// Copyright 2015 Matthew Collins
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

extern crate steven_gl as gl;
use glutin;

use std::ops::BitOr;
use std::ffi;
use std::mem;
use std::ptr;
use std::ops::{Deref, DerefMut};

/// Inits the gl library. This should be called once a context is ready.
pub fn init(window: &mut glutin::Window) {
    gl::load_with(|s| window.get_proc_address(s) as *const _);
}

/// Dsed to specify how the vertices will be handled
/// to draw.
pub type DrawType = u32;

/// Treats each set of 3 vertices as a triangle
pub const TRIANGLES: DrawType = gl::TRIANGLES;
/// Means the previous vertex connects to the next
/// one in a continuous strip.
pub const LINE_STRIP: DrawType = gl::LINE_STRIP;
/// Treats each set of 2 vertices as a line
pub const LINES: DrawType = gl::LINES;
/// Treats each vertex as a point
pub const POINTS: DrawType = gl::POINTS;

pub fn draw_elements(ty: DrawType, count: usize, dty: Type, offset: usize) {
    unsafe {
        gl::DrawElements(ty, count as i32, dty, offset as *const gl::types::GLvoid);
    }
}

/// Sets the size of the viewport of this context.
pub fn viewport(x: i32, y: i32, w: i32, h: i32) {
    unsafe {
        gl::Viewport(x, y, w, h);
    }
}

/// Sets the color the color buffer should be cleared to
/// when Clear is called with the color flag.
pub fn clear_color(r: f32, g: f32, b: f32, a: f32) {
    unsafe {
        gl::ClearColor(r, g, b, a);
    }
}

/// ClearFlags is a set of flags to mark what should be cleared during
/// a Clear call.
pub enum ClearFlags {
    /// Marks the color buffer to be cleared
    Color,
    /// Marks the depth buffer to be cleared
    Depth,
    Internal(u32),
}

impl ClearFlags {
    fn internal(self) -> u32 {
        match self {
            ClearFlags::Color => gl::COLOR_BUFFER_BIT,
            ClearFlags::Depth => gl::DEPTH_BUFFER_BIT,
            ClearFlags::Internal(val) => val,
        }
    }
}

impl BitOr for ClearFlags {
    type Output = ClearFlags;

    fn bitor(self, rhs: ClearFlags) -> ClearFlags {
        ClearFlags::Internal(self.internal() | rhs.internal())
    }
}

/// Clears the buffers specified by the passed flags.
pub fn clear(flags: ClearFlags) {
    unsafe { gl::Clear(flags.internal()) }
}

/// Func is a function to be preformed on two values.
pub type Func = u32;

pub const NEVER: Func = gl::NEVER;
pub const LESS: Func = gl::LESS;
pub const LESS_OR_EQUAL: Func = gl::LEQUAL;
pub const GREATER: Func = gl::GREATER;
pub const ALWAYS: Func = gl::ALWAYS;
pub const EQUAL: Func = gl::EQUAL;

pub fn depth_func(f: Func) {
    unsafe {
        gl::DepthFunc(f);
    }
}

/// Flag is a setting that can be enabled or disabled on the context.
pub type Flag = u32;

pub const DEPTH_TEST: Flag = gl::DEPTH_TEST;
pub const CULL_FACE_FLAG: Flag = gl::CULL_FACE;
pub const STENCIL_TEST: Flag = gl::STENCIL_TEST;
pub const BLEND: Flag = gl::BLEND;
pub const MULTISAMPLE: Flag = gl::MULTISAMPLE;

/// Enables the passed flag.
pub fn enable(f: Flag) {
    unsafe {
        gl::Enable(f);
    }
}

/// Disables the passed flag.
pub fn disable(f: Flag) {
    unsafe {
        gl::Disable(f);
    }
}

