;
	}

	/**
	 * Convert an amount to the store's default currency in order to store in the stats table.
	 *
	 * @param float $amount The amount to convert into the store's default currency.
	 * @param float $exchange_rate The exchange rate to use for the conversion.
	 *
	 * @return float The converted amount.
	 */
	private function convert_amount( float $amount, float $exchange_rate ): float {
		return $amount * $exchange_rate;
	}

	/**
	 * Check whether the order stats table is referenced in the clauses, to work out whether
	 * to add the JOIN columns for Multi-Currency.
	 *
	 * @param array $clauses The array containing the clauses used.
	 *
	 * @return boolean Whether the order stats table is referenced.
	 */
	private function is_order_stats_table_used_in_clauses( array $clauses ): bool {
		global $wpdb;

		foreach ( $clauses as $clause ) {
			if ( strpos( $clause, "{$wpdb->prefix}wc_order_stats" ) !== false ) {
				return true;
			}
		}

		return false;
	}

	/**
	 * There are some queries which are made in the analytics which are actually sub-queries
	 * which are used to join on an individual item/coupon/tax code. In these cases, rather than
	 * the context being the expected format e.g. product_stats_total, it will simply be 'product'.
	 * In these cases, we don't want to add the join columns or select them.
	 *
	 * @param string $context The context the query was made in.
	 *
	 * @return boolean
	 */
	private function is_supported_context( string $context ): bool {
		$unsupported_contexts = [ 'products', 'coupons', 'taxes', 'variations', 'categories' ];

		if ( in_array( $context, $unsupported_contexts, true ) ) {
			return false;
		}

		return true;
	}

	/**
	 * Generate a case when statement using the provided variables.
	 *
	 * @param string $variable The SQL variable we want to check for NULL.
	 * @param string $then     The THEN clause.
	 * @param string $else     The ELSE clause.
	 *
	 * @return string
	 */
	private function generate_case_when( string $variable, string $then, string $else ): string {
		return "CASE WHEN {$variable} IS NOT NULL THEN {$then} ELSE {$else} END";
	}

	/**
	 * Perform an SQL query to determine whether Multi Currency has ever been used on this store,
	 * by checking how many orders are in the database where an exchange currency rate has been stored.
	 *
	 * @return bool
	 */
	private function has_multi_currency_orders() {
		global $wpdb;

		// Using full SQL instead of variables to keep WPCS happy.
		if ( $this->is_cot_enabled() ) {
			$result = $wpdb->get_var(
				"SELECT EXISTS(
					SELECT 1
					FROM {$wpdb->prefix}wc_orders_meta
					WHERE meta_key = '_wcpay_multi_currency_order_exchange_rate'
					LIMIT 1)
				AS count;"
			);
		} else {
			$result = $wpdb->get_var(
				"SELECT EXISTS(
					SELECT 1
					FROM {$wpdb->postmeta}
					WHERE meta_key = '_wcpay_multi_currency_order_exchange_rate'
					LIMIT 1)
				AS count;"
			);
		}

		return intval( $result ) === 1;
	}

	/**
	 * Get the SQL replacements variable.
	 *
	 * @return array
	 */
	private function get_sql_replacements(): array {
		return $this->sql_replacements;
	}

	/**
	 * Check the passed in query params to see if currency has been passed in.
	 * Will return null if no currency variable was passed in, otherwise will
	 * return the currency.
	 *
	 * @return array
	 */
	private function get_customer_currency_args_from_request(): array {
		$args = [
			'currency_is'     => [],
			'currency_is_not' => [],
			'currency'        => null,
		];

