<?php

declare(strict_types=1);

namespace OCA\WorkflowDeckAutomation\Service;

use OCA\Deck\Db\Card;
use OCA\WorkflowDeckAutomation\Db\Workflow;
use OCA\WorkflowDeckAutomation\Db\WorkflowMapper;
use OCP\AppFramework\Utility\ITimeFactory;
use OCP\Files\IRootFolder;
use OCP\IUser;
use OCP\IUserManager;
use OCP\IUserSession;
use Psr\Log\LoggerInterface;
use Throwable;

/**
 * Evaluates all enabled workflows and moves overdue cards.
 *
 * Deck's permission checks read the *live* user session, not a value
 * frozen at construction, and this runner has to evaluate rules for many
 * different users within a single background-job process. So workflows
 * are grouped by owner and, for each owner, we temporarily impersonate
 * that user (push their IUser onto the session, restore afterwards) —
 * the standard Nextcloud pattern for multi-user cron jobs.
 */
class WorkflowRunner {
	public const TARGET_BOARD = 'board';
	public const TARGET_SOURCE_STACK = 'sourceStack';
	public const TARGET_TARGET_STACK = 'targetStack';

	private ?IUser $impersonationRestore = null;

	public function __construct(
		private WorkflowMapper $workflowMapper,
		private DeckIntegrationService $deckService,
		private NotificationMailer $mailer,
		private IUserManager $userManager,
		private IUserSession $userSession,
		private IRootFolder $rootFolder,
		private ITimeFactory $timeFactory,
		private LoggerInterface $logger,
	) {
	}

	public function run(): void {
		$workflows = $this->workflowMapper->findAllEnabled();
		if ($workflows === []) {
			return;
		}

		$byUser = [];
		foreach ($workflows as $workflow) {
			$byUser[$workflow->getUserId()][] = $workflow;
		}

		foreach ($byUser as $userId => $userWorkflows) {
			// Nothing may escape this loop. Job::start() calls setLastRun()
			// *before* run() and only clears `reserved_at` afterwards via
			// setExecutionTime(), which is not in a finally — so a single
			// uncaught throwable leaves the job reserved, and JobList::getNext()
			// then skips it until the reservation is 12 hours stale. One bad
			// workflow would silently take the whole app offline for half a day.
			try {
				$this->runForUser((string)$userId, $userWorkflows);
			} catch (Throwable $e) {
				$this->logger->error('Workflow run failed for {user}: ' . $e->getMessage(), [
					'app' => 'workflow_deck_automation',
					'user' => $userId,
					'exception' => $e,
				]);
			}
		}
	}

	/**
	 * @param Workflow[] $workflows
	 */
	private function runForUser(string $userId, array $workflows): void {
		$user = $this->userManager->get($userId);
		if ($user === null || !$user->isEnabled()) {
			return;
		}

		try {
			$this->deckService->assertDeckAvailable($user);
		} catch (DeckUnavailableException $e) {
			$this->logger->info('Skipping workflows for {user}: ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
				'user' => $userId,
			]);
			return;
		}

		$this->impersonate($user);
		try {
			foreach ($workflows as $workflow) {
				// Same reasoning as in run(): one broken workflow must not
				// stop the user's remaining ones.
				try {
					$this->runWorkflow($user, $workflow);
				} catch (Throwable $e) {
					$this->logger->error('Workflow {id} failed: ' . $e->getMessage(), [
						'app' => 'workflow_deck_automation',
						'id' => $workflow->getId(),
						'exception' => $e,
					]);
				}
			}
		} finally {
			$this->clearImpersonation();
		}
	}

	private function runWorkflow(IUser $user, Workflow $workflow): void {
		try {
			$brokenTarget = $this->findBrokenTarget($workflow);
		} catch (DeckUnavailableException $e) {
			// Could not determine it either way — leave the workflow alone
			// rather than disabling it over a temporary Deck problem.
			$this->logger->warning('Could not verify targets of workflow {id}: ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
				'id' => $workflow->getId(),
			]);
			return;
		}

		if ($brokenTarget !== null) {
			$this->disableBrokenWorkflow($user, $workflow, $brokenTarget);
			return;
		}

		try {
			$cards = $this->deckService->getActiveCardsInStack($workflow->getSourceStackId());
		} catch (DeckUnavailableException $e) {
			$this->logger->warning('Could not read stack for workflow {id}: ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
				'id' => $workflow->getId(),
			]);
			return;
		}

		$filterUserIds = $workflow->getFilterUserIdsArray();
		$filterLabelIds = $workflow->getFilterLabelIdsArray();

		foreach ($cards as $card) {
			if (!self::isOverdue($card->getDaysUntilDue())) {
				continue;
			}

