<?php
declare(strict_types=1);

namespace App\Services;

/** Structural coverage gate. Content accuracy still requires academic review. */
final class VideoCoverageValidator
{
    public static function valid(array $coverage, int $durationSeconds, string $videoSha256): bool
    {
        if ($durationSeconds <= 0 || $durationSeconds > 4 * 60 * 60 ||
            !preg_match('/^[0-9a-f]{64}$/i', $videoSha256) ||
            !hash_equals(strtolower($videoSha256), strtolower((string)($coverage['video_sha256'] ?? ''))) ||
            ($coverage['truncated'] ?? true) !== false ||
            !empty($coverage['gaps']) ||
            !is_array($coverage['segments'] ?? null) || $coverage['segments'] === []) {
            return false;
        }
        $lastEnd = 0.0;
        foreach ($coverage['segments'] as $segment) {
            if (!is_array($segment) ||
                !is_numeric($segment['start_seconds'] ?? null) ||
                !is_numeric($segment['end_seconds'] ?? null) ||
                !is_string($segment['transcript_ref'] ?? null) || trim($segment['transcript_ref']) === '' ||
                !is_string($segment['visual_ref'] ?? null) || trim($segment['visual_ref']) === '') {
                return false;
            }
            $start = (float)$segment['start_seconds'];
            $end = (float)$segment['end_seconds'];
            if (!is_finite($start) || !is_finite($end) ||
                abs($start - $lastEnd) > 0.5 || $end <= $start || $end > $durationSeconds + 0.5) {
                return false;
            }
            $lastEnd = $end;
        }
        return abs($lastEnd - $durationSeconds) <= 0.5;
    }
}