{{py:

"""

Template file for easily generate fused types consistent code using Tempita
(https://github.com/cython/cython/blob/master/Cython/Tempita/_tempita.py).

Generated file: sag_fast.pyx

Each class is duplicated for all dtypes (float and double). The keywords
between double braces are substituted during the build.
"""

# Authors: The scikit-learn developers
# SPDX-License-Identifier: BSD-3-Clause

# name_suffix, c_type, np_type
dtypes = [('64', 'double', 'np.float64'),
          ('32', 'float', 'np.float32')]

}}
"""SAG and SAGA implementation"""

import numpy as np
from libc.math cimport exp, fabs, isfinite, log
from libc.time cimport time, time_t
from libc.stdio cimport printf

from .._loss._loss cimport (
    CyLossFunction,
    CyHalfBinomialLoss,
    CyHalfMultinomialLoss,
    CyHalfSquaredError,
)
from ..utils._seq_dataset cimport SequentialDataset32, SequentialDataset64


{{for name_suffix, c_type, np_type in dtypes}}

cdef inline {{c_type}} fmax{{name_suffix}}({{c_type}} x, {{c_type}} y) noexcept nogil:
    if x > y:
        return x
    return y

{{endfor}}

{{for name_suffix, c_type, np_type in dtypes}}

cdef inline {{c_type}} _soft_thresholding{{name_suffix}}({{c_type}} x, {{c_type}} shrinkage) noexcept nogil:
    return fmax{{name_suffix}}(x - shrinkage, 0) - fmax{{name_suffix}}(- x - shrinkage, 0)

{{endfor}}


{{for name_suffix, c_type, np_type in dtypes}}

def sag{{name_suffix}}(
    SequentialDataset{{name_suffix}} dataset,
    {{c_type}}[:, ::1] weights_array,
    {{c_type}}[::1] intercept_array,
    int n_samples,
    int n_features,
    int n_classes,
    double tol,
    int max_iter,
    str loss_function,
    double step_size,
    double alpha,
    double beta,
    {{c_type}}[:, ::1] sum_gradient_init,
    {{c_type}}[:, ::1] gradient_memory_init,
    bint[::1] seen_init,
    int num_seen,
    bint fit_intercept,
    {{c_type}}[::1] intercept_sum_gradient_init,
    double intercept_decay,
    bint saga,
    bint verbose
):
    """Stochastic Average Gradient (SAG) and SAGA solvers.

    Used in Ridge and LogisticRegression.

    Some implementation details:

    - Just-in-time (JIT) update: In SAG(A), the average-gradient update is
    collinear with the drawn sample X_i. Therefore, if the data is sparse, the
    random sample X_i will change the average gradient only on features j where
    X_ij != 0. In some cases, the average gradient on feature j might change
    only after k random samples with no change. In these cases, instead of
    applying k times the same gradient step on feature j, we apply the gradient
    step only once, scaled by k. This is called the "just-in-time update", and
    it is performed in `lagged_update{{name_suffix}}`. This function also
    applies the proximal operator after the gradient step (if L1 regularization
    is used in SAGA).

    - Weight scale: In SAG(A), the weights are scaled down at each iteration
    due to the L2 regularization. To avoid updating all the weights at each
    iteration, the weight scale is factored out in a separate variable `wscale`
    which is only used in the JIT update. When this variable is too small, it
    is reset for numerical stability using the function
    `scale_weights{{name_suffix}}`. This reset requires applying all remaining
    JIT updates. This reset is also performed every `n_samples` iterations
    before each convergence check, so when the algorithm stops, we are sure
    that there is no remaining JIT updates.

    Reference
    ---------
    Schmidt, M., Roux, N. L., & Bach, F. (2013).
    Minimizing finite sums with the stochastic average gradient
    https://hal.inria.fr/hal-00860051/document
    (section 4.3)

    :arxiv:`Defazio, A., Bach F. & Lacoste-Julien S. (2014).
    "SAGA: A Fast Incremental Gradient Method With Support
    for Non-Strongly Convex Composite Objectives" <1407.0202>`
    """
    # the data pointer for x, the current sample
    cdef {{c_type}} *x_data_ptr = NULL
    # the index pointer for the column of the data
    cdef int *x_ind_ptr = NULL
    # the number of non-zero features for current sample
    cdef int xnnz = -1
    # the label value for current sample
    # the label value for current sample
    cdef {{c_type}} y
    # the sample weight
    cdef {{c_type}} sample_weight

