#[derive(Default)]

pub struct PipelineState {

    blending: bool,

}

impl PipelineState {

    pub fn new() -> Self {

        Self::default()

    }

    pub fn with_blend(mut self) -> Self {

        unsafe {

            gl::Enable(gl::BLEND);

            gl::BlendFunc(gl::SRC_ALPHA, gl::ONE_MINUS_SRC_ALPHA);

        }

        self.blending = true;

        self

    }

}

impl Drop for PipelineState {

    fn drop(&mut self) {

        if self.blending {

            unsafe { gl::Disable(gl::BLEND) }

        }

    }

}

#[derive(Debug)]

pub struct Texture2D {

}

impl Drop for Texture2D {

    fn drop(&mut self) {

            unsafe {

            }

        }

    }

}

impl Texture2D {

    pub fn with_data(

        data: &[u8],

        data_stride: u32,

        internal_format: u32,

        format: u32,

        ty: u32,

        filter: u32,

    ) -> Self {

        }

    }

    pub fn update(&self, region: Rect, data: &[u8], data_stride: u32, format: u32, ty: u32) {

        }

    }

}

#[derive(Debug)]

pub struct Buffer {

    pub handle: u32,

    pub ty: u32,

    pub usage: u32,

}

impl Buffer {

    pub fn empty(

        ty: u32,

        usage: u32,

        //size: isize

    ) -> Buffer {

        let mut buffer = 0;

        unsafe {

            gl::GenBuffers(1, &mut buffer);

            gl::BindBuffer(ty, buffer);

            //gl::BufferData(ty, size, ptr::null_mut(), usage);

        }

        Buffer {

            handle: buffer,

            ty,

            usage,

        }

    }

    fn with_data(ty: u32, usage: u32, data: &[u8]) -> Buffer {

        let mut buffer = 0;

        unsafe {

            gl::GenBuffers(1, &mut buffer);

            gl::BindBuffer(ty, buffer);

            gl::BufferData(ty, data.len() as isize, data.as_ptr() as _, usage);

        }

        Buffer {

            handle: buffer,

            ty,

            usage,

        }

    }

    pub fn ty(&self) -> u32 {

        self.ty

    }

    pub fn handle(&self) -> u32 {

        self.handle

    }

    pub fn write_typed<T>(&self, data: &[T]) {

        unsafe {

            let data =

                slice::from_raw_parts(data.as_ptr() as *const u8, data.len() * mem::size_of::<T>());

            gl::BindBuffer(self.ty, self.handle);

            gl::BufferData(

                self.ty,

                data.len() as isize,

                data.as_ptr() as *const _ as *const _,

                self.usage,

            );

        }

    }

    pub fn write(&self, data: &[u8]) {

        unsafe {

            gl::BindBuffer(self.ty, self.handle);

            gl::BufferData(

                self.ty,

                data.len() as isize,

                data.as_ptr() as *const _ as *const _,

                self.usage,

            );

        }

    }

}

impl Drop for Buffer {

    fn drop(&mut self) {

        unsafe {

            gl::DeleteBuffers(1, &self.handle);

        }

    }

}

#[derive(Debug)]

pub enum VariableBinding<'a> {

    Attribute(&'a str, u32),

    Uniform(&'a str, u32),

    UniformBlock(&'a str, u32),

    Sampler(&'a str, u32),

}

#[derive(Debug)]

pub struct Shader {

    pub program: u32,

}

impl Drop for Shader {

    fn drop(&mut self) {

        unsafe {

            gl::DeleteProgram(self.program);

        }

    }

}

impl Shader {

    pub fn new<'a>(

        vs: &str,

        ps: Option<&str>,

        bindings: &[VariableBinding<'a>],

    ) -> Result<Self, String> {

        unsafe fn compile_shader(ty: u32, shdr: &str) -> Result<u32, String> {

            let shader = gl::CreateShader(ty);

            let len = shdr.len() as i32;

            let shdr = shdr.as_ptr() as *const i8;

            gl::ShaderSource(shader, 1, &shdr, &len);

            gl::CompileShader(shader);

            let mut success = 0i32;

            gl::GetShaderiv(shader, gl::COMPILE_STATUS, &mut success as _);

            if success == gl::FALSE as i32 {

                let mut log_size = 0i32;

                gl::GetShaderiv(shader, gl::INFO_LOG_LENGTH, &mut log_size as _);

                let mut log = vec![0u8; log_size as usize];

                gl::GetShaderInfoLog(shader, log_size, ptr::null_mut(), log.as_mut_ptr() as _);

                gl::DeleteShader(shader);

                Err(String::from_utf8_unchecked(log))

            } else {

                Ok(shader)

            }

        }

        let vs = unsafe { compile_shader(gl::VERTEX_SHADER, vs)? };

        let ps = if let Some(ps) = ps {

            Some(unsafe { compile_shader(gl::FRAGMENT_SHADER, ps)? })

        } else {

            None

        };

        unsafe {

            let program = gl::CreateProgram();

            gl::AttachShader(program, vs);

            if let Some(ps) = ps {

                gl::AttachShader(program, ps);

