use std::cell::Cell;
use std::rc::Rc;

use glow::HasContext;

use crate::drawing::Uniforms;
use crate::{Canvas, Color, EventCtx, GeomBatch, GfxCtx, ScreenDims, ScreenRectangle};

#[cfg(feature = "native-backend")]
pub use crate::backend_glow_native::setup;

#[cfg(feature = "wasm-backend")]
pub use crate::backend_glow_wasm::setup;

pub(crate) unsafe fn build_program(
    gl: &glow::Context,
    vertex_shader_src: &str,
    fragment_shader_src: &str,
) -> anyhow::Result<glow::Program> {
    let program = gl.create_program().expect("Cannot create program");

    let shaders = [
        compile_shader(gl, glow::VERTEX_SHADER, vertex_shader_src)?,
        compile_shader(gl, glow::FRAGMENT_SHADER, fragment_shader_src)?,
    ];

    for shader in &shaders {
        gl.attach_shader(program, *shader);
    }

    gl.link_program(program);
    if !gl.get_program_link_status(program) {
        error!("Linking error: {}", gl.get_program_info_log(program));
        panic!("{}", gl.get_program_info_log(program));
    }

    for shader in &shaders {
        gl.detach_shader(program, *shader);
        gl.delete_shader(*shader);
    }

    gl.use_program(Some(program));

    gl.enable(glow::SCISSOR_TEST);
    gl.enable(glow::DEPTH_TEST);
    gl.depth_func(glow::LEQUAL);
    gl.enable(glow::BLEND);
    gl.blend_func_separate(
        glow::ONE,
        glow::ONE_MINUS_SRC_ALPHA,
        glow::ONE_MINUS_DST_ALPHA,
        glow::ONE,
    );

    Ok(program)
}

unsafe fn compile_shader(
    gl: &glow::Context,
    shader_type: u32,
    shader_source: &str,
) -> anyhow::Result<glow::Shader> {
    let shader = gl.create_shader(shader_type).map_err(|e| anyhow!(e))?;
    gl.shader_source(shader, shader_source);
    gl.compile_shader(shader);
    if !gl.get_shader_compile_status(shader) {
        bail!("error compiling shader: {}", gl.get_shader_info_log(shader));
    }

    Ok(shader)
}

// Represents one frame that's gonna be drawn
pub struct GfxCtxInnards<'a> {
    gl: &'a glow::Context,
    current_clip: Option<[i32; 4]>,
    transform_location: <glow::Context as glow::HasContext>::UniformLocation,
    window_location: <glow::Context as glow::HasContext>::UniformLocation,
}

impl<'a> GfxCtxInnards<'a> {
    pub fn new(
        gl: &'a glow::Context,
        program: &'a <glow::Context as glow::HasContext>::Program,
    ) -> Self {
        let (transform_location, window_location) = unsafe {
            (
                gl.get_uniform_location(*program, "transform").unwrap(),
                gl.get_uniform_location(*program, "window").unwrap(),
            )
        };
        GfxCtxInnards {
            gl,
            current_clip: None,
            transform_location,
            window_location,
        }
    }

    pub fn clear(&mut self, color: Color) {
        unsafe {
            self.gl.clear_color(color.r, color.g, color.b, color.a);
            self.gl.clear(glow::COLOR_BUFFER_BIT);

            self.gl.clear_depth_f32(1.0);
            self.gl.clear(glow::DEPTH_BUFFER_BIT);
        }
    }

    pub fn redraw(&mut self, obj: &Drawable, uniforms: &Uniforms, _: &PrerenderInnards) {
        unsafe {
            self.gl
                .uniform_3_f32_slice(Some(&self.transform_location), &uniforms.transform);
            self.gl
                .uniform_3_f32_slice(Some(&self.window_location), &uniforms.window);

            self.gl.bind_vertex_array(Some(obj.vert_array.id));
            self.gl
                .draw_elements(glow::TRIANGLES, obj.num_indices, glow::UNSIGNED_INT, 0);
            self.gl.bind_vertex_array(None);
        }
    }

