<?php
/**
 * Moves a try-on request through its lifecycle: claim, generate, store, finish.
 *
 * @package Fitzaro
 */

namespace Fitzaro\Job;

use Fitzaro\Database\Status;
use Fitzaro\Provider\Provider;
use Fitzaro\Provider\Submission;
use Fitzaro\Storage\FileStore;
use Fitzaro\Storage\Uuid;

defined( 'ABSPATH' ) || exit;

/**
 * Knows nothing about WordPress: storage, providers, the queue and the clock are injected, so
 * every path (including the ones that cost money) is unit-tested.
 *
 * Money rule: attempts is incremented before submit(), and nothing ever calls submit() for a
 * request whose attempts is above zero.
 */
final class Runner {

	/**
	 * Seconds a worker owns a request before the reaper may act on it.
	 */
	public const LEASE_SECONDS = 240;

	/**
	 * Seconds between polls of an asynchronous provider.
	 */
	public const POLL_INTERVAL = 5;

	/**
	 * Requests the reaper looks at per run.
	 */
	public const REAP_BATCH = 50;

	/**
	 * Request storage.
	 *
	 * @var Requests
	 */
	private $requests;

	/**
	 * Returns the provider for an ID, or null.
	 *
	 * @var callable
	 */
	private $providers;

	/**
	 * Builds provider input.
	 *
	 * @var InputBuilder
	 */
	private $inputs;

	/**
	 * Where results are written.
	 *
	 * @var FileStore
	 */
	private $files;

	/**
	 * Background queue.
	 *
	 * @var Scheduler
	 */
	private $scheduler;

	/**
	 * Returns the current Unix time.
	 *
	 * @var callable
	 */
	private $clock;

	/**
	 * Receives ( event, request ID, error code ) after a request finishes.
	 *
	 * @var callable|null
	 */
	private $notify;

	/**
	 * Creates the runner.
	 *
	 * @param Requests      $requests  Request storage.
	 * @param callable      $providers Receives a provider ID, returns a Provider or null.
	 * @param InputBuilder  $inputs    Builds provider input.
	 * @param FileStore     $files     Where results are written.
	 * @param Scheduler     $scheduler Background queue.
	 * @param callable      $clock     Returns the current Unix time.
	 * @param callable|null $notify    Receives ( 'completed'|'failed', ID, error code ).
	 */
	public function __construct( Requests $requests, callable $providers, InputBuilder $inputs, FileStore $files, Scheduler $scheduler, callable $clock, ?callable $notify = null ) {
		$this->requests  = $requests;
		$this->providers = $providers;
		$this->inputs    = $inputs;
		$this->files     = $files;
		$this->scheduler = $scheduler;
		$this->clock     = $clock;
		$this->notify    = $notify;
	}

	/**
	 * Claims a queued request and sends it to the provider. Does nothing when it is not queued.
	 *
	 * @param string $id Request UUID.
	 */
	public function run( string $id ): void {
		$row = $this->requests->find( $id );
		if ( null === $row ) {
			return;
		}

		$token = Uuid::v4();
		$now   = $this->now();
		if ( ! $this->requests->claim( $id, $token, $this->time( $now + self::LEASE_SECONDS ), $this->time( $now ) ) ) {
			return;
		}

		$provider = $this->provider( $row );
		if ( null === $provider ) {
			$this->fail( $id, JobError::NO_PROVIDER );
			return;
		}

		try {
			$input = $this->inputs->build( $row );
		} catch ( InputUnavailable $e ) {
			$this->fail( $id, $e->reason() );
			return;
		} catch ( \Throwable $e ) {
			$this->fail( $id, JobError::INTERNAL );
			return;
		}

		if ( ! $this->requests->mark_sent( $id, $token ) ) {
			return;
		}

		try {
			$submission = $provider->submit( $input );
		} catch ( \Throwable $e ) {
			// The message may contain request details or a key fragment; only the code is kept.
			$this->fail( $id, JobError::INTERNAL );
			return;
		}

		$this->settle( $id, $token, $submission );
	}

	/**
	 * Asks the provider about an asynchronous request. Does nothing unless it is waiting on one.
	 *
	 * @param string $id Request UUID.
	 */
	public function poll( string $id ): void {
		$row = $this->requests->find( $id );
		if ( null === $row || Status::RUNNING !== $row['status'] || '' === (string) ( $row['remote_id'] ?? '' ) ) {
			return;
		}

		$now = $this->now();
		if ( $now - LeasePolicy::timestamp( $row['created_at'] ?? null, $now ) > LeasePolicy::MAX_AGE ) {
			$this->fail( $id, JobError::TIMEOUT );
			return;
		}

