/**
 * CatalogueConfigStorage - Low-level storage for catalogue configuration
 *
 * Handles the 'catcfg:' prefix for storing catalogue configuration.
 *
 * Key format: catcfg:<path>
 * Value: Serialized (string type_label, string expression)
 *
 * @version 0.1
 * @since 0.1
 */
namespace Implexus.Storage.LowLevel {

/**
 * Configuration data for a Catalogue entity.
 */
public class CatalogueConfig : Object {
    /**
     * The type label for documents to catalogue.
     */
    public string type_label { get; set; }
    
    /**
     * The expression used to extract the grouping key.
     */
    public string expression { get; set; }
    
    /**
     * Creates a new CatalogueConfig.
     *
     * @param type_label The type label for documents
     * @param expression The expression to extract the grouping key
     */
    public CatalogueConfig(string type_label, string expression) {
        this.type_label = type_label;
        this.expression = expression;
    }
}

/**
 * Low-level storage for catalogue configuration.
 *
 * This class provides type-safe operations for storing and retrieving
 * catalogue configuration using the 'catcfg:' key prefix.
 */
public class CatalogueConfigStorage : Object {
    
    /**
     * Key prefix for catalogue config entries.
     */
    private const string PREFIX = "catcfg:";
    
    /**
     * The underlying Dbm storage.
     */
    private Dbm _dbm;
    
    /**
     * Creates a new CatalogueConfigStorage with the given Dbm backend.
     *
     * @param dbm The Dbm backend to use for storage
     */
    public CatalogueConfigStorage(Dbm dbm) {
        _dbm = dbm;
    }
    
    /**
     * Stores catalogue configuration.
     *
     * @param path The catalogue path
     * @param type_label The type label for documents to catalogue
     * @param expression The expression to extract the grouping key
     * @throws StorageError if the operation fails
     */
    public void store(Core.EntityPath path, string type_label, string expression) throws StorageError {
        string key = PREFIX + path.to_string();
        
        var writer = new ElementWriter();
        writer.write_element(new Invercargill.NativeElement<string>(type_label));
        writer.write_element(new Invercargill.NativeElement<string>(expression));
        
        _dbm.set(key, writer.to_binary_data());
    }
    
    /**
     * Loads catalogue configuration.
     *
     * @param path The catalogue path
     * @return The configuration, or null if not found
     * @throws StorageError if the data is corrupt
     */
    public CatalogueConfig? load(Core.EntityPath path) throws StorageError {
        string key = PREFIX + path.to_string();
        var data = _dbm.get(key);
        
        if (data == null) {
            return null;
        }
        
        var reader = new ElementReader((!) data);
        try {
            var label_element = reader.read_element();
            var expr_element = reader.read_element();
            
            if (label_element.is_null() || expr_element.is_null()) {
                return null;
            }
            
            string type_label = label_element.as<string>();
            string expression = expr_element.as<string>();
            
            return new CatalogueConfig(type_label, expression);
        } catch (Invercargill.ElementError e) {
            throw new StorageError.CORRUPT_DATA("Failed to read catalogue config: %s".printf(e.message));
        }
    }
    
    /**
     * Deletes catalogue configuration.
     *
     * @param path The catalogue path
     * @throws StorageError if the operation fails
     */
    public void delete(Core.EntityPath path) throws StorageError {
        string key = PREFIX + path.to_string();
        try {
            _dbm.delete(key);
        } catch (StorageError e) {
            // Key doesn't exist, that's fine
        }
    }
}

} // namespace Implexus.Storage.LowLevel