<?php
/**
 * Abstract feed base class.
 *
 * Provides the contract and shared utilities for all feed format
 * implementations (Google, OpenAI, Bing, Perplexity).
 *
 * @package AICommerce\Feed
 */

declare(strict_types=1);

namespace AICommerce\Feed;

/**
 * Base class for feed format implementations.
 */
abstract class AbstractFeed {

	/**
	 * Get the feed type identifier.
	 *
	 * @return string Unique feed type slug (e.g., 'google', 'openai').
	 */
	abstract public function get_type(): string;

	/**
	 * Get the human-readable feed name.
	 *
	 * @return string Feed display name.
	 */
	abstract public function get_name(): string;

	/**
	 * Get the file extension for this feed format.
	 *
	 * @return string File extension (e.g., 'xml', 'jsonl').
	 */
	abstract public function get_extension(): string;

	/**
	 * Get the required fields for this feed format.
	 *
	 * @return array List of required field keys from normalized product data.
	 */
	abstract public function get_required_fields(): array;

	/**
	 * Get the recommended fields for this feed format.
	 *
	 * @return array List of recommended field keys.
	 */
	abstract public function get_recommended_fields(): array;

	/**
	 * Generate the feed content from normalized product data.
	 *
	 * @param array $products Array of normalized product data arrays.
	 *
	 * @return string The generated feed content.
	 */
	abstract public function generate( array $products ): string;

	/**
	 * Get the content type header for this feed.
	 *
	 * @return string MIME type.
	 */
	abstract public function get_content_type(): string;

	/**
	 * Get the filename for this feed.
	 *
	 * @return string Feed filename.
	 */
	public function get_filename(): string {
		return $this->get_type() . '-feed.' . $this->get_extension();
	}

	/**
	 * Check if a product has all required fields for this feed.
	 *
	 * @param array $product_data Normalized product data.
	 *
	 * @return array{valid: bool, missing: array} Validation result.
	 */
	public function validate_product( array $product_data ): array {
		$missing = array();

		foreach ( $this->get_required_fields() as $field ) {
			if ( empty( $product_data[ $field ] ) ) {
				$missing[] = $field;
			}
		}

		return array(
			'valid'   => empty( $missing ),
			'missing' => $missing,
		);
	}

	/**
	 * Filter products to only those with required fields.
	 *
	 * @param array $products Array of normalized product data.
	 *
	 * @return array Filtered products.
	 */
	protected function filter_valid_products( array $products ): array {
		return array_filter(
			$products,
			function ( array $product ): bool {
				return $this->validate_product( $product )['valid'];
			}
		);
	}
}