Add (part of) YAML field infrastructure.

New files copied from a2482475a7ed0b6f54df10a87a8665e2361f3598 of
<git://github.com/rubykat/ikiplugins.git> by Kathryn Andersen
<perlkat@katspace.org>.

3 files changed, 1211 insertions, 0 deletions

diff --git a/.library/IkiWiki/Plugin/field.pm b/.library/IkiWiki/Plugin/field.pm
new file mode 100644
index 00000000..e53474e9
--- /dev/null
+++ b/.library/IkiWiki/Plugin/field.pm
@@ -0,0 +1,662 @@
+#!/usr/bin/perl
+# Ikiwiki field plugin.
+# See doc/plugin/contrib/field.mdwn for documentation.
+package IkiWiki::Plugin::field;
+use warnings;
+use strict;
+=head1 NAME
+
+IkiWiki::Plugin::field - front-end for per-page record fields.
+
+=head1 VERSION
+
+This describes version B<0.05> of IkiWiki::Plugin::field
+
+=cut
+
+our $VERSION = '0.05';
+
+=head1 PREREQUISITES
+
+    IkiWiki
+
+=head1 AUTHOR
+
+    Kathryn Andersen (RUBYKAT)
+    http://github.com/rubykat
+
+=head1 COPYRIGHT
+
+Copyright (c) 2009-2010 Kathryn Andersen
+
+This program is free software; you can redistribute it and/or
+modify it under the same terms as Perl itself.
+
+=cut
+
+use IkiWiki 3.00;
+
+my %Fields = (
+    _first => {
+	id => '_first',
+	seq => 'BB',
+    },
+    _last => {
+	id => '_last',
+	seq => 'YY',
+    },
+    _middle => {
+	id => '_middle',
+	seq => 'MM',
+    },
+);
+my @FieldsLookupOrder = ();
+
+my %Cache = ();
+
+sub field_get_value ($$);
+
+sub import {
+	hook(type => "getsetup", id => "field",  call => \&getsetup);
+	hook(type => "checkconfig", id => "field", call => \&checkconfig);
+	hook(type => "scan", id => "field", call => \&scan, last=>1);
+	hook(type => "pagetemplate", id => "field", call => \&pagetemplate);
+}
+
+# ===============================================
+# Hooks
+# ---------------------------
+sub getsetup () {
+	return
+		plugin => {
+			safe => 1,
+			rebuild => undef,
+		},
+		field_register => {
+			type => "hash",
+			example => "field_register => {meta => 'last'}",
+			description => "simple registration of fields by plugin",
+			safe => 0,
+			rebuild => undef,
+		},
+		field_allow_config => {
+			type => "boolean",
+			example => "field_allow_config => 1",
+			description => "allow config settings to be queried",
+			safe => 0,
+			rebuild => undef,
+		},
+		field_tags => {
+			type => "hash",
+			example => "field_tags => {BookAuthor => '/books/authors'}",
+			description => "fields flagged as tag-fields",
+			safe => 0,
+			rebuild => undef,
+		},
+}
+
+sub checkconfig () {
+    # use the simple by-plugin pagestatus method for
+    # those plugins registered with the field_register config option.
+    if (defined $config{field_register})
+    {
+	if (ref $config{field_register} eq 'ARRAY')
+	{
+	    foreach my $id (@{$config{field_register}})
+	    {
+		field_register(id=>$id);
+	    }
+	}
+	elsif (ref $config{field_register} eq 'HASH')
+	{
+	    foreach my $id (keys %{$config{field_register}})
+	    {
+		field_register(id=>$id, order=>$config{field_register}->{$id});
+	    }
+	}
+	else
+	{
+	    field_register(id=>$config{field_register});
+	}
+    }
+    if (!defined $config{field_allow_config})
+    {
+	$config{field_allow_config} = 0;
+    }
+} # checkconfig
+
+sub scan (@) {
+    my %params=@_;
+    my $page=$params{page};
+    my $content=$params{content};
+
+    # scan for tag fields
+    if ($config{field_tags})
+    {
+	foreach my $field (sort keys %{$config{field_tags}})
+	{
+	    my @values = field_get_value($field, $page);
+	    if (@values)
+	    {
+		foreach my $tag (@values)
+		{
+		    if ($tag)
+		    {
+			my $link = $config{field_tags}{$field} . '/'
+			. titlepage($tag);
+			add_link($page, $link, lc($field));
+		    }
+		}
+	    }
+	}
+    }
+} # scan
+
+sub pagetemplate (@) {
+    my %params=@_;
+    my $page=$params{page};
+    my $template=$params{template};
+
+    field_set_template_values($template, $page);
+} # pagetemplate
+
+# ===============================================
+# Field interface
+# ---------------------------
+
+sub field_register (%) {
+    my %param=@_;
+    if (!exists $param{id})
+    {
+	error 'field_register requires id parameter';
+	return 0;
+    }
+    if (exists $param{call} and !ref $param{call})
+    {
+	error 'field_register call parameter must be function';
+	return 0;
+    }
+
+    $Fields{$param{id}} = \%param;
