docbookwsi.php

<?php
// SPDX-License-Identifier: 0BSD
// © André L F S Bacci <ae#php.net>
/*
This script reads a RelaxNG XML file, and calculates all elements
that _not_ contain <text/> contents, in all alternatives. That is,
the list shows all elements that can have all inter-element
whitespace removed, without affecting the expected parsing of the
XML document that follows the RelaxNG specification.

If run with a second XML argument, the script will calculate all savings
that can be done by stripping these insignificant whitespace between
elements.

See mentions of 'docbookwsi' on source code for parts that need to be
updated if/when a new version of Docbook is used.                */

$argv0 = array_shift( $argv ) ?? null;
$rngFile = array_shift( $argv ) ?? null;
$xmlFile = array_shift( $argv ) ?? null;

if ( $rngFile == null )
{
    print "Usage: '$argv0' rngFile [xmlFile]\n\n";
    return;
}

$list = generate_element_trim_list( $rngFile );

if ( $xmlFile == null )
{
    foreach( $list as $elem => $hasText )
        if ( ! $hasText )
            print "$elem\n";
    exit( 0 );
}
else
    xml_trim_stats( $xmlFile , $list );

exit( 0 );

function generate_element_trim_list( string $rngFilename ) : array
{
    $doc = new DOMDocument();
    if ( ! $doc->load( $rngFilename , LIBXML_NOBLANKS ) )
        throw new Exception( "XML load failed.\n" );

    // First, we get all elements definitions that directly
    // mentions <text/>, and also gather all <ref>s they refer.

    $elemText = [];
    $elemRefs = [];

    $xpath1 = new DOMXpath( $doc );
    $xpath2 = new DOMXpath( $doc );
    $xpath1->registerNamespace ( 'rng' , 'http://relaxng.org/ns/structure/1.0' );
    $xpath2->registerNamespace ( 'rng' , 'http://relaxng.org/ns/structure/1.0' );

    $list = $xpath1->query( '//rng:element' );
    foreach( $list as $elem )
    {
        $name = $elem->getAttribute( 'name' );
        if ( $name == '' )
            continue;

        $text = count ( $xpath2->query( './/rng:text' , $elem ) );
        $refs = $xpath2->query( './/rng:ref' , $elem );

        $elemText[ $name ] = $text;
        $elemRefs[ $name ] = [];

        foreach( $refs as $ref )
        {
            $refName = $ref->getAttribute( 'name' );
            $elemRefs[ $name ][] = $refName;
        }
    }

    unset( $xpath1 );
    unset( $xpath2 );

    // After all elements are collected, and directly textual elements
    // are marked, we can remove all <element>s, as they cannot influence
    // if a parent element is trimmable or not, and so that any <text/>
    // inside of a <element> cannot be found by XPaths, while exploring
    // the original <element>'s <ref>erences.

    $xpath3 = new DOMXpath( $doc );
    $xpath3->registerNamespace ( 'rng' , 'http://relaxng.org/ns/structure/1.0' );

    $todoDels = [];
    $dels = $xpath3->query( '//rng:element' );
    foreach( $dels as $del )
        array_push( $todoDels , $del );
    foreach( $todoDels as $del )
        $del->parentNode->removeChild( $del );

    // Then, we explore all references of all elements, for
    // indirect mentions of <text/>s.

    foreach( $elemText as $name => $text )
    {
        $text = element_references_contains_text( $doc , $name , $elemRefs[ $name ] );
        $elemText[ $name ] |= $text;
    }

    return $elemText;
}

function element_references_contains_text( DOMDocument $doc , string $elemName , array $refs ) : bool
{
    $ret = false;
    $doneRefs = [];
    $todoRefs = array_unique( $refs );

    $xpath = new DOMXpath( $doc );
    $xpath->registerNamespace ( 'rng' , 'http://relaxng.org/ns/structure/1.0' );

    while ( ( $refName = array_pop( $todoRefs ) ) != null )
    {
        $doneRefs[ $refName ] = true;

        $defs = $xpath->query( "//rng:define[@name='$refName']" );
        if ( $defs->count() != 1 )
            throw new Exception( "Unique define search failed for '$refName'." );
        $def = $defs[0];

        $text = count ( $xpath->query( './/rng:text' , $def ) );
        if ( $text )
            return true;

        $subRefs = $xpath->query( './/rng:ref' , $def );
        foreach( $subRefs as $subRef )
        {
            $subRefName = $subRef->getAttribute( 'name' );
            if ( isset( $doneRefs[ $subRefName ] ) )
                continue;
            $todoRefs[] = $subRefName;
        }
    }

    return false;
}

function xml_trim_stats( string $xmlFilename , array $elemText )
{
    $doc = new DOMDocument();
    if ( ! $doc->load( $xmlFilename ) )
        throw new Exception( "XML load failed.\n" );

    $stats = [];
    xml_trim_stats_enter( $doc->documentElement , $elemText, $stats );
    arsort( $stats );

    $total = 0;
    foreach( $stats as $elem => $trimSize )
    {
        print "$trimSize $elem\n";
        $total += $trimSize;
    }
    print "\ntotal $total\n";
}

function xml_trim_stats_enter( DOMNode $node , array $elemText , array & $stats , int $level = 0 )
{
    $name = $node->nodeName;
    $text = $elemText[ $name ] ?? true;

    if ( ! $text )
    {
        $size = 0;
        $dels = [];

        foreach( $node->childNodes as $child )
            if ( $child->nodeType == XML_TEXT_NODE )
                if ( trim( $child->nodeValue ) == '' )
                    $dels[] = $child;

        foreach( $dels as $del )
        {
            $size += strlen( $del->nodeValue );
            $del->parentNode->removeChild( $del );
        }

        if ( isset( $stats[ $name ] ) )
            $stats[ $name ] += $size;
        else
            $stats[ $name ] = $size;
    }

    foreach( $node->childNodes as $child )
        xml_trim_stats_enter( $child , $elemText , $stats , $level + 1 );
}