class ProjectSecurityData

final class ProjectSecurityData {
    
    /**
     * The number of minor versions of Drupal core that receive security coverage.
     *
     * For example, if this value is 2 and the existing version is 9.0.1, the
     * 9.0.x branch will receive security coverage until the release of version
     * 9.2.0.
     *
     * @todo In https://www.drupal.org/node/2998285 determine if we want this
     *   policy to be expressed in the updates.drupal.org feed, instead of relying
     *   on a hard-coded constant.
     *
     * @see https://www.drupal.org/core/release-cycle-overview
     */
    const CORE_MINORS_WITH_SECURITY_COVERAGE = 2;
    
    /**
     * Define constants for versions with security coverage end dates.
     *
     * Two types of constants are supported:
     * - SECURITY_COVERAGE_END_DATE_[VERSION_MAJOR]_[VERSION_MINOR]: A date in
     *   'Y-m-d' or 'Y-m' format.
     * - SECURITY_COVERAGE_ENDING_WARN_DATE_[VERSION_MAJOR]_[VERSION_MINOR]: A
     *   date in 'Y-m-d' format.
     *
     * @see \Drupal\update\ProjectSecurityRequirement::getDateEndRequirement()
     */
    const SECURITY_COVERAGE_END_DATE_8_8 = '2020-12-02';
    const SECURITY_COVERAGE_ENDING_WARN_DATE_8_8 = '2020-06-02';
    const SECURITY_COVERAGE_END_DATE_8_9 = '2021-11';
    
    /**
     * The existing (currently installed) version of the project.
     *
     * Because this class only handles the Drupal core project, values will be
     * semantic version numbers such as 8.8.0, 8.8.0-alpha1, or 9.0.0.
     *
     * @var string|null
     */
    protected $existingVersion;
    
    /**
     * Releases as returned by update_get_available().
     *
     * @var array
     *
     * Each release item in the array has metadata about that release. This class
     * uses the keys:
     * - status (string): The status of the release.
     * - version (string): The version number of the release.
     *
     * @see update_get_available()
     */
    protected $releases;
    
    /**
     * Constructs a ProjectSecurityData object.
     *
     * @param string $existing_version
     *   The existing (currently installed) version of the project.
     * @param array $releases
     *   Project releases as returned by update_get_available().
     */
    private function __construct($existing_version = NULL, array $releases = []) {
        $this->existingVersion = $existing_version;
        $this->releases = $releases;
    }
    
    /**
     * Creates a ProjectSecurityData object from project data and releases.
     *
     * @param array $project_data
     *   Project data from Drupal\update\UpdateManagerInterface::getProjects() and
     *   processed by update_process_project_info().
     * @param array $releases
     *   Project releases as returned by update_get_available().
     *
     * @return static
     */
    public static function createFromProjectDataAndReleases(array $project_data, array $releases) {
        if (!($project_data['project_type'] === 'core' && $project_data['name'] === 'drupal')) {
            // Only Drupal core has an explicit coverage range.
            return new static();
        }
        return new static($project_data['existing_version'], $releases);
    }
    
    /**
     * Gets the security coverage information for a project.
     *
     * Currently only Drupal core is supported.
     *
     * @return array
     *   The security coverage information, or an empty array if no security
     *   information is available for the project. If security coverage is based
     *   on release of a specific version, the array will have the following
     *   keys:
     *   - security_coverage_end_version (string): The minor version the existing
     *     version will receive security coverage until.
     *   - additional_minors_coverage (int): The number of additional minor
     *     versions the existing version will receive security coverage.
     *   If the security coverage is based on a specific date, the array will have
     *   the following keys:
     *   - security_coverage_end_date (string): The month or date security
     *     coverage will end for the existing version. It can be in either
     *     'YYYY-MM' or 'YYYY-MM-DD' format.
     *   - (optional) security_coverage_ending_warn_date (string): The date, in
     *     the format 'YYYY-MM-DD', after which a warning should be displayed
     *     about upgrading to another version.
     */
    public function getCoverageInfo() {
        if (empty($this->releases[$this->existingVersion])) {
            // If the existing version does not have a release, we cannot get the
            // security coverage information.
            return [];
        }
        $info = [];
        $existing_release_version = ModuleVersion::createFromVersionString($this->existingVersion);
        // Check if the installed version has a specific end date defined.
        $version_suffix = $existing_release_version->getMajorVersion() . '_' . $this->getSemanticMinorVersion($this->existingVersion);
        if (defined("self::SECURITY_COVERAGE_END_DATE_{$version_suffix}")) {
            $info['security_coverage_end_date'] = constant("self::SECURITY_COVERAGE_END_DATE_{$version_suffix}");
            $info['security_coverage_ending_warn_date'] = defined("self::SECURITY_COVERAGE_ENDING_WARN_DATE_{$version_suffix}") ? constant("self::SECURITY_COVERAGE_ENDING_WARN_DATE_{$version_suffix}") : NULL;
        }
        elseif ($security_coverage_until_version = $this->getSecurityCoverageUntilVersion()) {
            $info['security_coverage_end_version'] = $security_coverage_until_version;
            $info['additional_minors_coverage'] = $this->getAdditionalSecurityCoveredMinors($security_coverage_until_version);
        }
        return $info;
    }
    
