package String::Numerify;

### Convert string to number with prefix support

use warnings;
use strict;

BEGIN
{
    require Exporter;
    *import = \&Exporter::import; # just inherit import() only

    our $VERSION   = 1.001;
    our @EXPORT_OK = qw(&num);
}

# prefix to exponent value conversion table
my %prefix2exp = (
    Y => +24, # yotta
    Z => +21, # zetta
    E => +18, # exa
    e => +18, # exa
    P => +15, # peta
    T => +12, # terra
    t => +12, # terra
    G => +9,  # giga
    g => +9,  # giga
    X => +6,  # mega
    M => +6,  # mega
    K => +3,  # kilo
    k => +3,  # kilo
    "" => 0,  # default is no prefix
    m => -3,  # milli
    u => -6,  # micro
    U => -6,  # micro
    n => -9,  # nano
    N => -9,  # nano
    p => -12, # pico
    f => -15, # femto
    F => -15, # femto
    a => -18, # atto
    z => -21, # zepto
    y => -24, # yocto
);

# define regexes to match decimal-point number
my $dp_regex1 = qr/(\d+[.]?\d*)/;
my $dp_regex2 = qr/(\d*[.]?\d+)/;

# examples: " -+--.13e4u99..99.0" => -0.0013 , "+-- 123.mA" => 0.123
sub num {
    my ($numstr) = @_;

    # string must contain digit
    if ($numstr =~ /\d/)
    {
        my ($sign, $exponent, $prefix) = ("+", 0, "");

        # does first digit appear before or after potential decimal point?
        my $dp_regex = ($numstr =~ /^[^.]*\d/s ? $dp_regex1 : $dp_regex2);

        # clean string for best chance at numerification
        $numstr   =~ s/^.*?([+-]?)$dp_regex(?:[eE]([+-]?\d+))?([YZEePTtGgXMKkmuUnNpfFazy])?.*/$2/s;
        $sign     = $1 if $1;
        $exponent = $3 if $3;
        $prefix   = $4 if $4;

        # convert prefixes -- example: ".16E2m" => ".16e-1" => 0.016
        if ($exponent || $prefix)
        {
            $exponent += $prefix2exp{$prefix};
            $numstr   .= "e".$exponent;
        }

        # numerify string according to nearest sign
        {
            no warnings 'numeric';
            $numstr = -+-$numstr;                 # high-precedence numerifier
            $numstr =   -$numstr if $sign eq "-"; # negative if last sign is "-"
        }
    }
    else
    {
        $numstr = undef;
    }

    return $numstr;
}

'String::Numerify';