<?php
/**
 * Google Merchant API integration using OAuth 2.0 authentication.
 *
 * This class implements authentication and API calls to the Google Merchant API
 * using OAuth 2.0 user authentication flow.
 *
 * @package InformatiqSmartPricing
 */

// Exit if accessed directly.
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Google Merchant API class.
 */
class Informatiq_SP_Google_API {
	/**
	 * Merchant API base URL.
	 *
	 * @var string
	 */
	const API_BASE_URL = 'https://merchantapi.googleapis.com';

	/**
	 * OAuth authorization endpoint.
	 *
	 * @var string
	 */
	const AUTH_URL = 'https://accounts.google.com/o/oauth2/auth';

	/**
	 * OAuth token endpoint.
	 *
	 * @var string
	 */
	const TOKEN_URL = 'https://oauth2.googleapis.com/token';

	/**
	 * API scope for Merchant Center.
	 *
	 * @var string
	 */
	const API_SCOPE = 'https://www.googleapis.com/auth/content';

	/**
	 * Access token.
	 *
	 * @var string
	 */
	private $access_token;

	/**
	 * Merchant ID (account ID).
	 *
	 * @var string
	 */
	private $merchant_id;

	/**
	 * OAuth Client ID.
	 *
	 * @var string
	 */
	private $client_id;

	/**
	 * OAuth Client Secret.
	 *
	 * @var string
	 */
	private $client_secret;

	/**
	 * Refresh token.
	 *
	 * @var string
	 */
	private $refresh_token;

	/**
	 * Logger instance.
	 *
	 * @var Informatiq_SP_Logger
	 */
	private $logger;

	/**
	 * Constructor.
	 *
	 * @param string               $merchant_id   Google Merchant ID.
	 * @param string               $client_id     OAuth Client ID.
	 * @param string               $client_secret OAuth Client Secret.
	 * @param string               $refresh_token OAuth Refresh Token.
	 * @param Informatiq_SP_Logger $logger        Logger instance.
	 * @throws Exception If initialization fails.
	 */
	public function __construct( $merchant_id, $client_id, $client_secret, $refresh_token, $logger ) {
		$this->merchant_id   = $merchant_id;
		$this->client_id     = $client_id;
		$this->client_secret = $client_secret;
		$this->refresh_token = $refresh_token;
		$this->logger        = $logger;

		if ( empty( $client_id ) || empty( $client_secret ) ) {
			throw new Exception( 'OAuth Client ID and Client Secret are required' );
		}

		if ( empty( $refresh_token ) ) {
			throw new Exception( 'Not authorized. Please authorize with Google first.' );
		}
	}

	/**
	 * Get the authorization URL for OAuth flow.
	 *
	 * @param string $client_id    OAuth Client ID.
	 * @param string $redirect_uri Redirect URI after authorization.
	 * @param string $state        State parameter for CSRF protection.
	 * @return string Authorization URL.
	 */
	public static function get_authorization_url( $client_id, $redirect_uri, $state ) {
		$params = array(
			'client_id'     => $client_id,
			'redirect_uri'  => $redirect_uri,
			'response_type' => 'code',
			'scope'         => self::API_SCOPE,
			'access_type'   => 'offline',
			'prompt'        => 'consent',
			'state'         => $state,
		);

		return self::AUTH_URL . '?' . http_build_query( $params );
	}

	/**
	 * Exchange authorization code for tokens.
	 *
	 * @param string $code          Authorization code from Google.
	 * @param string $client_id     OAuth Client ID.
	 * @param string $client_secret OAuth Client Secret.
	 * @param string $redirect_uri  Redirect URI used in authorization.
	 * @return array Tokens array with access_token and refresh_token.
	 * @throws Exception If token exchange fails.
	 */
	public static function exchange_code_for_tokens( $code, $client_id, $client_secret, $redirect_uri ) {
		$response = wp_remote_post(
			self::TOKEN_URL,
			array(
				'body' => array(
					'code'          => $code,
					'client_id'     => $client_id,
					'client_secret' => $client_secret,
					'redirect_uri'  => $redirect_uri,
					'grant_type'    => 'authorization_code',
				),
				'timeout' => 30,
			)
		);

		if ( is_wp_error( $response ) ) {
			throw new Exception( 'Token exchange failed: ' . $response->get_error_message() );
		}

		$body = json_decode( wp_remote_retrieve_body( $response ), true );

		if ( isset( $body['error'] ) ) {
			throw new Exception( 'Token error: ' . ( $body['error_description'] ?? $body['error'] ) );
		}

		if ( empty( $body['access_token'] ) || empty( $body['refresh_token'] ) ) {
			throw new Exception( 'Invalid token response from Google' );
		}

		return array(
			'access_token'  => $body['access_token'],
			'refresh_token' => $body['refresh_token'],
			'expires_in'    => $body['expires_in'] ?? 3600,
		);
	}

