use fontdue::Font;
use lru::LruCache;
use wgpu;

/*
A note on how Casey Muratori's refterm works in terms of font rendering,
because it's not bad and handles things that we're not going to handle
because I just want to get some dang text on the dang screen right now.

- Step 1: You break the text into runs of characters that need to be
  rendered together.

- Step 2: You figure out how many uniform cells this run occupies.

- Step 3: For each cell, you figure out if you already have the necessary
  part of the run in the texture atlas. (Right? Each part of the run has a
  distinct ID based on the actual run and the cell within the run.) If you
  don't have this [run,cell] in the atlas, then:

  - Step 3a: Render the run as a bitmap, if you haven't already.
  - Step 3b: Get coordinates from the cache for this [run,cell] pair,
    evicting something if necessary.
  - Step 3c: Copy the part of the bitmap for this [run,cell] into the
    texture atlas at the coordinates.

  Put the coordinates (either newly generated or pulled from the cache) into
  the cell.

- Step 4: Load all the cells onto the GPU and do a shader that renders the
  cells.

Specifically what I'm doing right now is going character-by-caracter, and not
doing runs and not handling things that are wider than a cell. I'm also not
doing the efficient big grid render because I want to render characters at
pixel offsets and kern between characters and whatnot, which is different
from what they're doing. Mine is almost certainly less efficient.
 */

#[derive(Eq, PartialEq, Hash)]
enum CellCacheKey {
    Garbage(u32),    // Exists so that I can prime the LRU, not used generally.
    GlyphIndex(u16), // Actual factual cache entries.
}

pub struct FontCache {
    font: Font,
    size: f32,
    texture: wgpu::Texture,
    cell_width: u16,
    cell_height: u16,
    pub view: wgpu::TextureView,
    pub sampler: wgpu::Sampler,

    cells: Vec<GlyphCell>,
    cell_cache: LruCache<CellCacheKey, usize>,
}

enum SlotState {
    Empty,
    Rendered(u16, fontdue::Metrics),
}

struct GlyphCell {
    // The coordinates in the atlas
    x: u16,
    y: u16,

    state: SlotState,
}

pub struct Glyph {
    pub x: f32,
    pub y: f32,
    pub adjust_x: f32,
    pub adjust_y: f32,
    pub w: f32,
    pub h: f32,
    pub advance_width: f32,
}

impl FontCache {
    pub fn new(device: &wgpu::Device, bytes: &[u8], size: f32) -> Self {
        let font = fontdue::Font::from_bytes(bytes, fontdue::FontSettings::default())
            .expect("Could not parse font");

        // Set up the texture that we'll use to cache the glyphs we're rendering.
        let atlas_width = 2048;
        let atlas_height = 2048;

        let texture = device.create_texture(&wgpu::TextureDescriptor {
            label: Some("Font Glyph Atlas"),
            size: wgpu::Extent3d {
                width: atlas_width.into(),
                height: atlas_height.into(),
                depth_or_array_layers: 1,
            },
            mip_level_count: 1,
            sample_count: 1, // 4 for multisample?
            dimension: wgpu::TextureDimension::D2,
            format: wgpu::TextureFormat::R8Unorm,
            usage: wgpu::TextureUsages::TEXTURE_BINDING
                | wgpu::TextureUsages::COPY_DST
                | wgpu::TextureUsages::RENDER_ATTACHMENT,
            view_formats: &[],
        });
        let view = texture.create_view(&wgpu::TextureViewDescriptor::default());
        let sampler = device.create_sampler(&wgpu::SamplerDescriptor {
            address_mode_u: wgpu::AddressMode::ClampToEdge,
            address_mode_v: wgpu::AddressMode::ClampToEdge,
            address_mode_w: wgpu::AddressMode::ClampToEdge,
            mag_filter: wgpu::FilterMode::Nearest,
            min_filter: wgpu::FilterMode::Nearest,
            mipmap_filter: wgpu::FilterMode::Nearest,
            ..Default::default()
        });

        // Measure the font to figure out the size of a cell in the cache.
        // NOTE: This metric nonsense is bad, probably.
        let mut char_height = 0;
        if let Some(line_metrics) = font.horizontal_line_metrics(size) {
            char_height = (line_metrics.new_line_size + 0.5) as usize;
        }

        let metrics = font.metrics('M', size);
        let mut char_width = metrics.width;
        char_height = metrics.height.max(char_height);

        let metrics = font.metrics('g', size);
        char_width = metrics.width.max(char_width);
        char_height = metrics.height.max(char_height);

        eprintln!("For this font, width={char_width} height={char_height}");

        // Allocate the individual cells in the texture atlas; this records
        // the state of what's in the cell and whatnot.
        let mut cells = vec![];
        for y in (0..atlas_height).step_by(char_height) {
            for x in (0..atlas_width).step_by(char_width) {
                cells.push(GlyphCell {
                    x,
                    y,
                    state: SlotState::Empty,
                });
            }
        }

