<?php

declare(strict_types=1);

namespace OCA\WorkflowDeckAutomation\Service;

use OCA\Deck\Db\AssignmentMapper;
use OCA\Deck\Db\BoardMapper;
use OCA\Deck\Db\Card;
use OCA\Deck\Db\CardMapper;
use OCA\Deck\Db\StackMapper;
use OCA\Deck\Service\BoardService;
use OCA\Deck\Service\CardService;
use OCA\Deck\Service\PermissionService;
use OCA\Deck\Service\StackService;
use OCP\App\IAppManager;
use OCP\AppFramework\Db\DoesNotExistException;
use OCP\IConfig;
use OCP\IUser;
use OCP\Server;
use Psr\Log\LoggerInterface;
use ReflectionProperty;
use Throwable;

/**
 * Single choke point for everything this app does with Deck.
 *
 * Deck's OCA\Deck\* classes are not a documented/stable public API (no
 * @since markers, no <public> declaration in its info.xml). We use them
 * directly anyway, per explicit product requirement (no HTTP/OCS calls
 * against Deck are allowed), but every resolution and call is guarded so a
 * Deck-side change degrades a single workflow instead of crashing the
 * whole background run.
 */
class DeckIntegrationService {
	private const DECK_APP_ID = 'deck';

	/**
	 * Deck's Acl::PERMISSION_READ, inlined so a moved or renamed constant
	 * cannot fatal this class. It is the key under which
	 * PermissionService::getPermissions() reports read access.
	 */
	private const ACL_PERMISSION_READ = 0;

	/**
	 * The property through which Deck carries "the current user" — a plain
	 * string frozen at construction rather than a session lookup. See
	 * beginUserContext().
	 */
	private const IDENTITY_PROPERTY = 'userId';

	/**
	 * Further Deck classes holding that same frozen uid. Unlike
	 * PermissionService these do not decide access, only whose name ends up
	 * on an activity entry or whose unread-comment counts are computed, so
	 * failing to pin them is logged and shrugged off.
	 */
	private const OPTIONAL_IDENTITY_CLASSES = [
		CardService::class,
		BoardService::class,
		'OCA\Deck\Activity\ActivityManager',
	];

	/**
	 * @var list<array{ReflectionProperty, object, ?string}>
	 */
	private array $identityRestore = [];

	public function __construct(
		private IAppManager $appManager,
		private IConfig $config,
		private LoggerInterface $logger,
	) {
	}

	/**
	 * Pins Deck to $user until endUserContext() — mandatory before any Deck
	 * call made on behalf of someone who is not the logged-in web user.
	 *
	 * IUserSession::setUser() alone is not enough, and that is not obvious:
	 * Deck's PermissionService — the class behind *every* permission check,
	 * including the ones inside CardService::reorder() — receives the current
	 * user as `private ?string $userId`. The app container fills that from
	 * `ISession::get('user_id')` through a **shared** service, so Pimple
	 * computes it once and caches it for the rest of the process, and
	 * ServerContainer keeps the app container just as long. Whoever was
	 * active when Deck's container first built PermissionService is therefore
	 * the user every later check is evaluated against.
	 *
	 * In the background job that is never the user we are impersonating: it
	 * is `null` whenever a Deck-owned job ran earlier in the same cron pass
	 * (cron.php works through many jobs in one process), and otherwise the
	 * first workflow owner we happened to touch. `null` fails every check,
	 * which is how intact boards started reporting NoPermissionException and
	 * got their workflows switched off.
	 *
	 * Deck exposes no API for this, so the frozen value is swapped directly
	 * and put back in endUserContext(). PermissionService is required: if it
	 * cannot be pinned this throws, and the caller has to skip the user
	 * rather than run them under someone else's permissions.
	 *
	 * @throws DeckUnavailableException
	 */
	public function beginUserContext(IUser $user): void {
		if ($this->identityRestore !== []) {
			throw new DeckUnavailableException('A Deck user context is already active');
		}

