<?php
/**
 * Byte-precise marker block editing.
 *
 * @package AIBlackout
 */

namespace AIBlackout\Enforcement;

defined( 'ABSPATH' ) || exit;

/**
 * Inserts, replaces and removes a marker-fenced block without disturbing
 * the rest of a file.
 *
 * @since 1.0.0
 */
class MarkerBlock {

	/**
	 * Returns the byte offsets of a marker block within a string.
	 *
	 * @param string $subject Full file contents.
	 * @param string $begin   Opening marker line.
	 * @param string $end     Closing marker line.
	 * @return array|null Array with 'start' and 'length', or null when not found.
	 */
	public static function locate( string $subject, string $begin, string $end ): ?array {
		$start = strpos( $subject, $begin );

		if ( false === $start ) {
			return null;
		}

		$end_pos = strpos( $subject, $end, $start );

		if ( false === $end_pos ) {
			return null;
		}

		$stop = $end_pos + strlen( $end );

		// Consume the newline that terminates the end marker, if present.
		if ( isset( $subject[ $stop ] ) && "\r" === $subject[ $stop ] ) {
			++$stop;
		}

		if ( isset( $subject[ $stop ] ) && "\n" === $subject[ $stop ] ) {
			++$stop;
		}

		return array(
			'start'  => $start,
			'length' => $stop - $start,
		);
	}

	/**
	 * Whether the subject contains the block.
	 *
	 * @param string $subject Full file contents.
	 * @param string $begin   Opening marker line.
	 * @param string $end     Closing marker line.
	 * @return bool True when present.
	 */
	public static function exists( string $subject, string $begin, string $end ): bool {
		return null !== self::locate( $subject, $begin, $end );
	}

	/**
	 * Replaces the block, or appends it when not already present.
	 *
	 * @param string $subject     Full file contents.
	 * @param string $begin       Opening marker line.
	 * @param string $end         Closing marker line.
	 * @param string $replacement The block to insert, including both markers.
	 * @return string Updated contents.
	 */
	public static function replace( string $subject, string $begin, string $end, string $replacement ): string {
		$location = self::locate( $subject, $begin, $end );

		if ( null === $location ) {
			if ( '' === $replacement ) {
				return $subject;
			}

			if ( '' === $subject ) {
				return $replacement;
			}

			$separator = "\n" === substr( $subject, -1 ) ? "\n" : "\n\n";

			return $subject . $separator . $replacement;
		}

		return substr( $subject, 0, $location['start'] )
			. $replacement
			. substr( $subject, $location['start'] + $location['length'] );
	}

	/**
	 * Removes the block, leaving everything else byte-identical.
	 *
	 * @param string $subject Full file contents.
	 * @param string $begin   Opening marker line.
	 * @param string $end     Closing marker line.
	 * @return string Updated contents.
	 */
	public static function remove( string $subject, string $begin, string $end ): string {
		$location = self::locate( $subject, $begin, $end );

		if ( null === $location ) {
			return $subject;
		}

		$result = substr( $subject, 0, $location['start'] )
			. substr( $subject, $location['start'] + $location['length'] );

		// A block appended to an existing file is preceded by a blank line.
		if ( '' !== $result && "\n\n" === substr( $result, -2 ) ) {
			$result = substr( $result, 0, -1 );
		}

		return $result;
	}

	/**
	 * Whether two strings differ only in line endings and trailing newlines.
	 *
	 * @param string $a First string.
	 * @param string $b Second string.
	 * @return bool True when the difference is whitespace only.
	 */
	public static function is_whitespace_only_difference( string $a, string $b ): bool {
		$normalize = static function ( string $value ): string {
			return rtrim( str_replace( array( "\r\n", "\r" ), "\n", $value ), "\n" );
		};

		return $normalize( $a ) === $normalize( $b );
	}
}