    # helper variable for indexes
    cdef int f_idx, s_idx, feature_ind, class_ind, j
    # the number of pass through all samples
    cdef int n_iter = 0
    # helper to track iterations through samples
    cdef int sample_itr
    # the index (row number) of the current sample
    cdef int sample_ind

    # the maximum change in weights, used to compute stopping criteria
    cdef {{c_type}} max_change
    # a holder variable for the max weight, used to compute stopping criteria
    cdef {{c_type}} max_weight

    # the start time of the fit
    cdef time_t start_time
    # the end time of the fit
    cdef time_t end_time

    # precomputation since the step size does not change in this implementation
    cdef {{c_type}} wscale_update = 1.0 - step_size * alpha

    # helper for cumulative sum
    cdef {{c_type}} cum_sum

    # the pointer to the coef_ or weights
    cdef {{c_type}}* weights = &weights_array[0, 0]

    # the sum of gradients for each feature
    cdef {{c_type}}* sum_gradient = &sum_gradient_init[0, 0]

    # the previously seen gradient for each sample
    cdef {{c_type}}* gradient_memory = &gradient_memory_init[0, 0]

    # the cumulative sums needed for JIT params
    cdef {{c_type}}[::1] cumulative_sums = np.empty(n_samples, dtype={{np_type}}, order="c")

    # the index for the last time this feature was updated
    cdef int[::1] feature_hist = np.zeros(n_features, dtype=np.int32, order="c")

    # the previous weights to use to compute stopping criteria
    cdef {{c_type}}[:, ::1] previous_weights_array = np.zeros((n_features, n_classes), dtype={{np_type}}, order="c")
    cdef {{c_type}}* previous_weights = &previous_weights_array[0, 0]

    cdef {{c_type}}[::1] prediction = np.zeros(n_classes, dtype={{np_type}}, order="c")

    cdef {{c_type}}[::1] gradient = np.zeros(n_classes, dtype={{np_type}}, order="c")

    # Intermediate variable that need declaration since cython cannot infer when templating
    cdef {{c_type}} val

    # Bias correction term in saga
    cdef {{c_type}} gradient_correction

    # the scalar used for multiplying z
    cdef {{c_type}} wscale = 1.0

    # return value (-1 if an error occurred, 0 otherwise)
    cdef int status = 0

    # the cumulative sums for each iteration for the sparse implementation
    cumulative_sums[0] = 0.0

    # the multipliative scale needed for JIT params
    cdef {{c_type}}[::1] cumulative_sums_prox
    cdef {{c_type}}* cumulative_sums_prox_ptr

    cdef bint prox = beta > 0 and saga

    # Loss function to optimize
    cdef CyLossFunction loss
    # Whether the loss function is multinomial
    cdef bint multinomial = False
    # Multinomial loss function
    cdef CyHalfMultinomialLoss multiloss

    if loss_function == "multinomial":
        multinomial = True
        multiloss = CyHalfMultinomialLoss()
    elif loss_function == "log":
        loss = CyHalfBinomialLoss()
    elif loss_function == "squared":
        loss = CyHalfSquaredError()
    else:
        raise ValueError("Invalid loss parameter: got %s instead of "
                         "one of ('log', 'squared', 'multinomial')"
                         % loss_function)

    if prox:
        cumulative_sums_prox = np.empty(n_samples, dtype={{np_type}}, order="c")
        cumulative_sums_prox_ptr = &cumulative_sums_prox[0]
    else:
        cumulative_sums_prox = None
        cumulative_sums_prox_ptr = NULL

    with nogil:
        start_time = time(NULL)
        for n_iter in range(max_iter):
            for sample_itr in range(n_samples):
                # extract a random sample
                sample_ind = dataset.random(&x_data_ptr, &x_ind_ptr, &xnnz, &y, &sample_weight)

                # cached index for gradient_memory
                s_idx = sample_ind * n_classes

                # update the number of samples seen and the seen array
                if seen_init[sample_ind] == 0:
                    num_seen += 1
                    seen_init[sample_ind] = 1

                # make the weight updates (just-in-time gradient step, and prox operator)
                if sample_itr > 0:
                   status = lagged_update{{name_suffix}}(
                       weights=weights,
                       wscale=wscale,
                       xnnz=xnnz,
                       n_samples=n_samples,
                       n_classes=n_classes,
                       sample_itr=sample_itr,
                       cumulative_sums=&cumulative_sums[0],
                       cumulative_sums_prox=cumulative_sums_prox_ptr,
                       feature_hist=&feature_hist[0],
                       prox=prox,
                       sum_gradient=sum_gradient,
                       x_ind_ptr=x_ind_ptr,
                       reset=False,
                       n_iter=n_iter
                   )
                   if status == -1:
                       break

