using System.Collections.Generic;
using Luneraria.Core;
using UnityEngine;

namespace Luneraria.View
{
    /// <summary>
    /// S4 fog of war in the terrain: a grid over the map (2 m cells) that follows the ground and
    /// darkens every point no vision source of the viewer's team reaches (LuneFog.Vision: own
    /// units 9 m, own buildings 10 m, wards 12 m). The alpha has a soft 2 m edge and is
    /// recomputed ten times a second. Presentation only; the rules never read it.
    /// </summary>
    public sealed class LuneFogOverlay : MonoBehaviour
    {
        public const float Cell = 2f;
        public const float Darkness = .55f;
        public const float Edge = 2f;
        public const float Interval = .1f;

        Mesh _mesh;
        Vec2[] _points;
        Color32[] _colors;
        float _timer;

        /// <summary>Darkness of every grid point (0 = seen), for tests.</summary>
        public float[] Alpha { get; private set; }
        public int Refreshes { get; private set; }

        public void Build(LuneGround ground, Material material)
        {
            int side = Mathf.CeilToInt((float)(LuneMap.HalfExtent * 2.0) / Cell) + 1;
            var vertices = new Vector3[side * side];
            _points = new Vec2[side * side];
            for (int row = 0; row < side; row++)
            {
                for (int column = 0; column < side; column++)
                {
                    var map = new Vec2(-LuneMap.HalfExtent + column * Cell, -LuneMap.HalfExtent + row * Cell);
                    float height = ground != null ? ground.StandHeight(map) : 0f;
                    _points[row * side + column] = map;
                    vertices[row * side + column] = LuneSpace.World(map, height + .45f);
                }
            }
            var triangles = new List<int>();
            for (int row = 0; row + 1 < side; row++)
            {
                for (int column = 0; column + 1 < side; column++)
                {
                    int a = row * side + column;
                    triangles.AddRange(new[] { a, a + side, a + 1, a + 1, a + side, a + side + 1 });
                }
            }
            _colors = new Color32[vertices.Length];
            Alpha = new float[vertices.Length];
            _mesh = new Mesh { name = "FogOverlay", indexFormat = UnityEngine.Rendering.IndexFormat.UInt32 };
            _mesh.SetVertices(vertices);
            _mesh.SetTriangles(triangles, 0);
            _mesh.SetColors(_colors);
            _mesh.RecalculateBounds();
            gameObject.AddComponent<MeshFilter>().sharedMesh = _mesh;
            var renderer = gameObject.AddComponent<MeshRenderer>();
            renderer.sharedMaterial = material;
            renderer.shadowCastingMode = UnityEngine.Rendering.ShadowCastingMode.Off;
            renderer.receiveShadows = false;
        }

        /// <summary>Recomputes the darkness at most every Interval seconds (force: now).</summary>
        public void Tick(float dt, List<KeyValuePair<Vec2, double>> sources, bool force = false)
        {
            _timer -= dt;
            if (!force && _timer > 0f)
                return;
            _timer = Interval;
            Refreshes++;
            for (int i = 0; i < _points.Length; i++)
            {
                double best = double.PositiveInfinity;
                foreach (KeyValuePair<Vec2, double> source in sources)
                {
                    double gap = _points[i].DistanceTo(source.Key) - source.Value;
                    if (gap < best)
                        best = gap;
                }
                float t = Mathf.Clamp01((float)(best + Edge * .5) / Edge);
                Alpha[i] = Darkness * t;
                _colors[i] = new Color32(0, 0, 0, (byte)Mathf.RoundToInt(Alpha[i] * 255f));
            }
            _mesh.SetColors(_colors);
        }
    }
}