<?php

declare(strict_types=1);

namespace OCA\WorkflowDeckAutomation\Service;

use DateTimeImmutable;
use DateTimeInterface;
use DateTimeZone;
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.
 *
 * This runner has to evaluate rules for many different users within a
 * single background-job process, so workflows are grouped by owner and
 * each owner is impersonated in turn. Impersonation here means two
 * things, and the second one is the load-bearing half: pushing the IUser
 * onto the session (the standard Nextcloud cron pattern), *and* pinning
 * Deck itself to that user via
 * DeckIntegrationService::beginUserContext(), because Deck's permission
 * checks never consult the session — they read a uid frozen once per
 * process. Both are undone in a finally.
 */
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 = [];
		$owners = [];
		foreach ($workflows as $workflow) {
			$this->followBoardOwner($workflow, $owners);
			$byUser[$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,
				]);
			}
		}
	}

	/**
	 * A workflow belongs to its board's owner, not to whoever created it: if
	 * Deck transferred the board, the workflow moves along to the new owner —
	 * it then runs as them, and they get its mails.
	 *
	 * Only a known owner rewrites `user_id`. A board that is gone keeps its
	 * last owner, so findBrokenTarget() can disable the workflow and mail
	 * them; a Deck error keeps it too, and the run just goes ahead as before.
	 *
	 * @param array<int, ?string> $owners per-run cache, board id => owner
	 */
	private function followBoardOwner(Workflow $workflow, array &$owners): void {
		$boardId = $workflow->getBoardId();
		if (!array_key_exists($boardId, $owners)) {
			try {
				$owners[$boardId] = $this->deckService->findBoardOwner($boardId);
			} catch (Throwable $e) {
				$this->logger->warning('Could not determine the owner of board {board}: ' . $e->getMessage(), [
					'app' => 'workflow_deck_automation',
					'board' => $boardId,
				]);
				$owners[$boardId] = null;
			}
		}

		$owner = $owners[$boardId];
		if ($owner === null || $owner === $workflow->getUserId()) {
			return;
		}

		$this->logger->info('Workflow {id} follows board {board} to its new owner {owner}.', [
			'app' => 'workflow_deck_automation',
			'id' => $workflow->getId(),
			'board' => $boardId,
			'owner' => $owner,
		]);
		$workflow->setUserId($owner);
		try {
			$this->workflowMapper->update($workflow);
		} catch (Throwable $e) {
			// Not persisted, but this run still goes to the right user; the
			// next one tries again.
			$this->logger->warning('Could not store the new owner of workflow {id}: ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
				'id' => $workflow->getId(),
			]);
		}
	}

	/**
	 * @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;
		}

		try {
			$this->impersonate($user);
		} catch (DeckUnavailableException $e) {
			// Deck could not be pinned to this user, so every permission
			// check would be answered for somebody else. Skipping costs one
			// run; continuing would move the wrong cards or, worse, read a
			// denial as "the board is gone" and disable a working workflow.
			$this->logger->error('Could not impersonate {user} towards Deck: ' . $e->getMessage(), [
				'app' => 'workflow_deck_automation',
				'user' => $userId,
			]);
			return;
		}

		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 = $this->findBrokenTarget($user, $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;
		}

		// Resolved at most once per run, and only if a card actually moves
		// and the workflow wants a mail — this is decoration, not a check.
		$targets = null;

		$now = $this->timeFactory->getDateTime();

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

			$this->logger->info('Card {card} ("{title}") matches workflow {id}; moving to stack {target}.', [
				'app' => 'workflow_deck_automation',
				'card' => $card->getId(),
				'title' => $card->getTitle(),
				'id' => $workflow->getId(),
				'target' => $workflow->getTargetStackId(),
			]);

			if (!$this->moveCard($workflow, $card)) {
				continue;
			}

			if ($workflow->getNotifyEmail()) {
				$targets ??= $this->deckService->describeTargets(
					$workflow->getBoardId(),
					$workflow->getSourceStackId(),
					$workflow->getTargetStackId(),
				);
				$this->mailer->sendCardMovedNotification($user, $workflow, $card, $targets);
			}
		}

		$workflow->setLastRun($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(IUser $user, Workflow $workflow): ?string {
		$stackIds = $this->deckService->findStackIds($workflow->getBoardId(), $user->getUID());
		if ($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 moveCard(Workflow $workflow, Card $card): bool {
		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 false;
		}

		$this->logger->info('Moved card {card} ("{title}") to stack {target} for workflow {id}.', [
			'app' => 'workflow_deck_automation',
			'card' => $card->getId(),
			'title' => $card->getTitle(),
			'target' => $workflow->getTargetStackId(),
			'id' => $workflow->getId(),
		]);

		return true;
	}

	/**
	 * Compares the card's actual due timestamp against $now instead of Deck's own
	 * Card::getDaysUntilDue(), which truncates both sides to midnight before diffing
	 * (DateInterval's %a is a whole-day count) and therefore reports 0 - not overdue -
	 * for any card whose due time has already passed today. That silently held back
	 * every card for up to 24h after it actually fell due; comparing the raw datetime
	 * instead matches what Deck's own UI shows (e.g. "vor 2 Stunden") and has no
	 * day-rounding step to get wrong.
	 *
	 * Both sides are compared as absolute instants, and the due date is first
	 * pinned to UTC via asStoredUtc() — see there for why.
	 */
	public static function isOverdue(?DateTimeInterface $duedate, DateTimeInterface $now): bool {
		return $duedate !== null && self::asStoredUtc($duedate) < $now;
	}

	/**
	 * Deck's `duedate` is a DATETIME column without a zone that holds UTC
	 * wall-clock time: Deck's frontend sends `toISOString()`, and the value is
	 * written as plain `Y-m-d H:i:s`. Entity hydrates it with
	 * `new \DateTime($string)`, i.e. in PHP's *default* timezone — correct only
	 * because Nextcloud sets that default to UTC during bootstrap. Reading the
	 * wall clock and pinning it to UTC explicitly makes the comparison
	 * independent of that default, so a server or CLI running with a local
	 * default zone cannot shift every due date by its UTC offset.
	 *
	 * Deck itself has two timezone-sensitive paths this deliberately avoids:
	 * Card::getDaysUntilDue() (day-truncated, see isOverdue()) and
	 * CardMapper::findOverdue(), which compares the UTC column against the
	 * database's `NOW()` — the DB session's local time.
	 */
	private static function asStoredUtc(DateTimeInterface $duedate): DateTimeImmutable {
		return new DateTimeImmutable($duedate->format('Y-m-d H:i:s.u'), new DateTimeZone('UTC'));
	}

	/**
	 * @throws DeckUnavailableException if Deck cannot be pinned to $user
	 */
	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',
			]);
		}

		try {
			// The session switch above is necessary but nowhere near
			// sufficient — Deck's permission checks never look at it. See
			// DeckIntegrationService::beginUserContext().
			$this->deckService->beginUserContext($user);
		} catch (DeckUnavailableException $e) {
			$this->clearImpersonation();
			throw $e;
		}
	}

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