#!/usr/bin/perl

# gmi2email -- subscribe to gemlogs and read individual Gemini pages by e-mail

# Copyright (C) 2021 Sean Whitton
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or (at
# your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# TESTING/DEVEL
#
# To forget about seen entries of a feed:
#
#     % perl -MDBI
#     -we'DBI->connect("dbi:SQLite:dbname=$ENV{HOME}/.cache/mailscripts/gmi2email.db",
#     "", "")->do("DELETE FROM seen WHERE uri LIKE \"gemini://example.com/%\"")'

use 5.028;
use strict;
use warnings;

use DBI;
use File::Spec::Functions "catfile";
use IO::Socket::SSL;
use MIME::Lite;
use Config::Tiny;
use Text::Wrap;
use Try::Tiny;
use Getopt::Long;
use Email::Date::Format "email_date";
use Time::Local;
use Mail::Field::AddrList;
use XML::Feed;

my ($from, $to, $subs, $inline_images, $no_mail);
GetOptions
  "from=s"          => \$from,
  "to=s"            => \$to,
  "subscriptions:s" => \$subs,
  "inline-images!"  => \$inline_images,
  "no-send!"        => \$no_mail;

my $conf_r = $ENV{XDG_CONFIG_HOME} || catfile $ENV{HOME}, ".config";
my $conf_f = catfile $conf_r, "mailscripts", "gmi2email.config";
-e $conf_f
  or (defined $to and defined $from)
  or die
  "no config file nor sufficient command line options: don't know who to mail";
my $conf = Config::Tiny->new->read($conf_f);
$subs ||= catfile $conf_r, "mailscripts", "gmi2email.subscriptions"
  if defined $subs;

my %to_mail_opts = (
    from => (
             $from
          or $conf->{_}->{from}
          or die "no From: address set in config or on command line"
    ),
    to => (
             $to
          or $conf->{_}->{to}
          or die "no To: address set in config or on command line"
    ),
    inline_images => $inline_images // $conf->{_}->{inline_images} // 0
);

@ARGV or $subs or die "nothing to do\n";

for (@ARGV) {
    my $data;
    if (-f) {
        open my $fh, "<", $_;
        $data = [<$fh>];
    } else {
        my $type;
        ($type, $data) = gemini_fetch($_, abs_links => 1);
        $type =~ m{^text/gemini} or die "$_ is not gemtext";
    }
    $no_mail or gemtext_to_mail($data, %to_mail_opts)->send;
}

exit unless $subs;
-r $subs or die "file $subs not readable";
open my $subs_fh, "<", $subs;

my $db_r = $ENV{XDG_CACHE_HOME} || catfile $ENV{HOME}, ".cache";
my $db_d = catfile $db_r, "mailscripts";
-d $db_d or mkdir $db_d;
my $db_f = catfile $db_d, "gmi2email.db";
my $dbh = DBI->connect("dbi:SQLite:dbname=$db_f", "", "");
$dbh->do("CREATE TABLE IF NOT EXISTS seen (uri TEXT PRIMARY KEY)")
  or die "failed to initialise database";

foreach my $sub (<$subs_fh>) {
    chomp $sub;
    my ($gemlog, $type, $data, $next);
    #<<<
    try {
        ($type, $data) = gemini_fetch($sub, abs_links => 1);
    } catch {
        my ($code) = /"gemini error: ([1-6])/;
        if (   defined $code and $code == 4
            or /missing or invalid gemini response/
            or /failed to establish SSL connection/) {
            warn "temporary failure retrieving $sub; will try again later:\n    $_";
            $next = 1, return;    # try again next run
        } else {
            die "while retrieving $sub $_";
        }
    };
    #>>>
    next if $next;
    if ($type =~ m{^text/gemini}) {
        for (@$data) {
            if (/^#\s*/ and not $gemlog) {
                $gemlog = $';
            } elsif (my ($uri, $y, $m, $d, $title)
                = /^=>\s*(\S+)\s+([0-9]{4})-([0-9]{2})-([0-9]{2})[\s-]*(.*)/) {
                send_subscribed_gemtext($uri, $gemlog // "unknown gemlog",
                    $title, timelocal 0, 0, 12, $d, $m - 1, $y);
            }
        }
    } elsif ($type =~ m{^(?:text|application)/(?:atom\+)?xml}) {
        my $feed = XML::Feed->parse(\$data);
        for ($feed->entries) {
            my $date = $_->issued // $_->modified;
            $date = $date->epoch if $date;
            send_subscribed_gemtext($_->link, $feed->title, $_->title, $date);
        }
    } else {
        die "$sub is not gemtext nor an Atom feed, so far as I can tell";
    }
}

sub send_subscribed_gemtext {
    my ($uri, $gemlog, $link_title, $feed_date) = @_;
    my ($rows)
      = $dbh->selectrow_array(
        "SELECT COUNT(*) FROM seen WHERE uri = \"$uri\"");
    return unless $rows == 0;
    my $mail = 1;
    my ($type, $data);
    #<<<
    try {
        ($type, $data) = gemini_fetch($uri, abs_links => 1);
    } catch {
        warn "when fetching $uri, $_";
        my ($code) = /"gemini error: ([1-6])/;
        if ($code == 4) {
            return;    # try again next run
        } else {
            $mail = 0;    # don't try this one again
        }
    };
    #>>>
    if ($type =~ m{^text/gemini}) {
        gemtext_to_mail(
            $data, %to_mail_opts,
            gemlog     => $gemlog // "unknown gemlog",
            link_title => $link_title,
            date       => email_date $feed_date // time
          )->send
          if $mail and !$no_mail;
    } else {
        warn "$uri is not gemtext";
    }
    $dbh->do("INSERT INTO seen VALUES (\"$uri\")");
}

sub gemini_fetch {
    my ($uri, %opts) = @_;