		$uid = $user->getUID();

		try {
			$this->pinDeckIdentity($this->resolve(PermissionService::class), $uid);
		} catch (Throwable $e) {
			$this->endUserContext();
			throw new DeckUnavailableException(
				'Could not run Deck as ' . $uid . ': ' . $e->getMessage(),
				0,
				$e,
			);
		}

		foreach (self::OPTIONAL_IDENTITY_CLASSES as $class) {
			try {
				$this->pinDeckIdentity($this->resolve($class), $uid);
			} catch (Throwable $e) {
				$this->logger->debug('Could not pin ' . $class . ' to ' . $uid . ': ' . $e->getMessage(), [
					'app' => 'workflow_deck_automation',
				]);
			}
		}
	}

	/**
	 * Restores what beginUserContext() replaced. Idempotent, so it can be
	 * called unconditionally from a finally block.
	 */
	public function endUserContext(): void {
		foreach (array_reverse($this->identityRestore) as [$property, $service, $previous]) {
			try {
				$property->setValue($service, $previous);
			} catch (Throwable $e) {
				$this->logger->warning('Could not restore Deck identity on ' . $service::class . ': ' . $e->getMessage(), [
					'app' => 'workflow_deck_automation',
				]);
			}
		}
		$this->identityRestore = [];
	}

	private function pinDeckIdentity(object $service, string $uid): void {
		$property = new ReflectionProperty($service, self::IDENTITY_PROPERTY);
		$previous = $property->isInitialized($service) ? $property->getValue($service) : null;
		$property->setValue($service, $uid);
		$this->identityRestore[] = [$property, $service, is_string($previous) ? $previous : null];
	}

	public function assertDeckAvailable(IUser $user): void {
		if (!$this->appManager->isEnabledForUser(self::DECK_APP_ID, $user)) {
			throw new DeckUnavailableException('Deck is not enabled for user ' . $user->getUID());
		}
		if (!class_exists(CardService::class) || !class_exists(BoardService::class) || !class_exists(StackService::class)) {
			throw new DeckUnavailableException('Deck internal classes are not available');
		}
	}

	/**
	 * The boards `$userId` owns — the only boards workflows may live on, and
	 * the boards whose workflows that user sees and manages.
	 *
	 * One query: BoardMapper::findAllByOwner() is `WHERE owner = :uid`, so
	 * shared boards never come back, and as a plain QBMapper it has none of
	 * the frozen-uid state of BoardService::getUserBoards(). It does return
	 * archived and trashed boards; trashed ones are dropped here, archived
	 * ones are kept but flagged — their workflows still exist and must stay
	 * visible, they just aren't offered as a new target.
	 *
	 * Throws instead of degrading to `[]`: an empty list would read as "you
	 * own no boards" and hide every workflow the user has.
	 *
	 * @return array<int, array{id: int, title: string, archived: bool}>
	 * @throws DeckUnavailableException
	 */
	public function listOwnedBoards(string $userId): array {
		$boards = $this->call(
			fn () => $this->resolve(BoardMapper::class)->findAllByOwner($userId),
			[],
			true,
		);

		$result = [];
		foreach ($boards as $board) {
			if (method_exists($board, 'getDeletedAt') && (int)$board->getDeletedAt() > 0) {
				continue;
			}
			$id = (int)$board->getId();
			$title = $board->getTitle();
			$result[] = [
				'id' => $id,
				'title' => (is_string($title) && $title !== '') ? $title : ('#' . $id),
				'archived' => method_exists($board, 'getArchived') && (bool)$board->getArchived(),
			];
		}

		return $result;
	}

	/**
	 * @return array<int, array{id: int, title: string}>
	 */
	public function listStacks(int $boardId): array {
		$stacks = $this->call(function () use ($boardId) {
			return $this->resolve(StackService::class)->findAll($boardId);
		}, []);

		return array_map(
			static fn ($stack) => ['id' => (int)$stack->getId(), 'title' => $stack->getTitle()],
			$stacks,
		);
	}