/// Sets the texture slot with the passed id as the
/// currently active one.
pub fn active_texture(id: u32) {
    unsafe {
        gl::ActiveTexture(gl::TEXTURE0 + id);
    }
}

/// Factor is used in blending
pub type Factor = u32;
pub const SRC_ALPHA: Factor = gl::SRC_ALPHA;
pub const ONE_MINUS_SRC_ALPHA: Factor = gl::ONE_MINUS_SRC_ALPHA;
pub const ONE_FACTOR: Factor = gl::ONE;
pub const ZERO_FACTOR: Factor = gl::ZERO;

/// Sets the factors to be used when blending.
pub fn blend_func(s_factor: Factor, d_factor: Factor) {
    unsafe {
        gl::BlendFunc(s_factor, d_factor);
    }
}

// Face specifies a face to act on.
pub type Face = u32;
pub const BACK: Face = gl::BACK;
pub const FRONT: Face = gl::FRONT;

/// Sets the face to be culled by the gpu.
pub fn cull_face(face: Face) {
    unsafe {
        gl::CullFace(face);
    }
}

// FaceDirection is used to specify an order of vertices, normally
// used to set which is considered to be the front face.
pub type FaceDirection = u32;
pub const CLOCK_WISE: FaceDirection = gl::CW;
pub const COUNTER_CLOCK_WISE: FaceDirection = gl::CCW;

/// Sets the direction of vertices used to specify the
/// front face (e.g. for culling).
pub fn front_face(dir: FaceDirection) {
    unsafe { gl::FrontFace(dir) }
}

/// Type is a type of data used by various operations.
pub type Type = u32;
pub const UNSIGNED_BYTE: Type = gl::UNSIGNED_BYTE;
pub const UNSIGNED_SHORT: Type = gl::UNSIGNED_SHORT;
pub const UNSIGNED_INT: Type = gl::UNSIGNED_INT;
pub const SHORT: Type = gl::SHORT;
pub const FLOAT: Type = gl::FLOAT;

/// TextureTarget is a target were a texture can be bound to
pub type TextureTarget = u32;

pub const TEXTURE_2D: TextureTarget = gl::TEXTURE_2D;
pub const TEXTURE_2D_MULTISAMPLE: TextureTarget = gl::TEXTURE_2D_MULTISAMPLE;
pub const TEXTURE_2D_ARRAY: TextureTarget = gl::TEXTURE_2D_ARRAY;
pub const TEXTURE_3D: TextureTarget = gl::TEXTURE_3D;

/// TextureFormat is the format of a texture either internally or
/// to be uploaded.
pub type TextureFormat = u32;

pub const RED: TextureFormat = gl::RED;
pub const RGB: TextureFormat = gl::RGB;
pub const RGBA: TextureFormat = gl::RGBA;
pub const RGBA8: TextureFormat = gl::RGBA8;
pub const RGBA16F: TextureFormat = gl::RGBA16F;
pub const R16F: TextureFormat = gl::R16F;
pub const DEPTH_COMPONENT24: TextureFormat = gl::DEPTH_COMPONENT24;
pub const DEPTH_COMPONENT: TextureFormat = gl::DEPTH_COMPONENT;

/// TextureParameter is a parameter that can be read or set on a texture.
pub type TextureParameter = u32;

pub const TEXTURE_MIN_FILTER: TextureParameter = gl::TEXTURE_MIN_FILTER;
pub const TEXTURE_MAG_FILTER: TextureParameter = gl::TEXTURE_MAG_FILTER;
pub const TEXTURE_WRAP_S: TextureParameter = gl::TEXTURE_WRAP_S;
pub const TEXTURE_WRAP_T: TextureParameter = gl::TEXTURE_WRAP_T;
pub const TEXTURE_MAX_LEVEL: TextureParameter = gl::TEXTURE_MAX_LEVEL;

