#include <GL/glew.h>
#include "bettola/game/chunk.h"
#include "chunk_mesh.h"

ChunkMesh::ChunkMesh(int chunk_x, int chunk_z, const BettolaLib::Game::Chunk& chunk) {
  /* Generate vertices from the heightmap. */
  for(int z = 0; z < BettolaLib::Game::CHUNK_HEIGHT; ++z) {
    for(int x = 0; x < BettolaLib::Game::CHUNK_WIDTH; ++x) {
      /* Vertex position. */
      _vertices.push_back((float)(chunk_x * (BettolaLib::Game::CHUNK_WIDTH-1)  + x));
      _vertices.push_back(chunk.heightmap[z * BettolaLib::Game::CHUNK_WIDTH+x] * 5.0f); /* 5x scale height */
      _vertices.push_back((float)(chunk_z * (BettolaLib::Game::CHUNK_HEIGHT-1) + z));
    }
  }

  /* Generate indices for the triangles. */
  for(int z = 0; z < BettolaLib::Game::CHUNK_HEIGHT-1; ++z) {
    for(int x = 0; x < BettolaLib::Game::CHUNK_WIDTH-1; ++x) {
      int top_left      = z * BettolaLib::Game::CHUNK_WIDTH + x;
      int top_right     = top_left + 1;
      int bottom_left   = (z+1) * BettolaLib::Game::CHUNK_WIDTH + x;
      int bottom_right  = bottom_left + 1;

      /* First triangle of the quad. */
      _indices.push_back(top_left);
      _indices.push_back(bottom_left);
      _indices.push_back(top_right);

      /* Second triangle of the quad. */
      _indices.push_back(top_right);
      _indices.push_back(bottom_left);
      _indices.push_back(bottom_right);
    }
  }

  _setup_mesh();
}

ChunkMesh::~ChunkMesh(void) {
  glDeleteVertexArrays(1, &_vao);
  glDeleteBuffers(1, &_vbo);
  glDeleteBuffers(1, &_ebo);
}

void ChunkMesh::_setup_mesh(void) {
  glGenVertexArrays(1, &_vao);
  glGenBuffers(1, &_vbo);
  glGenBuffers(1, &_ebo);

  glBindVertexArray(_vao);

  glBindBuffer(GL_ARRAY_BUFFER, _vbo);
  glBufferData(GL_ARRAY_BUFFER, _vertices.size()*sizeof(float), _vertices.data(), GL_STATIC_DRAW);

  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _ebo);
  glBufferData(GL_ELEMENT_ARRAY_BUFFER, _indices.size()*sizeof(unsigned int), _indices.data(), GL_STATIC_DRAW);

  /* Position attrib. */
  glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), (void*)0);
  glEnableVertexAttribArray(0);

  glBindVertexArray(0);
}

void ChunkMesh::draw(void) {
  glBindVertexArray(_vao);
  glDrawElements(GL_TRIANGLES, _indices.size(), GL_UNSIGNED_INT, 0);
  glBindVertexArray(0);
}