<?php
declare(strict_types=1);

namespace Unsupervised\Schedular\Guardian;

use Unsupervised\Schedular\Auth\RoleManager;
use Unsupervised\Schedular\Auth\UserName;
use Unsupervised\Schedular\Booking\BookingRepository;
use Unsupervised\Schedular\GroupClass\EnrollmentRepository;
use Unsupervised\Schedular\Val;

/**
 * Everything a guardian does on a child's behalf: creating the child's
 * login-less account, deciding who may act for whom, and resolving the payer and
 * contact behind a student id.
 */
class GuardianService {

	/**
	 * Marks a `wp_users` row as a child account: created by a guardian, holding
	 * the student role so every `student_id` lookup keeps working, but with no
	 * usable login. {@see ChildLoginGate} enforces the "no login" half.
	 */
	public const META_CHILD = 'us_child';

	/** A child's birth year (`YYYY`), collected at signup and editable after. */
	public const META_BIRTH_YEAR = 'us_birth_year';

	/**
	 * The full date of birth this feature used to collect. Nothing writes it any
	 * more: it is read once, to derive a birth year for a child who predates the
	 * change, and cleared the moment that child's record is next saved. Kept
	 * public so a site that wants to purge the old dates outright can find them.
	 */
	public const META_DOB = 'us_date_of_birth';

	/**
	 * The earliest birth year the form will accept. Old enough for any student a
	 * studio will ever enrol, and late enough to reject a typo like `19` or `190`
	 * that would otherwise be stored as a plausible-looking year.
	 */
	private const MIN_BIRTH_YEAR = 1900;

	/**
	 * Domain used for a child's placeholder login address. `.invalid` is reserved
	 * by RFC 2606 and can never resolve, so a child's address is guaranteed
	 * undeliverable — nothing about a child's account can ever be emailed to
	 * somewhere real by mistake.
	 */
	private const CHILD_EMAIL_DOMAIN = 'child.invalid';

	public function __construct(
		private GuardianRepository $guardians,
		private BookingRepository $bookings,
		private EnrollmentRepository $enrollments,
	) {}

	/**
	 * Create a login-less child account and link it to its guardian. The password
	 * is random and discarded — it is never stored anywhere readable, emailed, or
	 * shown — so the account cannot be signed into even if the gate were removed.
	 *
	 * Returns the new user ID, or a `WP_Error` when the name is blank, the birth
	 * year is missing or unusable, or WordPress refuses the insert.
	 */
	public function createChild( int $guardianId, string $name, string $birthYear = '', string $relationship = '' ): int|\WP_Error {
		$name = trim( $name );
		if ( '' === $name ) {
			return new \WP_Error( 'missing_name', __( 'Please give each student a name.', 'unsupervised-schedular' ) );
		}

		if ( 0 === self::normaliseBirthYear( $birthYear ) ) {
			return new \WP_Error( 'missing_birth_year', self::birthYearError() );
		}

		$email  = $this->childEmail();
		$userId = wp_insert_user(
			[
				'user_login'   => $email,
				'user_email'   => $email,
				'user_pass'    => wp_generate_password( 24, true, true ),
				'display_name' => $name,
				'nickname'     => $name,
				'role'         => RoleManager::STUDENT,
			]
		);

		if ( is_wp_error( $userId ) ) {
			return $userId;
		}

		$userId = (int) $userId;

		update_user_meta( $userId, self::META_CHILD, '1' );
		$this->setBirthYear( $userId, $birthYear );

		$linkId = $this->guardians->insert(
			new GuardianLink(
				guardianId:   $guardianId,
				studentId:    $userId,
				relationship: trim( $relationship ),
			)
		);

		// The child was just created, so it cannot already be linked — a failure
		// here means the insert itself failed, and leaving an unreachable orphan
		// user behind would be worse than reporting it.
		if ( $linkId <= 0 ) {
			$this->deleteUser( $userId );

			return new \WP_Error( 'link_failed', __( 'Could not add this student. Please contact the studio.', 'unsupervised-schedular' ) );
		}

		return $userId;
	}

	/**
	 * Rename a child and update their birth year. Refuses a student the caller
	 * is not the guardian of, so the family screen cannot be turned into an
	 * arbitrary user editor by posting someone else's id.
	 *
	 * Returns null on success, mirroring {@see \Unsupervised\Schedular\Registration\RegistrationGate::validate()}.
	 */
	public function updateChild( int $guardianId, int $studentId, string $name, string $birthYear = '' ): ?\WP_Error {
		if ( ! $this->guardians->isGuardianOf( $guardianId, $studentId ) ) {
			return new \WP_Error( 'forbidden', __( 'That is not one of your students.', 'unsupervised-schedular' ) );
		}

		$name = trim( $name );
		if ( '' === $name ) {
			return new \WP_Error( 'missing_name', __( 'Please give each student a name.', 'unsupervised-schedular' ) );
		}

		if ( 0 === self::normaliseBirthYear( $birthYear ) ) {
			return new \WP_Error( 'missing_birth_year', self::birthYearError() );
		}

