<?php

declare(strict_types=1);

namespace LinkCheckup\Features\Scanning;

use LinkCheckup\Shared\Scan\ScanPhase;
use LinkCheckup\Shared\Scan\ScanRunState;
use LinkCheckup\Shared\Scan\ScanState;
use LinkCheckup\Shared\Settings\Settings;
use LinkCheckup\Shared\Time\IsoTime;

use function max;

/**
 * @phpstan-type ScanSummary array{
 *     state: string,
 *     phase: string|null,
 *     done: int,
 *     total: int,
 *     eta_seconds: int|null,
 *     parallel: int,
 *     finished_at: string|null,
 *     posts_count: int
 * }
 */
final class ScanProgress {

	public const PARALLEL_CHECKS = 1;

	public function __construct(
		private CheckedPosts $checked_posts,
		private ScanLinks $scan_links,
		private IsoTime $iso_time
	) {
	}

	/** @return ScanSummary */
	public function describe(
		ScanState $state,
		Settings $settings,
		int $now
	): array {
		$scan_count  = $this->progress_of( $state, $settings );
		$finished_at = $this->iso_time->from_timestamp( $state->finished_at );

		return array(
			'state'       => $state->run_state->value,
			'phase'       => $state->phase?->value,
			'done'        => $scan_count->done,
			'total'       => $scan_count->total,
			'eta_seconds' => $this->eta_seconds( $state, $scan_count, $now ),
			'parallel'    => self::PARALLEL_CHECKS,
			'finished_at' => $finished_at,
			'posts_count' => $state->posts_count,
		);
	}

	private function progress_of(
		ScanState $state,
		Settings $settings
	): ScanCount {
		if ( ScanRunState::Idle === $state->run_state ) {
			return new ScanCount( 0, 0 );
		}

		if ( ScanPhase::Reading === $state->phase ) {
			return new ScanCount(
				$state->posts_read,
				$this->checked_posts->total( $settings )
			);
		}

		return new ScanCount(
			$this->scan_links->settled_since( (int) $state->started_at ),
			$this->scan_links->listed_total()
		);
	}

	private function eta_seconds(
		ScanState $state,
		ScanCount $scan_count,
		int $now
	): int|null {
		$is_running = ScanRunState::Running === $state->run_state;

		if ( ! $is_running || 0 === $scan_count->done ) {
			return null;
		}

		$remaining     = max( 0, $scan_count->total - $scan_count->done );
		$spent_seconds = max( 0, $now - (int) $state->started_at );
		$seconds       = $remaining * $spent_seconds / $scan_count->done;

		return (int) ceil( $seconds );
	}
}