#!/usr/bin/perl -w
#
# Updates the <div id=...> </div> that surround the headings
# in reference.md, for the ids' x:* (expansions) and c:* (conditions).
#
# Also updates the keyword index.
#
# With --check, checks that they are all up to date.

use strict;
use JSON qw(from_json);

our $install;

if (@ARGV==0) {
    $install = 1;
} elsif (@ARGV==1 && $ARGV[0] eq '--check') {
    $install = 0;
} else {
    die "bad usage\n";
}

our $input = "doc/reference.md";
our $output = "doc/reference.md.new";
our $handled = qr{^[xc]:};
our $div_id = qr{^\<div id="([^"]+)"\>\s*$};

our %targets; # $targets{$lno} = [ $id, ... ]

#---------- Read reference.md ----------

open F, $input or die $!;
our @f = <F>;
F->error and die $!;
close F;
unshift @f, "";

#---------- read the JSON telling us where the ref headings are ----------

open J, "maint/check-keywords-documented --json |" or die $!;
our $json;
{ local ($/) = undef; $json = <J>; }
J->error and die $!;
$json = from_json($json) or die $!;

foreach my $id (sort keys %{ $json->{ref_lines} }) {
    next unless $id =~ m{$handled};
    my %lno = map { $_, 1 } @{ $json->{ref_lines}{$id} };
    keys(%lno) == 1 or die "multiple for $id";
    my ($i) = keys %lno;
    push @{ $targets{$i} }, $id;
}

#---------- decide what divs need to go where, strip out old ones ----------

our @instructions;

foreach my $i (sort { $a <=> $b } keys %targets) {
    eval {
	die 'missing blank line before' if $f[$i-1] =~ m/\S/;
	die 'missing blank line after' if $f[$i+1] =~ m/\S/;
	my $delta = 2;
	for (
	    $delta = 2;
	    $f[$i+$delta] =~ m{^\</div\>\s*$};
	    $delta++
	) {
	    $f[$i-$delta] =~ m{$div_id}
	      or die "invalid pre-div \@+$delta \`$_`";
	    my $target = $1;
	    if ($target =~ m{$handled}) {
		$f[$i-$delta] = "";
		$f[$i+$delta] = "";
	    }
	}
	if ($delta > 2) {
	    die 'missing blank line before divs' if $f[$i-$delta] =~ m/\S/;
	    die 'missing blank line after divs' if $f[$i+$delta] =~ m/\S/;
	}
	push @instructions, [ $i, $delta ];
    }
      or die "$input:$i: error: $@";
}

#---------- check for misplaced divs (not deleted above) ----------

foreach my $i (1..$#f) {
    next unless $f[$i] =~ m{$div_id};
    my $id = $1;
    next unless $id =~ m{$handled};
    die "$input:$i: misplaced div for id=\"$id\"\n";
}

#---------- (re)insert the keyword divs ----------

foreach my $insn (@instructions) {
    my ($i, $delta) = @$insn;
    my $append_before = "";
    my $insert_after = "";
    if ($delta == 2) {
	$append_before = "\n\n";
	$insert_after = "\n\n";
    }
    foreach my $target (sort @{ $targets{$i} }) {
	$append_before .= "<div id=\"$target\">\n";
	$insert_after = "</div>\n" . $insert_after;
    }
    $f[$i-$delta] .= $append_before;
    $f[$i+$delta] = $insert_after . $f[$i+$delta];
    1;
}

#---------- make the indexes ----------

sub mkindex ($$) {
    my ($kind, $kformat) = @_;
    my $i = 0;
    for (;;) {
	die "missing meta for index $kind" if $i > @f;
	last if $f[$i] =~ m{^\<\!--\#\# index $kind \#\#--\>.*$};
	$i++;
    }
    for (my $j = $i+1;
	 $j < @f && $f[$j] =~ m{^\s};
	 $j++) {
	$f[$j] = "";
    }
    my $l = \ $f[$i];
    $$l .= "\n";
    my $ref_lines = $json->{ref_lines};
    foreach my $az ('a'..'z') {
	my @ids = grep { m{^$kind:$az} } sort keys %$ref_lines;
	next unless @ids;
	$$l .=
	  " * **".(sprintf $kformat, $az)."**: ".
	  (join ', ', map { s/^$kind://; "[`$_`](#$kind:$_)" } @ids).
	  "\n";
    }
    $$l .= "\n";
}

mkindex('x', '$%s…');
mkindex('c', '%s…');

#---------- write and handle output ----------

die unless shift(@f) eq '';

open O, "> $output" or die "$output: $!";
print O @f or die $!;
close O or die $!;

if ($install) {
    rename "$output", "$input" or die $!;
} else {
    $?=$!=0;
    system qw(diff -u), "$input", "$output";
    if ($? == 0) {
    } elsif ($? == 256) {
	print STDERR <<END or die $!;

Reference manual cross-reference divs mismatch.
Check output, and rerun maint/update-reference-xrefs.
END
	exit 1;
    } else {
	die "diff failed: $? / $!" unless $? == 256;
    }
}