	/**
	 * Ids of the board's stacks, for deciding whether a stored workflow still
	 * points at anything real.
	 *
	 * Returns `null` only on positive knowledge that the board is gone, in the
	 * trash, or no longer readable for `$userId`. Every other failure throws,
	 * because "Deck is broken right now" must never be mistaken for "the user
	 * deleted this board" — the caller reacts by switching the workflow off
	 * and mailing its owner.
	 *
	 * Deliberately assembled from pieces that cannot answer for the wrong
	 * user. BoardMapper and StackMapper are plain QBMappers with no user
	 * state (StackMapper::findAll() filters `deleted_at = 0` itself), and
	 * getPermissions() is handed the uid explicitly instead of falling back
	 * to PermissionService's construction-time `$userId`. Leaning on that
	 * frozen value — which is exactly what `StackService::findAll()` does
	 * internally — is what disabled workflows whose board was perfectly
	 * intact, so this must not be "simplified" back to one service call even
	 * once beginUserContext() has pinned the identity.
	 *
	 * @return int[]|null
	 * @throws DeckUnavailableException
	 */
	public function findStackIds(int $boardId, string $userId): ?array {
		try {
			$board = $this->resolve(BoardMapper::class)->find($boardId);
			if (method_exists($board, 'getDeletedAt') && (int)$board->getDeletedAt() > 0) {
				return null;
			}

			$permissions = $this->resolve(PermissionService::class)->getPermissions($boardId, $userId);
			if (!array_key_exists(self::ACL_PERMISSION_READ, $permissions)) {
				// Unknown shape: say nothing rather than something wrong.
				throw new DeckUnavailableException('Deck reported no read permission for board ' . $boardId);
			}
			if ($permissions[self::ACL_PERMISSION_READ] !== true) {
				return null;
			}

			$stacks = $this->resolve(StackMapper::class)->findAll($boardId);
		} catch (DeckUnavailableException $e) {
			throw $e;
		} catch (Throwable $e) {
			if ($this->isMissing($e)) {
				return null;
			}
			$this->logger->error('Could not list stacks of board ' . $boardId . ': ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
				'exception' => $e,
			]);
			throw new DeckUnavailableException('Deck call failed: ' . $e->getMessage(), 0, $e);
		}

		return array_map(static fn ($stack) => (int)$stack->getId(), $stacks);
	}

	/**
	 * The uid of the board's current owner — the user a workflow on that
	 * board belongs to. Workflows follow the board: when Deck transfers its
	 * ownership, they move to the new owner along with it.
	 *
	 * Read through BoardMapper, a plain QBMapper without user state, so it
	 * answers the same in a request and in cron. Trashed and archived boards
	 * still report their owner. `null` only if the board row is gone; every
	 * other failure throws, like findStackIds().
	 *
	 * @throws DeckUnavailableException
	 */
	public function findBoardOwner(int $boardId): ?string {
		try {
			$board = $this->resolve(BoardMapper::class)->find($boardId);
		} catch (DeckUnavailableException $e) {
			throw $e;
		} catch (Throwable $e) {
			if ($this->isMissing($e)) {
				return null;
			}
			throw new DeckUnavailableException('Could not read owner of board ' . $boardId . ': ' . $e->getMessage(), 0, $e);
		}

		$owner = $this->unwrapUid($board->getOwner());
		if ($owner === null) {
			throw new DeckUnavailableException('Board ' . $boardId . ' has no readable owner');
		}
		return $owner;
	}

