#!/usr/bin/perl

use strict;
use warnings;
use boolean qw(true false);

use DateTime;
use DateTime::Format::Natural;
use Getopt::Long qw(:config no_auto_abbrev no_ignore_case);
use Term::ReadLine;

use constant LANG_DEFAULT => 'en';

my %args;
my $extract;
my $lang;
my @supported_languages = qw(en);
my $trace;
my %valid_languages = map { $_ => true } @supported_languages;

{
    my $opts = {};
    $opts = parse_switches() if @ARGV;
    set_values($opts);
    process();
}

sub parse_switches
{
    my %opts;
    GetOptions(\%opts, qw(d|datetime=s
                          e|extract
                          f|format=s
                          h|help
                          l|lang=s
                          p|prefer_future
                          P|demand_future
                          s|supported
                          t|time_zone=s
                          T|trace
                          V|version)) or usage();

    usage()     if $opts{h};
    version()   if $opts{V};
    supported() if $opts{s};

    return \%opts;
}

sub set_values
{
    my $opts = shift;

    $extract = $opts->{e} || false;
    $lang    = $opts->{l} || LANG_DEFAULT;
    $trace   = $opts->{T} || false;

    if (exists $opts->{d}) {
        local $_ = $opts->{d};
        my ($got_date, $got_time) = (false) x 2;
        my $ignore = false;
        my %time;
        if (/^\S+? (?:\s+? \S+?)?$/x) {
            if (/^(\d{4}-\d{2}-\d{2})\b/) {
                @time{qw(year month day)} = split /-/, $1;
                $got_date = true;
            }
            if (/\b(\d{2}:\d{2}:\d{2})(?:\.(\d{3}))?$/) {
                @time{qw(hour minute second)} = split /:/, $1;
                $time{nanosecond} = $2 * 1_000_000 if $2; # milli to nano
                $got_time = true;
            }
        }
        if ($got_date || $got_time) {
            my %opts = exists $opts->{t} ? (time_zone => $opts->{t}) : ();
            if (!$got_date) { # time only
                my @units = qw(year month day);
                @time{@units} = map DateTime->now(%opts)->$_, @units;
            }
            eval { $opts->{d} = DateTime->new(%time, %opts) } or $ignore = true;
        }
        else {
            $ignore = true;
        }
        if ($ignore) {
            warn "ignoring invalid datetime string '$opts->{d}'\n";
            delete $opts->{d};
        }
    }

    my %table = (
        d => 'datetime',
        l => 'lang',
        f => 'format',
        p => 'prefer_future',
        P => 'demand_future',
        t => 'time_zone',
    );

    foreach my $opt (keys %$opts) {
        if (exists $table{$opt}) {
            $args{$table{$opt}} = $opts->{$opt};
        }
    }
}

sub usage
{
    print <<"USAGE";
Usage: $0 [switches]
   -d, --datetime=<string>     datetime string
   -e, --extract               extract expressions
   -f, --format=<format>       format of numeric dates
   -h, --help                  this help screen
   -l, --lang=<code>           language code
   -p, --prefer_future         prefer future dates
   -P, --demand_future         demand future dates
   -s, --supported             list of supported languages
   -t, --time_zone=<string>    time zone string
   -T, --trace                 print trace after processing
   -V, --version               print version
USAGE
    exit;
}

sub version
{
    print "  DateTime::Format::Natural $DateTime::Format::Natural::VERSION\n";
    exit;
}

sub supported
{
    print "$_\n" foreach @supported_languages;
    exit;
}

sub process
{
    unless ($valid_languages{lc $lang}) {
        warn "Language [$lang] isn't supported, switching to default [", LANG_DEFAULT, "]\n";
        $lang = $args{lang} = LANG_DEFAULT;
    }

    my $parser = DateTime::Format::Natural->new(%args);

    my $term = Term::ReadLine->new('dateparse');
    my $prompt = 'dateparse> ';

    while (defined(my $input = $term->readline($prompt))) {
        $term->addhistory($input) if $input =~ /\S/;
        last if $input =~ /^(?:q(?:uit)?|exit)$/i;

        if ($input =~ /^(?:\?|help)$/i) {
            print <<'EOT';

Commands
 ?, help                this help screen
 exit, q, quit          leave dateparse
 everything else        input string

EOT
            next;
        }

        my @expressions = $extract ? $parser->extract_datetime($input) : ($input);

        warn "no parsable expressions extracted\n" unless @expressions;

        foreach my $expression (@expressions) {
            print "extracted: $expression\n" if $extract;

            my @dt = $parser->parse_datetime_duration(string => $expression);
            my @traces = $parser->trace;

            if ($parser->success) {
                foreach my $dt (@dt) {
                    print $dt->strftime('%Y-%m-%d %H:%M:%S.%3N'), "\n";
                    if ($trace && @traces) {
                        print shift @traces, "\n";
                    }
                }
            }
            else {
                warn $parser->error, "\n";
            }
        }
    }
}

=head1 NAME

dateparse - frontend to DateTime::Format::Natural

=head1 SYNOPSIS

 Usage: dateparse [switches]
   -d, --datetime=<string>     datetime string *
   -e, --extract               extract expressions
   -f, --format=<format>       format of numeric dates
   -h, --help                  this help screen
   -l, --lang=<code>           language code
   -p, --prefer_future         prefer future dates
   -P, --demand_future         demand future dates
   -s, --supported             list of supported languages
   -t, --time_zone=<string>    time zone string
   -T, --trace                 print trace after processing
   -V, --version               print version

* The date must conform to YYYY-MM-DD and the time to hh:mm:ss(.ms).
Valid datetime strings consist of either date, date/time or time.

=head1 AUTHOR

Steven Schubiger <schubiger@cpan.org>

=head1 LICENSE

This program is free software; you may redistribute it and/or
modify it under the same terms as Perl itself.

See L<http://dev.perl.org/licenses/>

=cut