			$assignedUserIds = $this->deckService->getCardAssignedUserIds($card);
			$labelIds = $this->deckService->getCardLabelIds($card);
			if (!self::cardMatchesFilters($assignedUserIds, $labelIds, $filterUserIds, $filterLabelIds)) {
				continue;
			}

			$this->moveAndNotify($user, $workflow, $card);
		}

		$workflow->setLastRun($this->timeFactory->getDateTime());
		$this->workflowMapper->update($workflow);
	}

	/**
	 * Which of the workflow's Deck references no longer exists, if any.
	 *
	 * Deleting a board or stack leaves the workflow row untouched — there is
	 * no foreign key — and Deck keeps the orphaned cards readable until its
	 * own DeleteCron purges them, so the workflow would otherwise keep
	 * failing on every single run.
	 *
	 * @return self::TARGET_*|null
	 * @throws DeckUnavailableException if Deck could not be asked
	 */
	private function findBrokenTarget(Workflow $workflow): ?string {
		$stackIds = $this->deckService->findStackIds($workflow->getBoardId());
		if ($stackIds === null) {
			return self::TARGET_BOARD;
		}

		if (!in_array($workflow->getSourceStackId(), $stackIds, true)) {
			return self::TARGET_SOURCE_STACK;
		}
		if (!in_array($workflow->getTargetStackId(), $stackIds, true)) {
			return self::TARGET_TARGET_STACK;
		}

		return null;
	}

	/**
	 * @param self::TARGET_* $brokenTarget
	 */
	private function disableBrokenWorkflow(IUser $user, Workflow $workflow, string $brokenTarget): void {
		$workflow->setEnabled(false);
		$workflow->setLastRun($this->timeFactory->getDateTime());
		$this->workflowMapper->update($workflow);

		$this->logger->warning('Disabled workflow {id}: its {target} no longer exists', [
			'app' => 'workflow_deck_automation',
			'id' => $workflow->getId(),
			'target' => $brokenTarget,
		]);

		// Sent regardless of the workflow's notifyEmail setting: that flag is
		// about moved cards, this is a one-off notice that the automation the
		// user configured has been switched off. It stays one-off because a
		// disabled workflow is not picked up again.
		$this->mailer->sendWorkflowDisabledNotification($user, $workflow, $brokenTarget);
	}

	private function moveAndNotify(IUser $user, Workflow $workflow, Card $card): void {
		try {
			$this->deckService->moveCard($card->getId(), $workflow->getTargetStackId());
		} catch (Throwable $e) {
			$this->logger->error('Failed to move card {card} for workflow {id}: ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
				'card' => $card->getId(),
				'id' => $workflow->getId(),
			]);
			return;
		}

		if ($workflow->getNotifyEmail()) {
			$this->mailer->sendCardMovedNotification($user, $workflow, $card);
		}
	}

	public static function isOverdue(?int $daysUntilDue): bool {
		return $daysUntilDue !== null && $daysUntilDue < 0;
	}

	/**
	 * Pure filter-matching logic (kept static/side-effect free so it can
	 * be unit tested without real Deck objects). Both filters are OR
	 * inside themselves and AND between each other: an empty filter list
	 * means "no restriction on this dimension".
	 *
	 * @param string[] $cardAssignedUserIds
	 * @param int[] $cardLabelIds
	 * @param string[] $filterUserIds
	 * @param int[] $filterLabelIds
	 */
	public static function cardMatchesFilters(
		array $cardAssignedUserIds,
		array $cardLabelIds,
		array $filterUserIds,
		array $filterLabelIds,
	): bool {
		if ($filterUserIds !== [] && array_intersect($filterUserIds, $cardAssignedUserIds) === []) {
			return false;
		}
		if ($filterLabelIds !== [] && array_intersect($filterLabelIds, $cardLabelIds) === []) {
			return false;
		}
		return true;
	}

	private function impersonate(IUser $user): void {
		$this->impersonationRestore = $this->userSession->getUser();
		$this->userSession->setUser($user);
		try {
			// Best-effort filesystem setup; some Deck-internal helpers
			// (attachments, activity) expect an initialised user FS.
			$this->rootFolder->getUserFolder($user->getUID());
		} catch (Throwable $e) {
			$this->logger->debug('Filesystem setup failed for ' . $user->getUID() . ': ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
			]);
		}
	}

	private function clearImpersonation(): void {
		$this->userSession->setUser($this->impersonationRestore);
		$this->impersonationRestore = null;
	}
}