<?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;

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 Dynamic.
     */
    public function getDynamicActivities(Dynamic $dynamic): array
    {
        $activities = [];

        // 1. Chat Messages
        if ($dynamic->chat) {
            $messages = Message::where('chat_id', $dynamic->chat->id)
                ->with('user')
                ->get();

            foreach ($messages as $msg) {
                $activities[] = [
                    'id' => "dynamic_msg_{$msg->id}",
                    'type' => 'message',
                    'description' => $msg->content,
                    'user' => [
                        'name' => $msg->user ? $msg->user->name : 'Unknown User',
                    ],
                    'created_at' => $msg->created_at,
                ];
            }
        }

        // 2. Ledgers Created
        $ledgers = Ledger::where('dynamic_id', $dynamic->id)->get();
        foreach ($ledgers as $ledger) {
            $activities[] = [
                'id' => "ledger_created_{$ledger->id}",
                'type' => 'ledger_created',
                'description' => "New Ledger '{$ledger->name}' was created.",
                'user' => [
                    'name' => 'System',
                ],
                'created_at' => $ledger->created_at,
            ];
        }

        // Sort activities chronologically ascending
        usort($activities, fn($a, $b) => $a['created_at']->timestamp <=> $b['created_at']->timestamp);

        return $activities;
    }

    /**
     * Retrieve all activities for a Ledger.
     */
    public function getLedgerActivities(Ledger $ledger): array
    {
        $activities = [];

        // 1. Mutations (Creation and Status updates)
        $mutations = Mutation::where('ledger_id', $ledger->id)
            ->with('user')
            ->get();

        foreach ($mutations as $mutation) {
            // Log creation of mutation
            $verb = $mutation->type === 'penalty' ? 'issued demerit' : ($mutation->type === 'reward' ? 'credited points' : 'submitted entry');
            $activities[] = [
                'id' => "mutation_created_{$mutation->id}",
                'type' => 'mutation_created',
                'description' => "{$verb} ({$mutation->amount}): \"{$mutation->description}\"",
                'user' => [
                    'name' => $mutation->user ? $mutation->user->name : 'Unknown User',
                ],
                'created_at' => $mutation->created_at,
            ];

            // Log status approval/rejection update if different from creation
            if ($mutation->status !== 'pending' && $mutation->updated_at->gt($mutation->created_at->addSeconds(2))) {
                $activities[] = [
                    'id' => "mutation_updated_{$mutation->id}",
                    'type' => 'mutation_updated',
                    'description' => "Entry '{$mutation->description}' was " . strtoupper($mutation->status),
                    'user' => [
                        'name' => 'System',
                    ],
                    'created_at' => $mutation->updated_at,
                ];
            }
        }

        // 2. Mutation Comments
        if ($mutations->isNotEmpty()) {
            $comments = Message::whereHas('chat', function ($q) use ($mutations) {
                $q->where('chatable_type', Mutation::class)
                  ->whereIn('chatable_id', $mutations->pluck('id'));
            })
            ->with(['user', 'chat.chatable'])
            ->get();

            foreach ($comments as $comment) {
                /** @var Mutation|null $mutationEntity */
                $mutationEntity = $comment->chat->chatable;
                $context = $mutationEntity ? " on \"{$mutationEntity->description}\"" : "";
                
                $activities[] = [
                    'id' => "comment_{$comment->id}",
                    'type' => 'comment',
                    'description' => "Commented{$context}: \"{$comment->content}\"",
                    'user' => [
                        'name' => $comment->user ? $comment->user->name : 'Unknown User',
                    ],
                    'created_at' => $comment->created_at,
                ];
            }
        }

        // Sort activities chronologically ascending
        usort($activities, fn($a, $b) => $a['created_at']->timestamp <=> $b['created_at']->timestamp);

        return $activities;
    }

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

        // 1. Get all participating Dynamics
        $dynamics = $user->dynamics()->get();

        foreach ($dynamics as $dynamic) {
            $readAt = $this->getCursorReadAt($user, $dynamic);
            $activities = $this->getDynamicActivities($dynamic);

            $this->partitionActivities($activities, $readAt, $dynamic, 'Dynamic', route('dynamics.show', $dynamic->id), $groupedEntities);
        }

        // 2. Get all Ledgers under those Dynamics
        if ($dynamics->isNotEmpty()) {
            $ledgers = Ledger::whereIn('dynamic_id', $dynamics->pluck('id'))->get();

            foreach ($ledgers as $ledger) {
                $readAt = $this->getCursorReadAt($user, $ledger);
                $activities = $this->getLedgerActivities($ledger);

                $this->partitionActivities($activities, $readAt, $ledger, 'Ledger', route('dynamics.ledgers.show', [$ledger->dynamic_id, $ledger->id]), $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 $act) {
            if ($act['created_at']->gt($readAt)) {
                $unread[] = $act;
            } else {
                $alreadyRead[] = $act;
            }
        }

        if (!empty($unread)) {
            // We have unread activity! Let's pull the last two read items as context
            $context = array_slice($alreadyRead, -2);

            // Format timestamps for serializing to frontend
            $formatActivity = function ($act) {
                $act['created_at'] = $act['created_at']->toIso8601String();
                return $act;
            };

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