use std::fs;use std::path::Path;use std::path::PathBuf;use anyhow::Context;use anyhow::Result;use image::GenericImageView;use super::model::Pet;pub(super) fn prepare_png_frames(pet: &Pet, frame_dir: &Path) -> Result<Vec<PathBuf>> {    fs::create_dir_all(frame_dir).with_context(|| format!("create {}", frame_dir.display()))?;    let expected: Vec<PathBuf> = (0..pet.frame_count())        .map(|index| frame_dir.join(format!("frame_{index:03}.png")))        .collect();    let complete = expected.iter().all(|path| path.exists());    if !complete {        for stale in glob_frame_files(frame_dir)? {            let _ = fs::remove_file(stale);        }        let spritesheet = image::open(&pet.spritesheet_path)            .with_context(|| format!("read {}", pet.spritesheet_path.display()))?;        for row in 0..pet.rows {            for column in 0..pet.columns {                let index = row                    .checked_mul(pet.columns)                    .and_then(|row_offset| row_offset.checked_add(column))                    .context("pet frame index overflow")?;                let index = usize::try_from(index).context("pet frame index does not fit usize")?;                let path = expected                    .get(index)                    .context("pet frame index exceeds expected frame count")?;                let x = column                    .checked_mul(pet.frame_width)                    .context("pet frame x offset overflow")?;                let y = row                    .checked_mul(pet.frame_height)                    .context("pet frame y offset overflow")?;                let frame = spritesheet.try_view(x, y, pet.frame_width, pet.frame_height)?;                frame                    .to_image()                    .save_with_format(path, image::ImageFormat::Png)                    .with_context(|| format!("write {}", path.display()))?;            }        }    }    Ok(expected)}fn glob_frame_files(frame_dir: &Path) -> Result<Vec<PathBuf>> {    if !frame_dir.exists() {        return Ok(Vec::new());    }    let mut paths = Vec::new();    for entry in fs::read_dir(frame_dir).with_context(|| format!("read {}", frame_dir.display()))? {        let path = entry?.path();        if path            .file_name()            .and_then(|name| name.to_str())            .is_some_and(|name| name.starts_with("frame_") && name.ends_with(".png"))        {            paths.push(path);        }    }    Ok(paths)}#[cfg(test)]mod tests {    use std::collections::HashMap;    use image::ImageBuffer;    use image::Rgba;    use super::*;    #[test]    fn prepare_png_frames_slices_spritesheet_without_external_command() {        let dir = tempfile::tempdir().unwrap();        let spritesheet_path = dir.path().join("spritesheet.png");        let spritesheet: ImageBuffer<Rgba<u8>, Vec<u8>> = ImageBuffer::from_fn(2, 1, |x, _| {            if x == 0 {                Rgba([255, 0, 0, 255])            } else {                Rgba([0, 255, 0, 255])            }        });        spritesheet.save(&spritesheet_path).unwrap();        let frames = prepare_png_frames(            &Pet {                id: "tiny".to_string(),                display_name: "Tiny".to_string(),                description: String::new(),                spritesheet_path,                frame_width: 1,                frame_height: 1,                columns: 2,                rows: 1,                frame_count: 2,                animations: HashMap::new(),            },            &dir.path().join("frames"),        )        .unwrap();        assert_eq!(frames.len(), 2);        assert!(frames[0].exists());        assert!(frames[1].exists());    }}