<?php

namespace App\Services;

use App\Exceptions\ConsultantTransferException;
use App\Models\Customer;
use App\Models\ShoppingUser;
use App\Models\ShoppingUserMemberLog;
use App\Models\UserAbo;
use App\Models\UserCleanUpLog;
use App\User;
use Illuminate\Database\Eloquent\Builder;
use Illuminate\Database\Eloquent\Collection;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\Log;

/**
 * Überträgt den kompletten Berater- und Kundenstamm eines Beraters (Quelle)
 * auf einen anderen Berater (Ziel), z. B. wenn ein Berater aufhört
 * (Ticket dev/_tickets/2026-09-08.md, #1).
 *
 * Übertragen werden:
 * - die Firstline (users.m_sponsor = Quelle) — die darunter liegenden Teilbäume
 *   folgen automatisch, da sie an ihrer Firstline hängen
 * - geparkte Sponsor-Bezüge deaktivierter Berater (users.pre_sponsor = Quelle),
 *   damit eine spätere Reaktivierung unter dem Zielberater landet
 * - alle Kunden-Datensätze (shopping_users.member_id = Quelle, auch soft-deleted)
 * - alle Kunden-Abos (user_abos.member_id = Quelle), damit künftige Abo-Bestellungen
 *   dem Zielberater zugeordnet werden
 * - Portal-Logins der Kunden (customers.member_id = Quelle)
 *
 * Bewusst NICHT übertragen werden bestehende Bestellungen (shopping_orders.member_id)
 * und Umsatz-/Provisionsdaten: Sie sind Historie und bleiben beim ursprünglichen Berater.
 *
 * Jede Umhängung wird wie bei der automatischen User-Bereinigung protokolliert
 * (UserCleanUpLog, ShoppingUserMemberLog), sodass sie in der User-Bereinigung
 * unter "Downline-Übertragungen" / "Kunden-Übertragungen" nachvollziehbar ist.
 */
class ConsultantTransferService
{
    public const SYSLOG_ACTION = 'consultant-transfer';

    /**
     * Vorschau: Was würde bei einer Übertragung von $source bewegt?
     *
     * @return array{
     *     firstline: Collection<int, User>,
     *     firstline_count: int,
     *     downline_count: int,
     *     pre_sponsor_count: int,
     *     customers_count: int,
     *     customers_deleted_count: int,
     *     abos_count: int,
     *     abos_active_count: int,
     *     portal_customers_count: int
     * }
     */
    public function preview(User $source): array
    {
        $firstline = $this->firstlineQuery($source)->with('account')->orderBy('email')->get();
        $customers = ShoppingUser::withTrashed()->where('member_id', $source->id);
        $abos = UserAbo::withTrashed()->where('member_id', $source->id);

        return [
            'firstline' => $firstline,
            'firstline_count' => $firstline->count(),
            'downline_count' => count($this->downlineUserIds($source)),
            'pre_sponsor_count' => $this->preSponsorQuery($source)->count(),
            'customers_count' => (clone $customers)->count(),
            'customers_deleted_count' => (clone $customers)->whereNotNull('deleted_at')->count(),
            'abos_count' => (clone $abos)->count(),
            'abos_active_count' => (clone $abos)->where('active', true)->count(),
            'portal_customers_count' => Customer::where('member_id', $source->id)->count(),
        ];
    }

    /**
     * Prüft, ob eine Übertragung von $source auf $target zulässig ist.
     *
     * Ein Zielberater unterhalb der Firstline der Quelle würde einen Zyklus
     * erzeugen (seine eigene Upline würde unter ihn gehängt) und wird abgelehnt.
     * Ein Zielberater direkt in der Firstline ist erlaubt: Er behält seinen
     * eigenen Sponsor und bekommt die übrigen Firstline-Berater als Downline.
     *
     * @throws ConsultantTransferException
     */
    public function assertTransferable(User $source, User $target): void
    {
        if ($source->id === $target->id) {
            throw new ConsultantTransferException(__('msg.transfer_error_same_user'));
        }

        if ($target->deleted_at || ! $target->active || $target->blocked || ! $target->isActiveAccount()) {
            throw new ConsultantTransferException(__('msg.transfer_error_target_inactive'));
        }

        $isDirectChild = (int) $target->m_sponsor === (int) $source->id;
        if (! $isDirectChild && in_array($target->id, $this->downlineUserIds($source), true)) {
            throw new ConsultantTransferException(__('msg.transfer_error_target_in_downline'));
        }
    }

