#include "Raycaster.h"

#include "cuda_runtime.h"
#include "device_launch_parameters.h"

#include "linalg/linalg.h"
#include "consts.h"
#include "cuda_error.h"
#include "shading.h"
#include <iostream>
#include "objs/sphere.h"

// Samples the voxel nearest to the given coordinates. TODO: Can be re-used in other places so move
__device__ float sampleVolumeNearest(float* volumeData, const int volW, const int volH, const int volD, int vx, int vy, int vz) {
    if (vx < 0) vx = 0;
    if (vy < 0) vy = 0;
    if (vz < 0) vz = 0;
    if (vx >= volW) vx = volW  - 1;
    if (vy >= volH) vy = volH - 1;
    if (vz >= volD) vz = volD  - 1;

    int idx = vz * volW * volH + vy * volD + vx;
    return volumeData[idx];
}

// tri-linear interpolation - ready if necessary (but no visible improvement for full volume)
__device__ float sampleVolumeTrilinear(float* volumeData, const int volW, const int volH, const int volD, float fx, float fy, float fz) {
    int ix = (int)fx;
    int iy = (int)fy;
    int iz = (int)fz;

    float dx = fx - ix;
    float dy = fy - iy;
    float dz = fz - iz;

    float c00 = sampleVolumeNearest(volumeData, volW, volH, volD, ix, iy, iz) * (1.0f - dx) + sampleVolumeNearest(volumeData, volW, volH, volD, ix + 1, iy, iz) * dx;
    float c10 = sampleVolumeNearest(volumeData, volW, volH, volD, ix, iy + 1, iz) * (1.0f - dx) + sampleVolumeNearest(volumeData, volW, volH, volD, ix + 1, iy + 1, iz) * dx;
    float c01 = sampleVolumeNearest(volumeData, volW, volH, volD, ix, iy, iz + 1) * (1.0f - dx) + sampleVolumeNearest(volumeData, volW, volH, volD, ix + 1, iy, iz + 1) * dx;
    float c11 = sampleVolumeNearest(volumeData, volW, volH, volD, ix, iy + 1, iz + 1) * (1.0f - dx) + sampleVolumeNearest(volumeData, volW, volH, volD, ix + 1, iy + 1, iz + 1) * dx;

    float c0 = c00 * (1.0f - dy) + c10 * dy;
    float c1 = c01 * (1.0f - dy) + c11 * dy;

    return c0 * (1.0f - dz) + c1 * dz;
}


// Transfer function
__device__ float4 transferFunction(float density, Vec3 grad, Point3 pos, Vec3 rayDir) {
  float4 result;
  // Basic transfer function. TODO: Move to a separate file, and then improve
  float alphaSample = density * 0.1f;
  // result.w = 1.0f - expf(-density * 0.1f);

  Color3 baseColor = Color3::init(density, 0.1f*density, 1.f - density);  // TODO: Implement a proper transfer function

  Vec3 normal = -grad.normalize();

  Vec3 lightDir = (d_lightPos - pos).normalize();
  Vec3 viewDir  = -rayDir.normalize();

  // Apply Phong
  Vec3 shadedColor = phongShading(normal, lightDir, viewDir, baseColor);

  // Compose
  result.x = (1.0f - alphaSample) * shadedColor.x * alphaSample;
  result.y = (1.0f - alphaSample) * shadedColor.y * alphaSample;
  result.z = (1.0f - alphaSample) * shadedColor.z * alphaSample;
  result.w = (1.0f - alphaSample) * alphaSample;

  // TODO: Add silhouette - Take gradient of volume dot with view direction (if small then this is a silhouette)
  if (grad.dot(viewDir) < epsilon / 100000.0f) {
    result.x = 0.0f;
    result.y = 0.0f;
    result.z = 0.0f;
    result.w = 1.0f;
  }

  return result;
}


// TODO: instead of IMAGEWIDTH and IMAGEHEIGHT this should reflect the windowSize;
__global__ void raycastKernel(float* volumeData, FrameBuffer framebuffer) {
    int px = blockIdx.x * blockDim.x + threadIdx.x;
    int py = blockIdx.y * blockDim.y + threadIdx.y;
    if (px >= IMAGE_WIDTH || py >= IMAGE_HEIGHT) return;

    float accumR = 0.0f;
    float accumG = 0.0f;
    float accumB = 0.0f;

    // Multiple samples per pixel
    for (int s = 0; s < SAMPLES_PER_PIXEL; s++) {
        // Map to [-1, 1]
        float u = ((px + 0.5f) / IMAGE_WIDTH ) * 2.0f - 1.0f;
        float v = ((py + 0.5f) / IMAGE_HEIGHT) * 2.0f - 1.0f;

        // TODO: Move this (and all similar transformation code) to its own separate file
        float tanHalfFov = tanf(fov * 0.5f);
        u *= tanHalfFov;
        v *= tanHalfFov;

        // Find ray direction
        Vec3 cameraRight = (d_cameraDir.cross(d_cameraUp)).normalize();
        d_cameraUp = (cameraRight.cross(d_cameraDir)).normalize();
        Vec3 rayDir = (d_cameraDir + cameraRight*u + d_cameraUp*v).normalize();

