From ddad857015508f30b064e44cd2bf55de6dc6c425 Mon Sep 17 00:00:00 2001
From: Egor fureunoir Gorbunov <contact@fureunoir.com>
Date: Tue, 17 Jun 2025 09:54:03 +0300
Subject: [PATCH] Features: 1) Implement marketological rounding method to
 handle psychological pricing; 2) Enhance rounding logic to consider price
 magnitude using logarithmic calculation;

Fixes: None;

Extra: 1) Update import to include `log10` from `math`; 2) Add detailed docstring explaining marketological rounding method logic.
---
 core/vendors/__init__.py | 36 +++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

diff --git a/core/vendors/__init__.py b/core/vendors/__init__.py
index 8e35dec6..3ae2ec56 100644
--- a/core/vendors/__init__.py
+++ b/core/vendors/__init__.py
@@ -1,6 +1,6 @@
 import json
 from contextlib import suppress
-from math import ceil
+from math import ceil, log10
 
 from django.db import IntegrityError
 
@@ -174,10 +174,36 @@ class AbstractVendor:
 
     @staticmethod
     def round_price_marketologically(price: float) -> float:
-        up_int = ceil(price)
-        s = str(up_int)
-        s = (s[:-1] if len(s) > 1 else "0") + "9"
-        return float(f"{int(s):.2f}")
+        """
+        Marketological rounding with no cents:
+
+        - Prices < 1: leave exactly as-is.
+        - Prices ≥ 1: drop any fractional part, then
+          bump to the next 'psychological' threshold
+          at the correct order of magnitude and subtract 1.
+
+        E.g.  2.34 → 2 → 3 – 1 = 2
+             12.34 → 12 → 13 – 1 = 12
+            123.45 → 123 → 130 – 1 = 129
+        """
+        if price < 1:
+            # sub-currency prices stay as they are
+            return round(price, 2)
+
+        # strip off any cents
+        whole = int(price)
+
+        # figure out the magnitude:
+        # 10**0 = 1 for [1–9], 10**1 = 10 for [10–99], 10**2 = 100 for [100–999], etc.
+        magnitude = 10 ** max(int(log10(whole)) - 1, 0)
+
+        # next multiple of that magnitude
+        next_threshold = ceil(whole / magnitude) * magnitude
+
+        # step back 1 to land on a “9” ending
+        psychological = next_threshold - 1
+
+        return float(psychological)
 
     def get_vendor_instance(self):
         try: