mod lerp;
mod poly;

use lerp::Lerp;
use poly::Poly;

use std::ffi::{CStr, CString};

use sdl2::event::Event;
use sdl2::keyboard::Keycode;

use gl::types::*;

fn shader_from_source(source: &CStr, shader_type: GLenum) -> GLuint {
    unsafe {
        let shader: GLuint = gl::CreateShader(shader_type);
        gl::ShaderSource(shader, 1, &source.as_ptr(), std::ptr::null());
        gl::CompileShader(shader);
        let mut success: gl::types::GLint = 1;
        gl::GetShaderiv(shader, gl::COMPILE_STATUS, &mut success);
        if success == 0 {
            println!("Compilation error: {}", source.to_str().unwrap());
        }
        shader
    }
}

fn compile_bezier_shader(a: Poly, b: Poly) -> GLuint {
    let vertex_shader_source = b"
    #version 410 core
    layout (location = 0) in vec3 aPos;

    void main() {
        gl_Position = vec4(aPos.xyz, 1.0);
    }
    "
    .to_vec();

    let fragment_shader_source = format!(
        "
    #version 410 core
    out vec4 FragColor;

    float pa[{sa}] = float[{sa}]({pa});
    float pb[{sb}] = float[{sb}]({pb});

    float eval_a(float[{sa}] v, float t) {{
        float result = 0.0;
        for (int i = 0; i < {sa}; i++) {{
          result += v[i] * pow(t, i);
        }}
        return result;
    }}

    float eval_b(float[{sb}] v, float t) {{
        float result = 0.0;
        for (int i = 0; i < {sb}; i++) {{
          result += v[i] * pow(t, i);
        }}
        return result;
    }}

    float inside(vec2 pos) {{
      float res = 100;
      float thr = 32;
      float closest = 1000000;
      float t = 0.0;
      while (t < 1.0) {{
        float step = t + 1.0 / res;
        vec2 a = vec2(eval_a(pa, t), eval_b(pb, t));
        vec2 b = vec2(eval_a(pa, step), eval_b(pb, step));
        float c = pow(length(a - b), 2);
        float d = distance(pos, a + clamp(dot(pos - a, b - a) / c, 0, 1) * (b - a));
        if (d < closest) {{
          closest = d;
        }}
        t = step;
      }}
      return 1 - closest / thr;
    }}

    void main() {{
      float r = inside(gl_FragCoord.xy);
        FragColor = vec4(r * 0.8, r * 0.2, r, 1.0);
    }}
    ",
        sa = a.degree() + 1,
        sb = b.degree() + 1,
        pa = &a,
        pb = &b
    )
    .into_bytes();

    let shader_program: GLuint;
    unsafe {
        let vertex_shader = shader_from_source(
            &CString::from_vec_unchecked(vertex_shader_source),
            gl::VERTEX_SHADER,
        );
        let fragment_shader = shader_from_source(
            &CString::from_vec_unchecked(fragment_shader_source),
            gl::FRAGMENT_SHADER,
        );
        shader_program = gl::CreateProgram();
        gl::AttachShader(shader_program, vertex_shader);
        gl::AttachShader(shader_program, fragment_shader);
        gl::LinkProgram(shader_program);
        gl::DeleteShader(vertex_shader);
        gl::DeleteShader(fragment_shader);
    }
    shader_program
}

fn main() {
    let a = Lerp::new(vec![200.0, 500.0, 500.0]).to_poly();
    let b = Lerp::new(vec![200.0, 500.0, 200.0]).to_poly();

    let sdl_context = sdl2::init().unwrap();
    let video_subsystem = sdl_context.video().unwrap();

    let gl_attr = video_subsystem.gl_attr();

    gl_attr.set_context_profile(sdl2::video::GLProfile::Core);
    gl_attr.set_context_version(4, 1);

    let window_w: u32 = 1920;
    let window_h: u32 = 1080;

    let window = video_subsystem
        .window("bezier", window_w, window_h)
        .position_centered()
        .opengl()
        .build()
        .unwrap();

    let _gl_context = window.gl_create_context().unwrap();

    gl::load_with(|s| video_subsystem.gl_get_proc_address(s) as *const std::os::raw::c_void);

    unsafe {
        gl::Viewport(0, 0, window_w as i32, window_h as i32);
    }

    let vertices: [f32; 18] = [1.0, 1.0, 0.0, 1.0, -1.0, 0.0, -1.0, 1.0, 0.0, 1.0, -1.0, 0.0, -1.0, -1.0, 0.0, -1.0, 1.0, 0.0];

    let mut vbo: GLuint = 0;
    let mut vao: GLuint = 0;
    unsafe {
        gl::GenVertexArrays(1, &mut vao);
        gl::BindVertexArray(vao);
        gl::GenBuffers(1, &mut vbo);
        gl::BindBuffer(gl::ARRAY_BUFFER, vbo);
        gl::BufferData(
            gl::ARRAY_BUFFER,
            (vertices.len() * std::mem::size_of::<f32>()) as GLsizeiptr,
            vertices.as_ptr() as *const GLvoid,
            gl::STATIC_DRAW,
        );
        gl::VertexAttribPointer(
            0,
            3,
            gl::FLOAT,
            gl::FALSE,
            (3 * std::mem::size_of::<f32>()) as GLint,
            std::ptr::null(),
        );
        gl::EnableVertexAttribArray(0);
    }

    let shader_program = compile_bezier_shader(a, b);

    let mut event_pump = sdl_context.event_pump().unwrap();
    'running: loop {
        for event in event_pump.poll_iter() {
            match event {
                Event::Quit { .. }
                | Event::KeyDown {
                    keycode: Some(Keycode::Escape),
                    ..
                } => break 'running,
                _ => {}
            }
        }

        unsafe {
            gl::Clear(gl::COLOR_BUFFER_BIT);
            gl::UseProgram(shader_program);
            gl::DrawArrays(gl::TRIANGLES, 0, 6);
        }

        window.gl_swap_window();
    }
}