    pub fn enable_clipping(&mut self, rect: ScreenRectangle, scale_factor: f64, canvas: &Canvas) {
        assert!(self.current_clip.is_none());
        // The scissor rectangle is in units of physical pixles, as opposed to logical pixels
        let left = (rect.x1 * scale_factor) as i32;
        // Y-inversion
        let bottom = ((canvas.window_height - rect.y2) * scale_factor) as i32;
        let width = ((rect.x2 - rect.x1) * scale_factor) as i32;
        let height = ((rect.y2 - rect.y1) * scale_factor) as i32;
        unsafe {
            self.gl.scissor(left, bottom, width, height);
        }
        self.current_clip = Some([left, bottom, width, height]);
    }

    pub fn disable_clipping(&mut self, scale_factor: f64, canvas: &Canvas) {
        assert!(self.current_clip.is_some());
        self.current_clip = None;
        unsafe {
            self.gl.scissor(
                0,
                0,
                (canvas.window_width * scale_factor) as i32,
                (canvas.window_height * scale_factor) as i32,
            );
        }
    }

    pub fn take_clip(&mut self, scale_factor: f64, canvas: &Canvas) -> Option<[i32; 4]> {
        let clip = self.current_clip?;
        self.disable_clipping(scale_factor, canvas);
        Some(clip)
    }

    pub fn restore_clip(&mut self, clip: Option<[i32; 4]>) {
        self.current_clip = clip;
        if let Some(c) = clip {
            unsafe {
                self.gl.scissor(c[0], c[1], c[2], c[3]);
            }
        }
    }
}

/// Geometry that's been uploaded to the GPU once and can be quickly redrawn many times. Create by
/// creating a `GeomBatch` and calling `ctx.upload(batch)`.
pub struct Drawable {
    vert_array: VertexArray,
    vert_buffer: Buffer,
    elem_buffer: Buffer,
    num_indices: i32,
    gl: Rc<glow::Context>,
}

impl Drop for Drawable {
    #[inline]
    fn drop(&mut self) {
        self.elem_buffer.destroy(&self.gl);
        self.vert_buffer.destroy(&self.gl);
        self.vert_array.destroy(&self.gl);
    }
}

impl Drawable {
    /// This has no effect when drawn.
    pub fn empty(ctx: &EventCtx) -> Drawable {
        ctx.upload(GeomBatch::new())
    }

    pub fn draw(&self, g: &mut GfxCtx) {
        g.redraw(self);
    }
}

struct VertexArray {
    id: <glow::Context as glow::HasContext>::VertexArray,
    was_destroyed: bool,
}

impl VertexArray {
    fn new(gl: &glow::Context) -> VertexArray {
        let id = unsafe { gl.create_vertex_array().unwrap() };
        VertexArray {
            id,
            was_destroyed: false,
        }
    }

    fn destroy(&mut self, gl: &glow::Context) {
        assert!(!self.was_destroyed, "already destroyed");
        self.was_destroyed = true;
        unsafe {
            gl.delete_vertex_array(self.id);
        }
    }
}

impl Drop for VertexArray {
    fn drop(&mut self) {
        assert!(
            self.was_destroyed,
            "failed to call `destroy` before dropped. Memory leaked."
        );
    }
}

struct Buffer {
    id: <glow::Context as glow::HasContext>::Buffer,
    was_destroyed: bool,
}

impl Buffer {
    fn new(gl: &glow::Context) -> Buffer {
        let id = unsafe { gl.create_buffer().unwrap() };
        Buffer {
            id,
            was_destroyed: false,
        }
    }

    fn destroy(&mut self, gl: &glow::Context) {
        assert!(!self.was_destroyed, "already destroyed");
        self.was_destroyed = true;
        unsafe { gl.delete_buffer(self.id) };
    }
}

impl Drop for Buffer {
    fn drop(&mut self) {
        assert!(
            self.was_destroyed,
            "failed to call `destroy` before dropped. Memory leaked."
        );
    }
}

#[cfg(feature = "wasm-backend")]
type WindowAdapter = crate::backend_glow_wasm::WindowAdapter;

#[cfg(feature = "native-backend")]
type WindowAdapter = crate::backend_glow_native::WindowAdapter;

pub struct PrerenderInnards {
    gl: Rc<glow::Context>,
    is_gl2: bool,
    window_adapter: Option<WindowAdapter>,
    program: <glow::Context as glow::HasContext>::Program,