	/**
	 * Get access token, refreshing if necessary.
	 *
	 * @return string Access token.
	 * @throws Exception If token retrieval fails.
	 */
	private function get_access_token() {
		// Return cached token if available.
		if ( $this->access_token ) {
			return $this->access_token;
		}

		// Refresh the access token.
		$response = wp_remote_post(
			self::TOKEN_URL,
			array(
				'body' => array(
					'client_id'     => $this->client_id,
					'client_secret' => $this->client_secret,
					'refresh_token' => $this->refresh_token,
					'grant_type'    => 'refresh_token',
				),
				'timeout' => 30,
			)
		);

		if ( is_wp_error( $response ) ) {
			throw new Exception( 'Token refresh failed: ' . $response->get_error_message() );
		}

		$body = json_decode( wp_remote_retrieve_body( $response ), true );

		if ( isset( $body['error'] ) ) {
			// If refresh token is invalid, user needs to re-authorize.
			if ( $body['error'] === 'invalid_grant' ) {
				// Clear the stored refresh token.
				delete_option( 'informatiq_sp_refresh_token' );
				throw new Exception( 'Authorization expired. Please re-authorize with Google.' );
			}
			throw new Exception( 'Token error: ' . ( $body['error_description'] ?? $body['error'] ) );
		}

		if ( empty( $body['access_token'] ) ) {
			throw new Exception( 'No access token in response' );
		}

		$this->access_token = $body['access_token'];

		return $this->access_token;
	}

	/**
	 * Make an API request to the Merchant API.
	 *
	 * @param string $method   HTTP method (GET, POST, etc.).
	 * @param string $endpoint API endpoint (relative to base URL).
	 * @param array  $data     Request data for POST/PUT requests.
	 * @return array Response data.
	 * @throws Exception If request fails.
	 */
	private function api_request( $method, $endpoint, $data = array() ) {
		$token = $this->get_access_token();

		$args = array(
			'method'  => $method,
			'headers' => array(
				'Authorization' => 'Bearer ' . $token,
				'Content-Type'  => 'application/json',
			),
			'timeout' => 60,
		);

		if ( ! empty( $data ) && in_array( $method, array( 'POST', 'PUT', 'PATCH' ), true ) ) {
			$args['body'] = wp_json_encode( $data );
		}

		$url      = self::API_BASE_URL . $endpoint;
		$response = wp_remote_request( $url, $args );

		if ( is_wp_error( $response ) ) {
			throw new Exception( 'API request failed: ' . $response->get_error_message() );
		}

		$status_code = wp_remote_retrieve_response_code( $response );
		$body        = json_decode( wp_remote_retrieve_body( $response ), true );

		if ( $status_code >= 400 ) {
			$error_message = isset( $body['error']['message'] ) ? $body['error']['message'] : 'Unknown error';
			throw new Exception( "API error ($status_code): $error_message" );
		}

		return $body ?? array();
	}

	/**
	 * Get competitive pricing for a product.
	 *
	 * @param string $sku  Product SKU.
	 * @param string $gtin Product GTIN (optional).
	 * @return float|null Lowest competitor price or null if not found.
	 */
	public function get_competitive_price( $sku, $gtin = '' ) {
		try {
			// Search for the product using SKU or GTIN.
			$product = $this->find_product_by_identifier( $sku, $gtin );

			if ( ! $product ) {
				$this->logger->warning( "Product not found in Google Merchant Center: SKU={$sku}, GTIN={$gtin}" );
				return null;
			}

			// Try to get competitive pricing data from reports.
			$competitive_price = $this->fetch_competitive_price_from_reports( $sku, $gtin );

			if ( $competitive_price ) {
				return $competitive_price;
			}

			// Fallback: Use product's own price as reference.
			if ( isset( $product['price']['amountMicros'] ) ) {
				$price = (float) $product['price']['amountMicros'] / 1000000;
				$this->logger->warning( "No competitive data available for SKU={$sku}, using own price as reference" );
				return $price;
			}

			return null;

		} catch ( Exception $e ) {
			$this->logger->error( 'Error fetching competitive price: ' . $e->getMessage() );
			return null;
		}
	}

	/**
	 * Find product by SKU or GTIN.
	 *
	 * Matching logic:
	 * 1. SKU matches offerId
	 * 2. SKU matches gtin (for stores where SKU is the barcode)
	 * 3. GTIN matches gtin
	 *
	 * @param string $sku  Product SKU.
	 * @param string $gtin Product GTIN.
	 * @return array|null Product data or null if not found.
	 */
	private function find_product_by_identifier( $sku, $gtin ) {
		try {
			$page_token = null;

			do {
				$endpoint = "/products/v1beta/accounts/{$this->merchant_id}/products";
				$endpoint .= '?pageSize=250';

				if ( $page_token ) {
					$endpoint .= '&pageToken=' . urlencode( $page_token );
				}