/// TextureValue is a value that be set on a texture's parameter.
pub type TextureValue = i32;

pub const NEAREST: TextureValue = gl::NEAREST as TextureValue;
pub const LINEAR: TextureValue = gl::LINEAR as TextureValue;
pub const LINEAR_MIPMAP_LINEAR: TextureValue = gl::LINEAR_MIPMAP_LINEAR as TextureValue;
pub const LINEAR_MIPMAP_NEAREST: TextureValue = gl::LINEAR_MIPMAP_NEAREST as TextureValue;
pub const NEAREST_MIPMAP_NEAREST: TextureValue = gl::NEAREST_MIPMAP_NEAREST as TextureValue;
pub const NEAREST_MIPMAP_LINEAR: TextureValue = gl::NEAREST_MIPMAP_LINEAR as TextureValue;
pub const CLAMP_TO_EDGE: TextureValue = gl::CLAMP_TO_EDGE as TextureValue;

/// Texture is a buffer of data used by fragment shaders.
pub struct Texture(u32);

impl Texture {
    // Allocates a new texture.
    pub fn new() -> Texture {
        let mut t = Texture(0);
        unsafe {
            gl::GenTextures(1, &mut t.0);
        }
        t
    }

    /// Binds the texture to the passed target.
    pub fn bind(&self, target: TextureTarget) {
        unsafe {
            gl::BindTexture(target, self.0);
        }
    }

    pub fn get_pixels(&self,
                      target: TextureTarget,
                      level: i32,
                      format: TextureFormat,
                      ty: Type,
                      pixels: &mut [u8]) {
        unsafe {
            gl::GetTexImage(target,
                            level,
                            format,
                            ty,
                            pixels.as_mut_ptr() as *mut gl::types::GLvoid);
        }
    }

    pub fn image_3d(&self,
                    target: TextureTarget,
                    level: i32,
                    width: u32,
                    height: u32,
                    depth: u32,
                    format: TextureFormat,
                    ty: Type,
                    pix: &[u8]) {
        unsafe {
            gl::TexImage3D(target,
                           level,
                           format as i32,
                           width as i32,
                           height as i32,
                           depth as i32,
                           0,
                           format,
                           ty,
                           pix.as_ptr() as *const gl::types::GLvoid);
        }
    }

    pub fn sub_image_3d(&self,
                        target: TextureTarget,
                        level: i32,
                        x: u32,
                        y: u32,
                        z: u32,
                        width: u32,
                        height: u32,
                        depth: u32,
                        format: TextureFormat,
                        ty: Type,
                        pix: &[u8]) {
        unsafe {
            gl::TexSubImage3D(target,
                              level,
                              x as i32,
                              y as i32,
                              z as i32,
                              width as i32,
                              height as i32,
                              depth as i32,
                              format,
                              ty,
                              pix.as_ptr() as *const gl::types::GLvoid);
        }
    }

    pub fn set_parameter(&self,
                         target: TextureTarget,
                         param: TextureParameter,
                         value: TextureValue) {
        unsafe {
            gl::TexParameteri(target, param, value);
        }
    }
}

impl Drop for Texture {
    fn drop(&mut self) {
        unsafe {
            gl::DeleteTextures(1, &self.0);
        }
    }
}

pub type ShaderType = u32;

pub const VERTEX_SHADER: ShaderType = gl::VERTEX_SHADER;
pub const FRAGMENT_SHADER: ShaderType = gl::FRAGMENT_SHADER;
pub const GEOMETRY_SHADER: ShaderType = gl::GEOMETRY_SHADER;

pub type ShaderParameter = u32;

pub const COMPILE_STATUS: ShaderParameter = gl::COMPILE_STATUS;
pub const INFO_LOG_LENGTH: ShaderParameter = gl::INFO_LOG_LENGTH;

pub struct Program(u32);

impl Program {
    pub fn new() -> Program {
        Program(unsafe { gl::CreateProgram() })
    }

