// Image GPU buffers — renders raster images as textured quads.
//
// Group 1 bindings per image:
//   binding 0 — texture_2d<f32>   (RGBA image texture)
//   binding 1 — sampler           (bilinear; nearest magnification for raster images)
//   binding 2 — ImageParams       (opacity uniform, 16 bytes)

use crate::scene::model::image_model::ImageModel;
use iced::wgpu;
use std::sync::Arc;

// ── Vertex ────────────────────────────────────────────────────────────────

#[repr(C)]
#[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
pub struct ImageVertex {
    pub pos: [f32; 3],
    pub uv: [f32; 2],
    pub pos_low: [f32; 3],
}

impl ImageVertex {
    pub fn layout<'a>() -> wgpu::VertexBufferLayout<'a> {
        const ATTRS: &[wgpu::VertexAttribute] = &[
            wgpu::VertexAttribute {
                offset: std::mem::offset_of!(ImageVertex, pos) as u64,
                shader_location: 0,
                format: wgpu::VertexFormat::Float32x3,
            },
            wgpu::VertexAttribute {
                offset: std::mem::offset_of!(ImageVertex, uv) as u64,
                shader_location: 1,
                format: wgpu::VertexFormat::Float32x2,
            },
            wgpu::VertexAttribute {
                offset: std::mem::offset_of!(ImageVertex, pos_low) as u64,
                shader_location: 2,
                format: wgpu::VertexFormat::Float32x3,
            },
        ];
        wgpu::VertexBufferLayout {
            array_stride: std::mem::size_of::<ImageVertex>() as u64,
            step_mode: wgpu::VertexStepMode::Vertex,
            attributes: ATTRS,
        }
    }
}

#[repr(C)]
#[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
pub struct ImageInstance {
    pub translation: [f32; 3],
    pub translation_low: [f32; 3],
    pub draw_depth: f32,
    pub _pad: [f32; 3],
}

impl ImageInstance {
    pub fn layout<'a>() -> wgpu::VertexBufferLayout<'a> {
        const ATTRS: &[wgpu::VertexAttribute] = &[
            wgpu::VertexAttribute {
                offset: std::mem::offset_of!(ImageInstance, translation) as u64,
                shader_location: 3,
                format: wgpu::VertexFormat::Float32x3,
            },
            wgpu::VertexAttribute {
                offset: std::mem::offset_of!(ImageInstance, translation_low) as u64,
                shader_location: 4,
                format: wgpu::VertexFormat::Float32x3,
            },
            wgpu::VertexAttribute {
                offset: std::mem::offset_of!(ImageInstance, draw_depth) as u64,
                shader_location: 5,
                format: wgpu::VertexFormat::Float32,
            },
        ];
        wgpu::VertexBufferLayout {
            array_stride: std::mem::size_of::<Self>() as u64,
            step_mode: wgpu::VertexStepMode::Instance,
            attributes: ATTRS,
        }
    }
}

// ── Uniform ───────────────────────────────────────────────────────────────

#[repr(C)]
#[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
struct ImageParams {
    opacity: f32,
    /// Signed draw-order depth (-1,1); applied as a clip-z bias in the shader
    /// so the raster orders against other entity types. 0.0 = neutral.
    draw_depth: f32,
    /// 1.0 when pixel alpha applies, 0.0 when pixels draw opaque.
    use_alpha: f32,
    _pad: f32,
} // 16 bytes

// ── Per-image GPU handle ──────────────────────────────────────────────────

pub struct ImageGpu {
    pub vertex_buffer: wgpu::Buffer,
    pub instance_buffer: Arc<wgpu::Buffer>,
    /// Number of triangle vertices in `vertex_buffer` — 6 for a plain quad, or
    /// more when the raster is clipped to a triangulated polygon.
    pub vertex_count: u32,
    pub instance_count: u32,
    pub bind_group: wgpu::BindGroup,
    _texture: wgpu::Texture,
    _sampler: Arc<wgpu::Sampler>,
    _params_buf: Arc<wgpu::Buffer>,
}

