feat: add referral

app/Models/User.php

@@ -18,6 +18,12 @@ class User extends Authenticatable
         'male' => 1,
         'female' => 2,
     ];
+
+    // Referral program (کد معرف)
+    const REFERRAL_POINTS_PER_INVITE = 100;   // points granted to the referrer per successful invite
+    const REFERRAL_SHARE = 0.10;              // referrer keeps 10% of each friend's earned xp, forever
+    const REFERRAL_SUBSCRIPTION_TARGET = 10;  // successful invites needed for the free-month milestone
+
     /**
      * The attributes that are mass assignable.
      *
@@ -69,6 +75,32 @@ public function otpTokens()
         return $this->hasMany(OtpTokens::class);
     }
 
+    public function referrer()
+    {
+        return $this->belongsTo(User::class, 'referred_by');
+    }
+
+    public function referrals()
+    {
+        return $this->hasMany(User::class, 'referred_by');
+    }
+
+    /**
+     * Award xp to this user and, if they were referred, credit the
+     * referrer their permanent 10% share of the earned points.
+     */
+    public function awardXp(int $amount): void
+    {
+        $this->increment('xp', $amount);
+
+        if ($this->referred_by) {
+            $share = (int) floor($amount * self::REFERRAL_SHARE);
+            if ($share > 0) {
+                self::where('id', $this->referred_by)->increment('referral_points', $share);
+            }
+        }
+    }
+
     public function transactions()
     {
         return $this->hasMany(Transaction::class);