use gl::types::GLfloat;
use glutin::prelude::GlDisplay;
use crate::backend::{opengl, Uniform};
use crate::math::{ Mat4, Vec3 };
use crate::{geometry, backend::gpu::GpuMesh};
use crate::shaders::Shader;
use std::ops::Deref;
use std::ffi::{ CStr, CString, c_void };
use super::gl::Gl;

#[derive(Debug)]
pub struct RenderState {
    pub projection: Mat4,
    pub view: Mat4,
    pub model: Mat4,
    pub camera_pos: Vec3,
    pub light_pos: Vec3,
    pub light_color: Vec3,
}

impl RenderState {
    pub fn new(aspect_ratio: f32) -> Self {
        let camera_pos = Vec3::new(0.0, 2.0, 5.0);
        Self {
            projection: Mat4::perspective(45.0_f32.to_radians(), aspect_ratio, 0.1, 100.0),
            view: Mat4::look_at(
                camera_pos,
                Vec3::new(0.0, 0.0, 0.0),
                Vec3::new(0.0, 1.0, 0.0),
            ),
            model: Mat4::identity(),
            camera_pos,
            light_pos: Vec3::new(3.0, 5.0, 3.0),
            light_color: Vec3::new(1.0, 1.0, 1.0),
        }
    }
}

fn get_gl_string(gl: &opengl::Gl, variant: gl::types::GLenum) -> Option<&'static CStr>{
  unsafe {
    let s = gl.GetString(variant);
    (!s.is_null()).then(|| CStr::from_ptr(s.cast()))
  }
}

pub struct GlRenderer {
  gl: Gl,
}

impl GlRenderer {
  pub fn new<D: GlDisplay>(gl_display: &D) -> Self {
    let gl = opengl::Gl::load_with(|symbol| {
      let symbol = CString::new(symbol).unwrap();
      gl_display.get_proc_address(symbol.as_c_str()).cast()
    });

    if let Some(renderer) = get_gl_string(&gl, gl::RENDERER) {
      println!("Running on {}", renderer.to_string_lossy());
    }

    if let Some(version) = get_gl_string(&gl, gl::VERSION) {
      println!("OpenGL version {}", version.to_string_lossy());
    }

    if let Some(shaders_version) = get_gl_string(&gl, gl::SHADING_LANGUAGE_VERSION) {
      println!("Shaders version on {}", shaders_version.to_string_lossy());
    }

    unsafe {
      gl.Enable(gl::DEPTH_TEST);
      gl.DepthFunc(gl::LESS);

      gl.Enable(gl::MULTISAMPLE);
    }

    Self {
      gl
    }
  }

  pub fn upload_mesh(&self, mesh: &geometry::Mesh) -> GpuMesh {
    unsafe {
      let gl = &self.gl;

      let mut vao = std::mem::zeroed();
      gl.GenVertexArrays(1, &mut vao);
      gl.BindVertexArray(vao);

      let mut vbo = std::mem::zeroed();
      gl.GenBuffers(1, &mut vbo);
      gl.BindBuffer(gl::ARRAY_BUFFER, vbo);

      for attribute in &mesh.format.attributes {
        let location = attribute.semantic.location();
        gl.VertexAttribPointer(
          attribute.semantic.location(),
          attribute.comp_count as i32,
          attribute.data_type.to_gpu(),
          attribute.normalized as u8,
          mesh.format.stride as i32,
          attribute.offset as *const c_void,
        );
        gl.EnableVertexAttribArray(location);
      }

      gl.BufferData(
        gl::ARRAY_BUFFER,
        mesh.vertex_data.len() as gl::types::GLsizeiptr,
        mesh.vertex_data.as_ptr() as *const _,
        gl::STATIC_DRAW,
      );

      let (ebo, index_count) = if !mesh.indices.is_empty() {
        let mut ebo = std::mem::zeroed();
        gl.GenBuffers(1, &mut ebo);
        gl.BindBuffer(gl::ELEMENT_ARRAY_BUFFER, ebo);
        gl.BufferData(
          gl::ELEMENT_ARRAY_BUFFER,
          (mesh.indices.len() * std::mem::size_of::<u32>()) as gl::types::GLsizeiptr,
          mesh.indices.as_ptr() as *const _,
          gl::STATIC_DRAW,
        );
        (Some(ebo), Some(mesh.indices.len() as i32))
      } else {
        (None, None)
      };

      gl.BindVertexArray(0);

