use ::context;
use context::Context;
use std::ffi::CStr;
use std::fs::File;
use std::io::BufReader;
use std::io::Read;
use std::mem;
use std::path::Path;
use texture::{Texture, TextureId};


#[derive(Clone, Debug)]
pub struct Program<'a> {
    cx: &'a ::context::Context,
    vert_obj: u32,
    frag_obj: u32,
    program_obj: u32,
    tex_ids: Vec<TextureId>,
    tex_locations: Vec<i32>,
}

#[derive(Clone, Debug)]
pub struct ProgramId {
    id: u32,
}

impl<'a> Program<'a> {
    pub fn from_paths<P: AsRef<Path>>(cx: &'a Context, vert_path: P, frag_path: P) -> Result<Program<'a>, String> {
        let vert_src = {
            let file = File::open(&vert_path)
                .map_err(|e| format!("{}", e))?;
            let mut reader = BufReader::new(file);
            let mut buf: Vec<u8> = vec![];
            reader.read_to_end(&mut buf)
                .map_err(|e| format!("{}", e))?;
            buf
        };

        let frag_src = {
            let file = File::open(&frag_path)
                .map_err(|e| format!("{}", e))?;
            let mut reader = BufReader::new(file);
            let mut buf: Vec<u8> = vec![];
            reader.read_to_end(&mut buf)
                .map_err(|e| format!("{}", e))?;
            buf
        };

        Self::new(cx, &vert_src, &frag_src)
    }

    pub fn new(cx: &'a Context, vert_src: &[u8], frag_src: &[u8]) -> Result<Program<'a>, String> {
        unsafe {
            let vert_obj = {
                let vert_obj = cx.gl.CreateShader(context::gl::VERTEX_SHADER);
                let vert_len = vert_src.len() as i32;
                cx.gl.ShaderSource(
                    vert_obj,
                    1,
                    [vert_src.as_ptr() as *const _].as_ptr(),
                    &vert_len as *const _);
                cx.gl.CompileShader(vert_obj);
                check_compile_errors(cx, vert_obj)?;
                check_gl_errors!(cx);
                vert_obj
            };

            let frag_obj = {
                let frag_obj = cx.gl.CreateShader(context::gl::FRAGMENT_SHADER);
                let frag_len = frag_src.len() as i32;
                cx.gl.ShaderSource(
                    frag_obj,
                    1,
                    [frag_src.as_ptr() as *const _].as_ptr(),
                    &frag_len as *const _);
                cx.gl.CompileShader(frag_obj);
                check_compile_errors(cx, frag_obj)?;
                check_gl_errors!(cx);
                frag_obj
            };

            let program_obj = {
                let prog = cx.gl.CreateProgram();
                cx.gl.AttachShader(prog, vert_obj);
                cx.gl.AttachShader(prog, frag_obj);
                cx.gl.LinkProgram(prog);
                check_link_errors(cx, prog)?;

                cx.gl.UseProgram(prog);
                check_gl_errors!(cx);
                prog
            };

            Ok(Program {
                cx: cx,
                vert_obj: vert_obj,
                frag_obj: frag_obj,
                program_obj: program_obj,
                tex_ids: vec![],
                tex_locations: vec![],
            })
        }
    }

    pub fn add_texture(&mut self, texture: &Texture, uniform_name: &CStr) {
        //TODO store reference to texture
        unsafe {
            let tex_loc = self.cx.gl.GetUniformLocation(self.program_obj, uniform_name.as_ptr() as *const _);
            check_gl_errors!(self.cx);

            self.tex_ids.push(texture.id());
            self.tex_locations.push(tex_loc);
        }
    }

    pub fn add_attribute(&mut self, name: &CStr, number_components: u32, stride: usize, offset: usize) {
        unsafe {
            let attrib_id = self.cx.gl.GetAttribLocation(self.program_obj, name.as_ptr() as *const _);
            self.cx.gl.VertexAttribPointer(
                attrib_id as u32,
                number_components as i32, // size
                context::gl::FLOAT, // type
                0, // normalized
                (stride * mem::size_of::<f32>()) as context::gl::types::GLsizei,
                (offset * mem::size_of::<f32>()) as *const () as *const _);
            self.cx.gl.EnableVertexAttribArray(attrib_id as u32);
        }
        check_gl_errors!(self.cx);
    }

    pub fn before_render(&self) {
        unsafe {
            //self.cx.gl.UseProgram(self.program_obj);
            //TODO check max texture number
            for (i, (tex_id, &tex_loc)) in self.tex_ids.iter().zip(&self.tex_locations).enumerate() {
                self.cx.gl.ActiveTexture(context::gl::TEXTURE0 + i as u32);
                self.cx.gl.BindTexture(context::gl::TEXTURE_2D, tex_id.id);
                self.cx.gl.Uniform1i(tex_loc, i as i32);
            }
        }
    }

    pub fn id(&self) -> ProgramId {
        ProgramId {
            id: self.program_obj,
        }
    }
}

fn check_link_errors(cx: &Context, program_obj: u32) -> Result<(), String> {
    unsafe {
        let mut link_success: i32 = mem::uninitialized();

        cx.gl.GetProgramiv(program_obj, context::gl::LINK_STATUS, &mut link_success);

        if link_success == 0 {
            let mut error_log_size: i32 = mem::uninitialized();
            cx.gl.GetProgramiv(program_obj, context::gl::INFO_LOG_LENGTH, &mut error_log_size);

            let mut error_log: Vec<u8> = Vec::with_capacity(error_log_size as usize);
            cx.gl.GetProgramInfoLog(program_obj, error_log_size, &mut error_log_size,
                                    error_log.as_mut_ptr() as *mut context::gl::types::GLchar);

            error_log.set_len(error_log_size as usize);

            Err(String::from_utf8_lossy(&error_log).into())
        } else {
            Ok(())
        }
    }
}

fn check_compile_errors(cx: &Context, shader_obj: u32) -> Result<(), String> {
    unsafe {
        // checking compilation success by reading a flag on the shader
        let compilation_success = {
            let mut compilation_success: i32 = mem::uninitialized();
            cx.gl.GetShaderiv(shader_obj, context::gl::COMPILE_STATUS, &mut compilation_success);
            compilation_success
        };

        if compilation_success != 1 {
            // compilation error
            let mut error_log_size: i32 = mem::uninitialized();
            cx.gl.GetShaderiv(shader_obj, context::gl::INFO_LOG_LENGTH, &mut error_log_size);
            let mut error_log: Vec<u8> = Vec::with_capacity(error_log_size as usize);

            cx.gl.GetShaderInfoLog(shader_obj, error_log_size, &mut error_log_size,
                                     error_log.as_mut_ptr() as *mut _);
            error_log.set_len(error_log_size as usize);

            Err(String::from_utf8_lossy(&error_log).into())
        } else {
            Ok(())
        }
    }
}