
        {
            ExpandNodeIconClass    = "ui-icon-font icon-caret-right cursor-pointer",
            CollapseNodeIconClass  = "ui-icon-font icon-caret-down cursor-pointer",
            NodeTitleClass         = "list-group-item uic-tree-title_text cursor-pointer",
            NodeTitleSelectedClass = "active"
        };

        public string? ExpandNodeIconClass    { get; set; }
        public string? CollapseNodeIconClass  { get; set; }
        public string? NodeTitleClass         { get; set; }
        public string? NodeTitleSelectedClass { get; set; }

    }


    private void OnToggleNode(TNode node, bool expand)
    {
        var expanded = Handler.IsExpanded(node);

        if (expanded && !expand)
        {
            Handler.SetIsExpanded(node, false);
        }
        else if (!expanded && expand)
        {
            Handler.SetIsExpanded(node, true);
            ExpandTransientChildren( node );
        }
    }

    ///Auto expand child nodes when there is only 1 child
    private void ExpandTransientChildren( TNode node )
    {
        if ( !AutoExpandTransientNodes )
            return;

        while (Handler.ChildSelector(node)?.Count > 0)
        {
            var children = Handler.ChildSelector( node ) ?? Array.Empty<TNode>();

            if ( children.Count != 1 )
                return;

            var first = children.FirstOrDefault();
            if (first == null || Handler.IsExpanded( first ) )
                return;

            Handler.SetIsExpanded(first, true);
            node = first;
        }
    }

    private void OnSelectNode(TNode node)
    {
        if (!Handler.IsSelectable(node))
            return;

        Handler.SetSelectedNode(node);
    }
}