    # regexp from Alex Schroeder's moku-pona program
    my ($scheme, $authority, $path, $query, $fragment)
      = $uri
      =~ m|(?:([^:/?#]+):)?(?://([^/?#]*))?([^?#]*)(?:\?([^#]*))?(?:#(.*))?|;
    $scheme and $scheme eq "gemini"
      or die "'$uri' does not use the gemini scheme";
    $authority or die "'$uri' lacks an authority";
    my ($host, $port) = split ":", $authority;
    my $cl = IO::Socket::SSL->new(
        PeerHost        => $host,
        PeerPort        => $port // 1965,
        SSL_verify_mode => SSL_VERIFY_NONE
    ) or die "while fetching $uri: failed to establish SSL connection\n";
    print $cl "$uri\r\n";

    my ($status, $meta) = <$cl> =~ /^([0-9]+) (\V+)/;
    defined $status and defined $meta
      or die "while fetching $uri: missing or invalid gemini response\n";
    if (30 <= $status and $status < 40) {
        $opts{orig_uri} = $uri unless $opts{redirects};
        die "too many redirects while fetching $opts{orig_uri}"
          if $opts{redirects} and $opts{redirects} > 5;
        $opts{redirects}++;
        return gemini_fetch($meta, %opts);
    } elsif ($status < 20 or $status >= 40) {
        die "while fetching $uri: gemini error: $status $meta";
    }

    if ($meta =~ "^text/gemini") {
        my @lines;
        if ($opts{abs_links}) {
            $authority =~ m{/$} or $authority .= "/";
            $path =~ m{/$}      or $path      .= "/";
            for (<$cl>) {
                s/\r?\n\z//;
                if (m{^=> (?!/)} and not m{^=> [a-z]+://}) {
                    push @lines, "=> gemini://$authority$path$'";
                } elsif (m{^=> /}) {
                    push @lines, "=> gemini://$authority$'";
                } else {
                    push @lines, $_;
                }
            }
        } else {
            @lines = <$cl>;
        }
        push @lines, "" unless $lines[$#lines] eq "";
        push @lines, "Retrieved from $uri\n            at " . localtime;
        return $meta, \@lines;
    } else {
        return $meta, do { local $/; <$cl> };
    }
}

sub gemtext_to_mail {
    my ($gemtext, %opts) = @_;
    $opts{from} or die "no From: address specified";
    $opts{to}   or die "no To: address specified";

    my $subject = $opts{link_title} // "";
    if ($gemtext->[0] =~ m{^#(?!#)\s*}) {
        $subject = $';
        shift @$gemtext;
        shift @$gemtext while $gemtext->[0] =~ /^$/;
    }

    if ($opts{gemlog}) {
        $opts{from}
          = Mail::Field->new("From")->create($opts{from}, $opts{gemlog})
          ->stringify;
        $subject = "$opts{gemlog}: $subject" if $subject;
    }

    my $msg = MIME::Lite->new(
        From    => $opts{from},
        To      => $opts{to},
        Subject => $subject,
        Type    => "multipart/mixed"
    );
    $msg->add(Date => $opts{date}) if $opts{date};

    my ($pre, @buffer);
    my $flush = sub {
        return unless @buffer;
        $msg->attach(Type => "TEXT", Data => join "\r\n", @buffer);
        undef @buffer;
    };
    my $pad
      = sub { push @buffer, "" unless !@buffer or $buffer[$#buffer] eq "" };
    for (@$gemtext) {
        if ($pre) {
            if (/^```/) {
                $pre = 0;
            } else {
                push @buffer, "    $_";
            }
        } elsif (/^```/) {
            &$pad;
            $pre = 1;
        } elsif (/^>\s*/) {
            &$pad;
            push @buffer, split "\n", wrap "> ", "> ", $';
        } elsif (/^\*\s*/) {
            &$pad;
            push @buffer, split "\n", wrap "• ", "  ", $';
        } elsif ($opts{inline_images}
            and my ($uri) = m{^=>\s*(gemini://\S+\.(?:jpg|jpeg|png|gif))}) {
            &$flush;
            my ($type, $data) = gemini_fetch($uri);
            $msg->attach(
                Type        => $type,
                Data        => $data,
                Filename    => (split "/", $uri)[-1],
                Disposition => "inline"
            );
        } elsif (/^=>/) {
            &$pad unless @buffer and $buffer[$#buffer] =~ /^=>/;
            push @buffer, $_;
        } elsif (/^#+/) {
            &$pad;
            push @buffer, $_;
        } else {
            &$pad;
            push @buffer, split "\n", wrap "", "", $_;
        }
    }

    &$flush;
    return $msg;
}