[Enhancement] Add schema validation and placeholders to index mappings

[pyek-bot]

Description

Added schema validation and placeholders to index mappings

Related Issues

Resolves #2951

Check List

• New functionality includes testing.
• Commits are signed per the DCO using --signoff.

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[dhrubo-os]

Do we need to have this check here considering we are going to check mapping.isBlank() in the replacePlaceholders method. Seems like redundant.

[pyek-bot]

i added this check here since this method can be used on its own, incase used in other places, i believe it is safer to have this additional check

[dhrubo-os]

Here we are creating string in every replace. May be we could use a StringBuilder to have in-place replacement?

May be something like this:

public static String replacePlaceholders(String mapping) throws IOException {
    if (mapping == null || mapping.isBlank()) {
        throw new IllegalArgumentException("Mapping cannot be null or empty");
    }

    // Preload resources into memory to avoid redundant I/O
    Map<String, String> loadedPlaceholders = new HashMap<>();
    for (Map.Entry<String, String> placeholder : MAPPING_PLACEHOLDERS.entrySet()) {
        URL url = IndexUtils.class.getClassLoader().getResource(placeholder.getValue());
        if (url == null) {
            throw new IOException("Resource not found: " + placeholder.getValue());
        }
        // Load and cache the content
        loadedPlaceholders.put(placeholder.getKey(), Resources.toString(url, Charsets.UTF_8));
    }

    // Use StringBuilder for efficient in-place replacements
    StringBuilder result = new StringBuilder(mapping);
    for (Map.Entry<String, String> entry : loadedPlaceholders.entrySet()) {
        String placeholder = entry.getKey();
        String replacement = entry.getValue();

        // Replace all occurrences of the placeholder
        int index;
        while ((index = result.indexOf(placeholder)) != -1) {
            result.replace(index, index + placeholder.length(), replacement);
        }
    }

    return result.toString();
}

[pyek-bot]

agreed, thanks for the suggestion, saves on the I/O and is more efficient!

[dhrubo-os]

Should we add try catch block to catch any exceptions like:

catch (JsonProcessingException e) {
        throw new IllegalArgumentException("Invalid JSON format: " + e.getMessage(), e);
    } catch (Exception e) {
        throw new OpenSearchParseException("Schema validation failed: " + e.getMessage(), e);
    }

[dhrubo-os]

What do you think about this:

if (!errors.isEmpty()) {
            String errorMessage = errors.stream()
                                        .map(ValidationMessage::getMessage)
                                        .collect(Collectors.joining(", "));
            throw new OpenSearchParseException(
                "Validation failed: " + errorMessage + 
                " for instance: " + instanceString + 
                " with schema: " + schemaString
            );
        }

[dhrubo-os]

Usually, I see that JSON files in the repository are named using snake_case. Let's follow the same convention.

[pyek-bot]

@dhrubo-os addressed review comments, please review!

[dhrubo-os]

[Nit] if you want to be fancy :D

/**
     * Checks if the provided mapping is a valid JSON and validates it against a schema.
     *
     * <p>The schema is located at <code>mappings/schema.json</code> and enforces the following validations:</p>
     *
     * <ul>
     *   <li>Mandatory fields:
     *     <ul>
     *       <li><code>_meta</code></li>
     *       <li><code>_meta.schema_version</code></li>
     *       <li><code>properties</code></li>
     *     </ul>
     *   </li>
     *   <li>No additional fields are allowed at the root level.</li>
     *   <li>No additional fields are allowed in the <code>_meta</code> object.</li>
     *   <li><code>properties</code> must be an object type.</li>
     *   <li><code>_meta</code> must be an object type.</li>
     *   <li><code>_meta.schema_version</code> must be an integer.</li>
     * </ul>
     *
     * <p><strong>Note:</strong> Validation can be made stricter if a specific schema is defined for each index.</p>
     */

[dhrubo-os]

It will look like this.

[pyek-bot]

that looks neat, ive added it