mod poly;

use poly::Poly;

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

use gl::types::*;

pub struct Bezier {
    pub degree: usize,
    pub vx: Vec<f32>,
    pub vy: Vec<f32>,
    pub px: Poly,
    pub py: Poly,
    pub dpx: Poly,
    pub dpy: Poly,
}

pub fn to_poly(v: &Vec<f32>) -> Poly {
    match v.len() {
        0 => Poly::new(vec![0.0]),
        1 => Poly::new(vec![v[0]]),
        2 => Poly::new(vec![v[0], v[1] - v[0]]),
        _ => {
            let mut pv = Vec::new();
            for i in 0..v.len() - 1 {
                pv.push(Poly::new(vec![v[i], v[i + 1] - v[i]]));
            }
            while pv.len() > 1 {
                let mut npv = Vec::new();
                for i in 0..pv.len() - 1 {
                    let c = &pv[i + 1] - &pv[i];
                    npv.push(&pv[i] + &c.shift());
                }
                pv = npv;
            }
            pv[0].clone()
        }
    }
}

impl Bezier {
    pub fn new() -> Bezier {
        Bezier {
            vx: Vec::<f32>::new(),
            vy: Vec::<f32>::new(),
            px: Poly::new(vec![]),
            py: Poly::new(vec![]),
            dpy: Poly::new(vec![]),
            dpx: Poly::new(vec![]),
            degree: 0,
        }
    }

    pub fn push(&mut self, x: i32, y: i32) {
        self.vx.push(x as f32);
        self.vy.push(y as f32);
        self.px = to_poly(&self.vx);
        self.py = to_poly(&self.vy);
        self.dpx = self.px.deriv();
        self.dpy = self.py.deriv();
        self.degree += 1;
    }

    pub fn remove(&mut self, index: usize) {
        self.vx.remove(index);
        self.vy.remove(index);
        self.px = to_poly(&self.vx);
        self.py = to_poly(&self.vy);
        self.dpx = self.px.deriv();
        self.dpy = self.py.deriv();
        self.degree -= 1;
    }

    pub fn show_x(&self) -> String {
        let mut s = String::new();
        for i in 0..self.degree {
            s.push_str(&self.vx[i].to_string());
            if i < self.degree - 1 {
                s.push_str(", ");
            }
        }
        s
    }

    pub fn show_y(&self) -> String {
        let mut s = String::new();
        for i in 0..self.degree {
            s.push_str(&self.vy[i].to_string());
            if i < self.degree - 1 {
                s.push_str(", ");
            }
        }
        s
    }

    pub fn draw(&self) {
        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 vx[{s}] = float[{s}]({vx});
        float vy[{s}] = float[{s}]({vy});
    
        float px[{sx}] = float[{sx}]({px});
        float py[{sy}] = float[{sy}]({py});
    
        float dpx[{dsx}] = float[{dsx}]({dpx});
        float dpy[{dsy}] = float[{dsy}]({dpy});
    
        float thr = 32;
        float step_size = 10;
        float inf = 1000000;
    
        float eval_px(float t) {{
            float result = 0.0;
            for (int i = 0; i < {sx}; i++) {{
              result += px[i] * pow(t, i);
            }}
            return result;
        }}
    
        float eval_py(float t) {{
            float result = 0.0;
            for (int i = 0; i < {sy}; i++) {{
              result += py[i] * pow(t, i);
            }}
            return result;
        }}
    
        float eval_dpx(float t) {{
            float result = 0.0;
            for (int i = 0; i < {dsx}; i++) {{
              result += dpx[i] * pow(t, i);
            }}
            return result;
        }}
    
        float eval_dpy(float t) {{
            float result = 0.0;
            for (int i = 0; i < {dsy}; i++) {{
              result += dpy[i] * pow(t, i);
            }}
            return result;
        }}
    
        float control(vec2 pos) {{
          float closest = inf;
          for (int i = 0; i < {s}; i++) {{
            float d = distance(pos, vec2(vx[i], vy[i]));
            if (d < closest) {{
              closest = d;
            }}
          }}
          return 1 - closest / thr;
        }}
    
        float inside(vec2 pos) {{
          float closest = inf;
          float t = 0.0;
          float dstep = 0.0;
          while (t < 1.0 - dstep) {{
            dstep = step_size / length(vec2(eval_dpx(t), eval_dpy(t)));
            float step = t + dstep;
            vec2 a = vec2(eval_px(t), eval_py(t));
            vec2 b = vec2(eval_px(step), eval_py(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);
          float c = control(gl_FragCoord.xy);
          FragColor = vec4(r, c, 0.0, 1.0);
        }}
        ",
            s = self.degree,
            vx = self.show_x(),
            vy = self.show_y(),
            px = &self.px,
            py = &self.py,
            sx = self.px.degree() + 1,
            sy = self.py.degree() + 1,
            dpx = &self.dpx,
            dpy = &self.dpy,
            dsx = self.dpx.degree() + 1,
            dsy = self.dpy.degree() + 1,
        )
        .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);
            gl::UseProgram(shader_program);
        }
    }
}

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
    }
}