    pub fn attach_shader(&self, shader: Shader) {
        unsafe {
            gl::AttachShader(self.0, shader.0);
        }
    }

    pub fn link(&self) {
        unsafe {
            gl::LinkProgram(self.0);
        }
    }

    pub fn use_program(&self) {
        unsafe {
            gl::UseProgram(self.0);
        }
    }

    pub fn uniform_location(&self, name: &str) -> Uniform {
        Uniform(unsafe {
            gl::GetUniformLocation(self.0, ffi::CString::new(name).unwrap().as_ptr())
        })
    }

    pub fn attribute_location(&self, name: &str) -> Attribute {
        Attribute(unsafe {
            gl::GetAttribLocation(self.0, ffi::CString::new(name).unwrap().as_ptr())
        })
    }
}

impl Drop for Program {
    fn drop(&mut self) {
        unsafe {
            gl::DeleteProgram(self.0);
        }
    }
}

pub struct Shader(u32);

impl Shader {
    pub fn new(ty: ShaderType) -> Shader {
        Shader(unsafe { gl::CreateShader(ty) })
    }

    pub fn set_source(&self, src: &str) {
        unsafe {
            gl::ShaderSource(self.0,
                             1,
                             &ffi::CString::new(src).unwrap().as_ptr(),
                             ptr::null());
        }
    }

    pub fn compile(&self) {
        unsafe {
            gl::CompileShader(self.0);
        }
    }

    pub fn get_parameter(&self, param: ShaderParameter) -> i32 {
        let mut ret: i32 = 0;
        unsafe {
            gl::GetShaderiv(self.0, param, &mut ret);
        }
        ret
    }

    pub fn get_info_log(&self) -> String {
        let len = self.get_parameter(INFO_LOG_LENGTH);

        let mut data = Vec::<u8>::with_capacity(len as usize);
        unsafe {
            data.set_len(len as usize);
            gl::GetShaderInfoLog(self.0, len, ptr::null_mut(), data.as_mut_ptr() as *mut i8);
        }
        String::from_utf8(data).unwrap()
    }
}

pub struct Uniform(i32);

impl Uniform {
    pub fn set_int(&self, val: i32) {
        unsafe {
            gl::Uniform1i(self.0, val);
        }
    }

    pub fn set_int3(&self, x: i32, y: i32, z: i32) {
        unsafe {
            gl::Uniform3i(self.0, x, y, z);
        }
    }

    pub fn set_float(&self, val: f32) {
        unsafe {
            gl::Uniform1f(self.0, val);
        }
    }

    pub fn set_float2(&self, x: f32, y: f32) {
        unsafe {
            gl::Uniform2f(self.0, x, y);
        }
    }

    pub fn set_float3(&self, x: f32, y: f32, z: f32) {
        unsafe {
            gl::Uniform3f(self.0, x, y, z);
        }
    }

    pub fn set_float4(&self, x: f32, y: f32, z: f32, w: f32) {
        unsafe {
            gl::Uniform4f(self.0, x, y, z, w);
        }
    }
}

pub struct Attribute(i32);

impl Attribute {
    pub fn enable(&self) {
        unsafe {
            gl::EnableVertexAttribArray(self.0 as u32);
        }
    }

    pub fn disable(&self) {
        unsafe {
            gl::DisableVertexAttribArray(self.0 as u32);
        }
    }

    pub fn vertex_pointer(&self, size: i32, ty: Type, normalized: bool, stride: i32, offset: i32) {
        unsafe {
            gl::VertexAttribPointer(self.0 as u32,
                                    size,
                                    ty,
                                    normalized as u8,
                                    stride,
                                    offset as *const gl::types::GLvoid);
        }
    }

    pub fn vertex_pointer_int(&self, size: i32, ty: Type, stride: i32, offset: i32) {
        unsafe {
            gl::VertexAttribIPointer(self.0 as u32,
                                     size,
                                     ty,
                                     stride,
                                     offset as *const gl::types::GLvoid);
        }
    }
}

