<?php

declare(strict_types=1);

namespace App\Services\Baselines;

use App\Services\Drift\DriftHasher;

/**
 * Computes the snapshot_identity_hash for baseline snapshot content dedupe.
 *
 * The identity hash is a sha256 over normalized snapshot items, enabling
 * detection of "nothing changed" when capturing the same inventory state.
 */
final class BaselineSnapshotIdentity
{
    public function __construct(
        private readonly DriftHasher $hasher,
        private readonly InventoryMetaContract $metaContract,
    ) {}

    /**
     * Compute identity hash over a set of snapshot items.
     *
     * Each item is represented as an associative array with:
     * - policy_type, subject_key, baseline_hash
     *
     * @param  array<int, array{policy_type: string, subject_key: ?string, baseline_hash: string}>  $items
     */
    public function computeIdentity(array $items): string
    {
        if ($items === []) {
            return hash('sha256', '[]');
        }

        $normalized = array_map(
            fn (array $item): string => implode('|', [
                trim((string) ($item['policy_type'] ?? '')),
                trim((string) ($item['subject_key'] ?? '')),
                trim((string) ($item['baseline_hash'] ?? '')),
            ]),
            $items,
        );

        sort($normalized, SORT_STRING);

        return hash('sha256', implode("\n", $normalized));
    }

    /**
     * Compute a stable content hash for a single inventory item's metadata.
     *
     * Hashes ONLY the Spec 116 meta contract output (not the full meta_jsonb payload).
     *
     * @param  array<string, mixed>  $metaJsonb
     */
    public function hashItemContent(string $policyType, string $subjectExternalId, array $metaJsonb): string
    {
        $contract = $this->metaContract->build(
            policyType: $policyType,
            subjectExternalId: $subjectExternalId,
            metaJsonb: $metaJsonb,
        );

        return $this->hasher->hashNormalized($contract);
    }
}