                # find the current prediction
                predict_sample{{name_suffix}}(
                    x_data_ptr=x_data_ptr,
                    x_ind_ptr=x_ind_ptr,
                    xnnz=xnnz,
                    w_data_ptr=weights,
                    wscale=wscale,
                    intercept=&intercept_array[0],
                    prediction=&prediction[0],
                    n_classes=n_classes
                )

                # compute the gradient for this sample, given the prediction
                if multinomial:
                    multiloss.cy_gradient(
                        y_true=y,
                        raw_prediction=prediction,
                        sample_weight=sample_weight,
                        gradient_out=gradient,
                    )
                else:
                    gradient[0] = loss.cy_gradient(y, prediction[0]) * sample_weight

                # L2 regularization by simply rescaling the weights
                wscale *= wscale_update

                # make the updates to the sum of gradients
                for j in range(xnnz):
                    feature_ind = x_ind_ptr[j]
                    val = x_data_ptr[j]
                    f_idx = feature_ind * n_classes
                    for class_ind in range(n_classes):
                        gradient_correction = \
                            val * (gradient[class_ind] -
                                   gradient_memory[s_idx + class_ind])
                        if saga:
                            # Note that this is not the main gradient step,
                            # which is performed just-in-time in lagged_update.
                            # This part is done outside the JIT update
                            # as it does not depend on the average gradient.
                            # The prox operator is applied after the JIT update
                            weights[f_idx + class_ind] -= \
                                (gradient_correction * step_size
                                 * (1 - 1. / num_seen) / wscale)
                        sum_gradient[f_idx + class_ind] += gradient_correction

                # fit the intercept
                if fit_intercept:
                    for class_ind in range(n_classes):
                        gradient_correction = (gradient[class_ind] -
                                               gradient_memory[s_idx + class_ind])
                        intercept_sum_gradient_init[class_ind] += gradient_correction
                        gradient_correction *= step_size * (1. - 1. / num_seen)
                        if saga:
                            intercept_array[class_ind] -= \
                                (step_size * intercept_sum_gradient_init[class_ind] /
                                 num_seen * intercept_decay) + gradient_correction
                        else:
                            intercept_array[class_ind] -= \
                                (step_size * intercept_sum_gradient_init[class_ind] /
                                 num_seen * intercept_decay)

                        # check to see that the intercept is not inf or NaN
                        if not isfinite(intercept_array[class_ind]):
                            status = -1
                            break
                    # Break from the n_samples outer loop if an error happened
                    # in the fit_intercept n_classes inner loop
                    if status == -1:
                        break

                # update the gradient memory for this sample
                for class_ind in range(n_classes):
                    gradient_memory[s_idx + class_ind] = gradient[class_ind]

                if sample_itr == 0:
                    cumulative_sums[0] = step_size / (wscale * num_seen)
                    if prox:
                        cumulative_sums_prox[0] = step_size * beta / wscale
                else:
                    cumulative_sums[sample_itr] = \
                        (cumulative_sums[sample_itr - 1] +
                         step_size / (wscale * num_seen))
                    if prox:
                        cumulative_sums_prox[sample_itr] = \
                        (cumulative_sums_prox[sample_itr - 1] +
                             step_size * beta / wscale)
                # If wscale gets too small, we need to reset the scale.
                # This also resets the just-in-time update system.
                if wscale < 1e-9:
                    if verbose:
                        with gil:
                            print("rescaling...")
                    status = scale_weights{{name_suffix}}(
                        weights=weights,
                        wscale=&wscale,
                        n_features=n_features,
                        n_samples=n_samples,
                        n_classes=n_classes,
                        sample_itr=sample_itr,
                        cumulative_sums=&cumulative_sums[0],
                        cumulative_sums_prox=cumulative_sums_prox_ptr,
                        feature_hist=&feature_hist[0],
                        prox=prox,
                        sum_gradient=sum_gradient,
                        n_iter=n_iter
                    )
                    if status == -1:
                        break

            # Break from the n_iter outer loop if an error happened in the
            # n_samples inner loop
            if status == -1:
                break

