Php Sequence Matcher Laravel Package

Getting Started

Minimal Steps

1. Verify PHP 8.3+ Compatibility:

   php -v  # Must be ≥8.3
   composer require jfcherng/php-sequence-matcher
   

2. Basic Comparison (Arrays/Strings):

   use jfcherng\SequenceMatcher\SequenceMatcher;
   use jfcherng\SequenceMatcher\Options;
   
   $matcher = new SequenceMatcher(
       ['a', 'b', 'c'],  // Sequence A
       ['x', 'b', 'y'],  // Sequence B
       new Options()      // Object-based config (PHP 8.3+)
   );
   

3. First Use Case: Generate Opcodes

   $opCodes = $matcher->getOpCodes();
   // Example output: [['replace', 0, 1, 0, 1], ['equal', 1, 2, 1, 2]]
   

4. Key Methods to Explore:

   • ratio() → Similarity score (0.0–1.0)
   • getMatchingBlocks() → Identical subsequences
   • getOpCodes() → Edit instructions (insert/delete/replace/equal)

Implementation Patterns

Core Workflows

1. Laravel Service Wrapper (Recommended)

   namespace App\Services;
   
   use jfcherng\SequenceMatcher\SequenceMatcher;
   use jfcherng\SequenceMatcher\Options;
   
   class SequenceMatcherService {
       public function __construct(
           private SequenceMatcher $matcher
       ) {}
   
       public static function create(array $a, array $b): self {
           return new self(
               new SequenceMatcher($a, $b, new Options())
           );
       }
   
       public function getChanges(): array {
           return $this->matcher->getOpCodes();
       }
   }
   

   Register in AppServiceProvider:

   $this->app->bind(SequenceMatcherService::class, function () {
       return SequenceMatcherService::create($oldData, $newData);
   });
   

2. Diff Rendering for UI

   $changes = [];
   foreach ($matcher->getOpCodes() as $op) {
       [$tag, $i1, $i2, $j1, $j2] = $op;
       switch ($tag) {
           case SequenceMatcher::OP_REP:
               $changes[] = "Line {$i1}: '{$old[$i1]}' → '{$new[$j1]}'";
               break;
           case SequenceMatcher::OP_DEL:
               $changes[] = "Line {$i1}: Removed '{$old[$i1]}'";
               break;
           case SequenceMatcher::OP_INS:
               $changes[] = "Line {$j1}: Added '{$new[$j1]}'";
               break;
       }
   }
   return view('diff', ['changes' => $changes]);
   

3. Schema Validation with Similarity Thresholds

   $similarity = $matcher->ratio();
   if ($similarity < 0.9) {
       throw new \RuntimeException(
           "Schema drift detected (similarity: {$similarity * 100}%)"
       );
   }
   

4. Token-Level Diffing (e.g., for Code)

   $tokensOld = token_get_all(file_get_contents('old.php'));
   $tokensNew = token_get_all(file_get_contents('new.php'));
   $matcher = new SequenceMatcher($tokensOld, $tokensNew);
   $diffs = $matcher->getOpCodes();
   

Integration Tips

• For Large Sequences (>10k elements): Use getMatchingBlocks() to identify identical chunks for partial processing.
• Case-Insensitive Matching: Pre-process sequences (e.g., array_map('strtolower', $sequence)).
• Laravel Caching: Cache SequenceMatcher instances for repeated comparisons:

  $matcher = Cache::remember(
      "diff_{$hashOld}_{$hashNew}",
      now()->addHours(1),
      fn() => new SequenceMatcher($old, $new, new Options())
  );
  

Gotchas and Tips

Pitfalls

1. PHP Version Mismatch:

   • Error: Class 'jfcherng\SequenceMatcher\Options' not found → Cause: PHP <8.3.
   • Fix: Upgrade PHP or use a fork (e.g., chrisboulton/php-diff for PHP 8.1).

2. Opcode Confusion (v3.0+):

   • Gotcha: OP_EQ is now 1 (not 'eq' string). Use constants:

     if ($op[0] === SequenceMatcher::OP_REP) { ... }
     

   • Tip: Enable strict typing in Options for IDE autocompletion.

3. Object-Based Options Overhead:

   • Issue: Serialization fails in Laravel cache/sessions.
   • Fix: Use serialize()-compatible wrappers or avoid caching SequenceMatcher directly.

4. Non-Greedy Matching:

   • Gotcha: Default behavior may not match Python difflib's greedy algorithm.
   • Tip: Adjust Options for custom behavior (check Options class docs).

5. Memory Spikes:

   • Warning: Large sequences (>50k elements) may exhaust memory.
   • Mitigation: Process in chunks or use getMatchingBlocks() for partial matches.

Debugging

• Verify Opcodes:

  $opCodes = $matcher->getOpCodes();
  dump($opCodes); // Debug structure: [tag, i1, i2, j1, j2]
  

• Check Similarity:

  $ratio = $matcher->ratio();
  dump($ratio); // Should be 0.0–1.0
  

• Inspect Matching Blocks:

  $blocks = $matcher->getMatchingBlocks();
  dump($blocks); // [[i1, i2, j1, j2], ...]
  

Extension Points

1. Custom Opcodes: Combine base opcodes (e.g., OP_INS | OP_DEL for complex edits).

   $op = SequenceMatcher::OP_INS | SequenceMatcher::OP_DEL;
   

2. Subclass Options: Extend for project-specific defaults:

   class AppOptions extends Options {
       public function __construct() {
           parent::__construct();
           $this->setAutoJunk(false); // Disable junk filtering
       }
   }
   

3. Laravel Facade: Create a facade for cleaner syntax:

   // app/Facades/SequenceMatcher.php
   namespace App\Facades;
   use Illuminate\Support\Facades\Facade;
   class SequenceMatcher extends Facade {
       protected static function getFacadeAccessor() {
           return 'sequenceMatcher';
       }
   }
   

   Bind in AppServiceProvider:

   $this->app->singleton('sequenceMatcher', function () {
       return new SequenceMatcher([], [], new Options());
   });
   

   Usage:

   $diffs = \App\Facades\SequenceMatcher::getOpCodes();
   

Laravel-Specific Quirks

• Service Container Binding: Avoid binding SequenceMatcher directly—wrap it in a service class to handle dynamic sequences.
• Queue Jobs: Serialize Options only, not the full SequenceMatcher:

  $job->handle(new Options($matcher->getOptions()));
  

• Testing: Mock SequenceMatcher in unit tests:

  $this->partialMock(SequenceMatcher::class, function ($mock) {
      $mock->method('getOpCodes')->willReturn([['equal', 0, 1, 0, 1]]);
  });