/**++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 *
 *                                              PANIC
 *                              Portable Algorithms and Numerics In C++
 *
 *                       Scientific computing from scratch, with feeling.
 *
 * Copyright (c) 2026 Michelle Bausager
 *
 * This file is part of PANIC.
 *
 * PANIC is free software licensed under the GNU General Public License v3.0 or later.
 * You may redistribute and/or modify it under the terms of the GPL.
 *
 * PANIC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the LICENSE file for the full license text.
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 *++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 *
 * Project Name:      PANIC
 * Module Name:       math
 * File Name:         mean.hpp
 * Revision:          0.1.0
 * Date:              30-07-2026
 * Author:            Michelle Bausager
 *
 * Description:
 * Functions to calculate mean of tensor arrays
 *
 *++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*/
#pragma once

#include <config/types.hpp>
#include <tensor/vector.hpp> // for panic::vector
#include <tensor/matrix.hpp> // for panic::matrix


namespace panic{
namespace math{




/**
 * @brief Returns the mean value of a vector
 *
 * Computes:
 * @code
 * result = mean(a)
 * @endcode
 *
 * @tparam T Numeric element type.
 * @param a Input vector.
 *
 * @return A new vector containing the result.
 * @return An empty vector if the operation fails.
 *
 * @note This overload is convenient, but may allocate a new vector.
 */
template <typename T>
panic::types::real_t mean(const panic::tensor::vector<T>& a);

/**
 * @brief Returns the mean value of a matrix.
 *
 * Computes:
 * @code
 * result = mean(A)
 * @endcode
 *
 * @tparam T Numeric element type.
 * @param A Input matrix.
 *
 * @return A new matrix containing the result.
 * @return An empty matrix if the operation fails.
 *
 */
template <typename T>
panic::types::real_t mean(const panic::tensor::matrix<T>& A);

/**
 * @brief Find the mean values row-wise of a matrix.
 *
 * Computes:
 * @code
 * c(i) = mean(A(i,j))
 * @endcode
 *
 * @tparam T Numeric element type.
 * @param A Input matrix.
 * @param c Output vector. Resized to match @p A.rows().
 *
 * @return true if @p c was resized and filled successfully.
 * @return false if vector sizes do not match or resizing @p c failed.
 */
template <typename T>
bool mean_rowwise(const panic::tensor::real_matrix& A, panic::tensor::real_vector& c);

/**
 * @brief Returns a new matrix containing the mean row-wise elementwise.
 *
 * Computes:
 * @code
 * result[i] = mean(A(i,j))
 * @endcode
 *
 * @tparam T Numeric element type.
 * @param A Input matrix.
 *
 * @return A new matrix containing the result.
 * @return An empty matrix if the operation fails.
 *
 * @note This overload is convenient, but may allocate a new vector.
 */
template <typename T>
panic::tensor::real_vector mean_rowwise(const panic::tensor::real_matrix& A);


/**
 * @brief Find the mean values column-wise of a matrix.
 *
 * Computes:
 * @code
 * C(j) = mean(A(i,j))
 * @endcode
 *
 * @tparam T Numeric element type.
 * @param A Input matrix.
 * @param C Output matrix. Resized to match @p A.cols().
 *
 * @return true if @p c was resized and filled successfully.
 * @return false if vector sizes do not match or resizing @p c failed.
 */
template <typename T>
bool mean_colwise(const panic::tensor::real_matrix& A, panic::tensor::real_vector& c);

/**
 * @brief Returns a new matrix containing the mean column-wise elementwise.
 *
 * Computes:
 * @code
 * result[j] = mean(A(i,j))
 * @endcode
 *
 * @tparam T Numeric element type.
 * @param A Input matrix.
 *
 * @return A new matrix containing the result.
 * @return An empty matrix if the operation fails.
 *
 * @note This overload is convenient, but may allocate a new vector.
 */
template <typename T>
panic::tensor::real_vector mean_colwise(const panic::tensor::real_matrix& A);

} // namespace math
} // namespace panic