    // TODO Prerender doesn't know what things are temporary and permanent. Could make the API more
    // detailed.
    pub total_bytes_uploaded: Cell<usize>,
}

impl PrerenderInnards {
    pub fn new(
        gl: glow::Context,
        is_gl2: bool,
        program: <glow::Context as glow::HasContext>::Program,
        window_adapter: Option<WindowAdapter>,
    ) -> PrerenderInnards {
        PrerenderInnards {
            gl: Rc::new(gl),
            is_gl2,
            program,
            window_adapter,
            total_bytes_uploaded: Cell::new(0),
        }
    }

    pub fn actually_upload(&self, permanent: bool, batch: GeomBatch) -> Drawable {
        let mut vertices: Vec<[f32; 8]> = Vec::new();
        let mut indices: Vec<u32> = Vec::new();

        for (color, poly, z) in batch.consume() {
            let idx_offset = vertices.len() as u32;
            let (pts, raw_indices) = poly.consume();
            for pt in pts {
                let style = color.shader_style(pt);
                vertices.push([
                    pt.x() as f32,
                    pt.y() as f32,
                    z as f32,
                    style[0],
                    style[1],
                    style[2],
                    style[3],
                    style[4],
                ]);
            }
            for idx in raw_indices {
                indices.push(idx_offset + (idx as u32));
            }
        }

        let (vert_buffer, vert_array, elem_buffer) = unsafe {
            let vert_array = VertexArray::new(&self.gl);
            let vert_buffer = Buffer::new(&self.gl);
            let elem_buffer = Buffer::new(&self.gl);

            self.gl.bind_vertex_array(Some(vert_array.id));

            self.gl
                .bind_buffer(glow::ARRAY_BUFFER, Some(vert_buffer.id));
            self.gl.buffer_data_u8_slice(
                glow::ARRAY_BUFFER,
                vertices.align_to::<u8>().1,
                // TODO Use permanent
                glow::STATIC_DRAW,
            );

            self.gl
                .bind_buffer(glow::ELEMENT_ARRAY_BUFFER, Some(elem_buffer.id));
            self.gl.buffer_data_u8_slice(
                glow::ELEMENT_ARRAY_BUFFER,
                indices.align_to::<u8>().1,
                glow::STATIC_DRAW,
            );

            let vertex_attributes: [i32; 3] = [
                3, // position is vec2
                4, // color is vec4
                1, // texture_id is float
            ];
            let stride = vertex_attributes.iter().sum::<i32>() * std::mem::size_of::<f32>() as i32;
            let mut offset = 0;
            for (i, size) in vertex_attributes.iter().enumerate() {
                self.gl.enable_vertex_attrib_array(i as u32);
                self.gl.vertex_attrib_pointer_f32(
                    i as u32,
                    *size,
                    glow::FLOAT,
                    false,
                    stride,
                    offset,
                );
                offset += size * std::mem::size_of::<f32>() as i32;
            }

            // Safety?
            self.gl.bind_vertex_array(None);
            self.gl.bind_buffer(glow::ARRAY_BUFFER, None);
            self.gl.bind_buffer(glow::ELEMENT_ARRAY_BUFFER, None);

            (vert_buffer, vert_array, elem_buffer)
        };
        let num_indices = indices.len() as i32;

        if permanent {
            /*self.total_bytes_uploaded.set(
                self.total_bytes_uploaded.get()
                    + vertex_buffer.get_size()
                    + index_buffer.get_size(),
            );*/
        }