+    if (!exists $param{call})
+    {
+	# closure to get the data from the pagestate hash
+	$Fields{$param{id}}->{call} = sub {
+	    my $field_name = shift;
+	    my $page = shift;
+	    if (exists $pagestate{$page}{$param{id}}{$field_name})
+	    {
+		return (wantarray
+			? ($pagestate{$page}{$param{id}}{$field_name})
+			: $pagestate{$page}{$param{id}}{$field_name});
+	    }
+	    elsif (exists $pagestate{$page}{$param{id}}{lc($field_name)})
+	    {
+		return (wantarray
+			? ($pagestate{$page}{$param{id}}{lc($field_name)})
+			: $pagestate{$page}{$param{id}}{lc($field_name)});
+	    }
+	    return undef;
+	};
+    }
+    # add this to the ordering hash
+    # first, last, order; by default, middle
+    my $when = ($param{first}
+		? '_first'
+		: ($param{last}
+		   ? '_last'
+		   : ($param{order}
+		      ? ($param{order} eq 'first'
+			 ? '_first'
+			 : ($param{order} eq 'last'
+			    ? '_last'
+			    : ($param{order} eq 'middle'
+			       ? '_middle'
+			       : $param{order}
+			      )
+			   )
+			)
+		      : '_middle'
+		     )
+		  ));
+    add_lookup_order($param{id}, $when);
+    return 1;
+} # field_register
+
+sub field_get_value ($$) {
+    my $field_name = shift;
+    my $page = shift;
+
+    # This will return the first value it finds
+    # where the value returned is not undefined.
+    # This will return an array of values if wantarray is true.
+
+    # The reason why it checks every registered plugin rather than have
+    # plugins declare which fields they know about, is that it is quite
+    # possible that a plugin doesn't know, ahead of time, what fields
+    # will be available; for example, a YAML format plugin would return
+    # any field that happens to be defined in a YAML page file, which
+    # could be anything!
+ 
+    my $value = undef;
+    my @array_value = undef;
+
+    # check the cache first
+    if (exists $Cache{$page}{$field_name}
+	and defined $Cache{$page}{$field_name})
+    {
+	return (wantarray
+	    ? @{$Cache{$page}{$field_name}{array}}
+	    : $Cache{$page}{$field_name}{scalar});
+    }
+
+    if (!@FieldsLookupOrder)
+    {
+	build_fields_lookup_order();
+    }
+    foreach my $id (@FieldsLookupOrder)
+    {
+	$value = $Fields{$id}{call}->($field_name, $page);
+	@array_value = $Fields{$id}{call}->($field_name, $page);
+	if (defined $value)
+	{
+	    last;
+	}
+    }
+
+    # extra definitions
+    if (!defined $value)
+    {
+	# Exception for titles
+	# If the title hasn't been found, construct it
+	if ($field_name eq 'title')
+	{
+	    $value = pagetitle(IkiWiki::basename($page));
+	}
+	# and set "page" if desired
+	elsif ($field_name eq 'page')
+	{
+	    $value = $page;
+	}
+	# the page above this page; aka the current directory
+	elsif ($field_name eq 'parent_page')
+	{
+	    if ($page =~ m{^(.*)/[-\.\w]+$})
+	    {
+		$value = $1;
+	    }
+	}
+	elsif ($field_name eq 'basename')
+	{
+	    $value = IkiWiki::basename($page);
+	}
+	elsif ($config{field_allow_config}
+	       and $field_name =~ /^config-(.*)$/i)
+	{
+	    my $cfield = $1;
+	    if (exists $config{$cfield})
+	    {
+		$value = $config{$cfield};
+	    }
+	}
+	elsif ($field_name =~ /^(.*)-tagpage$/)
+	{
+	    my $real_fn = $1;
+	    if (exists $config{field_tags}{$real_fn}
+		and defined $config{field_tags}{$real_fn})
+	    {
+		my @values = field_get_value($real_fn, $page);
+		if (@values)
+		{
+		    foreach my $tag (@values)
+		    {
+			if ($tag)
+			{
+			    my $link = $config{field_tags}{$real_fn} . '/' . $tag;
+			    push @array_value, $link;
+			}
+		    }
+		    $value = join(",", @array_value);
+		}
+	    }
+	}
+    }
+    if (defined $value)
+    {
+	if (!@array_value)
+	{
+	    @array_value = ($value);
+	}
+	# cache the value
+	$Cache{$page}{$field_name}{scalar} = $value;
+	$Cache{$page}{$field_name}{array} = \@array_value;
+    }
+    return (wantarray ? @array_value : $value);
+} # field_get_value
+
+# set the values for the given HTML::Template template
+sub field_set_template_values ($$;@) {
+    my $template = shift;
+    my $page = shift;
+    my %params = @_;
+
+    my $get_value_fn = (exists $params{value_fn}
+			? $params{value_fn}
+			: \&field_get_value);
+
+    # Find the parameter names in this template
+    # and see if you can find their values.
