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

namespace Utils {
    public class EndlessTerrain : MonoBehaviour {

        public const float ViewDistance = 300;
        public Transform viewer;

        public static Vector2 ViewerPosition;
        private int _chunkSize;
        private int _chunksVisibleInViewDistance;

        private Dictionary<Vector2, TerrainChunk> _terrainChunks = new();

        private void Start() {
            _chunkSize = MapGenerator.ChunkSize - 1;
            _chunksVisibleInViewDistance = Mathf.RoundToInt(ViewDistance / _chunkSize);
        }

        private void Update() {
            ViewerPosition = new Vector2(viewer.position.x, viewer.position.z);
            UpdateVisibleChunks();
        }

        private void UpdateVisibleChunks() {
            int currentChunkCoordX = Mathf.RoundToInt(ViewerPosition.x / _chunkSize);
            int currentChunkCoordY = Mathf.RoundToInt(ViewerPosition.y / _chunkSize);

            for (int yOffset = -_chunksVisibleInViewDistance; yOffset <= _chunksVisibleInViewDistance; yOffset++)
            for (int xOffset = -_chunksVisibleInViewDistance; xOffset <= _chunksVisibleInViewDistance;) {
                Vector2 viewedChunkCoord = new Vector2(currentChunkCoordX + xOffset, currentChunkCoordY + yOffset);

                if (_terrainChunks.ContainsKey(viewedChunkCoord))
                    _terrainChunks[viewedChunkCoord].UpdateTerrainChunk();
                else
                    _terrainChunks.Add(viewedChunkCoord, new TerrainChunk(viewedChunkCoord, _chunkSize));
            }
        }
        
        private class TerrainChunk {

            public Vector2 Position;
            public GameObject MeshObject;
            public Bounds Bounds;

            public TerrainChunk(Vector2 coord, int size) {
                Position = coord * size;
                Bounds = new Bounds(Position, Vector3.one * size);
                Vector3 position = new Vector3(Position.x, 0, Position.y);
                
                MeshObject = GameObject.CreatePrimitive(PrimitiveType.Plane);
                MeshObject.transform.position = position;
                MeshObject.transform.localScale = Vector3.one * size / 10f;
                SetVisible(false);
            }

            public void UpdateTerrainChunk() {
                float viewerDistance = Mathf.Sqrt(Bounds.SqrDistance(ViewerPosition));
                bool visible = viewerDistance <= ViewDistance;
                SetVisible(visible);
            }

            public void SetVisible(bool visible) {
                MeshObject.SetActive(visible);
            }
            
        }
    }
}