module.exports = function(hljs) {
  var PERL_KEYWORDS = 'getpwent getservent quotemeta msgrcv scalar kill dbmclose undef lc ' +
    'ma syswrite tr send umask sysopen shmwrite vec qx utime local oct semctl localtime ' +
    'readpipe do return format read sprintf dbmopen pop getpgrp not getpwnam rewinddir qq' +
    'fileno qw endprotoent wait sethostent bless s|0 opendir continue each sleep endgrent ' +
    'shutdown dump chomp connect getsockname die socketpair close flock exists index shmget' +
    'sub for endpwent redo lstat msgctl setpgrp abs exit select print ref gethostbyaddr ' +
    'unshift fcntl syscall goto getnetbyaddr join gmtime symlink semget splice x|0 ' +
    'getpeername recv log setsockopt cos last reverse gethostbyname getgrnam study formline ' +
    'endhostent times chop length gethostent getnetent pack getprotoent getservbyname rand ' +
    'mkdir pos chmod y|0 substr endnetent printf next open msgsnd readdir use unlink ' +
    'getsockopt getpriority rindex wantarray hex system getservbyport endservent int chr ' +
    'untie rmdir prototype tell listen fork shmread ucfirst setprotoent else sysseek link ' +
    'getgrgid shmctl waitpid unpack getnetbyname reset chdir grep split require caller ' +
    'lcfirst until warn while values shift telldir getpwuid my getprotobynumber delete and ' +
    'sort uc defined srand accept package seekdir getprotobyname semop our rename seek if q|0 ' +
    'chroot sysread setpwent no crypt getc chown sqrt write setnetent setpriority foreach ' +
    'tie sin msgget map stat getlogin unless elsif truncate exec keys glob tied closedir' +
    'ioctl socket readlink eval xor readline binmode setservent eof ord bind alarm pipe ' +
    'atan2 getgrent exp time push setgrent gt lt or ne m|0 break given say state when';
  var SUBST = {
    className: 'subst',
    begin: '[$@]\\{', end: '\\}',
    keywords: PERL_KEYWORDS
  };
  var METHOD = {
    begin: '->{', end: '}'
    // contains defined later
  };
  var VAR = {
    className: 'variable',
    variants: [
      {begin: /\$\d/},
      {begin: /[\$%@](\^\w\b|#\w+(::\w+)*|{\w+}|\w+(::\w*)*)/},
      {begin: /[\$%@][^\s\w{]/, relevance: 0}
    ]
  };
  var STRING_CONTAINS = [hljs.BACKSLASH_ESCAPE, SUBST, VAR];
  var PERL_DEFAULT_CONTAINS = [
    VAR,
    hljs.HASH_COMMENT_MODE,
    hljs.COMMENT(
      '^\\=\\w',
      '\\=cut',
      {
        endsWithParent: true
      }
    ),
    METHOD,
    {
      className: 'string',
      contains: STRING_CONTAINS,
      variants: [
        {
          begin: 'q[qwxr]?\\s*\\(', end: '\\)',
          relevance: 5
        },
        {
          begin: 'q[qwxr]?\\s*\\[', end: '\\]',
          relevance: 5
        },
        {
          begin: 'q[qwxr]?\\s*\\{', end: '\\}',
          relevance: 5
        },
        {
          begin: 'q[qwxr]?\\s*\\|', end: '\\|',
          relevance: 5
        },
        {
          begin: 'q[qwxr]?\\s*\\<', end: '\\>',
          relevance: 5
        },
        {
          begin: 'qw\\s+q', end: 'q',
          relevance: 5
        },
        {
          begin: '\'', end: '\'',
          contains: [hljs.BACKSLASH_ESCAPE]
        },
        {
          begin: '"', end: '"'
        },
        {
          begin: '`', end: '`',
          contains: [hljs.BACKSLASH_ESCAPE]
        },
        {
          begin: '{\\w+}',
          contains: [],
          relevance: 0
        },
        {
          begin: '\-?\\w+\\s*\\=\\>',
          contains: [],
          relevance: 0
        }
      ]
    },
    {
      className: 'number',
      begin: '(\\b0[0-7_]+)|(\\b0x[0-9a-fA-F_]+)|(\\b[1-9][0-9_]*(\\.[0-9_]+)?)|[0_]\\b',
      relevance: 0
    },
    { // regexp container
      begin: '(\\/\\/|' + hljs.RE_STARTERS_RE + '|\\b(split|return|print|reverse|grep)\\b)\\s*',
      keywords: 'split return print reverse grep',
      relevance: 0,
      contains: [
        hljs.HASH_COMMENT_MODE,
        {
          className: 'regexp',
          begin: '(s|tr|y)/(\\\\.|[^/])*/(\\\\.|[^/])*/[a-z]*',
          relevance: 10
        },
        {
          className: 'regexp',
          begin: '(m|qr)?/', end: '/[a-z]*',
          contains: [hljs.BACKSLASH_ESCAPE],
          relevance: 0 // allows empty "//" which is a common comment delimiter in other languages
        }
      ]
    },
    {
      className: 'sub',
      beginKeywords: 'sub', end: '(\\s*\\(.*?\\))?[;{]',
      relevance: 5
    },
    {
      className: 'operator',
      begin: '-\\w\\b',
      relevance: 0
    },
    {
      begin: "^__DATA__$",
      end: "^__END__$",
      subLanguage: 'mojolicious',
      contains: [
        {
            begin: "^@@.*",
            end: "$",
            className: "comment"
        }
      ]
    }
  ];
  SUBST.contains = PERL_DEFAULT_CONTAINS;
  METHOD.contains = PERL_DEFAULT_CONTAINS;

  return {
    aliases: ['pl'],
    keywords: PERL_KEYWORDS,
    contains: PERL_DEFAULT_CONTAINS
  };
};