+
+    # The reason we check the template for field names is because we
+    # don't know what fields the registered plugins provide; and this is
+    # reasonable because for some plugins (e.g. a YAML data plugin) they
+    # have no way of knowing, ahead of time, what fields they might be
+    # able to provide.
+
+    my @parameter_names = $template->param();
+    foreach my $field (@parameter_names)
+    {
+	my $type = $template->query(name => $field);
+	if ($type eq 'LOOP' and $field =~ /_LOOP$/i)
+	{
+	    # Loop fields want arrays.
+	    # Figure out what field names to look for:
+	    # * names are from the enclosed loop fields
+	    my @loop_fields = $template->query(loop => $field);
+
+	    my @loop_vals = ();
+	    my %loop_field_arrays = ();
+	    foreach my $fn (@loop_fields)
+	    {
+		if ($fn !~ /^__/) # not a special loop variable
+		{
+		    my @ival_array = $get_value_fn->($fn, $page);
+		    if (@ival_array)
+		    {
+			$loop_field_arrays{$fn} = \@ival_array;
+		    }
+		}
+	    }
+	    foreach my $fn (sort keys %loop_field_arrays)
+	    {
+		my $i = 0;
+		foreach my $v (@{$loop_field_arrays{$fn}})
+		{
+		    if (!defined $loop_vals[$i])
+		    {
+			$loop_vals[$i] = {};
+		    }
+		    $loop_vals[$i]{$fn} = $v;
+		    $i++;
+		}
+	    }
+	    $template->param($field => \@loop_vals);
+	}
+	else # not a loop field
+	{
+	    my $value = $get_value_fn->($field, $page);
+	    if (defined $value)
+	    {
+		$template->param($field => $value);
+	    }
+	}
+    }
+} # field_set_template_values
+
+# ===============================================
+# Private Functions
+# ---------------------------
+
+# Calculate the lookup order
+# <module, >module, AZ
+# This is crabbed from the PmWiki Markup function
+sub add_lookup_order  {
+    my $id = shift;
+    my $when = shift;
+
+    # may have given an explicit ordering
+    if ($when =~ /^[A-Z][A-Z]$/)
+    {
+	$Fields{$id}{seq} = $when;
+    }
+    else
+    {
+	my $cmp = '=';
+	my $seq_field = $when;
+	if ($when =~ /^([<>])(.+)$/)
+	{
+	    $cmp = $1;
+	    $seq_field = $2;
+	}
+	$Fields{$seq_field}{dep}{$id} = $cmp;
+	if (exists $Fields{$seq_field}{seq}
+	    and defined $Fields{$seq_field}{seq})
+	{
+	    $Fields{$id}{seq} = $Fields{$seq_field}{seq} . $cmp;
+	}
+    }
+    if ($Fields{$id}{seq})
+    {
+	foreach my $i (keys %{$Fields{$id}{dep}})
+	{
+	    my $m = $Fields{$id}{dep}{$i};
+	    add_lookup_order($i, "$m$id");
+	}
+	delete $Fields{$id}{dep};
+    }
+}
+
+sub build_fields_lookup_order {
+
+    # remove the _first, _last and _middle dummy fields
+    # because we don't need them anymore
+    delete $Fields{_first};
+    delete $Fields{_last};
+    delete $Fields{_middle};
+    my %lookup_spec = ();
+    # Make a hash of the lookup sequences
+    foreach my $id (sort keys %Fields)
+    {
+	my $seq = ($Fields{$id}{seq}
+		   ? $Fields{$id}{seq}
+		   : 'MM');
+	if (!exists $lookup_spec{$seq})
+	{
+	    $lookup_spec{$seq} = {};
+	}
+	$lookup_spec{$seq}{$id} = 1;
+    }
+
+    # get the field-lookup order by (a) sorting by lookup_spec
+    # and (b) sorting by field-name for the fields that registered
+    # the same field-lookup order
+    foreach my $ord (sort keys %lookup_spec)
+    {
+	push @FieldsLookupOrder, sort keys %{$lookup_spec{$ord}};
+    }
+} # build_fields_lookup_order
+
+# match field funcs
+# page-to-check, wanted
+sub match_a_field ($$) {
+    my $page=shift;
+    my $wanted=shift;
+
+    # The field name is first; the rest is the match
+    my $field_name;
+    my $glob;
+    if ($wanted =~ /^(\w+)\s+(.*)$/)
+    {
+	$field_name = $1;
+	$glob = $2;
+    }
+    else
+    {
+	return IkiWiki::FailReason->new("cannot match field");
+    }
+
+    # turn glob into a safe regexp
+    my $re=IkiWiki::glob2re($glob);
+
+    my $val = IkiWiki::Plugin::field::field_get_value($field_name, $page);