// VertexArray is used to store state needed to render vertices.
// This includes buffers, the format of the buffers and enabled
// attributes.
pub struct VertexArray(u32);

impl VertexArray {
    /// Allocates a new VertexArray.
    pub fn new() -> VertexArray {
        let mut va = VertexArray(0);
        unsafe {
            gl::GenVertexArrays(1, &mut va.0);
        }
        va
    }

    /// Marks the VertexArray as the currently active one, this
    /// means buffers/the format of the buffers etc will be bound to
    /// this VertexArray.
    pub fn bind(&self) {
        unsafe {
            gl::BindVertexArray(self.0);
        }
    }
}

impl Drop for VertexArray {
    fn drop(&mut self) {
        unsafe {
            gl::DeleteVertexArrays(1, &self.0);
        }
        self.0 = 0;
    }
}

/// BufferTarget is a target for a buffer to be bound to.
pub type BufferTarget = u32;

pub const ARRAY_BUFFER: BufferTarget = gl::ARRAY_BUFFER;
pub const ELEMENT_ARRAY_BUFFER: BufferTarget = gl::ELEMENT_ARRAY_BUFFER;

/// BufferUsage states how a buffer is going to be used by the program.
pub type BufferUsage = u32;

/// Marks the buffer as 'not going to change' after the
/// initial data upload to be rendered by the gpu.
pub const STATIC_DRAW: BufferUsage = gl::STATIC_DRAW;
/// Marks the buffer as 'changed frequently' during the
/// course of the program whilst being rendered by the gpu.
pub const DYNAMIC_DRAW: BufferUsage = gl::DYNAMIC_DRAW;
/// Marks the buffer as 'changed every frame' whilst being
/// rendered by the gpu.
pub const STREAM_DRAW: BufferUsage = gl::STREAM_DRAW;

/// Access states how a value will be accesed by the program.
pub type Access = u32;

/// States that the returned value will only be read.
pub const READ_ONLY: Access = gl::READ_ONLY;
/// States that the returned value will only be written
/// to.
pub const WRITE_ONLY: Access = gl::WRITE_ONLY;

/// Buffer is a storage for vertex data.
pub struct Buffer(u32);

impl Buffer {
    /// Allocates a new Buffer.
    pub fn new() -> Buffer {
        let mut b = Buffer(0);
        unsafe {
            gl::GenBuffers(1, &mut b.0);
        }
        b
    }

    /// Makes the buffer the currently active one for the given target.
    /// This will allow it to be the source of operations that act on a buffer
    /// (Data, Map etc).
    pub fn bind(&self, target: BufferTarget) {
        unsafe {
            gl::BindBuffer(target, self.0);
        }
    }

    pub fn set_data(&self, target: BufferTarget, data: &[u8], usage: BufferUsage) {
        unsafe {
            gl::BufferData(target,
                           data.len() as isize,
                           data.as_ptr() as *const gl::types::GLvoid,
                           usage);
        }
    }

    /// Maps the memory in the buffer on the gpu to memory which the program
    /// can access. The access flag will specify how the program plans to use the
    /// returned data. It'll unmap itself once the returned value is dropped.
    ///
    /// Warning: the passed length value is not checked in anyway so it is
    /// possible to overrun the memory. It is up to the program to ensure this
    /// length is valid.
    pub fn map(&self, target: BufferTarget, access: Access, length: usize) -> MappedBuffer {
        unsafe {
            MappedBuffer {
                inner: Vec::from_raw_parts(gl::MapBuffer(target, access) as *mut u8, 0, length),
                target: target,
            }
        }
    }
}

impl Drop for Buffer {
    fn drop(&mut self) {
        unsafe {
            gl::DeleteBuffers(1, &self.0);
        }
    }
}

pub struct MappedBuffer {
    inner: Vec<u8>,
    target: BufferTarget,
}

impl Deref for MappedBuffer {
    type Target = Vec<u8>;

    fn deref(&self) -> &Self::Target {
        &self.inner
    }
}

impl DerefMut for MappedBuffer {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.inner
    }
}

impl Drop for MappedBuffer {
    fn drop(&mut self) {
        unsafe {
            gl::UnmapBuffer(self.target);
        }
        mem::forget(mem::replace(&mut self.inner, Vec::new()));
    }
}