		$result = wp_update_user(
			[
				'ID'           => $studentId,
				'display_name' => $name,
				'nickname'     => $name,
			]
		);

		if ( is_wp_error( $result ) ) {
			return $result;
		}

		$this->setBirthYear( $studentId, $birthYear );

		return null;
	}

	/**
	 * Unlink a child and delete their account. Refused once the child has any
	 * lesson or enrolment history: their id is referenced by lessons, payments and
	 * credits, and deleting the user would orphan all of it. A studio admin
	 * handles those cases by hand.
	 *
	 * Returns null on success.
	 */
	public function removeChild( int $guardianId, int $studentId ): ?\WP_Error {
		if ( ! $this->guardians->isGuardianOf( $guardianId, $studentId ) ) {
			return new \WP_Error( 'forbidden', __( 'That is not one of your students.', 'unsupervised-schedular' ) );
		}

		if ( [] !== $this->bookings->findByStudent( $studentId ) || [] !== $this->enrollments->findByStudent( $studentId ) ) {
			return new \WP_Error(
				'has_history',
				__( 'This student has lessons or enrolments on record and cannot be removed here. Please contact the studio.', 'unsupervised-schedular' )
			);
		}

		$this->guardians->delete( $guardianId, $studentId );
		$this->deleteUser( $studentId );

		return null;
	}

	/**
	 * Whether `$actorId` may book, cancel and pay as `$studentId` — true for
	 * themselves, and for a guardian acting as one of their own children. This is
	 * the authorisation boundary the REST endpoints and form handlers check before
	 * honouring a submitted student id.
	 */
	public function canActFor( int $actorId, int $studentId ): bool {
		if ( $actorId <= 0 || $studentId <= 0 ) {
			return false;
		}

		return $actorId === $studentId || $this->guardians->isGuardianOf( $actorId, $studentId );
	}

	/**
	 * Who owes a student's charges: their guardian when they have one, otherwise
	 * themselves. Payments, credits and the billing-method override all resolve
	 * through this, so a family shares one balance and one billing setting.
	 */
	public function payerFor( int $studentId ): int {
		$link = $this->guardians->findByStudent( $studentId );

		return null !== $link ? $link->guardianId : $studentId;
	}

	/**
	 * The student ids whose lessons `$userId` may see: their own plus every child
	 * they are guardian for.
	 *
	 * @return list<int>
	 */
	public function householdIds( int $userId ): array {
		$ids = [ $userId ];

		foreach ( $this->guardians->findByGuardian( $userId ) as $link ) {
			$ids[] = $link->studentId;
		}

		return array_values( array_unique( $ids ) );
	}

	/**
	 * The people a user may book or enrol for: **children first**, then
	 * themselves. The order is the point — a guardian's normal case is booking for
	 * a child, so the first option (and hence the default selection) is a child,
	 * never the parent. Booking for a child by mistake is a correctable
	 * inconvenience; silently billing a parent's account for a lesson meant for
	 * their kid is the error worth designing out.
	 *
	 * The guardian is still offered, last, so a parent taking lessons alongside
	 * their children can book for themselves from the same account.
	 *
	 * @return list<array{id: int, name: string, is_self: bool}>
	 */
	public function bookableStudents( int $userId ): array {
		$out = [];

		foreach ( $this->children( $userId ) as $child ) {
			$out[] = [
				'id'      => $child['id'],
				'name'    => $child['name'],
				'is_self' => false,
			];
		}

		$self = get_userdata( $userId );

		$out[] = [
			'id'      => $userId,
			'name'    => UserName::format( $self instanceof \WP_User ? $self : null, $userId ),
			'is_self' => true,
		];

		return $out;
	}

	/**
	 * A guardian's children, in link order, with the details the family and admin
	 * screens display.
	 *
	 * @return list<array{id: int, name: string, birth_year: string, relationship: string}>
	 */
	public function children( int $guardianId ): array {
		$out = [];

		foreach ( $this->guardians->findByGuardian( $guardianId ) as $link ) {
			$user = get_userdata( $link->studentId );

			$out[] = [
				'id'           => $link->studentId,
				'name'         => UserName::format( $user instanceof \WP_User ? $user : null, $link->studentId ),
				'birth_year'   => $this->birthYear( $link->studentId ),
				'relationship' => $link->relationship,
			];
		}

		return $out;
	}

	/**
	 * The guardian behind a child, or null when the student books for themselves.
	 *
	 * @return array{id: int, name: string, email: string}|null
	 */
	public function guardianOf( int $studentId ): ?array {
		$link = $this->guardians->findByStudent( $studentId );
		if ( null === $link ) {
			return null;
		}

		$user = get_userdata( $link->guardianId );

		return [
			'id'    => $link->guardianId,
			'name'  => UserName::format( $user instanceof \WP_User ? $user : null, $link->guardianId ),
			'email' => $user instanceof \WP_User ? $user->user_email : '',
		];
	}