+
+    if (defined $val) {
+	if ($val=~/^$re$/i) {
+	    return IkiWiki::SuccessReason->new("$re matches $field_name of $page", $page => $IkiWiki::DEPEND_CONTENT, "" => 1);
+	}
+	else {
+	    return IkiWiki::FailReason->new("$re does not match $field_name of $page", "" => 1);
+	}
+    }
+    else {
+	return IkiWiki::FailReason->new("$page does not have a $field_name", "" => 1);
+    }
+} # match_a_field
+
+# check against individual items of a field
+# (treat the field as an array)
+# page-to-check, wanted
+sub match_a_field_item ($$) {
+    my $page=shift;
+    my $wanted=shift;
+
+    # The field name is first; the rest is the match
+    my $field_name;
+    my $glob;
+    if ($wanted =~ /^(\w+)\s+(.*)$/)
+    {
+	$field_name = $1;
+	$glob = $2;
+    }
+    else
+    {
+	return IkiWiki::FailReason->new("cannot match field");
+    }
+
+    # turn glob into a safe regexp
+    my $re=IkiWiki::glob2re($glob);
+
+    my @val_array = IkiWiki::Plugin::field::field_get_value($field_name, $page);
+
+    if (@val_array)
+    {
+	foreach my $val (@val_array)
+	{
+	    if (defined $val) {
+		if ($val=~/^$re$/i) {
+		    return IkiWiki::SuccessReason->new("$re matches $field_name of $page", $page => $IkiWiki::DEPEND_CONTENT, "" => 1);
+		}
+	    }
+	}
+	# not found
+	return IkiWiki::FailReason->new("$re does not match $field_name of $page", "" => 1);
+    }
+    else {
+	return IkiWiki::FailReason->new("$page does not have a $field_name", "" => 1);
+    }
+} # match_a_field_item
+
+# ===============================================
+# PageSpec functions
+# ---------------------------
+
+package IkiWiki::PageSpec;
+
+sub match_field ($$;@) {
+    my $page=shift;
+    my $wanted=shift;
+    return IkiWiki::Plugin::field::match_a_field($page, $wanted);
+} # match_field
+
+sub match_destfield ($$;@) {
+    my $page=shift;
+    my $wanted=shift;
+    my %params=@_;
+
+    return IkiWiki::FailReason->new("cannot match destpage") unless exists $params{destpage};
+
+    # Match the field on the destination page, not the source page
+    return IkiWiki::Plugin::field::match_a_field($params{destpage}, $wanted);
+} # match_destfield
+
+sub match_field_item ($$;@) {
+    my $page=shift;
+    my $wanted=shift;
+    return IkiWiki::Plugin::field::match_a_field_item($page, $wanted);
+} # match_field
+
+sub match_destfield_item ($$;@) {
+    my $page=shift;
+    my $wanted=shift;
+    my %params=@_;
+
+    return IkiWiki::FailReason->new("cannot match destpage") unless exists $params{destpage};
+
+    # Match the field on the destination page, not the source page
+    return IkiWiki::Plugin::field::match_a_field_item($params{destpage}, $wanted);
+} # match_destfield
+
+sub match_field_tagged ($$;@) {
+    my $page=shift;
+    my $wanted=shift;
+    my %params=@_;
+
+    # The field name is first; the rest is the match
+    my $field_name;
+    my $glob;
+    if ($wanted =~ /^(\w+)\s+(.*)$/)
+    {
+	$field_name = $1;
+	$glob = $2;
+    }
+    else
+    {
+	return IkiWiki::FailReason->new("cannot match field");
+    }
+    return match_link($page, $glob, linktype => lc($field_name), @_);
+}
+
+sub match_destfield_tagged ($$;@) {
+    my $page=shift;
+    my $wanted=shift;
+    my %params=@_;
+
+    return IkiWiki::FailReason->new("cannot match destpage") unless exists $params{destpage};
+
+    # Match the field on the destination page, not the source page
+    return IkiWiki::Plugin::field::match_field_tagged($params{destpage}, $wanted);
+}
+
+# ===============================================
+# SortSpec functions
+# ---------------------------
+package IkiWiki::SortSpec;
+
+sub cmp_field {
+    my $field = shift;
+    error(gettext("sort=field requires a parameter")) unless defined $field;
+
+    my $left = IkiWiki::Plugin::field::field_get_value($field, $a);
