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# Helper Perl script for html-to-rtf.pl
#
# based on hh2rtf by Steve Atkins at
#
# http://www.blighty.com/products/hh2rtf/  which says
#   `Freeware. You may not resell it or claim you wrote it. 
#    You can use it for anything, commercial or otherwise.'
#
# Modifications for R (C) 1999, 2001 B. D. Ripley

# HTML parser
# Jim Davis, July 15 1994

# This is an HTML parser not an SGML parser.  It does not parse a DTD,
# The DTD is implicit in the code, and specific to HTML.  
# The processing of the HTML can be customized by the user by
#   1) Defining routines to be called for various tags (see Begin and End arrays)
#   2) Defining routines html_content and html_whitespace

# This is not a validating parser.   It does not check the content model
# eg you can use DT outside a DL and it won't know.  It is too liberal in
# what tags are allowed to minimize what other tags.

# modified Nov '97 (steve@blighty.com) to support RTF generation
# modified 3 Aug to add a bunch of HTML 2.0 tags
# modified 3 Sept to print HTML stack to STDERR not STDOUT, to add new
#  routines html_begin_doc and html_end_doc for application specific cleanup
#  and to break parse_html into two pieces.
# modified 30 Sept 94.  parse_attributes now handles tag attributes that
#   don't have values.  thanks to  Bill Simpson-Young <bill@syd.dit.csiro.au>
#   for the code.
# modified 17 Apr 95 to support FORMS tags.
# modified 3 Dec 95 to support U, tolerate TABLE, TD, TR, TH
# modified 17 May 96 to support &# syntax for entities.  Thanks to
#  Robert Brown, dummy@c2.org

$whitespace_significant = 0;

# global variables: 
#  $line_buffer is line buffer
#  $line_count is input line number.

$line_buffer = "";
$line_count = 0;
$filename = "";

sub parse_html {
    local ($file) = @_;
    open (HTML, $file) or die "Could not open $file: $!\nStopped";
    $filename = $file;
    &parse_html_stream ();
    close (HTML);
}

# Global input HTML is the handle to the stream of HTML
sub parse_html_stream {
    local ($token, $new);

    ## initialization
    @stack=();
    $line_count = 0;
    $line_buffer = "";

    ## application specific initialization
    &html_begin_doc();
  main:
    while (1) {

    $original = $line_buffer;
    # if whitespace does not matter, trim any leading space.
    if (! $whitespace_significant) {
        $line_buffer =~ s/^\s+//;
    }

    # now dispatch on the type of token

    if ($line_buffer =~ /^(\s+)/) {
        $token = $1;
        $line_buffer = $';
        &html_whitespace ($token);}

    # This will lose if there is more than one comment on the line!
    elsif ($line_buffer =~ /^(\<!--.*-->)/) {
        $token = $1;
        $line_buffer = $';
        &html_comment ($token);}

    elsif ($line_buffer =~ /^(\<![^-][^\>]*\>)/) {
        $token = $1;
        $line_buffer = $';
        &html_comment ($token);}

    elsif ($line_buffer =~ /^(\<\/[^\>]*\>)/) {
        $token = $1;
        $line_buffer = $';
        &html_etag ($token);}

    elsif ($line_buffer =~ /^(\<[^!\/][^\>]*\>)/) {
        $token = $1;
        $line_buffer = $';
        &html_tag ($token);}

    elsif ($original =~ /^([^\n<]+)/) {
        $token = $1;
        $line_buffer = $';
        if ($line_buffer =~ /^\n/) {$token .= " ";}
        $token = &substitute_entities($token);
        &html_content ($token); }

    else {
        # No valid token in buffer.  Maybe it's empty, or maybe there's an
        # incomplete tag.  So get some more data.
        $new = <HTML>;
        if (! defined ($new)) {last main;}
        # if we're trying to find a match for a tag, then get rid of embedded newline
        # this is, I think, a kludge
        if ($line_buffer =~ /^\</ && $line_buffer =~ /\n$/) {
        chop $line_buffer;
        $line_buffer .= " ";}
        $line_buffer .= $new;
        $line_count++;}
    }