        Drawable {
            vert_array,
            vert_buffer,
            elem_buffer,
            num_indices,
            gl: self.gl.clone(),
        }
    }

    pub(crate) fn window(&self) -> &winit::window::Window {
        self.window_adapter.as_ref().expect("no window").window()
    }

    pub fn request_redraw(&self) {
        self.window().request_redraw();
    }

    pub fn set_cursor_icon(&self, icon: winit::window::CursorIcon) {
        self.window().set_cursor_icon(icon);
    }

    pub fn set_cursor_visible(&self, visible: bool) {
        self.window().set_cursor_visible(visible);
    }

    pub fn draw_new_frame(&self) -> GfxCtxInnards {
        GfxCtxInnards::new(&self.gl, &self.program)
    }

    pub fn window_resized(&self, new_size: ScreenDims, scale_factor: f64) {
        let physical_size = winit::dpi::LogicalSize::from(new_size).to_physical(scale_factor);
        self.window_adapter
            .as_ref()
            .expect("no window")
            .window_resized(new_size, scale_factor);
        unsafe {
            self.gl
                .viewport(0, 0, physical_size.width, physical_size.height);
            // I think it's safe to assume there's not a clip right now.
            self.gl
                .scissor(0, 0, physical_size.width, physical_size.height);
        }
    }

    pub fn window_size(&self, scale_factor: f64) -> ScreenDims {
        self.window().inner_size().to_logical(scale_factor).into()
    }

    pub fn set_window_icon(&self, icon: winit::window::Icon) {
        self.window().set_window_icon(Some(icon));
    }

    pub fn monitor_scale_factor(&self) -> f64 {
        self.window().scale_factor()
    }

    pub fn draw_finished(&self, gfx_ctx_innards: GfxCtxInnards) {
        self.window_adapter
            .as_ref()
            .expect("no window")
            .draw_finished(gfx_ctx_innards)
    }

    pub(crate) fn screencap(&self, dims: ScreenDims, filename: String) -> anyhow::Result<()> {
        let width = dims.width as u32;
        let height = dims.height as u32;

        let mut img = image::DynamicImage::new_rgba8(width, height);
        let pixels = img.as_mut_rgba8().unwrap();

        unsafe {
            self.gl.pixel_store_i32(glow::PACK_ALIGNMENT, 1);
            // TODO This starts at lower-left, I think we need to use window height here
            self.gl.read_pixels(
                0,
                0,
                width as i32,
                height as i32,
                glow::RGBA,
                glow::UNSIGNED_BYTE,
                glow::PixelPackData::Slice(pixels),
            );
        }

        image::save_buffer(
            &filename,
            &image::imageops::flip_vertical(&img),
            width,
            height,
            image::ColorType::Rgba8,
        )?;
        Ok(())
    }

    #[allow(unused)]
    pub fn use_program_for_renderonly(&self) {
        unsafe {
            self.gl.use_program(Some(self.program));
        }
    }

    pub fn upload_texture(&self, texture: SpriteTexture, scale: (f32, f32)) {
        if self.is_gl2 {
            texture
                .upload_gl2(&self.gl)
                .expect("failed to upload textures");

            unsafe {
                let location = self
                    .gl
                    .get_uniform_location(self.program, "texture_scale")
                    .unwrap();
                self.gl
                    .uniform_2_f32_slice(Some(&location), &[scale.0, scale.1]);
            }
        } else {
            warn!(
                "texture uploading for WebGL 1.0 is not yet supported. Enable WebGL 2.0 on your \
                 browser."
            );
        }
    }
}

/// Uploads a sprite sheet of textures to the GPU so they can be used by Fill::Texture and
/// friends to paint shapes.
///
/// `path` - image file which is a grid of images.
/// `sprite_length` - the width and height of an individual cell in the image grid
///
/// The image file can have any number of sprites, but they must all be the same size.
///
/// Once uploaded, textures are addressed by their id, starting from 1, from left to right, top to
/// bottom, like so:
///
///   ┌─┬─┬─┐
///   │1│2│3│
///   ├─┼─┼─┤
///   │4│5│6│
///   ├─┼─┼─┤
///   │7│8│9│
///   └─┴─┴─┘
///
/// Texture(0) is reserved for a pure white (no-op) texture.
///
/// Implementation is based on the the description of ArrayTextures from:
/// https://www.khronos.org/opengl/wiki/Array_Texture.
///
/// OpenGL texture arrays expect each texture's bytes to be contiguous, but it's conventional to
/// store textures in a grid within a single spritesheet image, where a row and column traverses
/// multiple sprites.
///
/// For example, if we had 6 textures, A-F, the input spritesheet bytes would be like:
/// [[AAA, BBB, CCC],
///  [AAA, BBB, CCC]
///  [AAA, BBB, CCC],
///  [DDD, EEE, FFF],
///  [DDD, EEE, FFF],
///  [DDD, EEE, FFF]]
///
/// Which we need to convert to:
/// [[AAAAAAAAA],
///  [BBBBBBBBB],
///  [CCCCCCCCC],
///  [DDDDDDDDD],
///  [EEEEEEEEE],
///  [FFFFFFFFF]]
pub struct SpriteTexture {
    texture_bytes: Vec<u8>,
    sprite_width: u32,
    sprite_height: u32,
    sprite_count: u32,
}