        // Allocate the LRU cache for the cells. Fill it with garbage so that
        // we can always "allocate" by pulling from the LRU.
        let mut cell_cache = LruCache::new(std::num::NonZeroUsize::new(cells.len()).unwrap());
        for i in 0..cells.len() {
            cell_cache.put(
                CellCacheKey::Garbage(i.try_into().expect("Too many cells!")),
                i,
            );
        }

        FontCache {
            font,
            size,
            texture,
            cell_width: char_width.try_into().unwrap(),
            cell_height: char_height.try_into().unwrap(),

            view,
            sampler,
            cells,
            cell_cache,
        }
    }

    pub fn get_char(&mut self, queue: &wgpu::Queue, c: char) -> Glyph {
        let index = self.font.lookup_glyph_index(c);
        let key = CellCacheKey::GlyphIndex(index);
        let cell = match self.cell_cache.get(&key) {
            Some(cell_index) => &mut self.cells[*cell_index],
            None => {
                let (_, cell_index) = self
                    .cell_cache
                    .pop_lru()
                    .expect("did not put all available things in the LRU cache");
                self.cell_cache.put(key, cell_index);
                let cell = &mut self.cells[cell_index];
                cell.state = SlotState::Empty; // This isn't what it used to be.
                cell
            }
        };

        // I mean, technically if we got an LRU hit here it's rendered, but
        // convincing the compiler of that is a pain.
        let metrics = match cell.state {
            SlotState::Rendered(_, metrics) => metrics,
            SlotState::Empty => {
                let (metrics, bitmap) = self.font.rasterize_indexed(index, self.size);

                // eprintln!("Rasterizing '{c}' (index {index}): {metrics:?}");
                // For a good time, call
                // {
                //     eprintln!();
                //     let mut i = 0;
                //     for _ in (0..metrics.height) {
                //         for _ in (0..metrics.width) {
                //             let bv = bitmap[i];
                //             let rc = if bv == 0 {
                //                 ' '
                //             } else if bv < 25 {
                //                 '.'
                //             } else {
                //                 'X'
                //             };
                //             eprint!("{rc}");
                //             i += 1;
                //         }
                //         eprintln!();
                //     }
                //     eprintln!();
                // }

                let mut texture = self.texture.as_image_copy();
                texture.origin.x = cell.x.into();
                texture.origin.y = cell.y.into();
                // eprintln!("  Rendering to {}, {}", texture.origin.x, texture.origin.y);

                queue.write_texture(
                    texture,
                    &bitmap,
                    wgpu::ImageDataLayout {
                        offset: 0,
                        bytes_per_row: Some(metrics.width as u32),
                        rows_per_image: None,
                    },
                    wgpu::Extent3d {
                        width: metrics.width as u32,
                        height: metrics.height as u32,
                        depth_or_array_layers: 1,
                    },
                );

                cell.state = SlotState::Rendered(index, metrics.clone());
                metrics
            }
        };

        Glyph {
            x: cell.x as f32,
            y: cell.y as f32,
            adjust_x: metrics.xmin as f32,
            adjust_y: (self.cell_height as f32)
                + floor(-metrics.bounds.height - metrics.bounds.ymin), // PositiveYDown,
            w: self.cell_width as f32,
            h: self.cell_height as f32,
            advance_width: metrics.advance_width,
        }
    }
}

fn floor(x: f32) -> f32 {
    let mut ui = x.to_bits();
    let e = (((ui >> 23) as i32) & 0xff) - 0x7f;

    if e >= 23 {
        return x;
    }
    if e >= 0 {
        let m: u32 = 0x007fffff >> e;
        if (ui & m) == 0 {
            return x;
        }
        if ui >> 31 != 0 {
            ui += m;
        }
        ui &= !m;
    } else {
        if ui >> 31 == 0 {
            ui = 0;
        } else if ui << 1 != 0 {
            return -1.0;
        }
    }
    f32::from_bits(ui)
}

// pub fn inconsolata() {
//     let font = include_bytes!("./Inconsolata-Regular.ttf") as &[u8];
//     let font = fontdue::Font::from_bytes(font, fontdue::FontSettings::default()).unwrap();

//     let text = "Hello World!";

//     // Break to characters.
//     let size = 16.0;
//     let mut prev = None;
//     let mut left = 0.0;
//     for c in text.chars() {
//         // TODO: Cache this.
//         let (metrics, bitmap) = font.rasterize(c, size);
//         left += match prev {
//             Some(pc) => match font.horizontal_kern(pc, c, size) {
//                 Some(k) => k,
//                 None => 0.0,
//             },
//             None => 0.0,
//         };
//         left += metrics.advance_width;
//     }
// }