packages/sql-faker/src/Compiler/Bison/Lexer/BisonScannerChain.php

1<?php
2
3declare(strict_types=1);
4
5namespace SqlFaker\Compiler\Bison\Lexer;
6
7/**
8 * Chooses which scanner owns the character under the cursor.
9 *
10 * Holding the order in one place is what makes the lexer's dispatch a lookup
11 * rather than a decision: no scanner needs to know which others exist, and the
12 * grammar language can gain a lexeme by adding a scanner to the chain.
13 *
14 * @visibility root
15 */
16final class BisonScannerChain
17{
18    /**
19     * @param list<BisonScanner> $scanners Scanners in the order they are consulted
20     */
21    public function __construct(private readonly array $scanners)
22    {
23    }
24
25    /**
26     * Builds the chain that reads GNU Bison and Yacc grammar files.
27     *
28     * The claimed characters do not overlap, so the order is documentation
29     * rather than precedence.
30     *
31     * @return self A chain covering every lexeme of the grammar language
32     */
33    public static function forBisonGrammar(): self
34    {
35        return new self([
36            new DirectiveScanner(),
37            new ActionScanner(),
38            new TypeTagScanner(),
39            new QuotedLiteralScanner(),
40            new NumberScanner(),
41            new IdentifierScanner(),
42            new PunctuationScanner(),
43        ]);
44    }
45
46    /**
47     * Finds the scanner that recognises a lexeme starting at the character.
48     *
49     * @param string $character A single character; never the empty string
50     *
51     * @return BisonScanner|null The first scanner that claims it, or null when none does
52     */
53    public function scannerFor(string $character): ?BisonScanner
54    {
55        foreach ($this->scanners as $scanner) {
56            if ($scanner->handles($character)) {
57                return $scanner;
58            }
59        }
60
61        return null;
62    }
63}
64