impl ImageGpu {
    pub fn from_models(
        device: &wgpu::Device,
        queue: &wgpu::Queue,
        models: &[ImageModel],
        bgl1: &wgpu::BindGroupLayout,
    ) -> Vec<Self> {
        let mut slots = rustc_hash::FxHashMap::default();
        let mut groups: Vec<Vec<&ImageModel>> = Vec::new();
        for (index, model) in models.iter().enumerate() {
            let key = model
                .render_instance
                .map(|instance| (true, instance.source_id))
                .unwrap_or((false, index as u64));
            let slot = *slots.entry(key).or_insert_with(|| {
                let slot = groups.len();
                groups.push(Vec::new());
                slot
            });
            groups[slot].push(model);
        }
        let sampler = |mag_filter| {
            Arc::new(device.create_sampler(&wgpu::SamplerDescriptor {
                label: Some("image.sampler"),
                address_mode_u: wgpu::AddressMode::ClampToEdge,
                address_mode_v: wgpu::AddressMode::ClampToEdge,
                address_mode_w: wgpu::AddressMode::ClampToEdge,
                mag_filter,
                min_filter: wgpu::FilterMode::Linear,
                mipmap_filter: wgpu::MipmapFilterMode::Nearest,
                ..Default::default()
            }))
        };
        // Raster images show square pixels when magnified.
        let smooth = sampler(wgpu::FilterMode::Linear);
        let pixelated = sampler(wgpu::FilterMode::Nearest);
        groups
            .into_iter()
            .flat_map(|group| {
                let sampler = if group.first().is_some_and(|m| m.pixelated) {
                    &pixelated
                } else {
                    &smooth
                };
                Self::new(device, queue, &group, bgl1, sampler)
            })
            .collect()
    }

    fn new(
        device: &wgpu::Device,
        queue: &wgpu::Queue,
        models: &[&ImageModel],
        bgl1: &wgpu::BindGroupLayout,
        sampler: &Arc<wgpu::Sampler>,
    ) -> Vec<Self> {
        let Some(&model) = models.first() else {
            return Vec::new();
        };
        if model.pixels.is_empty() || model.width == 0 || model.height == 0 {
            return Vec::new();
        }

        let limit = device.limits().max_texture_dimension_2d.max(1);
        let x_tiles = tile_ranges(model.width, limit);
        let y_tiles = tile_ranges(model.height, limit);
        let base = model
            .render_instance
            .map_or([0.0; 3], |instance| instance.translation);
        let instances: Vec<ImageInstance> = models
            .iter()
            .map(|model| {
                let translation = model
                    .render_instance
                    .map_or([0.0; 3], |instance| instance.translation);
                let delta = [
                    translation[0] - base[0],
                    translation[1] - base[1],
                    translation[2] - base[2],
                ];
                let high = delta.map(|value| value as f32);
                ImageInstance {
                    translation: high,
                    translation_low: [
                        (delta[0] - high[0] as f64) as f32,
                        (delta[1] - high[1] as f64) as f32,
                        (delta[2] - high[2] as f64) as f32,
                    ],
                    draw_depth: model.draw_depth,
                    _pad: [0.0; 3],
                }
            })
            .collect();
        let instance_buffer = Arc::new(super::gpu_upload::upload_buffer(
            device,
            queue,
            "image.instances",
            &instances,
            wgpu::BufferUsages::VERTEX,
        ));
        let params = ImageParams {
            opacity: model.opacity.clamp(0.0, 1.0),
            draw_depth: 0.0,
            use_alpha: if model.use_alpha { 1.0 } else { 0.0 },
            _pad: 0.0,
        };
        let params_buf = Arc::new(super::gpu_upload::upload_buffer(
            device,
            queue,
            "image.params",
            std::slice::from_ref(&params),
            wgpu::BufferUsages::UNIFORM,
        ));

        let mut output = Vec::with_capacity(x_tiles.len() * y_tiles.len());
        for y in &y_tiles {
            for x in &x_tiles {
                let verts = tile_vertices(model, *x, *y);
                if verts.is_empty() {
                    continue;
                }

