use std::ffi::CStr;
use std::ptr::null_mut;

#[derive(Debug)]
pub struct Shader
{
    shader: gl::types::GLuint,
}

impl Shader
{
    pub fn new(kind: Kind) -> Self
    {
        let shader = unsafe { gl::CreateShader(kind.into_gl()) };

        Self { shader }
    }

    pub fn set_source(&self, source: &str) -> Result<(), Error>
    {
        if !source.is_ascii() {
            return Err(Error::SourceNotAscii);
        }

        unsafe {
            #[allow(clippy::cast_possible_wrap, clippy::cast_possible_truncation)]
            gl::ShaderSource(
                self.shader,
                1,
                &source.as_ptr().cast(),
                &(source.len() as gl::types::GLint),
            );
        }

        Ok(())
    }

    pub fn compile(&self) -> Result<(), Error>
    {
        unsafe {
            gl::CompileShader(self.shader);
        }

        let mut compile_success = gl::types::GLint::default();

        unsafe {
            gl::GetShaderiv(self.shader, gl::COMPILE_STATUS, &mut compile_success);
        }

        if compile_success == 0 {
            let info_log = self.get_info_log();

            return Err(Error::CompileFailed(info_log));
        }

        Ok(())
    }

    fn get_info_log(&self) -> String
    {
        let mut buf = vec![gl::types::GLchar::default(); 512];

        unsafe {
            #[allow(clippy::cast_possible_wrap, clippy::cast_possible_truncation)]
            gl::GetShaderInfoLog(
                self.shader,
                buf.len() as gl::types::GLsizei,
                null_mut(),
                buf.as_mut_ptr(),
            );
        }

        let info_log = unsafe { CStr::from_ptr(buf.as_ptr()) };

        unsafe { String::from_utf8_unchecked(info_log.to_bytes().to_vec()) }
    }
}

impl Drop for Shader
{
    fn drop(&mut self)
    {
        unsafe {
            gl::DeleteShader(self.shader);
        }
    }
}

/// Shader kind.
#[derive(Debug, Clone, Copy)]
pub enum Kind
{
    Vertex,
    Fragment,
}

impl Kind
{
    fn into_gl(self) -> gl::types::GLenum
    {
        match self {
            Self::Vertex => gl::VERTEX_SHADER,
            Self::Fragment => gl::FRAGMENT_SHADER,
        }
    }
}

/// Shader program
#[derive(Debug)]
pub struct Program
{
    program: gl::types::GLuint,
}

impl Program
{
    pub fn new() -> Self
    {
        let program = unsafe { gl::CreateProgram() };

        Self { program }
    }

    pub fn attach(&self, shader: &Shader)
    {
        unsafe {
            gl::AttachShader(self.program, shader.shader);
        }
    }

    pub fn link(&self) -> Result<(), Error>
    {
        unsafe {
            gl::LinkProgram(self.program);
        }

        let mut link_success = gl::types::GLint::default();

        unsafe {
            gl::GetProgramiv(self.program, gl::LINK_STATUS, &mut link_success);
        }

        if link_success == 0 {
            let info_log = self.get_info_log();

            return Err(Error::CompileFailed(info_log));
        }

        Ok(())
    }

    pub fn activate(&self)
    {
        unsafe {
            gl::UseProgram(self.program);
        }
    }

    fn get_info_log(&self) -> String
    {
        let mut buf = vec![gl::types::GLchar::default(); 512];

        unsafe {
            #[allow(clippy::cast_possible_wrap, clippy::cast_possible_truncation)]
            gl::GetProgramInfoLog(
                self.program,
                buf.len() as gl::types::GLsizei,
                null_mut(),
                buf.as_mut_ptr(),
            );
        }

        let info_log = unsafe { CStr::from_ptr(buf.as_ptr()) };

        unsafe { String::from_utf8_unchecked(info_log.to_bytes().to_vec()) }
    }
}

impl Drop for Program
{
    fn drop(&mut self)
    {
        unsafe {
            gl::DeleteProgram(self.program);
        }
    }
}

/// Shader error.
#[derive(Debug, thiserror::Error)]
pub enum Error
{
    #[error("All characters in source are not within the ASCII range")]
    SourceNotAscii,

    #[error("Failed to compile: {0}")]
    CompileFailed(String),
}