#include <cstddef>
#include <utility>

#include "cbt/gfx.hpp"

#include "glad/glad.h"
#include "glm/gtc/type_ptr.hpp"

#include "cbt/opengl/shader.hpp"
#include "cbt/opengl/buffer.hpp"
#include "cbt/opengl/vao.hpp"
#include "cbt/opengl/texture.hpp"

namespace cbt::gfx {

struct pipeline::impl {
    opengl::shader m_prog;
    opengl::buffer m_vbo;
    opengl::buffer m_ebo{opengl::buffer_type::index};
    opengl::vao m_vao;

    GLint m_loc_proj = -1;
    GLint m_loc_view = -1;
    GLint m_loc_model = -1;

    GLsizei m_index_count = 0;
    GLsizei m_vertex_count = 0;

    bool m_valid = false;
    bool m_uses_index = false;
    bool m_depth_test = true;
    GLenum m_draw_mode = GL_TRIANGLES;
    GLenum m_index_gl_type = GL_UNSIGNED_INT;

    auto build(pipeline_desc const& desc) -> bool;
    auto bind_texture(char const* sampler_name, std::uint32_t texture_id, std::uint32_t unit) const -> void;
    auto bind_vec3(char const* name, glm::vec3 const& v) const -> void;
    auto bind_float(char const* name, float v) const -> void;
};

auto pipeline::impl::build(pipeline_desc const& desc) -> bool {
    if (!desc.vertex_shader_src || !desc.fragment_shader_src ||
        desc.vertex_data.empty() || desc.attributes.empty() || desc.vertex_stride == 0) {
        return false;
    }

    if (!m_prog.compile_vertex(desc.vertex_shader_src) ||
        !m_prog.compile_fragment(desc.fragment_shader_src) ||
        !m_prog.link()) {
        return false;
    }

    m_loc_proj = glGetUniformLocation(m_prog.id(), "u_proj");
    m_loc_view = glGetUniformLocation(m_prog.id(), "u_view");
    m_loc_model = glGetUniformLocation(m_prog.id(), "u_model");

    m_vbo.upload(desc.vertex_data.data(), desc.vertex_data.size());
    m_vertex_count = static_cast<GLsizei>(desc.vertex_data.size() / desc.vertex_stride);

    m_uses_index = !desc.index_data.empty();
    if (m_uses_index) {
        m_ebo.upload(desc.index_data.data(), desc.index_data.size());
        std::size_t const idx_size = (desc.index_type_ == index_type::uint16)
            ? sizeof(std::uint16_t)
            : sizeof(std::uint32_t);
        m_index_count = static_cast<GLsizei>(desc.index_data.size() / idx_size);
        m_index_gl_type = (desc.index_type_ == index_type::uint16)
            ? GL_UNSIGNED_SHORT
            : GL_UNSIGNED_INT;
    }

    m_draw_mode = GL_TRIANGLES;
    m_depth_test = desc.depth_test;

    m_vao.bind();
    m_vbo.bind();
    if (m_uses_index) {
        m_ebo.bind();
    }

    for (auto const& attr : desc.attributes) {
        glEnableVertexAttribArray(attr.location);
        glVertexAttribPointer(
            attr.location,
            static_cast<GLint>(attr.num_components),
            GL_FLOAT,
            GL_FALSE,
            static_cast<GLsizei>(desc.vertex_stride),
            reinterpret_cast<void*>(static_cast<std::uintptr_t>(attr.offset))
        );
    }

    m_vao.unbind();
    m_vbo.unbind();
    if (m_uses_index) {
        m_ebo.unbind();
    }

    if (desc.depth_test) {
        glEnable(GL_DEPTH_TEST);
    } else {
        glDisable(GL_DEPTH_TEST);
    }

    m_valid = true;
    return true;
}


auto pipeline::impl::bind_vec3(char const* name, glm::vec3 const& v) const -> void {
    if (!m_prog.valid()) return;
    m_prog.use();
    GLint const loc = glGetUniformLocation(m_prog.id(), name);
    if (loc != -1) {
        glUniform3fv(loc, 1, glm::value_ptr(v));
    }
    m_prog.unuse();
}

auto pipeline::impl::bind_float(char const* name, float v) const -> void {
    if (!m_prog.valid()) return;
    m_prog.use();
    GLint const loc = glGetUniformLocation(m_prog.id(), name);
    if (loc != -1) {
        glUniform1f(loc, v);
    }
    m_prog.unuse();
}

auto pipeline::impl::bind_texture(char const* sampler_name, std::uint32_t texture_id, std::uint32_t unit) const -> void {
    if (!m_prog.valid()) {
        return;
    }
    GLint loc = glGetUniformLocation(m_prog.id(), sampler_name);
    if (loc != -1) {
        glUniform1i(loc, static_cast<GLint>(unit));
        glActiveTexture(GL_TEXTURE0 + unit);
        glBindTexture(GL_TEXTURE_2D, texture_id);
    }
}

pipeline::pipeline() : m_impl(std::make_unique<impl>()) {}

pipeline::pipeline(pipeline_desc const& desc) : m_impl(std::make_unique<impl>()) {
    m_impl->build(desc);
}

pipeline::pipeline(pipeline&& other) noexcept
    : m_impl(std::move(other.m_impl)) {}

auto pipeline::operator=(pipeline&& other) noexcept -> pipeline& {
    if (this != &other) {
        m_impl = std::move(other.m_impl);
    }
    return *this;
}

pipeline::~pipeline() = default;