		$token = (string) $row['claim_token'];
		if ( ! $this->requests->extend_lease( $id, $token, $this->time( $now + self::LEASE_SECONDS ) ) ) {
			return;
		}

		$provider = $this->provider( $row );
		if ( null === $provider ) {
			$this->fail( $id, JobError::NO_PROVIDER );
			return;
		}

		try {
			$submission = $provider->poll( (string) $row['remote_id'] );
		} catch ( \Throwable $e ) {
			$this->fail( $id, JobError::INTERNAL );
			return;
		}

		$this->settle( $id, $token, $submission );
	}

	/**
	 * Recovers requests whose worker died, using LeasePolicy.
	 *
	 * @param int $limit Requests to look at.
	 */
	public function reap( int $limit = self::REAP_BATCH ): void {
		$now = $this->now();

		foreach ( $this->requests->unfinished( $limit ) as $row ) {
			$id = (string) $row['id'];

			switch ( LeasePolicy::decide( $row, $now ) ) {
				case LeasePolicy::REQUEUE:
					if ( $this->requests->requeue( $id ) ) {
						$this->scheduler->run_now( $id );
					}
					break;

				case LeasePolicy::REPOLL:
					if ( $this->requests->extend_lease( $id, (string) $row['claim_token'], $this->time( $now + self::LEASE_SECONDS ) ) ) {
						$this->scheduler->poll_later( $id, 0 );
					}
					break;

				case LeasePolicy::FAIL_TIMEOUT:
					$this->fail( $id, JobError::TIMEOUT );
					break;

				case LeasePolicy::FAIL_NOT_STARTED:
					$this->fail( $id, JobError::NOT_STARTED );
					break;
			}
		}
	}

	/**
	 * Acts on what the provider answered.
	 *
	 * @param string     $id         Request UUID.
	 * @param string     $token      Claim token.
	 * @param Submission $submission Provider answer.
	 */
	private function settle( string $id, string $token, Submission $submission ): void {
		if ( $submission->is_pending() ) {
			$lease = $this->time( $this->now() + self::LEASE_SECONDS );
			if ( $this->requests->set_pending( $id, $token, (string) $submission->remote_id(), $lease ) ) {
				$this->scheduler->poll_later( $id, self::POLL_INTERVAL );
			}
			return;
		}

		if ( ! $submission->is_done() ) {
			$this->fail( $id, $submission->error()->code() );
			return;
		}

		try {
			$path = $this->files->put( FileStore::RESULTS, (string) $submission->image() );
		} catch ( \Throwable $e ) {
			$this->requests->record_cost( $id, $submission->model(), $submission->cost() );
			$this->fail( $id, JobError::INTERNAL );
			return;
		}

		$completed = $this->requests->complete( $id, $token, $path, $submission->model(), $submission->cost(), $this->time( $this->now() ) );
		if ( ! $completed ) {
			// Cancelled or reaped meanwhile: nobody will ever be shown this file, but the provider still charged.
			$this->files->delete( $path );
			$this->requests->record_cost( $id, $submission->model(), $submission->cost() );
			return;
		}

		$this->emit( 'completed', $id, '' );
	}

	/**
	 * Fails a request and reports it when the change applied.
	 *
	 * @param string $id   Request UUID.
	 * @param string $code Error code.
	 */
	private function fail( string $id, string $code ): void {
		if ( $this->requests->fail( $id, $code, $this->time( $this->now() ) ) ) {
			$this->emit( 'failed', $id, $code );
		}
	}

	/**
	 * Provider for a row, or null.
	 *
	 * @param array<string, mixed> $row Request row.
	 */
	private function provider( array $row ): ?Provider {
		$provider = ( $this->providers )( (string) ( $row['provider'] ?? '' ) );

		return $provider instanceof Provider ? $provider : null;
	}

	/**
	 * Reports an event.
	 *
	 * @param string $event 'completed' or 'failed'.
	 * @param string $id    Request UUID.
	 * @param string $code  Error code, empty when completed.
	 */
	private function emit( string $event, string $id, string $code ): void {
		if ( null !== $this->notify ) {
			( $this->notify )( $event, $id, $code );
		}
	}

	/**
	 * Current Unix time.
	 */
	private function now(): int {
		return (int) ( $this->clock )();
	}

	/**
	 * UTC MySQL datetime for a Unix time.
	 *
	 * @param int $timestamp Unix time.
	 */
	private function time( int $timestamp ): string {
		return gmdate( 'Y-m-d H:i:s', $timestamp );
	}
}