<?php
declare(strict_types=1);

namespace App\Services;

/** Pure watch-v1 measurement rules. This measures playback evidence, not attention. */
final class WatchIntervalPolicy
{
    public static function evaluate(
        string $previousType,
        string $eventType,
        int $previousPositionMs,
        int $positionMs,
        int $serverDeltaSeconds,
        int $durationMs,
        string $fundingSource
    ): array {
        if ($eventType !== 'heartbeat' || !in_array($previousType, ['start', 'heartbeat', 'resume'], true)) {
            return ['seconds' => 0, 'status' => 'excluded', 'reason' => 'non_contiguous_event'];
        }
        if ($fundingSource === 'none') {
            return ['seconds' => 0, 'status' => 'excluded', 'reason' => 'unfunded_session'];
        }
        if ($durationMs <= 0 || $positionMs > $durationMs) {
            return ['seconds' => 0, 'status' => 'review', 'reason' => 'position_out_of_bounds'];
        }
        $clientDeltaMs = $positionMs - $previousPositionMs;
        if ($clientDeltaMs < 1000 || $clientDeltaMs > 90000 || $serverDeltaSeconds < 1 || $serverDeltaSeconds > 90) {
            return ['seconds' => 0, 'status' => 'review', 'reason' => 'implausible_delta'];
        }
        $seconds = min((int)floor($clientDeltaMs / 1000), $serverDeltaSeconds, 60);
        if ($seconds <= 0) return ['seconds' => 0, 'status' => 'excluded', 'reason' => 'zero_interval'];
        return ['seconds' => $seconds, 'status' => 'measured', 'reason' => 'contiguous_heartbeat'];
    }
}