//! Trim operation: extract a frame range from sample data.

use crate::error::CoreError;

/// Trim samples to the given frame range (inclusive start, exclusive end).
///
/// Operates on interleaved sample data. `start_frame` and `end_frame` are in
/// frame units (not sample units), so channel count is accounted for.
pub fn apply_trim(
    samples: &mut Vec<f32>,
    channels: u16,
    start_frame: usize,
    end_frame: usize,
) -> Result<(), CoreError> {
    let ch = channels as usize;
    if ch == 0 {
        return Err(CoreError::Internal("trim: channels must be > 0".to_string()));
    }
    let total_frames = samples.len() / ch;

    if start_frame >= end_frame {
        return Err(CoreError::Internal(
            "trim: start_frame must be less than end_frame".to_string(),
        ));
    }
    if end_frame > total_frames {
        return Err(CoreError::Internal(format!(
            "trim: end_frame ({end_frame}) exceeds total frames ({total_frames})"
        )));
    }

    let start_sample = start_frame * ch;
    let end_sample = end_frame * ch;
    samples.drain(end_sample..);
    samples.drain(..start_sample);
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn trim_mono() {
        let mut samples = vec![0.1, 0.2, 0.3, 0.4, 0.5];
        apply_trim(&mut samples, 1, 1, 4).unwrap();
        assert_eq!(samples, vec![0.2, 0.3, 0.4]);
    }

    #[test]
    fn trim_stereo() {
        // 4 frames of stereo: [L0,R0, L1,R1, L2,R2, L3,R3]
        let mut samples = vec![0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8];
        apply_trim(&mut samples, 2, 1, 3).unwrap();
        // Should keep frames 1 and 2: [L1,R1, L2,R2]
        assert_eq!(samples, vec![0.3, 0.4, 0.5, 0.6]);
    }

    #[test]
    fn trim_full_range_is_noop() {
        let mut samples = vec![0.1, 0.2, 0.3];
        apply_trim(&mut samples, 1, 0, 3).unwrap();
        assert_eq!(samples, vec![0.1, 0.2, 0.3]);
    }

    #[test]
    fn trim_invalid_range() {
        let mut samples = vec![0.1, 0.2, 0.3];
        assert!(apply_trim(&mut samples, 1, 2, 1).is_err());
    }

    #[test]
    fn trim_out_of_bounds() {
        let mut samples = vec![0.1, 0.2, 0.3];
        assert!(apply_trim(&mut samples, 1, 0, 10).is_err());
    }

    #[test]
    fn trim_single_frame() {
        let mut samples = vec![0.1, 0.2, 0.3, 0.4, 0.5];
        apply_trim(&mut samples, 1, 2, 3).unwrap();
        assert_eq!(samples, vec![0.3]);
    }
}