            # We scale the weights every n_samples iterations and reset the
            # just-in-time update system for numerical stability.
            # Because this reset is done before every convergence check, we are
            # sure there is no remaining lagged update when the algorithm stops.
            status = scale_weights{{name_suffix}}(
                weights=weights,
                wscale=&wscale,
                n_features=n_features,
                n_samples=n_samples,
                n_classes=n_classes,
                sample_itr=n_samples - 1,
                cumulative_sums=&cumulative_sums[0],
                cumulative_sums_prox=cumulative_sums_prox_ptr,
                feature_hist=&feature_hist[0],
                prox=prox,
                sum_gradient=sum_gradient,
                n_iter=n_iter
            )
            if status == -1:
                break

            # check if the stopping criteria is reached
            max_change = 0.0
            max_weight = 0.0
            for idx in range(n_features * n_classes):
                max_weight = fmax{{name_suffix}}(max_weight, fabs(weights[idx]))
                max_change = fmax{{name_suffix}}(max_change, fabs(weights[idx] - previous_weights[idx]))
                previous_weights[idx] = weights[idx]
            if ((max_weight != 0 and max_change / max_weight <= tol)
                or max_weight == 0 and max_change == 0):
                if verbose:
                    end_time = time(NULL)
                    with gil:
                        print("convergence after %d epochs took %d seconds" %
                              (n_iter + 1, end_time - start_time))
                break
            elif verbose:
                printf('Epoch %d, change: %.8g\n', n_iter + 1,
                                                  max_change / max_weight)
    n_iter += 1
    # We do the error treatment here based on error code in status to avoid
    # re-acquiring the GIL within the cython code, which slows the computation
    # when the sag/saga solver is used concurrently in multiple Python threads.
    if status == -1:
        raise ValueError(("Floating-point under-/overflow occurred at epoch"
                          " #%d. Scaling input data with StandardScaler or"
                          " MinMaxScaler might help.") % n_iter)

    if verbose and n_iter >= max_iter:
        end_time = time(NULL)
        print(("max_iter reached after %d seconds") %
              (end_time - start_time))

    return num_seen, n_iter

{{endfor}}


{{for name_suffix, c_type, np_type in dtypes}}

cdef int scale_weights{{name_suffix}}(
    {{c_type}}* weights,
    {{c_type}}* wscale,
    int n_features,
    int n_samples,
    int n_classes,
    int sample_itr,
    {{c_type}}* cumulative_sums,
    {{c_type}}* cumulative_sums_prox,
    int* feature_hist,
    bint prox,
    {{c_type}}* sum_gradient,
    int n_iter
) noexcept nogil:
    """Scale the weights and reset wscale to 1.0 for numerical stability, and
    reset the just-in-time (JIT) update system.

    See `sag{{name_suffix}}`'s docstring about the JIT update system.

    wscale = (1 - step_size * alpha) ** (n_iter * n_samples + sample_itr)
    can become very small, so we reset it every n_samples iterations to 1.0 for
    numerical stability. To be able to scale, we first need to update every
    coefficients and reset the just-in-time update system.
    This also limits the size of `cumulative_sums`.
    """

    cdef int status
    status = lagged_update{{name_suffix}}(
        weights,
        wscale[0],
        n_features,
        n_samples,
        n_classes,
        sample_itr + 1,
        cumulative_sums,
        cumulative_sums_prox,
        feature_hist,
        prox,
        sum_gradient,
        NULL,
        True,
        n_iter
    )
    # if lagged update succeeded, reset wscale to 1.0
    if status == 0:
        wscale[0] = 1.0
    return status

{{endfor}}


{{for name_suffix, c_type, np_type in dtypes}}

cdef int lagged_update{{name_suffix}}(
    {{c_type}}* weights,
    {{c_type}} wscale,
    int xnnz,
    int n_samples,
    int n_classes,
    int sample_itr,
    {{c_type}}* cumulative_sums,
    {{c_type}}* cumulative_sums_prox,
    int* feature_hist,
    bint prox,
    {{c_type}}* sum_gradient,
    int* x_ind_ptr,
    bint reset,
    int n_iter
) noexcept nogil:
    """Hard perform the JIT updates for non-zero features of present sample.

    See `sag{{name_suffix}}`'s docstring about the JIT update system.