      GpuMesh {
        vao,
        vbo,
        ebo,
        vertex_count: mesh.vertex_count as i32,
        index_count,
      }
    }
  }

  fn compile_shader(gl: &opengl::Gl, shader: gl::types::GLenum, source: &[u8]) -> gl::types::GLuint {
    unsafe {
      let shader = gl.CreateShader(shader);
      gl.ShaderSource(shader, 1, [source.as_ptr().cast()].as_ptr(), std::ptr::null());
      gl.CompileShader(shader);
      shader
    }
  }

  pub fn create_shader(&self, shader_src: &opengl::GlShaderSource) -> Shader {
    unsafe {
      let vertex_shader = Self::compile_shader(
        &self.gl,
        gl::VERTEX_SHADER,
        shader_src.vertex_src.as_bytes()
      );
      let fragment_shader = Self::compile_shader(
        &self.gl,
        gl::FRAGMENT_SHADER,
        shader_src.fragment_src.as_bytes()
      );

      let program = self.gl.CreateProgram();

      self.gl.AttachShader(program, vertex_shader);
      self.gl.AttachShader(program, fragment_shader);

      self.gl.LinkProgram(program);

      self.gl.DeleteShader(vertex_shader);
      self.gl.DeleteShader(fragment_shader);

      Shader(program)
    }
  }

  pub fn apply_uniform(&self, shader: Shader, uniform: &Uniform) {
    unsafe {
      match uniform {
        Uniform::Float(name, value) => {
          let location = self.GetUniformLocation(*shader, name.as_ptr());
          self.Uniform1f(location, *value);
        }
        Uniform::Int(name, value) => {
          let location = self.GetUniformLocation(*shader, name.as_ptr());
          self.Uniform1i(location, *value);
        }
        Uniform::Vec2(name, value) => {
          let location = self.GetUniformLocation(*shader, name.as_ptr());
          self.Uniform2f(location, value[0], value[1]);
        }
        Uniform::Vec3(name, value) => {
          let location = self.GetUniformLocation(*shader, name.as_ptr());
          self.Uniform3f(location, value[0], value[1], value[2]);
        }
        Uniform::Vec4(name, value) => {
          let location = self.GetUniformLocation(*shader, name.as_ptr());
          self.Uniform4f(location, value[0], value[1], value[2], value[3]);
        }
        Uniform::Mat4(name, value) => {
          let location = self.GetUniformLocation(*shader, name.as_ptr());
          self.UniformMatrix4fv(location, 1, gl::FALSE, value.as_ptr());
        }
      }
    }
  }

  pub fn clear(&self, red: GLfloat, green: GLfloat, blue: GLfloat, alpha: GLfloat) {
    unsafe {
      self.ClearColor(red, green, blue, alpha);
      self.Clear(gl::COLOR_BUFFER_BIT | gl::DEPTH_BUFFER_BIT);
    }
  }

  pub fn use_shader(&self, shader: Shader) {
    unsafe { self.UseProgram(*shader) };
  }

  pub fn resize(&self, width: i32, height: i32) {
    unsafe {
      self.gl.Viewport(0, 0, width, height);
    }
  }

  pub fn draw_mesh(&self, mesh: &GpuMesh) {
    unsafe {
      self.BindVertexArray(mesh.vao);

      if let (Some(ebo), Some(count)) = (mesh.ebo, mesh.index_count) {
        self.BindBuffer(gl::ELEMENT_ARRAY_BUFFER, ebo);
        self.DrawElements(gl::TRIANGLES, count, gl::UNSIGNED_INT, std::ptr::null());
      } else {
        self.DrawArrays(gl::TRIANGLES, 0, mesh.vertex_count);
      }
    }
  }
}

impl Deref for GlRenderer {
  type Target = opengl::Gl;

  fn deref(&self) -> &Self::Target {
      &self.gl
  }
}