				$response = $this->api_request( 'GET', $endpoint );

				if ( ! empty( $response['products'] ) ) {
					foreach ( $response['products'] as $product ) {
						// Check if offerId matches SKU.
						if ( isset( $product['offerId'] ) && $product['offerId'] === $sku ) {
							return $product;
						}

						// Check if SKU matches Google's GTIN (for stores where SKU is the barcode).
						if ( isset( $product['gtin'] ) && $product['gtin'] === $sku ) {
							$this->logger->info( "Product matched by GTIN={$sku} (SKU used as barcode)" );
							return $product;
						}

						// Check if separate GTIN field matches.
						if ( ! empty( $gtin ) && isset( $product['gtin'] ) && $product['gtin'] === $gtin ) {
							return $product;
						}
					}
				}

				$page_token = $response['nextPageToken'] ?? null;

			} while ( $page_token );

			return null;

		} catch ( Exception $e ) {
			$this->logger->error( 'Error finding product: ' . $e->getMessage() );
			return null;
		}
	}

	/**
	 * Fetch competitive pricing data from Reports API.
	 *
	 * @param string $sku  Product SKU.
	 * @param string $gtin Product GTIN.
	 * @return float|null Lowest competitor price or null.
	 */
	private function fetch_competitive_price_from_reports( $sku, $gtin ) {
		try {
			// Use the Reports API to search for competitive visibility data.
			$endpoint = "/reports/v1beta/accounts/{$this->merchant_id}/reports:search";

			// Try searching by offer_id first.
			$query = array(
				'query' => "SELECT
					offer_id,
					price_benchmark.price_benchmark_value,
					price_benchmark.price_benchmark_currency_code
				FROM PriceCompetitivenessProductView
				WHERE offer_id = '{$sku}'",
			);

			$response = $this->api_request( 'POST', $endpoint, $query );

			if ( ! empty( $response['results'] ) ) {
				foreach ( $response['results'] as $result ) {
					if ( isset( $result['priceBenchmark']['priceBenchmarkValue']['amountMicros'] ) ) {
						return (float) $result['priceBenchmark']['priceBenchmarkValue']['amountMicros'] / 1000000;
					}
				}
			}

			// If SKU looks like a GTIN (numeric, 8-14 digits), also try searching by gtin.
			if ( preg_match( '/^\d{8,14}$/', $sku ) ) {
				$query = array(
					'query' => "SELECT
						gtin,
						price_benchmark.price_benchmark_value,
						price_benchmark.price_benchmark_currency_code
					FROM PriceCompetitivenessProductView
					WHERE gtin = '{$sku}'",
				);

				$response = $this->api_request( 'POST', $endpoint, $query );

				if ( ! empty( $response['results'] ) ) {
					foreach ( $response['results'] as $result ) {
						if ( isset( $result['priceBenchmark']['priceBenchmarkValue']['amountMicros'] ) ) {
							return (float) $result['priceBenchmark']['priceBenchmarkValue']['amountMicros'] / 1000000;
						}
					}
				}
			}

			return null;

		} catch ( Exception $e ) {
			// Reports API might not be available for all accounts.
			$this->logger->info( 'Competitive pricing data not available: ' . $e->getMessage() );
			return null;
		}
	}

	/**
	 * Test API connection.
	 *
	 * @return bool True if connection successful.
	 */
	public function test_connection() {
		try {
			// Try to list products to test connection.
			$endpoint = "/products/v1beta/accounts/{$this->merchant_id}/products?pageSize=1";
			$this->api_request( 'GET', $endpoint );

			$this->logger->info( 'Google Merchant API connection test successful' );
			return true;

		} catch ( Exception $e ) {
			$this->logger->error( 'Google Merchant API connection test failed: ' . $e->getMessage() );
			return false;
		}
	}

	/**
	 * Get all products from Merchant Center.
	 *
	 * @return array Array of products.
	 */
	public function get_all_products() {
		try {
			$all_products = array();
			$page_token   = null;

			do {
				$endpoint = "/products/v1beta/accounts/{$this->merchant_id}/products";
				$endpoint .= '?pageSize=250';

				if ( $page_token ) {
					$endpoint .= '&pageToken=' . urlencode( $page_token );
				}

				$response     = $this->api_request( 'GET', $endpoint );
				$products     = $response['products'] ?? array();
				$all_products = array_merge( $all_products, $products );

				$page_token = $response['nextPageToken'] ?? null;

			} while ( $page_token );

			return $all_products;

		} catch ( Exception $e ) {
			$this->logger->error( 'Error fetching products: ' . $e->getMessage() );
			return array();
		}
	}
}