use crate::error::Result;
use candle_core::{Device, Tensor};

pub fn pick_device() -> Result<Device> {
    #[cfg(feature = "cuda")]
    if let Ok(d) = Device::new_cuda(0) {
        return Ok(d);
    }
    #[cfg(feature = "metal")]
    if let Ok(d) = Device::new_metal(0) {
        return Ok(d);
    }
    Ok(Device::Cpu)
}

/// Root-mean-square error between two equal-length f32 waveforms.
pub fn rms(a: &[f32], b: &[f32]) -> f32 {
    debug_assert_eq!(a.len(), b.len());
    let n = a.len() as f32;
    let sum_sq: f32 = a.iter().zip(b).map(|(x, y)| (x - y).powi(2)).sum();
    (sum_sq / n).sqrt()
}

/// CSM EOT signal: every codebook in the frame is zero. Caller must gate this
/// to frame_idx >= 1 to avoid spurious EOT on the first frame.
pub fn all_zero_codebooks(frame: &Tensor) -> Result<bool> {
    // frame shape: (1, num_codebooks) i64
    let v = frame.flatten_all()?.to_vec1::<i64>()?;
    Ok(v.iter().all(|x| *x == 0))
}