#!/usr/bin/perl
# make an executeble file

use strict;
use warnings;

sub usage; sub mkexec; sub guesstype; sub getcmd; sub launch_editor;

my $DEFAULT_TYPE = 'pl';
my $DEFAULT_MODE = 0755;

my $name = shift or usage;
my $type = ($ARGV[0] ? shift : guesstype $name);

my $bang = {
    pl   => `which perl`,
    sh   => `which sh`,
    py   => `which python`,
    bash => `which bash`,
    sed  => `which sed`,
    bc   => `which bc`
};

my $template = {
    pl   => "use strict;\nuse warnings;\n",
    py   => "if __name__ == '__main__':\n"
};

my $editors = [ qw/ vim editor / ];
my $cmds;
$cmds->{vim}->{test}    = "vim --version 2>/dev/null";
$cmds->{vim}->{run}     = "vim +\"normal G\$\" '%s'";
$cmds->{editor}->{test} = "editor --version 2>/dev/null";
$cmds->{editor}->{run}  = "editor '%s'";


if (exists $bang->{$type}) {
    -e $name || mkexec $name, mkbody($type);
    chmod $DEFAULT_MODE, $name;
    launch_editor $name;
} else {
    die "unknown type: $type\n";
}

sub usage {
    print STDERR "usage: $0 filename [type]\n";
    exit 0;
}

sub guesstype {
    my $name = shift;
    my ($ext) = $name =~ m|\.(\w+)$|;
    return ( $ext ? $ext : $DEFAULT_TYPE);
}

sub mkbody {
    my $type = shift;
    my $tmpl = "";
    $tmpl .= $template->{$type} if exists $template->{$type};
    return sprintf "#!%s\n%s\n", $bang->{$type}, $tmpl;
}

sub mkexec {
    my ($name, $body) = @_;
    open EXE, ">", $name    || die "cannot open $name for writing: $!\n";
    -W EXE                  || die "file $name is not writable\n";
    print EXE $body;
    close EXE               || die "cannot close $name: $!\n";
}

sub get_cmd {
    foreach (@$editors) {
        return $cmds->{$_}->{run} if `$cmds->{$_}->{test}`
    }
    warn "no supported editor available\n";
    return;
}

sub launch_editor {
    my $name = shift;
    my $form = get_cmd;
    if ($form) {
        my $command = sprintf get_cmd, $name;
        exec "$command";
    } else { return }
    warn "failed to launch editor: $form\n";
}