#!/usr/bin/perl

use strict;
use warnings;
use List::Util qw( min max sum );
use Data::Dumper;

my @funcs =
(
    undef,  # first_timestamp
    \&avg,
    \&max,
    \&min,
    \&first,
    \&last,
);

my @records = (
    #  Timestamp.usecs    AVGTEMP MAXTEMP MINTEMP STARTTEMP ENDTEMP
    [ 1234567891.123456,  36.5,   36.9,   36.2,   36.4,     36.6 ],
    [ 1234567891.654321,  36.6,   40.1,   36.2,   36.6,     36.8 ],
    [ 1234567893.123456,  36.3,   38.8,   35.1,   36.8,     37.3 ],
    [ 1234567893.654321,  36.2,   36.9,   36.2,   37.3,     37.1 ],
    [ 1234567894.123456,  36.8,   37.3,   36.2,   37.1,     37.4 ],
);

# Main

print "  Timestamp         AVG   MAX   MIN   START END\n";
print( '[ ', join( ', ', @{ $_ } ), " ]\n" ) for( @records );
print "\n";

my @output = downsample( 5, \@records );

print "  Timestamp   AVG    MAX   MIN   START  END\n";
print '[ ', join( ', ', @output ), " ]\n";

# Subs

sub downsample
{
    my( $resolution, $data ) = @_;
    my $newdata = transpose( $data );

    my $first_timestamp =
        first_timestamp_for_resolution( $resolution, $newdata->[0][0] );

    my @output;
    push( @output, $first_timestamp );

    push( @output, $funcs[$_]->( @{$newdata->[$_]} ) ) for ( 1..$#funcs );

    return( @output );
}

sub first_timestamp_for_resolution {
    my( $resolution, $value ) = @_;  # $resolution in seconds

    return( int( $value - ( $value % $resolution ) ) );
}

# from Math::Matrix
sub transpose {
    my( $matrix ) = shift;
    my( $m, @result );

    for my $col ( @{ $matrix->[0] } ) {
        push( @result, [] );
    }
    for my $row ( @{$matrix} ) {
        $m=0;
        for my $col ( @{$row} ) {
            push( @{ $result[$m++] }, $col );
        }
    }

    return( \@result );
}

sub first
{
    return( $_[0] );
}

sub last
{
    return( $_[-1] );
}

sub avg
{
    return( sum( @_ ) / scalar( @_ ) );
}