<?php

namespace App\Services\Mne;

use Illuminate\Support\Facades\DB;
use Ramsey\Uuid\Uuid;

final class CompatibilityBackfill
{
    /** @return array<string, int> */
    public function run(int $batchSize = 100): array
    {
        $counts = [];
        foreach (['identity' => ['users', 'identity_links', 'user_id'], 'sector' => ['sectors', 'sector_links', 'sector_id'],
            'business' => ['existing_businesses', 'business_links', 'legacy_business_id']] as $domain => [$source, $target, $key]) {
            // Start again on each invocation to detect edits behind a previous checkpoint.
            $last = null;
            $processed = 0;
            do {
                $batch = DB::transaction(function () use ($domain, $source, $target, $key, $last, $processed, $batchSize) {
                    DB::select('SELECT pg_advisory_xact_lock(290926,170004)');
                    $query = DB::table('public.'.$source)->orderBy('id')->limit($batchSize)->lockForUpdate();
                    if ($last !== null) {
                        $query->where('id', '>', $last);
                    }
                    $rows = $query->get();
                    $checksums = [];
                    foreach ($rows as $row) {
                        $checksum = hash('sha256', json_encode((array) $row, JSON_THROW_ON_ERROR));
                        $checksums[] = $checksum;
                        $stableId = (string) Uuid::uuid5(Uuid::NAMESPACE_URL, 'investmoz:'.$domain.':'.$row->id);
                        $data = ['id' => $stableId, $key => $row->id, 'source_system' => 'public.'.$source,
                            'source_checksum' => $checksum, 'status' => 'pending'];
                        if ($domain === 'sector') {
                            $data['canonical_sector_id'] = $stableId;
                            $data['source_code'] = $row->slug;
                            $data['status'] = $row->is_active && $row->deleted_at === null ? 'active' : 'pending';
                        }
                        $existing = DB::table('mne.'.$target)->where($key, $row->id)->first();
                        if (! $existing) {
                            DB::table('mne.'.$target)->insert($data);
                        } elseif ($existing->source_checksum !== $checksum) {
                            // Changed sources invalidate previous reconciliation; never activate by inference.
                            DB::table('mne.'.$target)->where($key, $row->id)->update(['source_checksum' => $checksum, 'status' => 'pending']);
                        }
                        if ($domain !== 'sector' && (! $existing || $existing->status !== 'active' || $existing->source_checksum !== $checksum)) {
                            DB::table('mne.compatibility_rejections')->upsert([[
                                'id' => $stableId, 'domain' => $domain, 'source_key' => (string) $row->id,
                                'code' => 'CANONICAL_MAPPING_REQUIRED', 'cause' => 'Explicit canonical mapping and reconciliation required',
                                'resolved_at' => null, 'resolution' => null,
                            ]], ['domain', 'source_key', 'code'], ['cause', 'resolved_at', 'resolution']);
                        }
                    }
                    if ($rows->isNotEmpty() || $processed === 0) {
                        DB::table('mne.compatibility_checkpoints')->updateOrInsert(['domain' => $domain], [
                            'last_key' => $rows->isEmpty() ? $last : (string) $rows->last()->id,
                            'processed' => $processed + $rows->count(), 'checksum' => hash('sha256', implode('', $checksums)), 'updated_at' => now(),
                        ]);
                    }

                    return $rows;
                });
                $processed += $batch->count();
                if ($batch->isNotEmpty()) {
                    $last = $batch->last()->id;
                }
            } while ($batch->count() === $batchSize);
            $counts[$domain] = $processed;
        }

        return $counts;
    }
}