		/* phpcs:disable WordPress.Security.NonceVerification */
		if ( isset( $_GET['currency_is'] ) && is_array( $_GET['currency_is'] ) ) {
			$args['currency_is'] = array_map( 'sanitize_text_field', wp_unslash( $_GET['currency_is'] ) );
		}

		if ( isset( $_GET['currency_is_not'] ) ) {
			$args['currency_is_not'] = array_map( 'sanitize_text_field', wp_unslash( $_GET['currency_is_not'] ) );
		}

		if ( isset( $_GET['currency'] ) ) {
			$args['currency'] = sanitize_text_field( wp_unslash( $_GET['currency'] ) );
		}
		/* phpcs:enable WordPress.Security.NonceVerification */

		return $args;
	}

	/**
	 * Set the SQL replacements variable.
	 *
	 * @return void
	 */
	private function set_sql_replacements() {
		$default_currency     = 'wcpay_multicurrency_default_currency_meta.meta_value';
		$exchange_rate        = 'wcpay_multicurrency_exchange_rate_meta.meta_value';
		$stripe_exchange_rate = 'wcpay_multicurrency_stripe_exchange_rate_meta.meta_value';

		$discount_amount       = $this->generate_case_when( $default_currency, $this->generate_case_when( $stripe_exchange_rate, "ROUND(discount_amount * {$stripe_exchange_rate}, 2)", "ROUND(discount_amount * (1 / {$exchange_rate} ), 2)" ), 'discount_amount' );
		$product_net_revenue   = $this->generate_case_when( $default_currency, $this->generate_case_when( $stripe_exchange_rate, "ROUND(product_net_revenue * {$stripe_exchange_rate}, 2)", "ROUND(product_net_revenue * (1 / {$exchange_rate} ), 2)" ), 'product_net_revenue' );
		$product_gross_revenue = $this->generate_case_when( $default_currency, $this->generate_case_when( $stripe_exchange_rate, "ROUND(product_gross_revenue * {$stripe_exchange_rate}, 2)", "ROUND(product_gross_revenue * (1 / {$exchange_rate} ), 2)" ), 'product_gross_revenue' );

		$this->sql_replacements = [
			'generic'    => [
				'discount_amount'       => $discount_amount,
				'product_net_revenue'   => $product_net_revenue,
				'product_gross_revenue' => $product_gross_revenue,
			],
			'orders'     => [
				'discount_amount' => $discount_amount,
			],
			'products'   => [
				'product_net_revenue'   => $product_net_revenue,
				'product_gross_revenue' => $product_gross_revenue,
			],
			'variations' => [
				'product_net_revenue'   => $product_net_revenue,
				'product_gross_revenue' => $product_gross_revenue,
			],
			'categories' => [
				'product_net_revenue'   => $product_net_revenue,
				'product_gross_revenue' => $product_gross_revenue,
			],
			'taxes'      => [
				'SUM(total_tax)'    => 'SUM(' . $this->generate_case_when( $default_currency, $this->generate_case_when( $stripe_exchange_rate, "ROUND(total_tax * {$stripe_exchange_rate}, 2)", "ROUND(total_tax * (1 / {$exchange_rate} ), 2)" ), 'total_tax' ) . ')',
				'SUM(order_tax)'    => 'SUM(' . $this->generate_case_when( $default_currency, $this->generate_case_when( $stripe_exchange_rate, "ROUND(order_tax * {$stripe_exchange_rate}, 2)", "ROUND(order_tax * (1 / {$exchange_rate} ), 2)" ), 'order_tax' ) . ')',
				'SUM(shipping_tax)' => 'SUM(' . $this->generate_case_when( $default_currency, $this->generate_case_when( $stripe_exchange_rate, "ROUND(shipping_tax * {$stripe_exchange_rate}, 2)", "ROUND(shipping_tax * (1 / {$exchange_rate} ), 2)" ), 'shipping_tax' ) . ')',
			],
			'coupons'    => [
				'discount_amount' => $discount_amount,
			],
		];
	}

	/**
	 * Checks whether Custom Order Tables are enabled.
	 *
	 * @return bool
	 */
	private function is_cot_enabled(): bool {
		return class_exists( OrderUtil::class ) && OrderUtil::custom_orders_table_usage_is_enabled();
	}
}