                let width = x.data_end - x.data_start;
                let height = y.data_end - y.data_start;
                let tex_label = format!(
                    "image.texture:{}:{}:{}",
                    model.file_path, x.content_start, y.content_start
                );
                let levels = mip_chain(
                    &model.pixels,
                    model.width,
                    x.data_start,
                    y.data_start,
                    width,
                    height,
                );
                let texture = device.create_texture(&wgpu::TextureDescriptor {
                    label: Some(&tex_label),
                    size: wgpu::Extent3d {
                        width,
                        height,
                        depth_or_array_layers: 1,
                    },
                    mip_level_count: levels.len() as u32,
                    sample_count: 1,
                    dimension: wgpu::TextureDimension::D2,
                    format: wgpu::TextureFormat::Rgba8Unorm,
                    usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
                    view_formats: &[],
                });
                for (level, (w, h, data)) in levels.iter().enumerate() {
                    queue.write_texture(
                        wgpu::TexelCopyTextureInfo {
                            texture: &texture,
                            mip_level: level as u32,
                            origin: wgpu::Origin3d::ZERO,
                            aspect: wgpu::TextureAspect::All,
                        },
                        data,
                        wgpu::TexelCopyBufferLayout {
                            offset: 0,
                            bytes_per_row: Some(4 * w),
                            rows_per_image: Some(*h),
                        },
                        wgpu::Extent3d {
                            width: *w,
                            height: *h,
                            depth_or_array_layers: 1,
                        },
                    );
                }
                let tex_view = texture.create_view(&wgpu::TextureViewDescriptor::default());
                let bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
                    label: Some("image.bind_group1"),
                    layout: bgl1,
                    entries: &[
                        wgpu::BindGroupEntry {
                            binding: 0,
                            resource: wgpu::BindingResource::TextureView(&tex_view),
                        },
                        wgpu::BindGroupEntry {
                            binding: 1,
                            resource: wgpu::BindingResource::Sampler(sampler),
                        },
                        wgpu::BindGroupEntry {
                            binding: 2,
                            resource: params_buf.as_entire_binding(),
                        },
                    ],
                });
                let vertex_buffer = super::gpu_upload::upload_buffer(
                    device,
                    queue,
                    "image.vbuf",
                    &verts,
                    wgpu::BufferUsages::VERTEX,
                );
                output.push(Self {
                    vertex_buffer,
                    instance_buffer: Arc::clone(&instance_buffer),
                    vertex_count: verts.len() as u32,
                    instance_count: instances.len() as u32,
                    bind_group,
                    _texture: texture,
                    _sampler: Arc::clone(sampler),
                    _params_buf: Arc::clone(&params_buf),
                });
            }
        }
        output
    }
}

#[derive(Clone, Copy)]
struct TileRange {
    content_start: u32,
    content_end: u32,
    data_start: u32,
    data_end: u32,
}

/// A tile's pixels and its smaller levels down to 1×1, so a far view
/// samples a level near its own size. A level keeps the most opaque of each
/// 2×2 block unless all four are equally opaque (then their average): thin
/// lines on a transparent page (PDF, DWF, DGN underlays) stay visible when
/// zoomed out instead of falling between samples, and opaque images are
/// averaged as usual.
fn mip_chain(
    pixels: &[u8],
    stride: u32,
    x0: u32,
    y0: u32,
    w: u32,
    h: u32,
) -> Vec<(u32, u32, Vec<u8>)> {
    let (stride, x0, y0) = (stride as usize, x0 as usize, y0 as usize);
    let mut base = Vec::with_capacity(w as usize * h as usize * 4);
    for row in 0..h as usize {
        let start = ((y0 + row) * stride + x0) * 4;
        base.extend_from_slice(&pixels[start..start + w as usize * 4]);
    }
    let mut levels = vec![(w, h, base)];
    loop {
        let (pw, ph, prev) = levels.last().expect("base level");
        if *pw == 1 && *ph == 1 {
            break;
        }
        let (pw, ph) = (*pw as usize, *ph as usize);
        let (nw, nh) = ((pw / 2).max(1), (ph / 2).max(1));
        let mut next = Vec::with_capacity(nw * nh * 4);
        for y in 0..nh {
            for x in 0..nw {
                let block = [(0, 0), (1, 0), (0, 1), (1, 1)].map(|(dx, dy)| {
                    let at = (((2 * y + dy).min(ph - 1)) * pw + (2 * x + dx).min(pw - 1)) * 4;
                    [prev[at], prev[at + 1], prev[at + 2], prev[at + 3]]
                });
                if block.iter().all(|p| p[3] == block[0][3]) {
                    let mut sum = [0u32; 4];
                    for p in &block {
                        for c in 0..4 {
                            sum[c] += p[c] as u32;
                        }
                    }
                    next.extend(sum.map(|v| ((v + 2) / 4) as u8));
                } else {
                    next.extend(*block.iter().max_by_key(|p| p[3]).expect("four pixels"));
                }
            }
        }
        levels.push((nw as u32, nh as u32, next));
    }
    levels
}

