mirror of
https://github.com/silverstripe/silverstripe-framework
synced 2024-10-22 14:05:37 +02:00
74 lines
2.3 KiB
PHP
74 lines
2.3 KiB
PHP
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<?php
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/**
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* A Directed Acyclic Graph - used for doing topological sorts on dependencies, such as the before/after conditions
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* in config yaml fragments
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*/
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class SS_DAG {
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/** @var array|null - The nodes/vertices in the graph. Should be a numeric sequence of items (no string keys, no gaps). */
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protected $data;
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/** @var array - The edges in the graph, in $to_idx => [$from_idx1, $from_idx2, ...] format */
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protected $dag;
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function __construct($data = null) {
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$data = $data ? array_values($data) : array();
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$this->data = $data;
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$this->dag = array_fill_keys(array_keys($data), array());
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}
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/**
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* Add another node/vertex
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* @param $item anything - The item to add to the graph
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*/
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function additem($item) {
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$this->data[] = $item;
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$this->dag[] = array();
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}
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/**
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* Add an edge from one vertex to another
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* @param $from integer|any - The index in $data of the node/vertex, or the node/vertex itself, that the edge goes from
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* @param $to integer|any - The index in $data of the node/vertex, or the node/vertex itself, that the edge goes to
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*
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* When passing actual nodes (as opposed to indexes), uses array_search with strict = true to find
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*/
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function addedge($from, $to) {
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$i = is_numeric($from) ? $from : array_search($from, $this->data, true);
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$j = is_numeric($to) ? $to : array_search($to, $this->data, true);
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if ($i === false) throw new Exception("Couldnt find 'from' item in data when adding edge to DAG");
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if ($j === false) throw new Exception("Couldnt find 'to' item in data when adding edge to DAG");
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if (!isset($this->dag[$j])) $this->dag[$j] = array();
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$this->dag[$j][] = $i;
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}
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/**
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* Sort graph so that each node (a) comes before any nodes (b) where an edge exists from a to b
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* @return array - The nodes
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* @throws Exception - If the graph is cyclic (and so can't be sorted)
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*/
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function sort() {
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$data = $this->data; $dag = $this->dag; $sorted = array();
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while (true) {
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$withedges = array_filter($dag, 'count');
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$starts = array_diff_key($dag, $withedges);
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if (!count($starts)) break;
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foreach ($starts as $i => $foo) $sorted[] = $data[$i];
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foreach ($withedges as $j => $deps) {
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$withedges[$j] = array_diff($withedges[$j], array_keys($starts));
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}
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$dag = $withedges;
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}
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if ($dag) throw new Exception("DAG has cyclic requirements");
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return $sorted;
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}
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}
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