	/**
	 * Who should hear about each of the given (moved) cards, according to
	 * every board member's own Deck notification setting for this board —
	 * the "Notifications: none / assigned cards / all cards" menu, stored as
	 * the user preference `deck` / `board:<id>:notify-due`. The decision
	 * itself is NotificationPolicy::shouldNotify(), a copy of Deck's rules.
	 *
	 * Like findStackIds(), assembled only from pieces that take the users
	 * explicitly and never consult Deck's frozen `$userId`:
	 * PermissionService::findUsers() reads the owner and ACL through mappers
	 * and expands groups and circles itself; AssignmentMapper is a plain
	 * mapper that also resolves group/circle assignments; the preference is
	 * read straight from IConfig.
	 *
	 * Throws on any failure, so the caller can log and skip the mail instead
	 * of mailing a half-resolved or wrong set of people.
	 *
	 * @param int[] $cardIds
	 * @return array<int, list<string>> card id => uids to notify
	 * @throws DeckUnavailableException
	 */
	public function findNotificationRecipients(int $boardId, array $cardIds): array {
		try {
			$board = $this->resolve(BoardMapper::class)->find($boardId, false, true);
			$owner = $this->unwrapUid($board->getOwner());
			// Deck notifies the owner of a board nobody else can see about
			// every card: "assigned" means nothing there.
			$unshared = count($board->getAcl() ?? []) === 0;

			// `true` bypasses PermissionService's per-process cache, which
			// would otherwise outlive ACL changes for the whole cron pass.
			$participants = $this->resolve(PermissionService::class)->findUsers($boardId, true);
			$assignments = $this->resolve(AssignmentMapper::class);

			$settings = [];
			foreach ($participants as $uid => $participant) {
				// Users of other instances (FederatedUser) have no local
				// account and no preference to read.
				if (!is_a($participant, 'OCA\Deck\Db\User')) {
					continue;
				}
				// Numeric uids come back as integer array keys.
				$uid = (string)$uid;
				$settings[$uid] = (string)$this->config->getUserValue(
					$uid,
					self::DECK_APP_ID,
					'board:' . $boardId . ':notify-due',
					NotificationPolicy::DECK_DEFAULT,
				);
			}

			$recipients = [];
			foreach ($cardIds as $cardId) {
				$recipients[$cardId] = [];
				foreach ($settings as $uid => $setting) {
					$uid = (string)$uid;
					$notify = NotificationPolicy::shouldNotify(
						$setting,
						$unshared && $uid === $owner,
						static fn (): bool => (bool)$assignments->isUserAssigned($cardId, $uid),
					);
					if ($notify) {
						$recipients[$cardId][] = $uid;
					}
				}
			}
		} catch (DeckUnavailableException $e) {
			throw $e;
		} catch (Throwable $e) {
			throw new DeckUnavailableException('Could not resolve notification recipients for board ' . $boardId . ': ' . $e->getMessage(), 0, $e);
		}

		return $recipients;
	}

	/**
	 * Deck's own exception classes are referenced by name: `is_a()` with a
	 * string simply returns false when the class does not exist, so a missing
	 * or renamed Deck degrades to "unknown error" instead of fataling.
	 *
	 * `OCA\Deck\NoPermissionException` is deliberately *not* treated as "the
	 * board is gone" here. It used to be, and that is what switched intact
	 * workflows off: Deck raises it for any check that fails, including every
	 * check evaluated against the wrong frozen uid — which says nothing at
	 * all about whether the board still exists.
	 */
	private function isMissing(Throwable $e): bool {
		if ($e instanceof DoesNotExistException) {
			return true;
		}
		return is_a($e, 'OCA\Deck\NotFoundException');
	}

	/**
	 * Titles of a workflow's board and stacks, for the notification mail.
	 *
	 * Best effort by design: this only decorates a mail that is being sent
	 * because a card *was* already moved, so anything unreadable degrades to
	 * `#<id>` rather than costing the user their notification.
	 *
	 * @return array{board: string, sourceStack: string, targetStack: string}
	 */
	public function describeTargets(int $boardId, int $sourceStackId, int $targetStackId): array {
		$titles = $this->call(function () use ($boardId) {
			$stackTitles = [];
			foreach ($this->resolve(StackMapper::class)->findAll($boardId) as $stack) {
				$stackTitles[(int)$stack->getId()] = (string)$stack->getTitle();
			}

			return [
				'board' => (string)$this->resolve(BoardMapper::class)->find($boardId)->getTitle(),
				'stacks' => $stackTitles,
			];
		}, ['board' => '', 'stacks' => []]);

		return [
			'board' => self::titleOr($titles['board'], $boardId),
			'sourceStack' => self::titleOr($titles['stacks'][$sourceStackId] ?? '', $sourceStackId),
			'targetStack' => self::titleOr($titles['stacks'][$targetStackId] ?? '', $targetStackId),
		];
	}

	private static function titleOr(string $title, int $id): string {
		return $title !== '' ? $title : ('#' . $id);
	}

