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use crate::core::*;

pub struct ImageEffect {
    gl: Gl,
    program: Program,
    positions: VertexBuffer,
    uvs: VertexBuffer
}

impl ImageEffect {
    pub fn new(gl: &Gl, fragment_shader: &str) -> Result<Self, Error>
    {
        let program = program::Program::from_source(&gl,
                                                    "in vec3 position;
                                                    in vec2 uv_coordinate;
                                                    out vec2 uv;
                                                    void main()
                                                    {
                                                        uv = uv_coordinate;
                                                        gl_Position = vec4(position, 1.0);
                                                    }",
                                                    fragment_shader)?;

        let positions = vec![
            -3.0, -1.0, 0.0,
            3.0, -1.0, 0.0,
            0.0, 2.0, 0.0
        ];
        let uvs = vec![
            -1.0, 0.0,
            2.0, 0.0,
            0.5, 1.5
        ];
        let positions = VertexBuffer::new_with_static_f32(&gl, &positions).unwrap();
        let uvs = VertexBuffer::new_with_static_f32(&gl, &uvs).unwrap();

        Ok(Self {gl: gl.clone(), program, positions, uvs})
    }

    pub fn program(&self) -> &Program {
        &self.program
    }

    pub fn apply(&self) {
        state::cull(&self.gl,state::CullType::Back);

        self.program.use_attribute_vec3_float(&self.positions, "position").unwrap();
        self.program.use_attribute_vec2_float(&self.uvs, "uv_coordinate").unwrap();
        self.program.draw_arrays(3);
    }
}