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package AI::MXNet::Callback;
use strict;
use warnings;
use List::Util qw/max/;
use AI::MXNet::Function::Parameters;
use Mouse;
use overload "&{}" => sub { my $self = shift; sub { $self->call(@_) } };

=head1 NAME

    AI::MXNet::Callback - A collection of predefined callback functions
=cut

=head2 module_checkpoint

    Callback to save the module setup in the checkpoint files.

    Parameters
    ----------
    $mod : subclass of AI::MXNet::Module::Base
        The module to checkpoint.
    $prefix : str
        The file prefix to checkpoint to
    $period=1 : int
        How many epochs to wait before checkpointing. Default is 1.
    $save_optimizer_states=0 : Bool
        Whether to save optimizer states for later training.

    Returns
    -------
    $callback : sub ref
        The callback function that can be passed as iter_end_callback to fit.
=cut

method module_checkpoint(
    AI::MXNet::Module::Base $mod,
    Str $prefix,
    Int $period=1,
    Int $save_optimizer_states=0
)
{
    $period = max(1, $period);
    return sub {
        my ($iter_no, $sym, $arg, $aux) = @_;
        if(($iter_no + 1) % $period == 0)
        {
            $mod->save_checkpoint($prefix, $iter_no + 1, $save_optimizer_states);
        }
    }
}

=head2 log_train_metric

    Callback to log the training evaluation result every period.

    Parameters
    ----------
    $period : Int
        The number of batches after which to log the training evaluation metric.
    $auto_reset : Bool
        Whether to reset the metric after the logging.

    Returns
    -------
    $callback : sub ref
        The callback function that can be passed as iter_epoch_callback to fit.
=cut

method log_train_metric(Int $period, Int $auto_reset=0)
{
    return sub {
        my ($param) = @_;
        if($param->nbatch % $period == 0 and defined $param->eval_metric)
        {
            my $name_value = $param->eval_metric->get_name_value;
            while(my ($name, $value) = each %{ $name_value })
            {
                AI::MXNet::Logging->info(
                    "Iter[%d] Batch[%d] Train-%s=%f",
                    $param->epoch, $param->nbatch, $name, $value
                );
            }
            $param->eval_metric->reset if $auto_reset;
        }
    }
}

package AI::MXNet::Speedometer;
use Mouse;
use Time::HiRes qw/time/;
extends 'AI::MXNet::Callback';

=head1 NAME

    AI::MXNet::Speedometer - A callback that logs training speed 
=cut

=head1 DESCRIPTION

    Calculate and log training speed periodically.

    Parameters
    ----------
    batch_size: int
        batch_size of data
    frequent: int
        How many batches between calculations.
        Defaults to calculating & logging every 50 batches.
    auto_reset: Bool
        Reset the metric after each log, defaults to true.
=cut

has 'batch_size' => (is => 'ro', isa => 'Int', required => 1);
has 'frequent'   => (is => 'ro', isa => 'Int', default  => 50);
has 'init'       => (is => 'rw', isa => 'Int', default  => 0);
has 'tic'        => (is => 'rw', isa => 'Num', default  => 0);
has 'last_count' => (is => 'rw', isa => 'Int', default  => 0);
has 'auto_reset' => (is => 'ro', isa => 'Bool', default  => 1);

method call(AI::MXNet::BatchEndParam $param)
{
    my $count = $param->nbatch;
    if($self->last_count > $count)
    {
        $self->init(0);
    }
    $self->last_count($count);

    if($self->init)
    {
        if(($count % $self->frequent) == 0)