	/**
	 * Cards in the given stack that are neither archived, deleted nor marked
	 * done.
	 *
	 * The `deletedAt` check is not redundant: Deck's
	 * `CardMapper::findAllByStack()` filters on `stack_id` and
	 * `archived = false` only, so cards sitting in the trash come back too —
	 * they are kept until Deck's own DeleteCron purges them. Without this we
	 * would move cards the user already deleted.
	 *
	 * @return Card[]
	 */
	public function getActiveCardsInStack(int $stackId): array {
		return $this->call(function () use ($stackId) {
			// Deliberately not enriched: CardService::enrichCards() only adds
			// labels, assignees and comment counts, and runs
			// BoardService::find(), a permission check against Deck's frozen
			// uid (see beginUserContext()). Assignments, where needed for
			// mails, come from findNotificationRecipients() instead.
			$cards = $this->resolve(CardMapper::class)->findAllByStack($stackId);

			return array_values(array_filter($cards, static function (Card $card) {
				if (method_exists($card, 'getDeletedAt') && (int)$card->getDeletedAt() > 0) {
					return false;
				}
				return !$card->getArchived() && $card->getDone() === null;
			}));
		}, []);
	}

	/**
	 * Moves a card to another stack using Deck's own reorder logic
	 * (the exact same code path behind Deck's "move card" action).
	 */
	public function moveCard(int $cardId, int $targetStackId): void {
		$this->call(function () use ($cardId, $targetStackId) {
			$this->resolve(CardService::class)->reorder($cardId, $targetStackId, 0);
			return null;
		}, null, true);
	}

	/**
	 * @template T
	 * @param callable(): T $callback
	 * @param T $fallback
	 * @return T
	 */
	private function call(callable $callback, mixed $fallback, bool $rethrow = false) {
		try {
			return $callback();
		} catch (DeckUnavailableException $e) {
			throw $e;
		} catch (Throwable $e) {
			$this->logger->error('Deck integration call failed: ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
				'exception' => $e,
			]);
			if ($rethrow) {
				throw new DeckUnavailableException('Deck call failed: ' . $e->getMessage(), 0, $e);
			}
			return $fallback;
		}
	}

	/**
	 * @template T of object
	 * @param class-string<T> $class
	 * @return T
	 */
	private function resolve(string $class) {
		if (!class_exists($class)) {
			throw new DeckUnavailableException("Deck class {$class} does not exist");
		}
		return Server::get($class);
	}

	/**
	 * Turns whatever Deck hands out for a "participant"/"owner" field into
	 * a plain uid.
	 *
	 * Enriched Deck entities do *not* return the raw uid string: their
	 * RelationalEntity base swaps resolved relations for a
	 * OCA\Deck\Db\RelationalObject wrapping a User/Group object, and its
	 * primary key is the uid we want. Unenriched entities still return the
	 * bare string, so both shapes are handled.
	 */
	private function unwrapUid(mixed $value): ?string {
		if (is_string($value)) {
			return $value !== '' ? $value : null;
		}
		if (!is_object($value)) {
			return null;
		}
		foreach (['getPrimaryKey', 'getUID', 'getUid', 'getId'] as $method) {
			if (method_exists($value, $method)) {
				$inner = $value->$method();
				if (is_string($inner) && $inner !== '') {
					return $inner;
				}
			}
		}
		if (method_exists($value, 'getObject')) {
			$inner = $value->getObject();
			foreach (['getUID', 'getUid', 'getId'] as $method) {
				if (is_object($inner) && method_exists($inner, $method)) {
					$uid = $inner->$method();
					if (is_string($uid) && $uid !== '') {
						return $uid;
					}
				}
			}
		}
		return null;
	}
}