    /**
     * Übertragung ausführen.
     *
     * @return array<string, int> Zusammenfassung der bewegten Datensätze
     *
     * @throws ConsultantTransferException
     */
    public function transfer(User $source, User $target, ?int $executedByUserId = null): array
    {
        $this->assertTransferable($source, $target);

        $summary = DB::transaction(function () use ($source, $target): array {
            return [
                'firstline' => $this->transferFirstline($source, $target),
                'pre_sponsor' => $this->transferPreSponsor($source, $target),
                'customers' => $this->transferCustomers($source, $target),
                'abos' => UserAbo::withTrashed()->where('member_id', $source->id)->update(['member_id' => $target->id]),
                'portal_customers' => Customer::where('member_id', $source->id)->update(['member_id' => $target->id]),
            ];
        });

        $this->logTransfer($source, $target, $executedByUserId, $summary);

        return $summary;
    }

    /**
     * IDs aller Berater unterhalb von $source (alle Ebenen, inkl. soft-deleted).
     *
     * @return array<int, int>
     */
    public function downlineUserIds(User $source): array
    {
        $ids = [];
        $visited = [$source->id => true];
        $frontier = [$source->id];

        while ($frontier !== []) {
            $children = User::withTrashed()
                ->whereIn('m_sponsor', $frontier)
                ->whereColumn('id', '!=', 'm_sponsor')
                ->pluck('id');

            $frontier = [];
            foreach ($children as $childId) {
                $childId = (int) $childId;
                if (isset($visited[$childId])) {
                    continue;
                }
                $visited[$childId] = true;
                $ids[] = $childId;
                $frontier[] = $childId;
            }
        }

        return $ids;
    }

    protected function transferFirstline(User $source, User $target): int
    {
        $count = 0;
        foreach ($this->firstlineQuery($source)->where('id', '!=', $target->id)->get() as $child) {
            UserCleanUpLog::create([
                'inactive_sponsor_id' => $source->id,
                'child_user_id' => $child->id,
                'new_sponsor_id' => $target->id,
            ]);
            $child->m_sponsor = $target->id;
            $child->save();
            $count++;
        }

        return $count;
    }

    protected function transferPreSponsor(User $source, User $target): int
    {
        $count = 0;
        foreach ($this->preSponsorQuery($source)->where('id', '!=', $target->id)->get() as $parked) {
            UserCleanUpLog::create([
                'inactive_sponsor_id' => $source->id,
                'child_user_id' => $parked->id,
                'new_sponsor_id' => $target->id,
            ]);
            $parked->pre_sponsor = $target->id;
            $parked->save();
            $count++;
        }

        return $count;
    }

    protected function transferCustomers(User $source, User $target): int
    {
        $count = 0;
        foreach (ShoppingUser::withTrashed()->where('member_id', $source->id)->get() as $customer) {
            ShoppingUserMemberLog::create([
                'pre_member_id' => $source->id,
                'shopping_user_id' => $customer->id,
                'new_member_id' => $target->id,
            ]);
            $customer->member_id = $target->id;
            $customer->save();
            $count++;
        }

        return $count;
    }

    /**
     * @return Builder<User>
     */
    protected function firstlineQuery(User $source)
    {
        return User::withTrashed()
            ->where('m_sponsor', $source->id)
            ->where('id', '!=', $source->id);
    }

    /**
     * @return Builder<User>
     */
    protected function preSponsorQuery(User $source)
    {
        return User::withTrashed()
            ->where('pre_sponsor', $source->id)
            ->where('id', '!=', $source->id);
    }

    /**
     * @param  array<string, int>  $summary
     */
    protected function logTransfer(User $source, User $target, ?int $executedByUserId, array $summary): void
    {
        $message = 'Berater-Stamm übertragen von '.$source->email.' (#'.$source->id.') an '.$target->email.' (#'.$target->id.'). Umfang: '.json_encode($summary);

        SysLog::action(self::SYSLOG_ACTION, 'cleanup', 3)
            ->setUserId($executedByUserId)
            ->setModel($source->id, User::class)
            ->setMessage($message)
            ->save();

        Log::channel('cleanup')->info(self::SYSLOG_ACTION.': '.$message.' | by_admin='.($executedByUserId ?? 'system'));
    }
}