<?php

namespace App\Services;

use App\Models\User;
use App\Models\Dynamic;
use App\Models\Ledger;
use App\Models\Mutation;
use App\Models\Message;
use App\Models\ReadCursor;
use Illuminate\Support\Carbon;
use Illuminate\Support\Str;

class ActivityService
{
    /**
     * Update the read cursor for a user on a specific entity.
     */
    public function updateCursor(User $user, $entity): void
    {
        ReadCursor::updateOrCreate(
            [
                'user_id' => $user->id,
                'cursorable_id' => $entity->id,
                'cursorable_type' => get_class($entity),
            ],
            [
                'read_at' => Carbon::now(),
            ]
        );
    }

    /**
     * Get the read cursor timestamp for a user on a specific entity.
     */
    public function getCursorReadAt(User $user, $entity): \Carbon\CarbonInterface
    {
        $cursor = ReadCursor::where([
            'user_id' => $user->id,
            'cursorable_id' => $entity->id,
            'cursorable_type' => get_class($entity),
        ])->first();

        // If no cursor exists, default to epoch (all activities are unread)
        return $cursor ? $cursor->read_at : Carbon::parse('1970-01-01');
    }

    /**
     * Retrieve all activities for a given entity.
     */
    public function getActivitiesForEntity($entity): array
    {
        if ($entity instanceof Dynamic) {
            $chatId = $entity->chat->id;
        } elseif ($entity instanceof Ledger) {
            $chatId = $entity->dynamic->chat->id;
        } else {
            return [];
        }

        $messages = Message::where('chat_id', $chatId)
            ->with(['user', 'subject'])
            ->latest()
            ->get();

        return $messages->map(function ($message) {
            $messageData = $message->toArray();
            $messageData['url'] = $this->getUrlForMessage($message);
            return $messageData;
        })->all();
    }

    /**
     * Get unread activities grouped by active entities (Dynamics, Ledgers) for the given user.
     */
    public function getUnreadEntitiesGrouped(User $user): array
    {
        $groupedEntities = [];
        $participatingDynamics = $user->dynamics()->with('ledgers')->get();

        $entities = $participatingDynamics->concat($participatingDynamics->flatMap(fn ($d) => $d->ledgers));

        foreach ($entities as $entity) {
            $readAt = $this->getCursorReadAt($user, $entity);
            $activities = $this->getActivitiesForEntity($entity);

            $this->partitionActivities($activities, $readAt, $entity, get_class($entity), $this->getUrlForEntity($entity), $groupedEntities);
        }

        return $groupedEntities;
    }

    /**
     * Partition activities into read and unread, and construct the grouped entity metadata.
     */
    private function partitionActivities(array $activities, \Carbon\CarbonInterface $readAt, $entity, string $type, string $url, array &$groupedEntities): void
    {
        $alreadyRead = [];
        $unread = [];

        foreach ($activities as $act) {
            if (Carbon::parse($act['created_at'])->gt($readAt)) {
                $unread[] = $act;
            } else {
                $alreadyRead[] = $act;
            }
        }

        if (!empty($unread)) {
            $context = array_slice($alreadyRead, 0, 2);

            $groupedEntities[] = [
                'id' => $entity->id,
                'name' => $entity->name,
                'type' => Str::afterLast($type, '\\'),
                'url' => $url,
                'unread_count' => count($unread),
                'context_activities' => $context,
                'new_activities' => $unread,
            ];
        }
    }

    private function getUrlForEntity($entity): string
    {
        if ($entity instanceof Dynamic) {
            return route('dynamics.show', $entity->id);
        }

        if ($entity instanceof Ledger) {
            return route('dynamics.ledgers.show', [$entity->dynamic_id, $entity->id]);
        }

        return '';
    }

    private function getUrlForMessage(Message $message): string
    {
        if ($message->subject) {
            return $this->getUrlForEntity($message->subject);
        }

        if ($message->chat->chatable) {
            return $this->getUrlForEntity($message->chat->chatable);
        }

        return '';
    }
}