    ## cleanup
    &html_end_doc();

    if ($#stack > -1) {
    print STDERR "Stack not empty at end of document\n";
    &print_html_stack();}
}


sub html_tag {
    local ($tag) = @_;
    local ($element) = &tag_element ($tag);
    local (%attributes) = &tag_attributes ($tag);

    # the tag might minimize (be an implicit end) for the previous tag
    local ($prev_element);
    while (&Minimizes(&stack_top_element(), $element)) {
    $prev_element = &stack_pop_element ();
    if ($debug)  {
        print STDERR "MINIMIZING $prev_element with $element on $line_count\n";}
    &html_end ($prev_element, 0);}

    push (@stack, $tag);

    &html_begin ($element, $tag, %attributes);

    if (&Empty($element)) {
    pop(@stack);
    &html_end ($element, 0);}
}

sub html_etag {
    local ($tag) = @_;
    local ($element) = &tag_element ($tag);

    # pop stack until find matching tag.  This is probably a bad idea,
    # or at least too general.
    local ( $prev_element) = &stack_pop_element();
    until ($prev_element eq $element) {
    if ($debug) {
        print STDERR "MINIMIZING $prev_element with /$element on $line_count \n";}
    &html_end ($prev_element, 0);

    if ($#stack == -1) {
        print STDERR "No match found for /$element.  You will lose\n";
        last;}
    $prev_element = &stack_pop_element();}

    &html_end ($element, 1);
}


# For each element, the names of elements which minimize it.
# This is of course totally HTML dependent and probably I have it wrong too
$Minimize{"DT"} = "DT:DD";
$Minimize{"DD"} = "DT:DD";
$Minimize{"LI"} = "LI";
$Minimize{"P"} = "P:DT:LI:H1:H2:H3:H4:H5:H6:BLOCKQUOTE:UL:OL:DL";
$Minimize{"TR"} = "TR";
$Minimize{"TD"} = "TD:TH";
$Minimize{"TH"} = "TD:TH";

# Does element E2 minimize E1?
sub Minimizes {
    local ($e1, $e2) = @_;
    local ($value) = 0;
    $elt = "";
    foreach $elt (split (/:/, $Minimize{$e1})) {
    if ($elt eq $e2) {$value = 1;}}
    $value;
}

$Empty{"BASE"} = 1;
$Empty{"BR"} = 1;
$Empty{"HR"} = 1;
$Empty{"IMG"} = 1;
$Empty{"ISINDEX"} = 1;
$Empty{"LINK"} = 1;
$Empty{"META"} = 1;
$Empty{"NEXTID"} = 1;
$Empty{"INPUT"} = 1;

# Empty tags have no content and hence no end tags
sub Empty {
    local ($element) = @_;
    $Empty{$element};
}

sub print_html_stack {
    print STDERR "\n  ==\n";
    foreach $elt (reverse @stack) {print STDERR "  $elt\n";}
    print STDERR "  ==========\n";
}

# The element on top of stack, if any.
sub stack_top_element {
    if ($#stack >= 0) {
    &tag_element ($stack[$#stack]);
    }
}

sub stack_pop_element {
    &tag_element (pop (@stack));}

# The element from the tag, normalized.
sub tag_element {
    local ($tag) = @_;
    $tag =~ /<\/?([^\s>]+)/;
    local ($element) = $1;
    $element =~ tr/a-z/A-Z/;
    $element;
}

# associative array of the attributes of a tag.
sub tag_attributes {
    local ($tag) = @_;
    $tag =~ /^<[A-Za-z0-9]+\s+(.*)>$/;
    &parse_attributes($1);
}

# string should be something like
# KEY="value" KEY2="longer value"  KEY3="tags o doom"
# output is an associative array (like a lisp property list)
# attributes names are not case sensitive, do I downcase them
# Maybe (probably) I should substitute for entities when parsing attributes.