auto pipeline::valid() const -> bool {
    return m_impl && m_impl->m_valid;
}

auto pipeline::draw(
    glm::mat4 const& model,
    glm::mat4 const& view,
    glm::mat4 const& proj
) const -> void {
    if (!valid()) {
        return;
    }

    auto& impl = *m_impl;
    impl.m_prog.use();

    if (impl.m_loc_proj != -1) {
        glUniformMatrix4fv(impl.m_loc_proj, 1, GL_FALSE, glm::value_ptr(proj));
    }
    if (impl.m_loc_view != -1) {
        glUniformMatrix4fv(impl.m_loc_view, 1, GL_FALSE, glm::value_ptr(view));
    }
    if (impl.m_loc_model != -1) {
        glUniformMatrix4fv(impl.m_loc_model, 1, GL_FALSE, glm::value_ptr(model));
    }

    if (impl.m_depth_test) {
        glEnable(GL_DEPTH_TEST);
    } else {
        glDisable(GL_DEPTH_TEST);
    }

    impl.m_vao.bind();
    if (impl.m_uses_index) {
        glDrawElements(impl.m_draw_mode, impl.m_index_count, impl.m_index_gl_type, nullptr);
    } else {
        glDrawArrays(impl.m_draw_mode, 0, impl.m_vertex_count);
    }
    impl.m_vao.unbind();
    impl.m_prog.unuse();

    // Reset texture state to prevent leakage on scene switches or between passes
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, 0);
}

auto pipeline::bind_texture(char const* sampler_name, std::uint32_t texture_id, std::uint32_t unit) const -> void {
    if (m_impl) {
        m_impl->bind_texture(sampler_name, texture_id, unit);
    }
}

auto pipeline::bind_vec3(char const* name, glm::vec3 const& v) const -> void {
    if (m_impl) {
        m_impl->bind_vec3(name, v);
    }
}

auto pipeline::bind_float(char const* name, float v) const -> void {
    if (m_impl) {
        m_impl->bind_float(name, v);
    }
}

struct render_target::impl {
    GLuint m_fbo = 0;
    opengl::texture m_color{opengl::texture_target::_2d};
    GLuint m_depth_rbo = 0;
    int m_width = 0;
    int m_height = 0;
    bool m_valid = false;

    auto build(int width, int height) -> bool;
    auto cleanup() -> void;
};

auto render_target::impl::build(int width, int height) -> bool {
    m_width = width;
    m_height = height;

    glGenFramebuffers(1, &m_fbo);
    if (m_fbo == 0) {
        return false;
    }

    // Color texture
    m_color = opengl::texture(opengl::texture_target::_2d);
    m_color.bind(0);
    m_color.upload(nullptr, width, height, opengl::texture_format::rgba, opengl::texture_type::ubyte);
    m_color.set_filter(GL_LINEAR, GL_LINEAR);
    m_color.set_wrap(GL_CLAMP_TO_EDGE, GL_CLAMP_TO_EDGE);
    m_color.unbind();

    // Depth renderbuffer
    glGenRenderbuffers(1, &m_depth_rbo);
    glBindRenderbuffer(GL_RENDERBUFFER, m_depth_rbo);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, width, height);
    glBindRenderbuffer(GL_RENDERBUFFER, 0);

    // Attach to FBO
    glBindFramebuffer(GL_FRAMEBUFFER, m_fbo);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_color.id(), 0);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, m_depth_rbo);

    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    glBindFramebuffer(GL_FRAMEBUFFER, 0);

    if (status != GL_FRAMEBUFFER_COMPLETE) {
        cleanup();
        return false;
    }

    m_valid = true;
    return true;
}

auto render_target::impl::cleanup() -> void {
    if (m_fbo != 0) {
        glDeleteFramebuffers(1, &m_fbo);
        m_fbo = 0;
    }
    if (m_depth_rbo != 0) {
        glDeleteRenderbuffers(1, &m_depth_rbo);
        m_depth_rbo = 0;
    }
    m_valid = false;
}

render_target::render_target(int width, int height) : m_impl(std::make_unique<impl>()) {
    m_impl->build(width, height);
}

render_target::render_target(render_target&& other) noexcept
    : m_impl(std::move(other.m_impl)) {}

auto render_target::operator=(render_target&& other) noexcept -> render_target& {
    if (this != &other) {
        m_impl = std::move(other.m_impl);
    }
    return *this;
}

render_target::~render_target() {
    if (m_impl) {
        m_impl->cleanup();
    }
}

auto render_target::bind() const -> void {
    if (!valid()) return;
    glBindFramebuffer(GL_FRAMEBUFFER, m_impl->m_fbo);
    glViewport(0, 0, m_impl->m_width, m_impl->m_height);
}

auto render_target::unbind() const -> void {
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
}

auto render_target::color_id() const -> std::uint32_t {
    return m_impl ? m_impl->m_color.id() : 0;
}

auto render_target::width() const -> int {
    return m_impl ? m_impl->m_width : 0;
}

auto render_target::height() const -> int {
    return m_impl ? m_impl->m_height : 0;
}

auto render_target::valid() const -> bool {
    return m_impl && m_impl->m_valid;
}

auto render_target::resize(int width, int height) -> void {
    if (m_impl && m_impl->m_width == width && m_impl->m_height == height) {
        return;
    }
    if (m_impl) {
        m_impl->cleanup();
    }
    if (!m_impl) {
        m_impl = std::make_unique<impl>();
    }
    m_impl->build(width, height);
}

} // namespace cbt::gfx