/*
 * // Copyright (c) Radzivon Bartoshyk 12/2025. All rights reserved.
 * //
 * // Redistribution and use in source and binary forms, with or without modification,
 * // are permitted provided that the following conditions are met:
 * //
 * // 1.  Redistributions of source code must retain the above copyright notice, this
 * // list of conditions and the following disclaimer.
 * //
 * // 2.  Redistributions in binary form must reproduce the above copyright notice,
 * // this list of conditions and the following disclaimer in the documentation
 * // and/or other materials provided with the distribution.
 * //
 * // 3.  Neither the name of the copyright holder nor the names of its
 * // contributors may be used to endorse or promote products derived from
 * // this software without specific prior written permission.
 * //
 * // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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 */
use crate::{DetrendError, DetrendSample};
use num_traits::AsPrimitive;

pub(crate) fn detrend_constant<T: DetrendSample>(signal: &[T]) -> Result<Vec<T>, DetrendError>
where
    f64: AsPrimitive<T>,
    usize: AsPrimitive<T>,
{
    if signal.is_empty() {
        return Ok(Vec::new());
    }
    // Remove mean
    let mut mean_x: T = T::zero();
    for &q in signal.iter() {
        mean_x += q;
    }
    mean_x /= signal.len().as_();
    let mut result = vec![T::zero(); signal.len()];
    for (dst, &src) in result.iter_mut().zip(signal.iter()) {
        *dst = src - mean_x;
    }
    Ok(result)
}