fn tile_ranges(size: u32, limit: u32) -> Vec<TileRange> {
    if size <= limit {
        return vec![TileRange {
            content_start: 0,
            content_end: size,
            data_start: 0,
            data_end: size,
        }];
    }
    let gutter = u32::from(limit > 2);
    let content_size = (limit - gutter * 2).max(1);
    let mut ranges = Vec::new();
    let mut start = 0;
    while start < size {
        let end = start.saturating_add(content_size).min(size);
        ranges.push(TileRange {
            content_start: start,
            content_end: end,
            data_start: start.saturating_sub(gutter),
            data_end: end.saturating_add(gutter).min(size),
        });
        start = end;
    }
    ranges
}

fn tile_vertices(model: &ImageModel, x: TileRange, y: TileRange) -> Vec<ImageVertex> {
    let source: Vec<ImageVertex> = model
        .verts
        .iter()
        .map(|vertex| ImageVertex {
            pos: vertex.pos,
            uv: vertex.uv,
            pos_low: vertex.pos_low,
        })
        .collect();
    if x.content_start == 0
        && x.content_end == model.width
        && y.content_start == 0
        && y.content_end == model.height
    {
        return source;
    }

    let bounds = [
        (0, x.content_start as f32 / model.width as f32, true),
        (0, x.content_end as f32 / model.width as f32, false),
        (1, y.content_start as f32 / model.height as f32, true),
        (1, y.content_end as f32 / model.height as f32, false),
    ];
    let mut output = Vec::new();
    for triangle in source.chunks_exact(3) {
        let mut polygon = triangle.to_vec();
        for (axis, boundary, keep_greater) in bounds {
            polygon = clip_vertices(&polygon, axis, boundary, keep_greater);
        }
        for index in 1..polygon.len().saturating_sub(1) {
            output.push(polygon[0]);
            output.push(polygon[index]);
            output.push(polygon[index + 1]);
        }
    }

    let data_width = (x.data_end - x.data_start) as f32;
    let data_height = (y.data_end - y.data_start) as f32;
    for vertex in &mut output {
        vertex.uv = [
            ((vertex.uv[0] * model.width as f32 - x.data_start as f32) / data_width)
                .clamp(0.0, 1.0),
            ((vertex.uv[1] * model.height as f32 - y.data_start as f32) / data_height)
                .clamp(0.0, 1.0),
        ];
    }
    output
}

fn clip_vertices(
    input: &[ImageVertex],
    axis: usize,
    boundary: f32,
    keep_greater: bool,
) -> Vec<ImageVertex> {
    if input.is_empty() {
        return Vec::new();
    }
    let inside = |vertex: &ImageVertex| {
        if keep_greater {
            vertex.uv[axis] >= boundary
        } else {
            vertex.uv[axis] <= boundary
        }
    };
    let mut output = Vec::new();
    let mut previous = *input.last().unwrap();
    let mut previous_inside = inside(&previous);
    for &current in input {
        let current_inside = inside(&current);
        if current_inside != previous_inside {
            output.push(intersect_vertex(previous, current, axis, boundary));
        }
        if current_inside {
            output.push(current);
        }
        previous = current;
        previous_inside = current_inside;
    }
    output
}

fn intersect_vertex(
    start: ImageVertex,
    end: ImageVertex,
    axis: usize,
    boundary: f32,
) -> ImageVertex {
    let distance = end.uv[axis] - start.uv[axis];
    let t = if distance.abs() > f32::EPSILON {
        ((boundary - start.uv[axis]) / distance).clamp(0.0, 1.0)
    } else {
        0.0
    };
    ImageVertex {
        pos: interpolate3(start.pos, end.pos, t),
        uv: [
            start.uv[0] + (end.uv[0] - start.uv[0]) * t,
            start.uv[1] + (end.uv[1] - start.uv[1]) * t,
        ],
        pos_low: interpolate3(start.pos_low, end.pos_low, t),
    }
}

fn interpolate3(start: [f32; 3], end: [f32; 3], t: f32) -> [f32; 3] {
    [
        start[0] + (end[0] - start[0]) * t,
        start[1] + (end[1] - start[1]) * t,
        start[2] + (end[2] - start[2]) * t,
    ]
}