        // Intersect (for simplicity just a 3D box from 0 to 1 in all dimensions) - TODO: Think about whether this is the best way to do this
        float tNear = 0.0f;
        float tFar  = 1e6f;
        auto intersectAxis = [&](float start, float dir, float minV, float maxV) {
            if (fabsf(dir) < epsilon) {
                // Ray parallel to axis. If outside min..max, no intersection.
                if (start < minV || start > maxV) {
                    tNear = 1e9f;
                    tFar  = -1e9f;
                }
            } else {
                float t0 = (minV - start) / dir;
                float t1 = (maxV - start) / dir;
                if (t0 > t1) {
                    float tmp = t0;
                    t0 = t1;
                    t1 = tmp;
                }
                if (t0 > tNear) tNear = t0;
                if (t1 < tFar ) tFar  = t1;
            }
        };

        intersectAxis(d_cameraPos.x, rayDir.x, 0.0f, (float)VOLUME_WIDTH);
        intersectAxis(d_cameraPos.y, rayDir.y, 0.0f, (float)VOLUME_HEIGHT);
        intersectAxis(d_cameraPos.z, rayDir.z, 0.0f, (float)VOLUME_DEPTH);

        if (tNear > tFar){
          // No intersectionn
          accumR = 0.9f;
          accumG = 0.9f;
          accumB = 0.9f;
        } else {
          if (tNear < 0.0f) tNear = 0.0f;

          float colorR = 0.0f, colorG = 0.0f, colorB = 0.0f;
          float alphaAccum = 0.0f;

          float tCurrent = tNear;
          while (tCurrent < tFar && alphaAccum < alphaAcumLimit) {
              Point3 pos = d_cameraPos + rayDir * tCurrent;

              // Convert to volume indices
              // float fx = pos.x * (VOLUME_WIDTH  - 1);
              // float fy = pos.y * (VOLUME_HEIGHT - 1);
              // float fz = pos.z * (VOLUME_DEPTH  - 1);
              int ix = (int)roundf(pos.x);
              int iy = (int)roundf(pos.y);
              int iz = (int)roundf(pos.z);

              // Sample (pick appropriate method based on volume size)
              float density = sampleVolumeNearest(volumeData, VOLUME_WIDTH, VOLUME_HEIGHT, VOLUME_DEPTH, ix, iy, iz);
              // float density = sampleVolumeTrilinear(volumeData, VOLUME_WIDTH, VOLUME_HEIGHT, VOLUME_DEPTH, pos.x, pos.y, pos.z);

              // If density ~ 0, skip shading
              if (density > minAllowedDensity) {
                Vec3 grad = computeGradient(volumeData, VOLUME_WIDTH, VOLUME_HEIGHT, VOLUME_DEPTH, ix, iy, iz);
                float4 color = transferFunction(density, grad, pos, rayDir);
                colorR += color.x;
                colorG += color.y;
                colorB += color.z;
                alphaAccum += color.w;
              }


              tCurrent += stepSize;
          }

          accumR += colorR;
          accumG += colorG;
          accumB += colorB;

          // float leftover = 1.0f - alphaAccum;
          // accumR = accumR + leftover * 0.9f;
          // accumG = accumG + leftover * 0.9f;
          // accumB = accumB + leftover * 0.9f;
        }
    }

    // Average samples
    accumR /= (float)SAMPLES_PER_PIXEL;
    accumG /= (float)SAMPLES_PER_PIXEL;
    accumB /= (float)SAMPLES_PER_PIXEL;

    // Final colour
    framebuffer.writePixel(px, py, accumR, accumG, accumB);
    // int fbIndex = (py * IMAGE_WIDTH + px) * 3;
    // framebuffer[fbIndex + 0] = (unsigned char)(fminf(accumR, 1.f) * 255);
    // framebuffer[fbIndex + 1] = (unsigned char)(fminf(accumG, 1.f) * 255);
    // framebuffer[fbIndex + 2] = (unsigned char)(fminf(accumB, 1.f) * 255);
}


Raycaster::Raycaster(cudaGraphicsResource_t resources, int w, int h, float* data) {
	this->resources = resources;
	this->w = w;
	this->h = h;

	this->fb = new FrameBuffer(w, h);
  this->data = data;

	// camera_info = CameraInfo(Vec3(0.0f, 0.0f, 0.0f), Vec3(0.0f, 0.0f, 0.0f), 90.0f, (float) w, (float) h);
	// d_camera = thrust::device_new<Camera*>();

	check_cuda_errors(cudaDeviceSynchronize());
}


void Raycaster::render() {
  check_cuda_errors(cudaGraphicsMapResources(1, &this->resources));
	check_cuda_errors(cudaGraphicsResourceGetMappedPointer((void**)&(this->fb->buffer), &(this->fb->buffer_size), resources));

  // FIXME: might not be the best parallelization configuraiton
	int tx = 16;
	int ty = 16;
	dim3 threadSize(this->w / tx + 1, this->h / ty + 1);
	dim3 blockSize(tx, ty);

  // TODO: pass camera info at some point
	// frame buffer is implicitly copied to the device each frame
  raycastKernel<<<threadSize, blockSize>>> (this->data, *this->fb);

  check_cuda_errors(cudaGetLastError());
  check_cuda_errors(cudaDeviceSynchronize());
  check_cuda_errors(cudaGraphicsUnmapResources(1, &this->resources));
}


void Raycaster::resize(int w, int h) {
  this->w = w;
  this->h = h;

  delete this->fb;  
  this->fb = new FrameBuffer(w, h);

  // TODO: should be globals probably
	int tx = 8;
	int ty = 8;

	dim3 blocks(w / tx + 1, h / ty + 1);
	dim3 threads(tx, ty);

  check_cuda_errors(cudaDeviceSynchronize());
}