package envoy.server.util;

import java.util.regex.Pattern;

/**
 * Implements a comparison algorithm between Envoy versions and defines minimal and maximal client
 * versions compatible with this server.
 *
 * @author Kai S. K. Engelbart
 * @since Envoy Server Standalone v0.1-beta
 */
public final class VersionUtil {

	/**
	 * The minimal client version compatible with this server.
	 *
	 * @since Envoy Server Standalone v0.1-beta
	 */
	public static final String MIN_CLIENT_VERSION = "0.1-beta";

	/**
	 * The maximal client version compatible with this server.
	 *
	 * @since Envoy Server Standalone v0.1-beta
	 */
	public static final String MAX_CLIENT_VERSION = "0.2-beta";

	private static final Pattern versionPattern =
		Pattern.compile("(?<major>\\d).(?<minor>\\d)(?:-(?<suffix>\\w+))?");

	private VersionUtil() {}

	/**
	 * Parses an Envoy Client version string and checks whether that version is compatible with this
	 * server.
	 *
	 * @param version the version string to parse
	 * @return {@code true} if the given version is compatible with this server
	 * @since Envoy Server Standalone v0.1-beta
	 */
	public static boolean verifyCompatibility(String version) {
		final var currentMatcher = versionPattern.matcher(version);

		if (!currentMatcher.matches())
			return false;

		final var	minMatcher	= versionPattern.matcher(MIN_CLIENT_VERSION);
		final var	maxMatcher	= versionPattern.matcher(MAX_CLIENT_VERSION);

		if (!minMatcher.matches() || !maxMatcher.matches())
			throw new RuntimeException("Invalid min or max client version configured!");

		// Compare suffixes
		{
			final var	currentSuffix	= convertSuffix(currentMatcher.group("suffix"));
			final var	minSuffix		= convertSuffix(minMatcher.group("suffix"));
			final var	maxSuffix		= convertSuffix(maxMatcher.group("suffix"));

			if (currentSuffix < minSuffix || currentSuffix > maxSuffix)
				return false;
		}

		// Compare major
		{
			final var	currentMajor	= Integer.parseInt(currentMatcher.group("major"));
			final var	minMajor		= Integer.parseInt(minMatcher.group("major"));
			final var	maxMajor		= Integer.parseInt(maxMatcher.group("major"));

			if (currentMajor < minMajor || currentMajor > maxMajor)
				return false;
		}

		// Compare minor
		{
			final var	currentMinor	= Integer.parseInt(currentMatcher.group("minor"));
			final var	minMinor		= Integer.parseInt(minMatcher.group("minor"));
			final var	maxMinor		= Integer.parseInt(maxMatcher.group("minor"));

			if (currentMinor < minMinor || currentMinor > maxMinor)
				return false;
		}

		return true;
	}

	private static int convertSuffix(String suffix) {
		switch (suffix == null ? "" : suffix) {
			case "alpha":
				return 0;
			case "beta":
				return 1;
			default:
				return 2;
		}
	}
}