using System.Collections.Generic;
using System.Linq;
using Spectre.Console.Rendering;

namespace Spectre.Console
{
    /// <summary>
    /// Representation of non-circular tree data.
    /// Each node added to the tree may only be present in it a single time, in order to facilitate cycle detection.
    /// </summary>
    public sealed class Tree : Renderable, IHasTreeNodes
    {
        private readonly TreeNode _root;

        /// <summary>
        /// Gets or sets the tree style.
        /// </summary>
        public Style? Style { get; set; }

        /// <summary>
        ///  Gets or sets the tree guide lines.
        /// </summary>
        public TreeGuide Guide { get; set; } = TreeGuide.Line;

        /// <summary>
        /// Gets the tree's child nodes.
        /// </summary>
        public List<TreeNode> Nodes => _root.Nodes;

        /// <summary>
        /// Gets or sets a value indicating whether or not the tree is expanded or not.
        /// </summary>
        public bool Expanded { get; set; } = true;

        /// <summary>
        /// Initializes a new instance of the <see cref="Tree"/> class.
        /// </summary>
        /// <param name="renderable">The tree label.</param>
        public Tree(IRenderable renderable)
        {
            _root = new TreeNode(renderable);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Tree"/> class.
        /// </summary>
        /// <param name="label">The tree label.</param>
        public Tree(string label)
        {
            _root = new TreeNode(new Markup(label));
        }

        /// <inheritdoc />
        protected override IEnumerable<Segment> Render(RenderContext context, int maxWidth)
        {
            var result = new List<Segment>();
            var visitedNodes = new HashSet<TreeNode>();

            var stack = new Stack<Queue<TreeNode>>();
            stack.Push(new Queue<TreeNode>(new[] { _root }));

            var levels = new List<Segment>();
            levels.Add(GetGuide(context, TreeGuidePart.Continue));

            while (stack.Count > 0)
            {
                var stackNode = stack.Pop();
                if (stackNode.Count == 0)
                {
                    levels.RemoveLast();
                    if (levels.Count > 0)
                    {
                        levels.AddOrReplaceLast(GetGuide(context, TreeGuidePart.Fork));
                    }

                    continue;
                }

                var isLastChild = stackNode.Count == 1;
                var current = stackNode.Dequeue();
                if (!visitedNodes.Add(current))
                {
                    throw new CircularTreeException("Cycle detected in tree - unable to render.");
                }

                stack.Push(stackNode);

                if (isLastChild)
                {
                    levels.AddOrReplaceLast(GetGuide(context, TreeGuidePart.End));
                }

                var prefix = levels.Skip(1).ToList();
                var renderableLines = Segment.SplitLines(current.Renderable.Render(context, maxWidth - Segment.CellCount(prefix)));

                foreach (var (_, isFirstLine, _, line) in renderableLines.Enumerate())
                {
                    if (prefix.Count > 0)
                    {
                        result.AddRange(prefix.ToList());
                    }

                    result.AddRange(line);
                    result.Add(Segment.LineBreak);

                    if (isFirstLine && prefix.Count > 0)
                    {
                        var part = isLastChild ? TreeGuidePart.Space : TreeGuidePart.Continue;
                        prefix.AddOrReplaceLast(GetGuide(context, part));
                    }
                }

                if (current.Expanded && current.Nodes.Count > 0)
                {
                    levels.AddOrReplaceLast(GetGuide(context, isLastChild ? TreeGuidePart.Space : TreeGuidePart.Continue));
                    levels.Add(GetGuide(context, current.Nodes.Count == 1 ? TreeGuidePart.End : TreeGuidePart.Fork));

                    stack.Push(new Queue<TreeNode>(current.Nodes));
                }
            }

            return result;
        }

        private Segment GetGuide(RenderContext context, TreeGuidePart part)
        {
            var guide = Guide.GetSafeTreeGuide(safe: !context.Unicode);
            return new Segment(guide.GetPart(part), Style ?? Style.Plain);
        }
    }
}