Fea: add decimal support to currency system with ISO 4217 data integration (#976)

* feat: add decimal support to currency system with ISO 4217 data integration

* Harden currency formatting: add decimal bounds, input validation, and robust error handling

* Fixed issues raised by coderrabitai

* Fixed linting issue

.github/scripts/update_currencies.py

@@ -1,16 +1,33 @@
 #!/usr/bin/env python3
+import csv
+import io
 import json
 import logging
+import os
 import sys
 from pathlib import Path
 
 import requests
-from requests.adapters import HTTPAdapter, Retry
+from requests.adapters import HTTPAdapter
+from urllib3.util.retry import Retry
 
 API_URL    = 'https://restcountries.com/v3.1/all?fields=name,common,currencies'
+# Default to a pinned commit for supply-chain security
+DEFAULT_ISO_4217_URL = 'https://raw.githubusercontent.com/datasets/currency-codes/052b3088938ba32028a14e75040c286c5e142145/data/codes-all.csv'
+ISO_4217_URL = os.environ.get('ISO_4217_URL', DEFAULT_ISO_4217_URL)
 SAVE_PATH  = Path('backend/internal/core/currencies/currencies.json')
 TIMEOUT    = 10  # seconds
 
+# Known currency decimal overrides
+CURRENCY_DECIMAL_OVERRIDES = {
+    "BTC": 8,  # Bitcoin uses 8 decimal places
+    "JPY": 0,  # Japanese Yen has no decimal places
+    "BHD": 3,  # Bahraini Dinar uses 3 decimal places
+}
+DEFAULT_DECIMALS = 2
+MIN_DECIMALS = 0
+MAX_DECIMALS = 6
+
 
 def setup_logging():
     logging.basicConfig(
@@ -19,7 +36,93 @@ def setup_logging():
     )
 
 
+def get_currency_decimals(code, iso_data):
+    """
+    Get the decimal places for a currency code.
+    Checks overrides first, then ISO data, then uses default.
+    Clamps result to safe range [MIN_DECIMALS, MAX_DECIMALS].
+    """
+    # Normalize the input code
+    normalized_code = (code or "").strip().upper()
+    
+    # First check overrides
+    if normalized_code in CURRENCY_DECIMAL_OVERRIDES:
+        decimals = CURRENCY_DECIMAL_OVERRIDES[normalized_code]
+    # Then check ISO data
+    elif normalized_code in iso_data:
+        decimals = iso_data[normalized_code]
+    # Finally use default
+    else:
+        decimals = DEFAULT_DECIMALS
+    
+    # Ensure it's an integer and clamp to safe range
+    try:
+        decimals = int(decimals)
+    except (ValueError, TypeError):
+        decimals = DEFAULT_DECIMALS
+    
+    return max(MIN_DECIMALS, min(MAX_DECIMALS, decimals))
+
+
+def fetch_iso_4217_data():
+    """
+    Fetch ISO 4217 currency data to get minor units (decimal places).
+    Returns a dict mapping currency code to minor units.
+    """
+    # Log the resolved URL for transparency
+    logging.info("Fetching ISO 4217 data from: %s", ISO_4217_URL)
+    if not ISO_4217_URL.lower().startswith("https://"):
+        logging.error("Refusing non-HTTPS ISO_4217_URL: %s", ISO_4217_URL)
+        return {}
+    
+    session = requests.Session()
+    retries = Retry(
+        total=3,
+        backoff_factor=1,
+        status_forcelist=[429, 500, 502, 503, 504],
+        allowed_methods=frozenset(['GET'])
+    )
+    session.mount('https://', HTTPAdapter(max_retries=retries))
+
+    try:
+        # Add Accept header for CSV content
+        headers = {'Accept': 'text/csv'}
+        resp = session.get(ISO_4217_URL, timeout=TIMEOUT, headers=headers)
+        resp.raise_for_status()
+    except requests.exceptions.RequestException as e:
+        logging.error("Failed to fetch ISO 4217 data: %s", e)
+        return {}
+
+    # Parse CSV data
+    iso_data = {}
+    try:
+        # Decode with utf-8-sig to strip BOM if present
+        csv_content = resp.content.decode('utf-8-sig')
+        csv_reader = csv.DictReader(io.StringIO(csv_content))
+        
+        for row in csv_reader:
+            code = row.get('AlphabeticCode', '').strip()
+            minor_unit = row.get('MinorUnit', '').strip()
+            
+            if code and minor_unit != 'N.A.':
+                try:
+                    # Convert minor unit to int (decimal places)
+                    iso_data[code] = int(minor_unit) if minor_unit.isdigit() else 2
+                except (ValueError, TypeError):
+                    iso_data[code] = 2  # Default to 2 if parsing fails
+                    
+        logging.info("Successfully loaded decimal data for %d currencies from ISO 4217", len(iso_data))
+        return iso_data
+        
+    except Exception as e:
+        logging.error("Failed to parse ISO 4217 CSV data: %s", e)
+        return {}
+
+
 def fetch_currencies():
+    # First, fetch ISO 4217 data for decimal places
+    iso_data = fetch_iso_4217_data()
+    
     session = requests.Session()
     retries = Retry(
         total=3,
@@ -46,11 +149,15 @@ def fetch_currencies():
     for country in countries:
         country_name = country.get('name', {}).get('common') or "Unknown"
         for code, info in country.get('currencies', {}).items():
+            # Get decimal places using the helper function
+            decimals = get_currency_decimals(code, iso_data)
+            
             results.append({
-                'code':   code,
-                'local':  country_name,
-                'symbol': info.get('symbol', ''),
-                'name':   info.get('name', '')
+                'code':     code,
+                'local':    country_name,
+                'symbol':   info.get('symbol', ''),
+                'name':     info.get('name', ''),
+                'decimals': decimals
             })
 
     # sort by country name for consistency