using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using System;

namespace SemiColinGames {
  class LinesOfSight {
    public static void Draw(Player player, AABB[] collisionTargets, GraphicsDevice graphics,
        BasicEffect lightingEffect) {
      // TODO: DrawIndexedPrimitives
      Color color = Color.FromNonPremultiplied(new Vector4(0, 0, 1, 0.6f));
      Vector2 eyePos = player.EyePosition;
      int numConePoints = 60;
      // TODO: don't new[] every frame.
      VertexPositionColor[] conePoints = new VertexPositionColor[numConePoints];
      float visionRange = 150;
      float visionRangeSq = visionRange * visionRange;
      float fov = FMath.DegToRad(120);
      float fovStep = fov / (numConePoints - 1);

      Vector2 ray = new Vector2(visionRange * player.GetFacing, 0);
      if (player.GetPose == Player.Pose.Stretching) {
        ray = ray.Rotate(player.GetFacing * FMath.DegToRad(-30));
      }
      if (player.GetPose == Player.Pose.Crouching) {
        ray = ray.Rotate(player.GetFacing * FMath.DegToRad(30));
      }

      for (int i = 0; i < conePoints.Length; i++) {
        float angle = -fov / 2 + fovStep * i;
        Vector2 rotated = ray.Rotate(angle);
        Vector2 closestHit = Vector2.Add(eyePos, rotated);
        float hitTime = 1f;

        Vector2 halfTileSize = new Vector2(World.TileSize / 2.0f, World.TileSize / 2.0f);
        for (int j = 0; j < collisionTargets.Length; j++) {
          AABB box = collisionTargets[j];
          if (Math.Abs(box.Position.X - player.Position.X) > visionRange + halfTileSize.X) {
            continue;
          }
          Vector2 delta = Vector2.Add(halfTileSize, Vector2.Subtract(box.Position, eyePos));
          if (delta.LengthSquared() > visionRangeSq) {
            continue;
          }
          Hit? maybeHit = box.IntersectSegment(eyePos, rotated);
          if (maybeHit != null) {
            Hit hit = maybeHit.Value;
            if (hit.Time < hitTime) {
              hitTime = hit.Time;
              closestHit = hit.Position;
            }
          }
        }

        float tint = 0.6f - hitTime / 2;
        Color tinted = Color.FromNonPremultiplied(new Vector4(0, 0, 1, tint));
        conePoints[i] = new VertexPositionColor(new Vector3(closestHit, 0), tinted);
      }

      // TODO: don't new[] every frame.
      VertexPositionColor[] vertices = new VertexPositionColor[numConePoints * 3];
      VertexPositionColor eyeVertex = new VertexPositionColor(new Vector3(eyePos, 0), color);
      for (int i = 0; i < numConePoints - 1; i++) {
        vertices[i * 3] = eyeVertex;
        vertices[i * 3 + 1] = conePoints[i];
        vertices[i * 3 + 2] = conePoints[i + 1];
      }

      VertexBuffer vertexBuffer = new VertexBuffer(
          graphics, typeof(VertexPositionColor), vertices.Length, BufferUsage.WriteOnly);
      vertexBuffer.SetData<VertexPositionColor>(vertices);

      graphics.SetVertexBuffer(vertexBuffer);

      foreach (EffectPass pass in lightingEffect.CurrentTechnique.Passes) {
        pass.Apply();
        graphics.DrawPrimitives(PrimitiveType.TriangleList, 0, vertices.Length / 3);
      }
    }
  }
}