/*
This Source Code Form is subject to the
terms of the Mozilla Public License, v.
2.0. If a copy of the MPL was not
distributed with this file, You can
obtain one at
http://mozilla.org/MPL/2.0/.
*/

#include "stdafx.h"
#include "rendering/opengl33precipitation.h"

#include "utilities/Globals.h"
#include "rendering/renderer.h"
#include "simulation/simulationenvironment.h"

opengl33_precipitation::~opengl33_precipitation() {
    // TODO: release allocated resources
}

void
opengl33_precipitation::create( int const Tesselation ) {

    m_vertices.clear();
    m_uvs.clear();
    m_indices.clear();

    auto const heightfactor { 10.f }; // height-to-radius factor
    auto const verticaltexturestretchfactor { 1.5f }; // crude motion blur

	// create geometry chunk
    auto const latitudes { 3 }; // just a cylinder with end cones
    auto const longitudes { Tesselation };
    auto const longitudehalfstep { 0.5f * static_cast<float>( 2.0 * M_PI * 1.f / longitudes ) }; // for crude uv correction

    std::uint16_t index = 0;

//    auto const radius { 25.f }; // cylinder radius
    std::vector<float> radii { 25.f, 10.f, 5.f, 1.f };
    for( auto radius : radii ) {

        for( int i = 0; i <= latitudes; ++i ) {

            auto const latitude{ static_cast<float>( M_PI * ( -0.5f + (float)( i ) / latitudes ) ) };
            auto const z{ std::sin( latitude ) };
            auto const zr{ std::cos( latitude ) };

            for( int j = 0; j <= longitudes; ++j ) {
                // NOTE: for the first and last row half of the points we create end up unused but, eh
                auto const longitude{ static_cast<float>( 2.0 * M_PI * (float)( j ) / longitudes ) };
                auto const x{ std::cos( longitude ) };
                auto const y{ std::sin( longitude ) };
                // NOTE: cartesian to opengl swap would be: -x, -z, -y
                m_vertices.emplace_back( glm::vec3( -x * zr, -z * heightfactor, -y * zr ) * radius );
                // uvs
                // NOTE: first and last row receives modified u values to deal with limitation of mapping onto triangles
                auto u = (
                    i == 0 ? longitude + longitudehalfstep :
                    i == latitudes ? longitude - longitudehalfstep :
                    longitude );
                m_uvs.emplace_back(
                    u / ( 2.0 * M_PI ) * radius,
                    1.f - (float)( i ) / latitudes * radius * heightfactor * 0.5f / verticaltexturestretchfactor );

                if( ( i == 0 ) || ( j == 0 ) ) {
                    // initial edge of the dome, don't start indices yet
                    ++index;
                }
                else {
                    // the end cones are built from one triangle of each quad, the middle rows use both
                    if( i < latitudes ) {
                        m_indices.emplace_back( index - 1 - ( longitudes + 1 ) );
                        m_indices.emplace_back( index - 1 );
                        m_indices.emplace_back( index );
                    }
                    if( i > 1 ) {
                        m_indices.emplace_back( index );
                        m_indices.emplace_back( index - ( longitudes + 1 ) );
                        m_indices.emplace_back( index - 1 - ( longitudes + 1 ) );
                    }
                    ++index;
                }
            } // longitude
        } // latitude
    } // radius
}

void 
opengl33_precipitation::update() {

	if (!m_shader)
	{
        gl::shader vert("precipitation.vert");
		gl::shader frag("precipitation.frag");
		m_shader.emplace(std::vector<std::reference_wrapper<const gl::shader>>({vert, frag}));
	}

	if (!m_vertexbuffer) {
		m_vao.emplace();
		m_vao->bind();

        if( m_vertices.empty() ) {
            // create visualization mesh
            create( 18 );
        }
        // build the buffers
		m_vertexbuffer.emplace();
		m_vertexbuffer->allocate(gl::buffer::ARRAY_BUFFER, m_vertices.size() * sizeof( glm::vec3 ), GL_STATIC_DRAW);
		m_vertexbuffer->upload(gl::buffer::ARRAY_BUFFER, m_vertices.data(), 0, m_vertices.size() * sizeof( glm::vec3 ));

		m_vao->setup_attrib(*m_vertexbuffer, 0, 3, GL_FLOAT, sizeof(glm::vec3), 0);

		m_uvbuffer.emplace();
		m_uvbuffer->allocate(gl::buffer::ARRAY_BUFFER, m_uvs.size() * sizeof( glm::vec2 ), GL_STATIC_DRAW);
		m_uvbuffer->upload(gl::buffer::ARRAY_BUFFER, m_uvs.data(), 0, m_uvs.size() * sizeof( glm::vec2 ));

		m_vao->setup_attrib(*m_uvbuffer, 1, 2, GL_FLOAT, sizeof(glm::vec2), 0);

		m_indexbuffer.emplace();
		m_indexbuffer->allocate(gl::buffer::ELEMENT_ARRAY_BUFFER, m_indices.size() * sizeof( unsigned short ), GL_STATIC_DRAW);
		m_indexbuffer->upload(gl::buffer::ELEMENT_ARRAY_BUFFER, m_indices.data(), 0, m_indices.size() * sizeof( unsigned short ));
		m_vao->setup_ebo(*m_indexbuffer);

		m_vao->unbind();
        // NOTE: vertex and index source data is superfluous past this point, but, eh
    }

    // TODO: include weather type check in the entry conditions
    if( m_overcast == Global.Overcast ) { return; }

    m_overcast = Global.Overcast;

    std::string const densitysuffix { (
        m_overcast < 1.35 ?
            "_light" :
            "_medium" ) };
    if( Global.Weather == "rain:" ) {
        m_texture = GfxRenderer->Fetch_Texture( "fx/rain" + densitysuffix );
    }
    else if( Global.Weather == "snow:" ) {
        m_texture = GfxRenderer->Fetch_Texture( "fx/snow" + densitysuffix );
    }
}

void
opengl33_precipitation::render() {

    if( !m_shader ) { return; }
    if( !m_vao )    { return; }

    GfxRenderer->Bind_Texture( 0, m_texture );

    m_shader->bind();
    m_vao->bind();

    ::glDrawElements( GL_TRIANGLES, static_cast<GLsizei>( m_indices.size() ), GL_UNSIGNED_SHORT, reinterpret_cast<void const*>( 0 ) );

    m_vao->unbind();
}