#include "particle_batch.hpp"

#include <iostream>

// TODO: use VAO's as soon as this is working

int getDivisorForIndex(int index)
{
    return (index == 0) ? 1 : 4;
}

namespace endofthejedi {
    ParticleBatch::ParticleBatch(size_t numParticles, float particleSize, float maxAge)
        : m_numParticles(numParticles)
        , m_particleRadius(particleSize)
        , m_maxAge(maxAge)
        , m_age(0.0)

        // 2d quad drawn as a triangle fan
        , m_data_quad({
                1.0f, -1.0f,
                1.0f,  1.0f,
               -1.0f,  1.0f,
               -1.0f, -1.0f})
    {
        //std::cout<<"[ParticleBatch] create for " << numParticles << " num particles" << std::endl;

        m_data_position.resize(m_numParticles);
        m_data_velocity.resize(m_numParticles);
        m_data_kind.resize(m_numParticles);
        m_data_max_age.resize(m_numParticles);

        std::string vss_particles = "../data/shader/particle.vert";
        std::string fss_particles = "../data/shader/particle.frag";

        m_shader.init();
        m_shader.loadFile(vss_particles, GL_VERTEX_SHADER);
        m_shader.loadFile(fss_particles, GL_FRAGMENT_SHADER);
    }

    ParticleBatch::~ParticleBatch()
    {
        // TODO: find out if stuff must be deallocated
    }

    void ParticleBatch::setParticle(size_t index, const glm::vec2 &p, const glm::vec2 &v)
    {
        if (index >= m_numParticles) {
            return;
        }

        //std::cout<<"[ParticleBatch] setParticle " << index << std::endl;

        m_data_position[index] = p;
        m_data_velocity[index] = v;
        m_data_kind[index]     = 0.0;
        m_data_max_age[index]  = 0.0;
    }

    void ParticleBatch::bind()
    {
        //std::cout<<"[ParticleBatch] bind" << std::endl;

        for (size_t i=0; i<5; i++) {
            //std::cout<<"vbo #" << i << ": " << m_data_vbos[i] << std::endl;
            glEnableVertexAttribArray(i);
            glBindBuffer(GL_ARRAY_BUFFER, m_data_vbos[i]);

            if (i != 0) {
                glVertexAttribDivisor(i, getDivisorForIndex(i-1));
            }

            // TODO: i or index? at first argument?
            glVertexAttribPointer(
                    i,
                    dataSizeForIndex(i),
                    GL_FLOAT,  // Data is floating point type
                    GL_FALSE,  // No fixed point scaling
                    0,         // stride: no
                    NULL);     // No offset
        }
    }

    void ParticleBatch::upload()
    {
        //std::cout<<"[ParticleBatch] upload to vbo's " << std::endl;

        glGenBuffers(4, m_data_vbos);            // Generate buffer

        for (size_t i=0; i<4; i++) {
            size_t bufferDataSize = dataSizeForIndex(i) * m_numParticles * sizeof(float);

            glEnableVertexAttribArray(i);
            glBindBuffer(GL_ARRAY_BUFFER, m_data_vbos[i]);

            // fill buffer with the loaded mesh position data
            glBufferData(
                    GL_ARRAY_BUFFER,        // Buffer target
                    bufferDataSize,         // Buffer data size
                    dataSourceForIndex(i),  // Buffer data pointer
                    GL_STATIC_DRAW);        // Usage - Data never changes;
        }
    }

    void ParticleBatch::render()
    {
        //std::cout<<"[ParticleBatch] render " << std::endl;

        m_shader.bind();

        // TODO: does that work?
        glBindAttribLocation(m_shader.program(), 0, "in_vertex");
        glBindAttribLocation(m_shader.program(), 1, "in_position");
        glBindAttribLocation(m_shader.program(), 2, "in_velocity");

        glUniform1f(m_shader.location("time"),   m_age);
        glUniform1f(m_shader.location("maxAge"), m_maxAge);
        glUniform1f(m_shader.location("size"),   m_particleRadius);

        bind();

        //glDrawArrays(GL_TRIANGLE_FAN, 0, 4*m_numParticles);

        //glDrawArraysInstanced( GLenum mode, GLint first, GLsizei count, GLsizei primcount);
        glDrawArraysInstanced(GL_TRIANGLE_FAN, 0, 4, 4*m_numParticles);

#if 0
        glBegin(GL_QUADS);
        for (size_t index=0; index<m_numParticles; index++) {
            for (int i=0; i<4; i++) {
                glm::vec2 p = m_data_position[index] + triangles[i];
                //glColor3f(1.0, 0.0, 0.0);
                glVertex2f(p.x, p.y);
            }
        }
        glEnd();
#endif

    }

    size_t ParticleBatch::dataSizeForIndex(int i)
    {
        switch(i) {
            case 0:
            case 1:
            case 2:
                return 2;

            case 3:
            case 4:
                return 1;

            default:
                std::cerr << "bad" << std::endl;
                exit(-1);
        }
    }

    void *ParticleBatch::dataSourceForIndex(int i)
    {
        switch(i) {
            case 0: return (void *) m_data_quad.data();
            case 1: return (void *) m_data_position.data();
            case 2: return (void *) m_data_velocity.data();
            case 3: return (void *) m_data_kind.data();
            case 4: return (void *) m_data_max_age.data();
            default:
                std::cerr << "bad" << std::endl;
                exit(-1);
        }
    }

    void ParticleBatch::tick(float dt)
    {
        m_age += dt;
    }

    bool ParticleBatch::done() const
    {
        return m_age >= m_maxAge;
    }
}