+    my $right = IkiWiki::Plugin::field::field_get_value($field, $b);
+
+    $left = "" unless defined $left;
+    $right = "" unless defined $right;
+    return $left cmp $right;
+}
+
+sub cmp_field_natural {
+    my $field = shift;
+    error(gettext("sort=field requires a parameter")) unless defined $field;
+
+    eval q{use Sort::Naturally};
+    error $@ if $@;
+
+    my $left = IkiWiki::Plugin::field::field_get_value($field, $a);
+    my $right = IkiWiki::Plugin::field::field_get_value($field, $b);
+
+    $left = "" unless defined $left;
+    $right = "" unless defined $right;
+    return Sort::Naturally::ncmp($left, $right);
+}
+
+1;
diff --git a/.library/IkiWiki/Plugin/getfield.pm b/.library/IkiWiki/Plugin/getfield.pm
new file mode 100644
index 00000000..3a967d8e
--- /dev/null
+++ b/.library/IkiWiki/Plugin/getfield.pm
@@ -0,0 +1,123 @@
+#!/usr/bin/perl
+# Ikiwiki getfield plugin.
+# Substitute field values in the content of the page.
+# See plugin/contrib/getfield for documentation.
+package IkiWiki::Plugin::getfield;
+use strict;
+=head1 NAME
+
+IkiWiki::Plugin::getfield - query the values of fields
+
+=head1 VERSION
+
+This describes version B<0.02> of IkiWiki::Plugin::getfield
+
+=cut
+
+our $VERSION = '0.02';
+
+=head1 PREREQUISITES
+
+    IkiWiki
+    IkiWiki::Plugin::field
+
+=head1 AUTHOR
+
+    Kathryn Andersen (RUBYKAT)
+    http://github.com/rubykat
+
+=head1 COPYRIGHT
+
+Copyright (c) 2009 Kathryn Andersen
+
+This program is free software; you can redistribute it and/or
+modify it under the same terms as Perl itself.
+
+=cut
+
+use IkiWiki 3.00;
+
+sub import {
+	hook(type => "getsetup", id => "getfield",  call => \&getsetup);
+	hook(type => "filter", id => "getfield", call => \&do_filter, last=>1);
+
+	IkiWiki::loadplugin("field");
+}
+
+#---------------------------------------------------------------
+# Hooks
+# --------------------------------
+
+sub getsetup () {
+	return
+		plugin => {
+			safe => 1,
+			rebuild => undef,
+		},
+}
+
+sub do_filter (@) {
+    my %params=@_;
+    my $page = $params{page};
+    my $destpage = ($params{destpage} ? $params{destpage} : $params{page});
+
+    my $page_file=$pagesources{$page};
+    my $page_type=pagetype($page_file);
+    if (defined $page_type)
+    {
+	while ($params{content} =~ /{{\$([-\w\/]+#)?[-\w]+}}/)
+	{
+	    # substitute {{$var}} variables (source-page)
+	    $params{content} =~ s/{{\$([-\w]+)}}/get_field_value($1,$page)/eg;
+
+	    # substitute {{$page#var}} variables (source-page)
+	    $params{content} =~ s/{{\$([-\w\/]+)#([-\w]+)}}/get_other_page_field_value($2,$page,$1)/eg;
+	}
+    }
+
+    $page_file=$pagesources{$destpage};
+    $page_type=pagetype($page_file);
+    if (defined $page_type)
+    {
+	while ($params{content} =~ /{{\+\$([-\w\/]+#)?[-\w]+\+}}/)
+	{
+	    # substitute {{+$var+}} variables (dest-page)
+	    $params{content} =~ s/{{\+\$([-\w]+)\+}}/get_field_value($1,$destpage)/eg;
+	    # substitute {{+$page#var+}} variables (source-page)
+	    $params{content} =~ s/{{\+\$([-\w\/]+)#([-\w]+)\+}}/get_other_page_field_value($2,$destpage,$1)/eg;
+	}
+    }
+
+    return $params{content};
+} # do_filter
+
+#---------------------------------------------------------------
+# Private functions
+# --------------------------------
+sub get_other_page_field_value ($$$) {
+    my $field = shift;
+    my $page = shift;
+    my $other_page = shift;
+
+    my $use_page = bestlink($page, $other_page);
+    my $val = get_field_value($field, $use_page);
+    if ($val eq $field)
+    {
+	return "${other_page}#$field";
+    }
+    return $val;
+
+} # get_other_page_field_value
+
+sub get_field_value ($$) {
+    my $field = shift;
+    my $page = shift;
+
+    my $value = IkiWiki::Plugin::field::field_get_value($field,$page);
+    return $value if defined $value;
+
+    # if there is no value, return the field name.
