#include <cstddef>
#include <cmath>
#include <vector>

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

#include "scenes/sphere.hpp"

namespace cbt::scenes {

sphere::sphere() {
    m_start = std::chrono::steady_clock::now();
}

auto sphere::init() -> bool {
    if (!build_shader()) {
        return false;
    }
    build_mesh();
    glEnable(GL_DEPTH_TEST);
    return true;
}

auto sphere::update(float) -> void {}

auto sphere::render() -> void {
    auto now = std::chrono::steady_clock::now();
    auto elapsed = std::chrono::duration<float>(now - m_start).count();

    glClearColor(0.15f, 0.15f, 0.2f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    auto aspect = 1280.0f / 720.0f;
    auto proj = glm::perspective(glm::radians(45.0f), aspect, 0.1f, 100.0f);
    auto view = glm::translate(glm::mat4{1.0f}, glm::vec3{0.0f, 0.0f, -4.0f});
    auto model = glm::rotate(glm::mat4{1.0f}, elapsed, glm::vec3{1.0f, 0.3f, 0.2f});

    m_prog.use();
    glUniformMatrix4fv(m_loc_proj, 1, GL_FALSE, glm::value_ptr(proj));
    glUniformMatrix4fv(m_loc_view, 1, GL_FALSE, glm::value_ptr(view));
    glUniformMatrix4fv(m_loc_model, 1, GL_FALSE, glm::value_ptr(model));

    m_vao.bind();
    glDrawElements(GL_TRIANGLES, m_index_count, GL_UNSIGNED_INT, nullptr);
    m_vao.unbind();
    m_prog.unuse();
}

auto sphere::build_mesh() -> void {
    struct vertex {
        glm::vec3 position;
        glm::vec3 normal;
        glm::vec2 uv;
    };

    std::uint32_t const div = 32;
    std::vector<vertex> vertices;
    std::vector<std::uint32_t> indices;

    // Generate 6 cube faces, each with div x div vertices
    auto add_face = [&](glm::vec3 const& center, glm::vec3 const& u_axis,
                        glm::vec3 const& v_axis) -> void {
        for (std::uint32_t i = 0; i < div; ++i) {
            for (std::uint32_t j = 0; j < div; ++j) {
                float const s = float(i) / float(div - 1) * 2.0f - 1.0f;
                float const t = float(j) / float(div - 1) * 2.0f - 1.0f;

                // Position on cube face
                glm::vec3 pos = center + u_axis * s + v_axis * t;

                // FIX: normalize to project onto unit sphere
                // (the original nrz.cpp used a broken formula with p=50.0)
                float const len = glm::length(pos);
                glm::vec3 normal = pos / len;

                vertices.push_back({normal, normal, {float(i) / float(div - 1), float(j) / float(div - 1)}});
            }
        }
    };

    // +X face (right)
    add_face(glm::vec3{1.0f, 0.0f, 0.0f}, glm::vec3{0.0f, 1.0f, 0.0f}, glm::vec3{0.0f, 0.0f, 1.0f});
    // -X face (left)
    add_face(glm::vec3{-1.0f, 0.0f, 0.0f}, glm::vec3{0.0f, 1.0f, 0.0f}, glm::vec3{0.0f, 0.0f, -1.0f});
    // +Y face (top)
    add_face(glm::vec3{0.0f, 1.0f, 0.0f}, glm::vec3{1.0f, 0.0f, 0.0f}, glm::vec3{0.0f, 0.0f, -1.0f});
    // -Y face (bottom)
    add_face(glm::vec3{0.0f, -1.0f, 0.0f}, glm::vec3{1.0f, 0.0f, 0.0f}, glm::vec3{0.0f, 0.0f, 1.0f});
    // +Z face (front)
    add_face(glm::vec3{0.0f, 0.0f, 1.0f}, glm::vec3{1.0f, 0.0f, 0.0f}, glm::vec3{0.0f, 1.0f, 0.0f});
    // -Z face (back)
    add_face(glm::vec3{0.0f, 0.0f, -1.0f}, glm::vec3{-1.0f, 0.0f, 0.0f}, glm::vec3{0.0f, 1.0f, 0.0f});

    // Generate indices for each face
    std::uint32_t offset = 0;
    for (std::uint32_t face = 0; face < 6; ++face) {
        for (std::uint32_t i = 0; i < div - 1; ++i) {
            for (std::uint32_t j = 0; j < div - 1; ++j) {
                std::uint32_t const a = offset + i * div + j;
                std::uint32_t const b = offset + (i + 1) * div + j;
                std::uint32_t const c = offset + (i + 1) * div + j + 1;
                std::uint32_t const d = offset + i * div + j + 1;

                // Two triangles per quad (consistent winding)
                indices.push_back(a);
                indices.push_back(b);
                indices.push_back(d);

                indices.push_back(b);
                indices.push_back(c);
                indices.push_back(d);
            }
        }
        offset += div * div;
    }

    m_index_count = static_cast<GLsizei>(indices.size());

    m_vbo.upload(vertices.data(), vertices.size() * sizeof(vertex));
    m_ebo.upload(indices.data(), indices.size() * sizeof(std::uint32_t));

    m_vao.bind();
    m_vbo.bind();
    m_ebo.bind();

    // location 0: position (vec3)
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(vertex), nullptr);

    // location 1: normal (vec3)
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(vertex),
                         reinterpret_cast<void*>(offsetof(vertex, normal)));

    // location 2: uv (vec2)
    glEnableVertexAttribArray(2);
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(vertex),
                         reinterpret_cast<void*>(3 * sizeof(float) + 3 * sizeof(float)));

    m_ebo.unbind();
    m_vbo.unbind();
    m_vao.unbind();
}

auto sphere::build_shader() -> bool {
    char const* vert_src = R"glsl(
        #version 410 core
        layout(location = 0) in vec3 a_pos;
        layout(location = 1) in vec3 a_normal;
        layout(location = 2) in vec2 a_uv;
        uniform mat4 u_model;
        uniform mat4 u_view;
        uniform mat4 u_proj;
        out vec3 v_normal;
        out vec3 v_world_pos;
        out vec2 v_uv;
        void main() {
            gl_Position = u_proj * u_view * u_model * vec4(a_pos, 1.0);
            v_normal = mat3(u_model) * a_normal;
            v_world_pos = (u_model * vec4(a_pos, 1.0)).xyz;
            v_uv = a_uv;
        }
    )glsl";

    char const* frag_src = R"glsl(
        #version 410 core
        in vec3 v_normal;
        in vec3 v_world_pos;
        in vec2 v_uv;
        out vec4 frag_color;
        void main() {
            vec3 light_dir = normalize(vec3(1.0, 1.0, 2.0));
            vec3 normal = normalize(v_normal);
            float diff = max(dot(normal, light_dir), 0.0);
            vec3 ambient = vec3(0.2);
            vec3 color = vec3(0.4, 0.6, 1.0);
            vec3 result = (ambient + diff * 0.8) * color;
            frag_color = vec4(result, 1.0);
        }
    )glsl";

    if (!m_prog.compile_vertex(vert_src) || !m_prog.compile_fragment(frag_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");

    return true;
}

}