            }

            for bind in bindings {

                match bind {

                    &VariableBinding::Attribute(ref name, id) => {

                        let c_str = CString::new(name.as_bytes()).unwrap();

                        gl::BindAttribLocation(

                            program,

                            id,

                            c_str.to_bytes_with_nul().as_ptr() as *const _,

                        );

                    }

                    _ => {}

                }

            }

            gl::LinkProgram(program);

            let mut success = 0i32;

            gl::GetProgramiv(program, gl::LINK_STATUS, &mut success);

            if success == gl::FALSE as i32 {

                let mut log_size = 0i32;

                gl::GetProgramiv(program, gl::INFO_LOG_LENGTH, &mut log_size as _);

                let mut log = vec![0u8; log_size as usize];

                gl::GetProgramInfoLog(program, log_size, ptr::null_mut(), log.as_mut_ptr() as _);

                gl::DeleteProgram(program);

                return Err(String::from_utf8_unchecked(log));

            }

            //gl::DetachShader(program, vs);

            if let Some(ps) = ps {

                //gl::DetachShader(program, ps);

            }

            gl::UseProgram(program);

            // after linking we setup sampler bindings as specified in the shader

            for bind in bindings {

                match bind {

                    VariableBinding::Uniform(name, id) => {

                        let c_str = CString::new(name.as_bytes()).unwrap();

                        let index = gl::GetUniformLocation(

                            program,

                            c_str.to_bytes_with_nul().as_ptr() as *const _,

                        );

                        // TODO: impl for block?

                    }

                    VariableBinding::UniformBlock(name, id) => {

                        let c_str = CString::new(name.as_bytes()).unwrap();

                        let index = gl::GetUniformBlockIndex(

                            program,

                            c_str.to_bytes_with_nul().as_ptr() as *const _,

                        );

                        gl::UniformBlockBinding(program, index, *id);

                    }

                    VariableBinding::Sampler(name, id) => {

                        let c_str = CString::new(name.as_bytes()).unwrap();

                        let index = gl::GetUniformLocation(

                            program,

                            c_str.to_bytes_with_nul().as_ptr() as *const _,

                        );

                        gl::Uniform1i(index, *id as i32);

                    }

                    _ => {}

                }

            }

            Ok(Shader { program })

        }

    }

    pub fn bind(&self) {

        unsafe {

            gl::UseProgram(self.program);

        }

    }

    pub fn set_matrix(&self, name: &str, matrix: *const f32) {

        unsafe {

            let c_str = CString::new(name).unwrap();

            let index = gl::GetUniformLocation(

                self.program,

                c_str.to_bytes_with_nul().as_ptr() as *const _,

            );

            gl::UniformMatrix4fv(index, 1, gl::FALSE, matrix);

        }

    }

    pub fn bind_texture_2d(&self, index: u32, texture: &Texture2D) {

        self.bind();

        }

    }

}

pub enum InputFormat {

    Float(u32, bool),

    Integer(u32),

}

pub struct InputElement {

    pub shader_slot: u32,

    pub buffer_slot: u32,

    pub format: InputFormat,

    pub components: u32,

    pub stride: u32,

    pub offset: u32,

}

// TODO:

pub struct InputLayout {

    pub elements: Vec<InputElement>,

}

pub struct LayoutGuard {

    vao: u32,

}

impl Drop for LayoutGuard {

    fn drop(&mut self) {

        unsafe {

            gl::DeleteVertexArrays(1, [self.vao].as_ptr());

            gl::BindVertexArray(0);

        }

    }

}

impl InputLayout {

    pub fn new(elements: Vec<InputElement>) -> Self {

        InputLayout { elements }

    }

    pub fn bind(

        &mut self,

        buffers: &[(u32, &Buffer)],

        index_buffer: Option<&Buffer>,

    ) -> LayoutGuard {

        let mut vao = 0;

        unsafe {

            gl::GenVertexArrays(1, &mut vao);

            gl::BindVertexArray(vao);

        }

        for &(slot, ref buffer) in buffers {

            unsafe {

                gl::BindBuffer(buffer.ty(), buffer.handle());

            }

            for attr in self.elements.iter().filter(|a| a.buffer_slot == slot) {

                unsafe {

                    gl::EnableVertexAttribArray(attr.shader_slot);

                    match attr.format {

                        InputFormat::Float(fmt, normalized) => {

                            gl::VertexAttribPointer(

                                attr.shader_slot,

                                attr.components as i32,

                                fmt,

                                if normalized { gl::TRUE } else { gl::FALSE },

                                attr.stride as i32,

                                attr.offset as *const _,

                            );

                        }

                        InputFormat::Integer(fmt) => {

                            gl::VertexAttribIPointer(

                                attr.shader_slot,

                                attr.components as i32,

                                fmt,

                                attr.stride as i32,

                                attr.offset as *const _,

                            );

                        }

                    }

                }

            }

        }

        if let Some(buf) = index_buffer {

            unsafe {

                gl::BindBuffer(gl::ELEMENT_ARRAY_BUFFER, buf.handle());

            }

        }

        LayoutGuard { vao }

    }

}