    /**
     * Gets the release the current minor will receive security coverage until.
     *
     * For the sake of example, assume that the currently installed version of
     * Drupal is 8.7.11 and that static::CORE_MINORS_WITH_SECURITY_COVERAGE is 2.
     * When Drupal 8.9.0 is released, the supported minor versions will be 8.8
     * and 8.9. At that point, Drupal 8.7 will no longer have security coverage.
     * Therefore, this function would return "8.9.0".
     *
     * @todo In https://www.drupal.org/node/2998285 determine how we will know
     *    what the final minor release of a particular major version will be. This
     *    method should not return a version beyond that minor.
     *
     * @return string|null
     *   The version the existing version will receive security coverage until or
     *   NULL if this cannot be determined.
     */
    private function getSecurityCoverageUntilVersion() {
        $existing_release_version = ModuleVersion::createFromVersionString($this->existingVersion);
        if (!empty($existing_release_version->getVersionExtra())) {
            // Only full releases receive security coverage.
            return NULL;
        }
        return $existing_release_version->getMajorVersion() . '.' . ($this->getSemanticMinorVersion($this->existingVersion) + static::CORE_MINORS_WITH_SECURITY_COVERAGE) . '.0';
    }
    
    /**
     * Gets the number of additional minor releases with security coverage.
     *
     * This function compares the currently installed (existing) version of
     * the project with two things:
     * - The latest available official release of that project.
     * - The target minor release where security coverage for the current release
     *   should expire. This target release is determined by
     *   getSecurityCoverageUntilVersion().
     *
     * For the sake of example, assume that the currently installed version of
     * Drupal is 8.7.11 and that static::CORE_MINORS_WITH_SECURITY_COVERAGE is 2.
     *
     * Before the release of Drupal 8.8.0, this function would return 2.
     *
     * After the release of Drupal 8.8.0 and before the release of 8.9.0, this
     * function would return 1 to indicate that the next minor version release
     * will end security coverage for 8.7.
     *
     * When Drupal 8.9.0 is released, this function would return 0 to indicate
     * that security coverage is over for 8.7.
     *
     * If the currently installed version is 9.0.0, and there is no 9.1.0 release
     * yet, the function would return 2. Once 9.1.0 is out, it would return 1.
     * When 9.2.0 is released, it would again return 0.
     *
     * Note: callers should not test this function's return value with empty()
     * since 0 is a valid return value that has different meaning than NULL.
     *
     * @param string $security_covered_version
     *   The version until which the existing version receives security coverage.
     *
     * @return int|null
     *   The number of additional minor releases that receive security coverage,
     *   or NULL if this cannot be determined.
     *
     * @see \Drupal\update\ProjectSecurityData\getSecurityCoverageUntilVersion()
     */
    private function getAdditionalSecurityCoveredMinors($security_covered_version) {
        $security_covered_version_major = ModuleVersion::createFromVersionString($security_covered_version)->getMajorVersion();
        $security_covered_version_minor = $this->getSemanticMinorVersion($security_covered_version);
        foreach ($this->releases as $release) {
            $release_version = ModuleVersion::createFromVersionString($release['version']);
            if ($release_version->getMajorVersion() === $security_covered_version_major && $release['status'] === 'published' && !$release_version->getVersionExtra()) {
                // The releases are ordered with the most recent releases first.
                // Therefore, if we have found a published, official release with the
                // same major version as $security_covered_version, then this release
                // can be used to determine the latest minor.
                $latest_minor = $this->getSemanticMinorVersion($release['version']);
                break;
            }
        }
        // If $latest_minor is set, we know that $security_covered_version_minor and
        // $latest_minor have the same major version. Therefore, we can subtract to
        // determine the number of additional minor releases with security coverage.
        return isset($latest_minor) ? $security_covered_version_minor - $latest_minor : NULL;
    }
    
    /**
     * Gets the minor version for a semantic version string.
     *
     * @param string $version
     *   The semantic version string.
     *
     * @return int
     *   The minor version as an integer.
     */
    private function getSemanticMinorVersion($version) {
        return (int) explode('.', $version)[1];
    }

}