// Frame buffers

pub type Attachment = u32;
pub const COLOR_ATTACHMENT_0: Attachment = gl::COLOR_ATTACHMENT0;
pub const COLOR_ATTACHMENT_1: Attachment = gl::COLOR_ATTACHMENT1;
pub const COLOR_ATTACHMENT_2: Attachment = gl::COLOR_ATTACHMENT2;
pub const DEPTH_ATTACHMENT: Attachment = gl::DEPTH_ATTACHMENT;

pub struct Framebuffer(u32);

impl Framebuffer {
    pub fn new() -> Framebuffer {
        let mut fb = Framebuffer(0);
        unsafe {
            gl::GenFramebuffers(1, &mut fb.0);
        }
        fb
    }

    pub fn bind(&self) {
        unsafe {
            gl::BindFramebuffer(gl::FRAMEBUFFER, self.0);
        }
    }

    pub fn bind_read(&self) {
        unsafe {
            gl::BindFramebuffer(gl::READ_FRAMEBUFFER, self.0);
        }
    }

    pub fn bind_draw(&self) {
        unsafe {
            gl::BindFramebuffer(gl::DRAW_FRAMEBUFFER, self.0);
        }
    }

    pub fn texture_2d(&self, attachment: Attachment, target: TextureTarget, tex: &Texture, level: i32) {
        unsafe {
            gl::FramebufferTexture2D(gl::FRAMEBUFFER, attachment, target, tex.0, level);
        }
    }
}

impl Drop for Framebuffer {
    fn drop(&mut self) {
        unsafe {
            gl::DeleteFramebuffers(1, &self.0);
        }
    }
}

pub fn unbind_framebuffer() {
    unsafe {
        gl::BindFramebuffer(gl::FRAMEBUFFER, 0);
    }
}

pub fn unbind_framebuffer_read() {
    unsafe {
        gl::BindFramebuffer(gl::READ_FRAMEBUFFER, 0);
    }
}

pub fn unbind_framebuffer_draw() {
    unsafe {
        gl::BindFramebuffer(gl::DRAW_FRAMEBUFFER, 0);
    }
}

pub fn draw_buffers(bufs: &[Attachment]) {
    unsafe {
        gl::DrawBuffers(
                bufs.len() as i32,
                bufs.as_ptr()
        );
    }
}

pub fn bind_frag_data_location(p: &Program, cn: u32, name: &str) {
    unsafe {
        gl::BindFragDataLocation(p.0, cn, ffi::CString::new(name).unwrap().as_ptr());
    }
}

pub fn blit_framebuffer(
    sx0: i32, sy0: i32, sx1: i32, sy1: i32,
    dx0: i32, dy0: i32, dx1: i32, dy1: i32,
    mask: ClearFlags, filter: TextureValue) {
    unsafe {
        gl::BlitFramebuffer(
            sx0, sy0, sx1, sy1,
            dx0, dy0, dx1, dy1,
            mask.internal(), filter as u32
        );
    }
}

pub fn read_buffer(a: Attachment) {
    unsafe {
        gl::ReadBuffer(a);
    }
}

pub type TargetBuffer = u32;
pub const COLOR: TargetBuffer = gl::COLOR;

pub fn clear_buffer(buffer: TargetBuffer, draw_buffer: i32, values: &[f32]) {
    unsafe {
        gl::ClearBufferfv(buffer, draw_buffer, values.as_ptr());
    }
}