sub parse_attributes {
    local ($string) = @_;
    local (%attributes);
    local ($name, $val);
  get: while (1) {
      if ($string =~ /^ *([A-Za-z]+)=\"([^\"]*)\"/) {
      $name = $1;
      $val = $2;
      $string = $';
      $name =~ tr/A-Z/a-z/;
      $attributes{$name} = $val; }
      elsif ($string =~ /^ *([A-Za-z]+)=(\S*)/) {
      $name = $1;
      $val = $2;
      $string = $';
      $name =~ tr/A-Z/a-z/;
      $attributes{$name} = $val;}
      elsif ($string =~ /^ *([A-Za-z]+)/) {
      $name = $1;
      $val = "";
      $string = $';
      $name =~ tr/A-Z/a-z/;
      $attributes{$name} = $val;}
      else {last;}
  }
    %attributes;
}

sub substitute_entities {
    local ($string) = @_;
    $string =~ s/&amp;/&/og;
    $string =~ s/&lt;/</og;
    $string =~ s/&gt;/>/og;
    $string =~ s/&quot;/\"/og;
    $string =~ s/&nbsp;/ /og;
    $string =~ s/&rarr;/->/og;
    $string =~ s/&reg;/(tm)/og;
    $string =~ s/&#150;/{--}/og; # en dash
    $string =~ s/&#151;/{---}/og;# em dash
    local($ch);
    while ($string =~ /\&#([^;]*);/) {
       $ch=sprintf("%c", $1);
       $string =~ s/\&#[^;]*;/$ch/;
       }
    $string;
}


@HTML_elements = (
          "A",
          "ADDRESS",
          "B",
          "BASE",
          "BLINK",  #  Netscape addition :-(
          "BLOCKQUOTE",
          "BODY",
          "BR",
          "CITE",
          "CENTER", # Netscape addition :-(
          "CODE",
          "DD",
          "DIR",
          "DIV",
          "DFN",
          "DL",
          "DT",
          "EM",
          "FONT",       # Yach!
          "FORM",
          "H1", "H2", "H3", "H4", "H5", "H6",
          "HEAD",
          "HR",
          "HTML",
          "I",
          "ISINDEX",
          "IMG",
          "INPUT",
          "KBD",
          "LI",
          "LINK",
          "MENU",
          "META",
          "NEXTID",
          "OBJECT", 
          "OL",
          "OPTION",
          "P",
          "PARAM",
          "PRE",
          "SAMP",
          "SCRIPT",
          "SELECT",
          "STRIKE",
          "STRONG",
          "TABLE",
          "TD",
          "TH",
          "TR",
          "TITLE",
          "TEXTAREA",
          "TT",
          "U",
          "UL",
          "VAR",
          );

sub define_element {
    local ($element) = @_;
    $Begin{$element} = "Noop";
    $End{$element} = "Noop";
}

foreach $element (@HTML_elements) {&define_element($element);}

# do nothing
sub Noop {
    local ($element, $xxx) = @_;
}

# called when a tag begins.  Dispatches using Begin
sub html_begin {
    local ($element, $tag, %attributes) = @_;

    local ($routine) = $Begin{$element};
    if ($routine eq "") {
    print STDERR "Unknown HTML element $element ($tag) on line $line_count\n";}
    else {eval "&$routine;"}
}

# called when a tag ends.  Explicit is 0 if tag end is because of minimization
# not that you should care.
sub html_end {
    local ($element, $explicit) = @_;
    local ($routine) = $End{$element};
    if ($routine eq "") {
    print STDERR "Unknown HTML element \"$element\" (END $explicit) on line $line_count\n";}
    else {eval "&$routine(\"$element\", $explicit)";}
}

sub html_content {
    local ($word) = @_;
}

sub html_whitespace {
    local ($whitespace) = @_;
}

sub html_comment {
    local ($tag) = @_;
}

# redefine these for application-specific initialization and cleanup

sub html_begin_doc {}

sub html_end_doc {}

# return a "true value" when loaded by perl.
1;