+    return $field;
+} # get_field_value
+
+1;
diff --git a/.library/IkiWiki/Plugin/ymlfront.pm b/.library/IkiWiki/Plugin/ymlfront.pm
new file mode 100644
index 00000000..3811591b
--- /dev/null
+++ b/.library/IkiWiki/Plugin/ymlfront.pm
@@ -0,0 +1,426 @@
+#!/usr/bin/perl
+# YAML format for structured data
+# See plugins/contrib/ymlfront for documentation.
+package IkiWiki::Plugin::ymlfront;
+use warnings;
+use strict;
+=head1 NAME
+
+IkiWiki::Plugin::ymlfront - add YAML-format data to a page
+
+=head1 VERSION
+
+This describes version B<0.03> of IkiWiki::Plugin::ymlfront
+
+=cut
+
+our $VERSION = '0.03';
+
+=head1 PREREQUISITES
+
+    IkiWiki
+    IkiWiki::Plugin::field
+    YAML::Any
+
+=head1 AUTHOR
+
+    Kathryn Andersen (RUBYKAT)
+    http://github.com/rubykat
+
+=head1 COPYRIGHT
+
+Copyright (c) 2009 Kathryn Andersen
+
+This program is free software; you can redistribute it and/or
+modify it under the same terms as Perl itself.
+
+=cut
+use IkiWiki 3.00;
+
+sub import {
+	hook(type => "getsetup", id => "ymlfront", call => \&getsetup);
+	hook(type => "checkconfig", id => "ymlfront", call => \&checkconfig);
+	hook(type => "filter", id => "ymlfront", call => \&filter, first=>1);
+	hook(type => "preprocess", id => "ymlfront", call => \&preprocess, scan=>1);
+	hook(type => "scan", id => "ymlfront", call => \&scan);
+	hook(type => "checkcontent", id => "ymlfront", call => \&checkcontent);
+
+	IkiWiki::loadplugin('field');
+	IkiWiki::Plugin::field::field_register(id=>'ymlfront',
+					       call=>\&yml_get_value,
+					       first=>1);
+}
+
+# ------------------------------------------------------------
+# Hooks
+# --------------------------------
+sub getsetup () {
+	return
+		plugin => {
+			safe => 1,
+			rebuild => 1,
+		},
+		ymlfront_delim => {
+			type => "array",
+			example => "ymlfront_sep => [qw(--YAML-START-- --YAML-END--)]",
+			description => "delimiters of YAML data",
+			safe => 0,
+			rebuild => undef,
+		},
+}
+
+sub checkconfig () {
+    eval q{use YAML::Any};
+    eval q{use YAML} if $@;
+    if ($@)
+    {
+	return error ("ymlfront: failed to use YAML::Any or YAML");
+    }
+
+    $YAML::UseBlock = 1;
+    $YAML::Syck::ImplicitUnicode = 1;
+
+    if (!defined $config{ymlfront_delim})
+    {
+	$config{ymlfront_delim} = [qw(--- ---)];
+    }
+} # checkconfig
+
+# scan gets called before filter
+sub scan (@) {
+    my %params=@_;
+    my $page = $params{page};
+
+    my $page_file=$pagesources{$page} || return;
+    my $page_type=pagetype($page_file);
+    if (!defined $page_type)
+    {
+	return;
+    }
+    # clear the old data
+    if (exists $pagestate{$page}{ymlfront})
+    {
+	delete $pagestate{$page}{ymlfront};
+    }
+    my $parsed_yml = parse_yml(%params);
+    if (defined $parsed_yml
+	and defined $parsed_yml->{yml})
+    {
+	# save the data to pagestate
+	foreach my $fn (keys %{$parsed_yml->{yml}})
+	{
+	    my $fval = $parsed_yml->{yml}->{$fn};
+	    $pagestate{$page}{ymlfront}{$fn} = $fval;
+	}
+    }
+    # update meta hash
+    if (exists $pagestate{$page}{ymlfront}{title}
+	and $pagestate{$page}{ymlfront}{title})
+    {
+	$pagestate{$page}{meta}{title} = $pagestate{$page}{ymlfront}{title};
+    }
+    if (exists $pagestate{$page}{ymlfront}{description}
+	and $pagestate{$page}{ymlfront}{description})
+    {
+	$pagestate{$page}{meta}{description} = $pagestate{$page}{ymlfront}{description};
+    }
+    if (exists $pagestate{$page}{ymlfront}{author}
+	and $pagestate{$page}{ymlfront}{author})
+    {
+	$pagestate{$page}{meta}{author} = $pagestate{$page}{ymlfront}{author};
+    }
+} # scan
+
+# use this for data in a [[!ymlfront ...]] directive
+sub preprocess (@) {
+    my %params=@_;
+    my $page = $params{page};
+
+    if (! exists $params{data}
+	or ! defined $params{data}
+	or !$params{data})
+    {
+	error gettext("missing data parameter")
+    }
+    # All the work of this is done in scan mode;
+    # when in preprocessing mode, just return an empty string.