impl SpriteTexture {
    pub fn new(
        sprite_bytes: Vec<u8>,
        sprite_width: u32,
        sprite_height: u32,
    ) -> anyhow::Result<Self> {
        let dynamic_img = image::load_from_memory(&sprite_bytes)?;

        let img = if let image::DynamicImage::ImageRgba8(img) = dynamic_img {
            img
        } else {
            todo!("support other image formats");
        };

        let bytes_per_pixel = 4;

        let (img_width, img_height) = img.dimensions();
        let sprites_per_row = img_width / sprite_width;
        let sprites_per_column = img_height / sprite_height;
        let sprite_count = sprites_per_row * sprites_per_column;

        assert_eq!(
            sprites_per_row * sprite_width,
            img_width,
            "sprites must align exactly"
        );
        assert_eq!(
            sprites_per_column * sprite_height,
            img_height,
            "sprites must align exactly"
        );

        info!(
            "img_size: {}x{}px ({} px), sprite_size: {}x{}px, sprites: {}x{} ({} sprites)",
            img_width,
            img_height,
            img.pixels().len(),
            sprite_width,
            sprite_height,
            sprites_per_row,
            sprites_per_column,
            sprite_count
        );

        let mut texture_bytes: Vec<u8> = Vec::with_capacity(img.pixels().len() * bytes_per_pixel);

        // In order to avoid branching in our shader logic, all shapes are rendered with a texture.
        // Even "non-textured" styles like Fill::Color, use a "default" no-op (pure white) texture,
        // which we generate here.
        texture_bytes.append(&mut vec![
            255;
            (sprite_width * sprite_height) as usize
                * bytes_per_pixel
        ]);

        use image::GenericImageView;
        for y in 0..sprites_per_column {
            for x in 0..sprites_per_row {
                let sprite_cell = img.view(
                    x * sprite_width,
                    y * sprite_height,
                    sprite_width,
                    sprite_height,
                );
                for p in sprite_cell.pixels() {
                    texture_bytes.extend_from_slice(&p.2 .0);
                }
            }
        }

        Ok(Self {
            texture_bytes,
            sprite_width,
            sprite_height,
            sprite_count,
        })
    }

    // Utilizes `tex_storage_3d` which isn't supported by WebGL 1.0.
    fn upload_gl2(&self, gl: &glow::Context) -> anyhow::Result<()> {
        let texture_id = unsafe {
            gl.create_texture()
                .map_err(|err| anyhow!("error creating texture: {}", err))?
        };

        let format = glow::RGBA;
        let target = glow::TEXTURE_2D_ARRAY;
        let mipmap_levels: u32 = 2;
        let internal_format = glow::RGBA;

        unsafe {
            gl.bind_texture(target, Some(texture_id));
        }

        // Allocate the storage.
        unsafe {
            gl.tex_storage_3d(
                target,
                mipmap_levels as i32,
                internal_format,
                self.sprite_width as i32,
                self.sprite_height as i32,
                self.sprite_count as i32,
            );
        }

        unsafe {
            // Upload pixel data for each mipmap level
            for mipmap_level in 0..mipmap_levels {
                let width = self.sprite_width as i32 / 2i32.pow(mipmap_level);
                let height = self.sprite_height as i32 / 2i32.pow(mipmap_level);
                gl.tex_image_3d(
                    target,
                    mipmap_level as i32,
                    format as i32,
                    width,
                    height,
                    self.sprite_count as i32,
                    0,
                    format,
                    glow::UNSIGNED_BYTE,
                    Some(&self.texture_bytes),
                );
            }
            gl.generate_mipmap(target);
        }

        Ok(())
    }
}