use candle::{Device, Result, Tensor};

pub fn linspace(start: f64, stop: f64, steps: usize) -> Result<Tensor> {
    if steps < 1 {
        candle::bail!("cannot use linspace with steps {steps} <= 1")
    }
    let delta = (stop - start) / (steps - 1) as f64;
    let vs = (0..steps)
        .map(|step| start + step as f64 * delta)
        .collect::<Vec<_>>();
    Tensor::from_vec(vs, steps, &Device::Cpu)
}

/// Saves an image to disk using the image crate, this expects an input with shape
/// (c, width, height).
pub fn save_image<P: AsRef<std::path::Path>>(img: &Tensor, p: P) -> Result<()> {
    let p = p.as_ref();
    let (channel, width, height) = img.dims3()?;
    if channel != 3 {
        candle::bail!("save_image expects an input of shape (3, width, height)")
    }
    let img = img.transpose(0, 1)?.t()?.flatten_all()?;
    let pixels = img.to_vec1::<u8>()?;
    let image: image::ImageBuffer<image::Rgb<u8>, Vec<u8>> =
        match image::ImageBuffer::from_raw(width as u32, height as u32, pixels) {
            Some(image) => image,
            None => candle::bail!("error saving image {p:?}"),
        };
    image.save(p).map_err(candle::Error::wrap)?;
    Ok(())
}