+    my $scan=! defined wantarray;
+
+    if (!$scan)
+    {
+	return '';
+    }
+
+    # clear the old data
+    if (exists $pagestate{$page}{ymlfront})
+    {
+	delete $pagestate{$page}{ymlfront};
+    }
+    my $parsed_yml = parse_yml(%params);
+    if (defined $parsed_yml
+	and defined $parsed_yml->{yml})
+    {
+	# save the data to pagestate
+	foreach my $fn (keys %{$parsed_yml->{yml}})
+	{
+	    my $fval = $parsed_yml->{yml}->{$fn};
+	    $pagestate{$page}{ymlfront}{$fn} = $fval;
+	}
+    }
+    # update meta hash
+    if (exists $pagestate{$page}{ymlfront}{title}
+	and $pagestate{$page}{ymlfront}{title})
+    {
+	$pagestate{$page}{meta}{title} = $pagestate{$page}{ymlfront}{title};
+    }
+    if (exists $pagestate{$page}{ymlfront}{description}
+	and $pagestate{$page}{ymlfront}{description})
+    {
+	$pagestate{$page}{meta}{description} = $pagestate{$page}{ymlfront}{description};
+    }
+    if (exists $pagestate{$page}{ymlfront}{author}
+	and $pagestate{$page}{ymlfront}{author})
+    {
+	$pagestate{$page}{meta}{author} = $pagestate{$page}{ymlfront}{author};
+    }
+    return '';
+} # preprocess
+
+sub filter (@) {
+    my %params=@_;
+    my $page = $params{page};
+
+    my $page_file=$pagesources{$page} || return $params{content};
+    my $page_type=pagetype($page_file);
+    if (!defined $page_type)
+    {
+	return $params{content};
+    }
+    my $parsed_yml = parse_yml(%params);
+    if (defined $parsed_yml
+	and defined $parsed_yml->{yml}
+	and defined $parsed_yml->{content})
+    {
+	$params{content} = $parsed_yml->{content};
+	# also check for a content value
+	if (exists $pagestate{$page}{ymlfront}{content}
+	    and defined $pagestate{$page}{ymlfront}{content}
+	    and $pagestate{$page}{ymlfront}{content})
+	{
+	    $params{content} .= $pagestate{$page}{ymlfront}{content};
+	}
+    }
+
+    return $params{content};
+} # filter
+
+# check the correctness of the YAML code before saving a page
+sub checkcontent {
+    my %params=@_;
+    my $page = $params{page};
+
+    my $page_file=$pagesources{$page};
+    if ($page_file)
+    {
+	my $page_type=pagetype($page_file);
+	if (!defined $page_type)
+	{
+	    return undef;
+	}
+    }
+    my $parsed_yml = parse_yml(%params);
+    if (!defined $parsed_yml)
+    {
+	debug("ymlfront: Save of $page failed: $@");
+	return gettext("YAML data incorrect: $@");
+    }
+    return undef;
+} # checkcontent
+
+# ------------------------------------------------------------
+# Field functions
+# --------------------------------
+sub yml_get_value ($$) {
+    my $field_name = shift;
+    my $page = shift;
+
+    my $value = undef;
+    if (exists $pagestate{$page}{ymlfront}{$field_name})
+    {
+	$value = $pagestate{$page}{ymlfront}{$field_name};
+    }
+    elsif (exists $pagestate{$page}{ymlfront}{lc($field_name)})
+    {
+	$value = $pagestate{$page}{ymlfront}{lc($field_name)};
+    }
+    if (defined $value)
+    {
+	if (ref $value)
+	{
+	    my @value_array = @{$value};
+	    return (wantarray
+		    ? @value_array
+		    : join(",", @value_array));
+	}
+	else
+	{
+	    return (wantarray ? ($value) : $value);
+	}
+    }
+    return undef;
+} # yml_get_value
+
+# ------------------------------------------------------------
+# Helper functions
+# --------------------------------
+
+# parse the YAML data from the given content
+# Expects page, content
+# Returns { yml=>%yml_data, content=>$content } or undef
+sub parse_yml {
+    my %params=@_;
+    my $page = $params{page};
+    my $content = $params{content};
+
+    my $page_file=$pagesources{$page};
+    if ($page_file)
+    {
+	my $page_type=pagetype($page_file);
+	if (!defined $page_type)
+	{
+	    return undef;
+	}
+    }
+    my $start_of_content = '';
+    my $yml_str = '';
+    my $rest_of_content = '';
+    if ($params{data})
+    {
+	$yml_str = $params{data};
+    }
+    elsif ($content)
+    {
+	my $regex = qr{
+	    (\\?)		# 1: escape?
