using System.Collections.Generic;
using UnityEngine;

namespace MazeGen
{
    /// <summary>
    /// Draws the agent's traveled path (start room -> current room) as a line, one segment
    /// per hop. Only the most recently added hop is drawn bright; every earlier hop is
    /// dimmed down so the eye is drawn to where the agent is right now, not the whole trail.
    /// </summary>
    [RequireComponent(typeof(LineRenderer))]
    public class PathVisualizer : MonoBehaviour
    {
        private static readonly Color BrightColor = new Color(1f, 0.1f, 0.75f);
        private static readonly Color DimColor = new Color(0.55f, 0.2f, 0.4f, 0.35f);
        private const float LineWidth = 0.15f;

        private readonly List<LineRenderer> _segments = new List<LineRenderer>();
        private Vector3? _lastPoint;
        private Material _lineMaterial;

        private void Awake()
        {
            // The LineRenderer required on this GameObject itself is left unused/empty -
            // each hop gets its own child LineRenderer so it can be colored independently.
            GetComponent<LineRenderer>().positionCount = 0;
            _lineMaterial = new Material(Shader.Find("Sprites/Default"));
        }

        public void AppendPoint(Vector2 worldPos)
        {
            Vector3 point = new Vector3(worldPos.x, worldPos.y, -0.5f);

            if (_lastPoint.HasValue)
            {
                DimExistingSegments();
                _segments.Add(CreateSegment(_lastPoint.Value, point));
            }

            _lastPoint = point;
        }

        private void DimExistingSegments()
        {
            foreach (var segment in _segments)
            {
                segment.startColor = DimColor;
                segment.endColor = DimColor;
            }
        }

        private LineRenderer CreateSegment(Vector3 a, Vector3 b)
        {
            var segmentGO = new GameObject("PathSegment");
            segmentGO.transform.SetParent(transform, false);

            var line = segmentGO.AddComponent<LineRenderer>();
            line.positionCount = 2;
            line.SetPositions(new[] { a, b });
            line.widthMultiplier = LineWidth;
            line.useWorldSpace = true;
            line.sortingOrder = 2;
            line.material = _lineMaterial;
            line.startColor = BrightColor;
            line.endColor = BrightColor;
            return line;
        }

        public void Clear()
        {
            foreach (var segment in _segments)
                if (segment != null) Destroy(segment.gameObject);

            _segments.Clear();
            _lastPoint = null;
        }
    }
}