<?php
declare(strict_types=1);

function findJsonEnd(string $html, int $start): ?int {
  $length = strlen($html);
  $stack = [];

  $inString = false;
  $escaped = false;

  for ($i = $start; $i < $length; $i++) {
    $char = $html[$i];

    if ($inString) {
      if ($escaped) {
        $escaped = false;
        continue;
      }

      if ($char === '\\') {
        $escaped = true;
        continue;
      }

      if ($char === '"') {
        $inString = false;
      }

      continue;
    }

    if ($char === '"') {
      $inString = true;
      continue;
    }

    if ($char === '{' || $char === '[') {
      $stack[] = $char;
      continue;
    }

    if ($char === '}' || $char === ']') {
      if (empty($stack)) {
        return null;
      }

      $open = array_pop($stack);
      if (($open === '{' && $char !== '}') || ($open === '[' && $char !== ']')) {
        return null;
      }

      if (empty($stack)) {
        return $i + 1;
      }
    }
  }

  return null;
}

function repair(string $html): string {
  $length = strlen($html);
  $offset = 0;
  $output = '';
  $changed = false;

  while ($offset < $length) {
    $match = preg_match(
      '/data-mage-init\s*=\s*"/i',
      $html,
      $matches,
      PREG_OFFSET_CAPTURE,
      $offset
    );

    if ($match !== 1) {
      $output .= substr($html, $offset);
      break;
    }

    $attributeOffset = $matches[0][1];
    $attributeToken = $matches[0][0];
    $attributeTokenLength = strlen($attributeToken);

    // Only process data-mage-init when it appears to be an actual attribute boundary, not as part of another token.
    // Example: foo-data-mage-init="..."
    if ($attributeOffset === 0) {
      $output .= substr($html, $offset, $attributeTokenLength);
      $offset = $attributeTokenLength;
      continue;
    }
    $previousCharacter = $html[$attributeOffset - 1];
    if (!ctype_space($previousCharacter)) {
      $output .= substr(
        $html,
        $offset,
        ($attributeOffset + $attributeTokenLength) - $offset
      );
      $offset = $attributeOffset + $attributeTokenLength;
      continue;
    }

    // Copy everything before data-mage-init="...
    $output .= substr(
      $html,
      $offset,
      $attributeOffset - $offset
    );

    $jsonStart = $attributeOffset + $attributeTokenLength;

    // The malformed value must begin with a JSON object or array.
    if ($jsonStart >= $length || ($html[$jsonStart] !== '{' && $html[$jsonStart] !== '[')) {
      $output .= $attributeToken;
      $offset = $jsonStart;
      continue;
    }

    $jsonEnd = findJsonEnd($html, $jsonStart);

    // Could not safely identify a JSON value. Leave this occurrence untouched.
    if ($jsonEnd === null || $jsonEnd >= $length) {
      $output .= $attributeToken;
      $offset = $jsonStart;
      continue;
    }

    // The malformed attribute should end with a literal ".
    //
    // Example:
    // data-mage-init="{"key":"value"}"
    //                                ^
    if ($html[$jsonEnd] !== '"') {
      $output .= $attributeToken;
      $offset = $jsonStart;
      continue;
    }

    // Ensure it's the end of the HTML attribute.
    $afterJson = $jsonEnd + 1;
    if ($afterJson < $length) {
      $nextCharacter = $html[$afterJson];
      if ($nextCharacter !== '>' && $nextCharacter !== '/' && !ctype_space($nextCharacter)) {
        $output .= $attributeToken;
        $offset = $jsonStart;
        continue;
      }
    }

    // Extract the JSON from $html
    $json = substr(
      $html,
      $jsonStart,
      $jsonEnd - $jsonStart
    );

    // Validate that this really is JSON.
    try {
      json_decode($json, true, 512, JSON_THROW_ON_ERROR);
    } catch (\JsonException $e) {
      $output .= $attributeToken;
      $offset = $jsonStart;
      continue;
    }

    // JSON normally contains double quotes and no apostrophes, so single quotes are the safest HTML attribute delimiter.
    if (strpos($json, "'") === false) {
      $output .= 'data-mage-init=\'' . $json . '\'';
    } else {
      // The JSON contains a literal apostrophe, so use double quotes and HTML-escape its double quotes.
      $escapedJson = htmlspecialchars(
        $json,
        ENT_COMPAT | ENT_SUBSTITUTE,
        'UTF-8',
        false
      );

      $output .= 'data-mage-init="' . $escapedJson . '"';
    }

    $changed = true;

    // Consume the final quote of the malformed attribute.
    $offset = $afterJson;
  }

  return $changed ? $output : $html;
}

$tests = [
  [
    'name' => 'Basic',
    'input' => '<div data-mage-init="{"key":"value"}"></div>',
    'expected' => '<div data-mage-init=\'{"key":"value"}\'></div>',
  ],
  [
    'name' => 'Magento JSON',
    'input' => '<div data-mage-init="{"Magento_Ui/js/core/app":{"components":{"x":{"component":"foo"}}}}"></div>',
    'expected' => '<div data-mage-init=\'{"Magento_Ui/js/core/app":{"components":{"x":{"component":"foo"}}}}\'></div>',
  ],
  [
    'name' => 'Nested JSON string',
    'input' => '<div data-mage-init="{"config":{"label":"He said \\"hello\\""}}"></div>',
    'expected' => '<div data-mage-init=\'{"config":{"label":"He said \\"hello\\""}}\'></div>',
  ],
  [
    'name' => 'JSON with apostrophe',
    'input' => '<div data-mage-init="{"label":"Bob\'s product"}"></div>',
    'expected' => '<div data-mage-init="{&quot;label&quot;:&quot;Bob\'s product&quot;}"></div>',
  ],
  [
    'name' => 'Already valid libxml output',
    'input' => '<div data-mage-init="{&quot;key&quot;:&quot;value&quot;}"></div>',
    'expected' => '<div data-mage-init="{&quot;key&quot;:&quot;value&quot;}"></div>',
  ],
  [
    'name' => 'Other attribute',
    'input' => '<div foo-data-mage-init="{"key":"value"}"></div>',
    'expected' => '<div foo-data-mage-init="{"key":"value"}"></div>',
  ],
  [
    'name' => 'Multiple attributes',
    'input' =>
      '<div data-mage-init="{"one":"1"}"></div>' .
      '<div data-mage-init="{"two":"2"}"></div>',
    'expected' =>
      '<div data-mage-init=\'{"one":"1"}\'></div>' .
      '<div data-mage-init=\'{"two":"2"}\'></div>',
  ],
];

foreach ($tests as $test) {
  $actual = repair($test['input']);

  echo $test['name'] . ': '
    . ($actual === $test['expected'] ? 'PASS' : 'FAIL')
    . PHP_EOL;

  if ($actual !== $test['expected']) {
    echo "Expected: " . $test['expected'] . PHP_EOL;
    echo "Actual:   " . $actual . PHP_EOL;
  }
}