	/**
	 * Who to contact about a student: their guardian when they have one, otherwise
	 * the student. What an instructor looking at a child's lesson actually needs —
	 * a child's own address is an undeliverable placeholder.
	 *
	 * @return array{id: int, name: string, email: string}
	 */
	public function contactFor( int $studentId ): array {
		$guardian = $this->guardianOf( $studentId );
		if ( null !== $guardian ) {
			return $guardian;
		}

		$user = get_userdata( $studentId );

		return [
			'id'    => $studentId,
			'name'  => UserName::format( $user instanceof \WP_User ? $user : null, $studentId ),
			'email' => $user instanceof \WP_User ? $user->user_email : '',
		];
	}

	/**
	 * A student's display name, or an empty string when the user is gone. Used
	 * wherever a charge or lesson has to say whose it is.
	 */
	public function studentName( int $studentId ): string {
		$user = get_userdata( $studentId );

		return UserName::format( $user instanceof \WP_User ? $user : null );
	}

	/**
	 * Whether a user is a child account (created by a guardian, cannot sign in).
	 */
	public static function isChild( int $userId ): bool {
		return '1' === Val::string( get_user_meta( $userId, self::META_CHILD, true ) );
	}

	/**
	 * Delete a child's user account. Split out so the front-end paths pull in the
	 * admin user functions `wp_delete_user()` lives in — it is not loaded on the
	 * front end, where the family screen runs.
	 */
	public function deleteUser( int $userId ): void {
		if ( ! function_exists( 'wp_delete_user' ) ) {
			require_once ABSPATH . 'wp-admin/includes/user.php';
		}

		wp_delete_user( $userId );
	}

	/**
	 * Store a child's birth year, or clear it when blank or out of range.
	 *
	 * Either way the legacy full date of birth goes with it. That is what makes
	 * the read fallback in {@see birthYear()} safe: without it, clearing the year
	 * on a child who predates this change would leave the old date behind for the
	 * fallback to resurrect on the very next read.
	 */
	private function setBirthYear( int $userId, string $birthYear ): void {
		delete_user_meta( $userId, self::META_DOB );

		$year = self::normaliseBirthYear( $birthYear );

		if ( 0 === $year ) {
			delete_user_meta( $userId, self::META_BIRTH_YEAR );
			return;
		}

		update_user_meta( $userId, self::META_BIRTH_YEAR, (string) $year );
	}

	/**
	 * A submitted birth year as an integer, or 0 when it is blank, not a number,
	 * or outside {@see MIN_BIRTH_YEAR}..this year. A year in the future is a typo
	 * every time, so it is refused rather than stored.
	 *
	 * Public and static so the signup form can reject a bad year up front, before
	 * it creates any users, without a second copy of the rule to keep in step.
	 */
	public static function normaliseBirthYear( string $birthYear ): int {
		$birthYear = trim( $birthYear );

		if ( '' === $birthYear || 1 !== preg_match( '/^\d{4}$/', $birthYear ) ) {
			return 0;
		}

		$year = (int) $birthYear;

		if ( $year < self::MIN_BIRTH_YEAR || $year > (int) current_time( 'Y' ) ) {
			return 0;
		}

		return $year;
	}

	/**
	 * The message shown when a birth year is missing or unusable. One phrasing,
	 * shared by the signup form and the profile screen, so a guardian is told the
	 * same thing whichever way they got there.
	 */
	public static function birthYearError(): string {
		return sprintf(
			/* translators: %d: the earliest birth year the form accepts. */
			__( 'Please give each student a birth year, as four digits from %d onwards.', 'unsupervised-schedular' ),
			self::MIN_BIRTH_YEAR
		);
	}

	/**
	 * A child's birth year, or an empty string when none is recorded.
	 *
	 * Falls back to the year of the full date of birth this feature used to
	 * collect, so a child added before the change still shows one. The fallback
	 * is read-only and one-way: {@see setBirthYear()} drops the old date as soon
	 * as the record is saved again.
	 */
	private function birthYear( int $userId ): string {
		$year = Val::string( get_user_meta( $userId, self::META_BIRTH_YEAR, true ) );
		if ( '' !== $year ) {
			return $year;
		}

		$legacy = Val::string( get_user_meta( $userId, self::META_DOB, true ) );

		return 1 === preg_match( '/^(\d{4})-/', $legacy, $m ) ? $m[1] : '';
	}

	/**
	 * An unused placeholder address for a child's account. WordPress requires a
	 * unique email per user, so the random suffix is retried against
	 * `email_exists()` rather than assumed unique.
	 */
	private function childEmail(): string {
		do {
			$email = 'us-child-' . wp_generate_password( 12, false, false ) . '@' . self::CHILD_EMAIL_DOMAIN;
		} while ( false !== email_exists( $email ) );

		return strtolower( $email );
	}
}