    The updates that awaits are kept in memory using cumulative_sums,
    cumulative_sums_prox, wscale and feature_hist. See original SAGA paper
    (Defazio et al. 2014) for details. If reset=True, we also reset wscale to
    1 (this is done at the end of each epoch).
    """
    cdef int feature_ind, class_ind, idx, f_idx, lagged_ind, last_update_ind
    cdef {{c_type}} cum_sum, grad_step, prox_step, cum_sum_prox
    for feature_ind in range(xnnz):
        if not reset:
            feature_ind = x_ind_ptr[feature_ind]
        f_idx = feature_ind * n_classes

        cum_sum = cumulative_sums[sample_itr - 1]
        if prox:
            cum_sum_prox = cumulative_sums_prox[sample_itr - 1]
        if feature_hist[feature_ind] != 0:
            cum_sum -= cumulative_sums[feature_hist[feature_ind] - 1]
            if prox:
                cum_sum_prox -= cumulative_sums_prox[feature_hist[feature_ind] - 1]
        if not prox:
            for class_ind in range(n_classes):
                idx = f_idx + class_ind
                weights[idx] -= cum_sum * sum_gradient[idx]
                if reset:
                    weights[idx] *= wscale
                    if not isfinite(weights[idx]):
                        # returning here does not require the gil as the return
                        # type is a C integer
                        return -1
        else:
            for class_ind in range(n_classes):
                idx = f_idx + class_ind
                if fabs(sum_gradient[idx] * cum_sum) < cum_sum_prox:
                    # In this case, we can perform all the gradient steps and
                    # all the proximal steps in this order, which is more
                    # efficient than unrolling all the lagged updates.
                    # Idea taken from scikit-learn-contrib/lightning.
                    weights[idx] -= cum_sum * sum_gradient[idx]
                    weights[idx] = _soft_thresholding{{name_suffix}}(weights[idx],
                                                      cum_sum_prox)
                else:
                    last_update_ind = feature_hist[feature_ind]
                    if last_update_ind == -1:
                        last_update_ind = sample_itr - 1
                    for lagged_ind in range(sample_itr - 1,
                                   last_update_ind - 1, -1):
                        if lagged_ind > 0:
                            grad_step = (cumulative_sums[lagged_ind]
                               - cumulative_sums[lagged_ind - 1])
                            prox_step = (cumulative_sums_prox[lagged_ind]
                               - cumulative_sums_prox[lagged_ind - 1])
                        else:
                            grad_step = cumulative_sums[lagged_ind]
                            prox_step = cumulative_sums_prox[lagged_ind]
                        weights[idx] -= sum_gradient[idx] * grad_step
                        weights[idx] = _soft_thresholding{{name_suffix}}(weights[idx],
                                                          prox_step)

                if reset:
                    weights[idx] *= wscale
                    # check to see that the weight is not inf or NaN
                    if not isfinite(weights[idx]):
                        return -1
        if reset:
            feature_hist[feature_ind] = sample_itr % n_samples
        else:
            feature_hist[feature_ind] = sample_itr

    if reset:
        cumulative_sums[sample_itr - 1] = 0.0
        if prox:
            cumulative_sums_prox[sample_itr - 1] = 0.0

    return 0

{{endfor}}


{{for name_suffix, c_type, np_type in dtypes}}

cdef void predict_sample{{name_suffix}}(
    {{c_type}}* x_data_ptr,
    int* x_ind_ptr,
    int xnnz,
    {{c_type}}* w_data_ptr,
    {{c_type}} wscale,
    {{c_type}}* intercept,
    {{c_type}}* prediction,
    int n_classes
) noexcept nogil:
    """Compute the prediction given sparse sample x and dense weight w.

    Parameters
    ----------
    x_data_ptr : pointer
        Pointer to the data of the sample x

    x_ind_ptr : pointer
        Pointer to the indices of the sample  x

    xnnz : int
        Number of non-zero element in the sample  x

    w_data_ptr : pointer
        Pointer to the data of the weights w

    wscale : {{c_type}}
        Scale of the weights w

    intercept : pointer
        Pointer to the intercept

    prediction : pointer
        Pointer to store the resulting prediction

    n_classes : int
        Number of classes in multinomial case. Equals 1 in binary case.

    """
    cdef int feature_ind, class_ind, j
    cdef {{c_type}} innerprod

    for class_ind in range(n_classes):
        innerprod = 0.0
        # Compute the dot product only on non-zero elements of x
        for j in range(xnnz):
            feature_ind = x_ind_ptr[j]
            innerprod += (w_data_ptr[feature_ind * n_classes + class_ind] *
                          x_data_ptr[j])

        prediction[class_ind] = wscale * innerprod + intercept[class_ind]


{{endfor}}
