use wgpu::*;

use crate::GlyphAtlas;

use super::{
    atlas::PAGE,
    texture::{sampled_group, write_region},
};

/// The glyph atlas on the GPU: one array texture whose layers are the pages
/// `GlyphAtlas` packs.
///
/// One array rather than a texture per page because a layer index is ordinary
/// Vulkan 1.0 / GLES sampling, where a `binding_array` would need
/// `VK_EXT_descriptor_indexing`, which a real share of Android GPUs lack.
pub struct GpuPages {
    device: Device,
    queue: Queue,
    texture: Texture,
    group: BindGroup,
}

impl GpuPages {
    pub fn new(
        device: &Device,
        queue: &Queue,
        layout: &BindGroupLayout,
        sampler: &Sampler,
    ) -> Self {
        let texture = create_array(device, 1);
        Self {
            device: device.clone(),
            queue: queue.clone(),
            group: atlas_group(device, layout, &texture, sampler),
            texture,
        }
    }

    pub fn update(&mut self, atlas: &mut GlyphAtlas, layout: &BindGroupLayout, sampler: &Sampler) {
        if atlas.page_count() > self.texture.depth_or_array_layers() {
            self.grow(atlas.page_count(), layout, sampler);
        }
        for (upload, page) in atlas.uploads() {
            let dst = TexelCopyTextureInfo {
                texture: &self.texture,
                mip_level: 0,
                origin: Origin3d {
                    x: upload.rect.x,
                    y: upload.rect.y,
                    z: upload.layer,
                },
                aspect: TextureAspect::All,
            };
            write_region(&self.queue, dst, page, upload.rect);
        }
    }

    pub fn group(&self) -> &BindGroup {
        &self.group
    }

    /// Doubles until `needed` fits and copies the old layers across GPU side.
    /// The new texture stales the group, so that is rebuilt here.
    fn grow(&mut self, needed: u32, layout: &BindGroupLayout, sampler: &Sampler) {
        let old = self.texture.depth_or_array_layers();
        let mut layers = old;
        while layers < needed {
            layers *= 2;
        }
        let texture = create_array(&self.device, layers);
        let mut encoder = self
            .device
            .create_command_encoder(&CommandEncoderDescriptor {
                label: Some("atlas grow"),
            });
        encoder.copy_texture_to_texture(
            self.texture.as_image_copy(),
            texture.as_image_copy(),
            Extent3d {
                width: PAGE,
                height: PAGE,
                depth_or_array_layers: old,
            },
        );
        self.queue.submit(std::iter::once(encoder.finish()));
        self.group = atlas_group(&self.device, layout, &texture, sampler);
        self.texture = texture;
    }
}

fn atlas_group(
    device: &Device,
    layout: &BindGroupLayout,
    texture: &Texture,
    sampler: &Sampler,
) -> BindGroup {
    let view = texture.create_view(&TextureViewDescriptor {
        dimension: Some(TextureViewDimension::D2Array),
        ..Default::default()
    });
    sampled_group(device, layout, &view, sampler, "ui atlas")
}

fn create_array(device: &Device, layers: u32) -> Texture {
    device.create_texture(&TextureDescriptor {
        label: Some("glyph atlas"),
        size: Extent3d {
            width: PAGE,
            height: PAGE,
            depth_or_array_layers: layers,
        },
        mip_level_count: 1,
        sample_count: 1,
        dimension: TextureDimension::D2,
        format: TextureFormat::Rgba8Unorm,
        usage: TextureUsages::TEXTURE_BINDING | TextureUsages::COPY_DST | TextureUsages::COPY_SRC,
        view_formats: &[],
    })
}