+		\[\[(!)		# directive open; 2: prefix
+		(ymlfront)	# 3: command
+		(		# 4: the parameters..
+				\s+	# Must have space if parameters present
+				(?:
+				 (?:[-\w]+=)?		# named parameter key?
+				 (?:
+				  """.*?"""	# triple-quoted value
+				  |
+				  "[^"]*?"	# single-quoted value
+				  |
+				  [^"\s\]]+	# unquoted value
+				 )
+				 \s*			# whitespace or end
+				 # of directive
+				)
+				*)?		# 0 or more parameters
+		\]\]		# directive closed
+	}sx;
+	my $ystart = $config{ymlfront_delim}[0];
+	my $yend = $config{ymlfront_delim}[1];
+	if ($ystart eq '---'
+	    and $yend eq '---'
+	    and $content =~ /^---[\n\r](.*?[\n\r])---[\n\r](.*)$/s)
+	{
+	    $yml_str = $1;
+	    $rest_of_content = $2;
+	}
+	elsif ($content =~ /^(.*?)${ystart}[\n\r](.*?[\n\r])${yend}([\n\r].*)$/s)
+	{
+	    $yml_str = $2;
+	    $rest_of_content = $1 . $3;
+	} 
+	elsif ($content =~ /$regex/)
+	{
+	    my $escape=$1;
+	    my $prefix=$2;
+	    my $command=$3;
+	    my $params=$4;
+	    if ($escape)
+	    {
+		$rest_of_content = $content;
+	    }
+	    else
+	    {
+		my %phash = ();
+		while ($params =~ m{
+		       (?:([-\w]+)=)?		# 1: named parameter key?
+		       (?:
+			"""(.*?)"""	# 2: triple-quoted value
+			|
+			"([^"]*?)"	# 3: single-quoted value
+			|
+			(\S+)		# 4: unquoted value
+		       )
+		       (?:\s+|$)		# delimiter to next param
+		       }sgx) {
+		    my $key=$1;
+		    my $val;
+		    if (defined $2) {
+			$val=$2;
+			$val=~s/\r\n/\n/mg;
+			$val=~s/^\n+//g;
+			$val=~s/\n+$//g;
+		    }
+		    elsif (defined $3) {
+			$val=$3;
+		    }
+		    elsif (defined $4) {
+			$val=$4;
+		    }
+
+		    if (defined $key) {
+			$phash{$key} = $val;
+		    }
+		    else {
+			$phash{''} = $val;
+		    }
+		}
+		if (defined $phash{data})
+		{
+		    $yml_str = $phash{data};
+		    $content =~ /^(.*?)\[\[!ymlfront.*?\]\](.*?)$/s;
+		    $start_of_content = $1;
+		    $rest_of_content = $2;
+		}
+	    }
+	}
+    }
+    if ($yml_str)
+    {
+	# if {{$page}} is there, do an immediate substitution
+	$yml_str =~ s/\{\{\$page\}\}/$page/sg;
+
+	my $ydata;
+	eval q{$ydata = Load($yml_str);};
+	if ($@)
+	{
+	    debug("ymlfront: Load of $page failed: $@");
+	    return undef;
+	}
+	if (!$ydata)
+	{
+	    debug("ymlfront: no YAML for $page");
+	    return undef;
+	}
+	my %lc_data = ();
+	if ($ydata)
+	{
+	    # make lower-cased versions of the data
+	    foreach my $fn (keys %{$ydata})
+	    {
+		my $fval = $ydata->{$fn};
+		$lc_data{lc($fn)} = $fval;
+	    }
+	}
+	return { yml=>\%lc_data,
+	    content=>$start_of_content . $rest_of_content};
+    }
+    return { yml=>undef, content=>$content };
+} # parse_yml
+1;