<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Conversation extends Model
{
    public function participants()
    {
        return $this->belongsToMany(User::class, 'conversation_participants')
            ->withPivot('last_read_at');
    }

    public function messages()
    {
        return $this->hasMany(Message::class)->orderBy('created_at');
    }

    public function lastMessage()
    {
        return $this->hasOne(Message::class)->latestOfMany('created_at');
    }

    public function unreadCountFor(int $userId): int
    {
        $pivot = $this->participants->firstWhere('id', $userId)?->pivot;
        $lastRead = $pivot?->last_read_at;

        $q = $this->messages()->where('user_id', '!=', $userId);
        if ($lastRead) {
            $q->where('created_at', '>', $lastRead);
        }
        return $q->count();
    }

    // Find existing DM between two users or return null
    public static function between(int $a, int $b): ?self
    {
        return self::whereHas('participants', fn($q) => $q->where('user_id', $a))
            ->whereHas('participants', fn($q) => $q->where('user_id', $b))
            ->whereHas('participants', fn($q) => $q->havingRaw('COUNT(*) = 2'), null, null, fn($q) => $q->select(\DB::raw('COUNT(*)')))
            ->first();
    }
}