<?php declare(strict_types=1);

namespace PhpParser;

class NodeTraverser implements NodeTraverserInterface
{
    /**
     * If NodeVisitor::enterNode() returns DONT_TRAVERSE_CHILDREN, child nodes
     * of the current node will not be traversed for any visitors.
     *
     * For subsequent visitors enterNode() will still be called on the current
     * node and leaveNode() will also be invoked for the current node.
     */
    const DONT_TRAVERSE_CHILDREN = 1;

    /**
     * If NodeVisitor::enterNode() or NodeVisitor::leaveNode() returns
     * STOP_TRAVERSAL, traversal is aborted.
     *
     * The afterTraverse() method will still be invoked.
     */
    const STOP_TRAVERSAL = 2;

    /**
     * If NodeVisitor::leaveNode() returns REMOVE_NODE for a node that occurs
     * in an array, it will be removed from the array.
     *
     * For subsequent visitors leaveNode() will still be invoked for the
     * removed node.
     */
    const REMOVE_NODE = 3;

    /** @var NodeVisitor[] Visitors */
    protected $visitors;

    /** @var bool Whether traversal should be stopped */
    protected $stopTraversal;

    /**
     * Constructs a node traverser.
     */
    public function __construct() {
        $this->visitors = [];
    }

    /**
     * Adds a visitor.
     *
     * @param NodeVisitor $visitor Visitor to add
     */
    public function addVisitor(NodeVisitor $visitor) {
        $this->visitors[] = $visitor;
    }

    /**
     * Removes an added visitor.
     *
     * @param NodeVisitor $visitor
     */
    public function removeVisitor(NodeVisitor $visitor) {
        foreach ($this->visitors as $index => $storedVisitor) {
            if ($storedVisitor === $visitor) {
                unset($this->visitors[$index]);
                break;
            }
        }
    }

    /**
     * Traverses an array of nodes using the registered visitors.
     *
     * @param Node[] $nodes Array of nodes
     *
     * @return Node[] Traversed array of nodes
     */
    public function traverse(array $nodes) : array {
        $this->stopTraversal = false;

        foreach ($this->visitors as $visitor) {
            if (null !== $return = $visitor->beforeTraverse($nodes)) {
                $nodes = $return;
            }
        }

        $nodes = $this->traverseArray($nodes);

        foreach ($this->visitors as $visitor) {
            if (null !== $return = $visitor->afterTraverse($nodes)) {
                $nodes = $return;
            }
        }

        return $nodes;
    }

    /**
     * Recursively traverse a node.
     *
     * @param Node $node Node to traverse.
     *
     * @return Node Result of traversal (may be original node or new one)
     */
    protected function traverseNode(Node $node) : Node {
        foreach ($node->getSubNodeNames() as $name) {
            $subNode =& $node->$name;

            if (\is_array($subNode)) {
                $subNode = $this->traverseArray($subNode);
                if ($this->stopTraversal) {
                    break;
                }
            } elseif ($subNode instanceof Node) {
                $traverseChildren = true;
                foreach ($this->visitors as $visitor) {
                    $return = $visitor->enterNode($subNode);
                    if (null !== $return) {
                        if ($return instanceof Node) {
                            $this->ensureReplacementReasonable($subNode, $return);
                            $subNode = $return;
                        } elseif (self::DONT_TRAVERSE_CHILDREN === $return) {
                            $traverseChildren = false;
                        } elseif (self::STOP_TRAVERSAL === $return) {
                            $this->stopTraversal = true;
                            break 2;
                        } else {
                            throw new \LogicException(
                                'enterNode() returned invalid value of type ' . gettype($return)
                            );
                        }
                    }
                }

                if ($traverseChildren) {
                    $subNode = $this->traverseNode($subNode);
                    if ($this->stopTraversal) {
                        break;
                    }
                }

                foreach ($this->visitors as $visitor) {
                    $return = $visitor->leaveNode($subNode);
                    if (null !== $return) {
                        if ($return instanceof Node) {
                            $this->ensureReplacementReasonable($subNode, $return);
                            $subNode = $return;
                        } elseif (self::STOP_TRAVERSAL === $return) {
                            $this->stopTraversal = true;
                            break 2;
                        } elseif (\is_array($return)) {
                            throw new \LogicException(
                                'leaveNode() may only return an array ' .
                                'if the parent structure is an array'
                            );
                        } else {
                            throw new \LogicException(
                                'leaveNode() returned invalid value of type ' . gettype($return)
                            );
                        }
                    }
                }
            }
        }

        return $node;
    }

    /**
     * Recursively traverse array (usually of nodes).
     *
     * @param array $nodes Array to traverse
     *
     * @return array Result of traversal (may be original array or changed one)
     */
    protected function traverseArray(array $nodes) : array {
        $doNodes = [];

        foreach ($nodes as $i => &$node) {
            if ($node instanceof Node) {
                $traverseChildren = true;
                foreach ($this->visitors as $visitor) {
                    $return = $visitor->enterNode($node);
                    if (null !== $return) {
                        if ($return instanceof Node) {
                            $this->ensureReplacementReasonable($node, $return);
                            $node = $return;
                        } elseif (self::DONT_TRAVERSE_CHILDREN === $return) {
                            $traverseChildren = false;
                        } elseif (self::STOP_TRAVERSAL === $return) {
                            $this->stopTraversal = true;
                            break 2;
                        } else {
                            throw new \LogicException(
                                'enterNode() returned invalid value of type ' . gettype($return)
                            );
                        }
                    }
                }

                if ($traverseChildren) {
                    $node = $this->traverseNode($node);
                    if ($this->stopTraversal) {
                        break;
                    }
                }

                foreach ($this->visitors as $visitor) {
                    $return = $visitor->leaveNode($node);
                    if (null !== $return) {
                        if ($return instanceof Node) {
                            $this->ensureReplacementReasonable($node, $return);
                            $node = $return;
                        } elseif (\is_array($return)) {
                            $doNodes[] = [$i, $return];
                            break;
                        } elseif (self::REMOVE_NODE === $return) {
                            $doNodes[] = [$i, []];
                            break;
                        } elseif (self::STOP_TRAVERSAL === $return) {
                            $this->stopTraversal = true;
                            break 2;
                        } elseif (false === $return) {
                            throw new \LogicException(
                                'bool(false) return from leaveNode() no longer supported. ' .
                                'Return NodeTraverser::REMOVE_NODE instead'
                            );
                        } else {
                            throw new \LogicException(
                                'leaveNode() returned invalid value of type ' . gettype($return)
                            );
                        }
                    }
                }
            } elseif (\is_array($node)) {
                throw new \LogicException('Invalid node structure: Contains nested arrays');
            }
        }

        if (!empty($doNodes)) {
            while (list($i, $replace) = array_pop($doNodes)) {
                array_splice($nodes, $i, 1, $replace);
            }
        }

        return $nodes;
    }

    private function ensureReplacementReasonable($old, $new) {
        if ($old instanceof Node\Stmt && $new instanceof Node\Expr) {
            throw new \LogicException(
                "Trying to replace statement ({$old->getType()}) " .
                "with expression ({$new->getType()}). Are you missing a " .
                "Stmt_Expression wrapper?"
            );
        }

        if ($old instanceof Node\Expr && $new instanceof Node\Stmt) {
            throw new \LogicException(
                "Trying to replace expression ({$old->getType()}) " .
                "with statement ({$new->getType()})"
            );
        }
    }
}
