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plugins/system/nrframework/NRFramework/Parser/Parser.php

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+<?php
+
+/**
+ *  @author          Tassos.gr <info@tassos.gr>
+ *  @link            https://www.tassos.gr
+ *  @copyright       Copyright © 2024 Tassos All Rights Reserved
+ *  @license         GNU GPLv3 <http://www.gnu.org/licenses/gpl.html> or later
+*/
+
+namespace NRFramework\Parser;
+
+defined('_JEXEC') or die;
+
+use NRFramework\Parser\Lexer;
+use NRFramework\Parser\RingBuffer;
+
+/**
+ *  Parser base class
+ *  LL(k) recursive-decent parser with backtracking support
+ */
+abstract class Parser
+{
+    /**
+     *  Lexer instance (feeds the parser with tokens)
+     *  
+     *  @var NRFramework\Parser\Lexer
+     */
+    protected $input = null;
+
+    /**
+     *  Ring buffer of the next k tokens
+     *  from the input stream
+     *
+     *  @var RingBuffer
+     */
+    protected $lookahead = null;
+
+    /**
+     *  k: Number of lookahead tokens
+     *
+     *  @var int
+     */
+    protected $k;
+
+    /**
+     *  Array(stack) containing  the current 
+     *  contents of the lookahead buffer when 
+     *  marking the position of the stream
+     * 
+     *  @var array
+     */
+    protected $lookahead_history = null;
+
+    /**
+     *  Lexer constructor
+     *
+     *  @param Lexer   $input
+     *  @param integer $k, number of lookahead tokens
+     */
+    public function __construct(Lexer $input, $k = 1)
+    {
+        if (!is_integer($k) || ($k < 1))
+        {
+            throw new \InvalidArgumentException('Parser: $k must be greater than 0!');
+        }
+        $this->k                 = $k;
+        $this->input             = $input;
+        $this->lookahead_history = [];
+
+        // initialize lookahead buffer
+        $this->resetBuffer();
+    }
+
+    /**
+     *  Checks the type of the next token.
+     *  Advances the position in the token stream.
+     *  
+     *  @param string $type
+     *  @return void
+     * 
+     *  @throws Exception
+     */
+    public function match($type)
+    {
+        if ($this->lookahead[0]->type === $type)
+        {
+            $this->consume();
+            return;
+        }
+
+        throw new Exceptions\SyntaxErrorException('Expecting token ' . $type . ', found ' . $this->lookahead[0]);
+    }
+
+    /**
+     *  Retrieves the next token from the input stream
+     *  and add it to the buffer.
+     *
+     *  @return void
+     */
+    public function consume()
+    {
+        $this->lookahead[] = $this->input->nextToken();
+    }
+
+    /**
+     *  Marks the position in the token stream
+     * 
+     *  @return void
+     */
+    public function mark()
+    {
+        array_push($this->lookahead_history, $this->lookahead);
+        $this->input->mark();
+    }
+
+    /**
+     *  Reset to a previously marked position
+     *  in the token stream
+     * 
+     *  @return void
+     */
+    public function reset()
+    {
+        $this->input->reset();
+
+        // reset lookahead buffer if not marked
+        if (empty($this->lookahead_history))
+        {
+            $this->resetBuffer();
+        }
+        // normal reset
+        else
+        {
+            $this->lookahead = array_pop($this->lookahead_history);
+        }
+    }
+
+    /**
+     *  Resets and refills the lookahead buffer starting
+     *  from the current position in the token stream
+     *
+     *  @return void
+     */
+    protected function resetBuffer()
+    {
+        $this->lookahead = new RingBuffer($this->k);
+        for ($i=0; $i < $this->k; $i++)
+        {
+            $this->consume();
+        }
+    }
+}