use glow::*;
use iced_glow::glow;
use iced_glow::Color;

pub struct Scene {
    program: glow::Program,
    vertex_array: glow::VertexArray,
}

impl Scene {
    pub fn new(gl: &glow::Context, shader_version: &str) -> Self {
        unsafe {
            let vertex_array = gl
                .create_vertex_array()
                .expect("Cannot create vertex array");
            gl.bind_vertex_array(Some(vertex_array));

            let program = gl.create_program().expect("Cannot create program");

            let (vertex_shader_source, fragment_shader_source) = (
                r#"const vec2 verts[3] = vec2[3](
                    vec2(0.5f, 1.0f),
                    vec2(0.0f, 0.0f),
                    vec2(1.0f, 0.0f)
                );
                out vec2 vert;
                void main() {
                    vert = verts[gl_VertexID];
                    gl_Position = vec4(vert - 0.5, 0.0, 1.0);
                }"#,
                r#"precision highp float;
                in vec2 vert;
                out vec4 color;
                void main() {
                    color = vec4(vert, 0.5, 1.0);
                }"#,
            );

            let shader_sources = [
                (glow::VERTEX_SHADER, vertex_shader_source),
                (glow::FRAGMENT_SHADER, fragment_shader_source),
            ];

            let mut shaders = Vec::with_capacity(shader_sources.len());

            for (shader_type, shader_source) in shader_sources.iter() {
                let shader = gl
                    .create_shader(*shader_type)
                    .expect("Cannot create shader");
                gl.shader_source(
                    shader,
                    &format!("{}\n{}", shader_version, shader_source),
                );
                gl.compile_shader(shader);
                if !gl.get_shader_compile_status(shader) {
                    panic!("{}", gl.get_shader_info_log(shader));
                }
                gl.attach_shader(program, shader);
                shaders.push(shader);
            }

            gl.link_program(program);
            if !gl.get_program_link_status(program) {
                panic!("{}", gl.get_program_info_log(program));
            }

            for shader in shaders {
                gl.detach_shader(program, shader);
                gl.delete_shader(shader);
            }

            gl.use_program(Some(program));
            Self {
                program,
                vertex_array,
            }
        }
    }

    pub fn clear(&self, gl: &glow::Context, background_color: Color) {
        let [r, g, b, a] = background_color.into_linear();
        unsafe {
            gl.clear_color(r, g, b, a);
            gl.clear(glow::COLOR_BUFFER_BIT);
        }
    }

    pub fn draw(&self, gl: &glow::Context) {
        unsafe {
            gl.bind_vertex_array(Some(self.vertex_array));
            gl.use_program(Some(self.program));
            gl.draw_arrays(glow::TRIANGLES, 0, 3);
        }
    }

    pub fn cleanup(&self, gl: &glow::Context) {
        unsafe {
            gl.delete_program(self.program);
            gl.delete_vertex_array(self.vertex_array);
        }
    }
}