use sdl2::event::Event;
use sdl2::keyboard::Keycode;

use std::convert::TryInto;
use std::ffi::{CStr, CString};
use std::time::Duration;

const VERT_SHADER_SRC: &str = 
"
#define lowp
#define mediump
#define highp
#line 0
uniform highp mat4 uni_model;
uniform highp mat4 uni_viewproj;

attribute highp vec4 attr_pos;
attribute mediump vec2 attr_uv;
attribute lowp vec3 attr_normal;

varying lowp vec4 vary_color;
varying mediump vec2 vary_uv;

void main (void) {
	vary_uv = attr_uv;
	
	lowp vec4 light_color = vec4 (1.0);
	
	vary_color = light_color;
	
	vec4 world_pos = uni_model * attr_pos;
	
	gl_Position = uni_viewproj * world_pos;
}";

const FRAG_SHADER_SRC: &str = 
"
#define lowp
#define mediump
#define highp
#line 0
uniform lowp sampler2D uni_texture;

varying lowp vec4 vary_color;
varying mediump vec2 vary_uv;

void main (void) {
	gl_FragColor = texture2D (uni_texture, vary_uv) * vary_color;
	//gl_FragColor = vec4 (1.0, 0.0, 1.0, 1.0);
}
";

pub struct ShaderObject {
	id: u32,
}

impl ShaderObject {
	pub fn id (&self) -> u32 {
		self.id
	}
	
	pub fn new (shader_type: u32, source: &str) -> Result <ShaderObject, String>
	{
		let id = unsafe {
			gl::CreateShader (shader_type)
		};
		
		let sources = [
			source.as_ptr () as *const i8,
		];
		
		let lengths = [
			source.len ().try_into ().unwrap (),
		];
		
		let success = unsafe {
			gl::ShaderSource (id, sources.len ().try_into ().unwrap (), sources.as_ptr (), lengths.as_ptr ());
			gl::CompileShader (id);
			
			let mut success = 0;
			gl::GetShaderiv (id, gl::COMPILE_STATUS, &mut success);
			success == 1
		};
		
		if success {
			Ok (ShaderObject {
				id,
			})
		}
		else {
			let mut info_log = vec! [0u8; 4096];
			let mut log_length = 0;
			
			unsafe {
				gl::GetShaderInfoLog (id, (info_log.len () - 1).try_into ().unwrap (), &mut log_length, info_log.as_mut_ptr () as *mut i8);
			}
			
			info_log.truncate (log_length.try_into ().unwrap ());
			
			let info = String::from_utf8 (info_log).unwrap ();
			
			Err (info)
		}
	}
}

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

pub struct ShaderProgram {
	id: u32,
}

impl ShaderProgram {
	pub fn new (vert: &ShaderObject, frag: &ShaderObject) 
	-> Result <ShaderProgram, String> 
	{
		let id = unsafe {
			gl::CreateProgram ()
		};
		
		unsafe {
			gl::AttachShader (id, vert.id ());
			gl::AttachShader (id, frag.id ());
			
			gl::LinkProgram (id);
		}
		
		let success = unsafe {
			let mut success = 0;
			gl::GetProgramiv (id, gl::LINK_STATUS, &mut success);
			success == 1
		};
		
		if success {
			Ok (ShaderProgram {
				id,
			})
		}
		else {
			let mut info_log = vec! [0u8; 4096];
			let mut log_length = 0;
			
			unsafe {
				gl::GetProgramInfoLog (id, (info_log.len () - 1).try_into ().unwrap (), &mut log_length, info_log.as_mut_ptr () as *mut i8);
			}
			
			info_log.truncate (log_length.try_into ().unwrap ());
			
			let info = String::from_utf8 (info_log).unwrap ();
			
			Err (info)
		}
	}
	
	pub fn get_uniform_location (&self, name: &CStr) -> i32 {
		unsafe {
			gl::UseProgram (self.id);
			gl::GetUniformLocation (self.id, name.as_ptr ())
		}
	}
}

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

fn main () {
	let sdl_context = sdl2::init ().unwrap ();
	let video_subsystem = sdl_context.video ().unwrap ();
	
	let window = video_subsystem.window ("OpenGL? In my Rust?", 1280, 720)
		.position_centered ()
		.opengl ()
		.build ()
	.unwrap ();
	
	gl::load_with (|s| {
		let result = video_subsystem.gl_get_proc_address (s) as *const _;
		//println! ("{:?}", result);
		
		result
	});
	
	assert! (gl::ClearColor::is_loaded ());
	
	let gl_ctx = window.gl_create_context ().unwrap ();
	
	window.gl_make_current (&gl_ctx).unwrap ();
	
	// I love how with Rust I can throw unwrap ()s everywhere
	// It's safer than C / C++'s default behavior of unchecked errors
	// It's more programmer-friendly and explicit than C#'s unchecked
	// exceptions that can appear almost anywhere at runtime with no
	// compile-time warning
	// And I'm still not actually checking errors - Just checkmarking
	// that I know where they are.
	
	let vert_shader = ShaderObject::new (gl::VERTEX_SHADER, VERT_SHADER_SRC).unwrap ();
	let frag_shader = ShaderObject::new (gl::FRAGMENT_SHADER, FRAG_SHADER_SRC).unwrap ();
	
	let shader_program = ShaderProgram::new (&vert_shader, &frag_shader).unwrap ();
	
	let uni_model = shader_program.get_uniform_location (&CString::new ("uni_model").unwrap ());
	let uni_viewproj = shader_program.get_uniform_location (CStr::from_bytes_with_nul (b"uni_viewproj\0").unwrap ());
	
	println! ("uni_model: {}", uni_model);
	println! ("uni_viewproj: {}", uni_viewproj);
	
	let mut event_pump = sdl_context.event_pump ().unwrap ();
	'running: loop {
		let _mouse = event_pump.mouse_state ();
		
		for event in event_pump.poll_iter() {
			match event {
				Event::Quit {..} |
				Event::KeyDown { keycode: Some (Keycode::Escape), .. } => {
					break 'running
				},
				_ => (),
			}
		}
		
		window.gl_make_current (&gl_ctx).unwrap ();
		
		unsafe {
			gl::ClearColor (1.0f32, 0.0f32, 1.0f32, 1.0f32);
			gl::Clear (gl::COLOR_BUFFER_BIT | gl::DEPTH_BUFFER_BIT);
		}
		
		window.gl_swap_window ();
		
		::std::thread::sleep (Duration::from_millis (15));
	}
}