Add Dot importer

[clue]

This library currently focuses on exporting a Graph instance into a format that GraphViz can read in order to produce a resulting graph image, i.e. export via the Dot language.

However, we currently have no means to import from a Dot language definition into a Graph instance, i.e. import via Dot language.

This is non-trivial, but I suppose all building blocks are ready. We can probably focus on the 80% use case and exclude some of the advanced features like sub-graphs and graph clusters.

Any volunteers? :)

[Gounlaf]

dumb "implementation" for my need

{
  "require": {
    "php": ">=7.3",
    "farafiri/php-parsing-tool": "^2.0",
    "graphp/graphviz": "^0.2.2"
  }
}

// based on https://graphviz.gitlab.io/_pages/doc/info/lang.html
// not sure about ID definition =/

$grammar = <<<DOT_GRAMMAR
graph :=> 'strict'? ('graph'|'digraph') ID? '{' stmt_list '}'.
ID :=> /"(.*?)"|([-]?(.[0-9]+|[0-9]+(.[0-9]*)?))|([a-zA-Z\200-\377_][0-9a-zA-Z\200-\377_]*)/.
stmt_list :=> (stmt ';'? stmt_list)?.
stmt :=> node_stmt
    :=> edge_stmt
    :=> attr_stmt
    :=> ID '=' ID
    :=> subgraph.
attr_stmt :=> ('graph'|'node'|'edge') attr_list.
attr_list :=> '[' a_list? ']' attr_list?.
a_list :=> ID '=' ID (';' | ',')? a_list?.
edge_stmt :=> (node_id | subgraph) edgeRHS attr_list?.
edgeRHS :=> edgeop (node_id | subgraph) edgeRHS?.
edgeop :=> ('->'|'--').
node_stmt :=> node_id attr_list?.
node_id :=> ID port?.
port :=> ':' ID (':' compass_pt)?
    :=> ':' compass_pt.
subgraph :=> (subgraph ID?)? '{' stmt_list '}'.
compass_pt :=> ('n'|'ne'|'e'|'se'|'s'|'sw'|'w'|'nw'|'c'|'_').
DOT_GRAMMAR;

$parser = new \ParserGenerator\Parser($grammar, ['ignoreWhitespaces' => true]);
$parsed = $parser->parse($smallOne, 'graph');
if (false === $parsed) {
    fwrite(STDERR, $parser->getErrorString($smallOne));
    exit(1);
}

$graph = new \Fhaculty\Graph\Graph();

function cleanValue(\ParserGenerator\SyntaxTreeNode\Base $node) {
    return trim($node->toString(), '"\'');
}

function parseAttributes($stmt, \Fhaculty\Graph\Attribute\AttributeAware $attributeAware) {
    $attrList = $stmt->findFirst('attr_list');
    if ($attrList) {
        foreach ($attrList->findAll('a_list') as $aList) {
            [$attribute, $value] = $aList->findAll('ID');
            $attributeAware->setAttribute('graphviz.' . cleanValue($attribute), cleanValue($value));
        }
    }
}

foreach ($parsed->findAll('stmt') as $stmt) {
    $nodeId = cleanValue($stmt->findFirst('node_id'));
    $left = $graph->createVertex($nodeId, true);

    $edgeRHS = $stmt->findFirst('edgeRHS');

    if ($edgeRHS === null) {
        parseAttributes($stmt, $left);
    } else {
        $rightId = cleanValue($edgeRHS->findFirst('node_id'));
        $right = $graph->createVertex($rightId, true);

        if (cleanValue($edgeRHS->findFirst('edgeop')) === '->') {
            $edge = $left->createEdgeTo($right);
        } else {
            $edge = $left->createEdge($right);
        }

        parseAttributes($stmt, $edge);
    }
}

$graphviz = new Graphp\GraphViz\GraphViz();
var_dump($graphviz->createScript($graph));