| 1 | import json |
| 2 | from typing import Dict, List, Optional, Any |
| 3 | |
| 1 | 4 | class RestAPI: |
| 2 | 5 | def __init__(self, database: dict | None = None): |
| 3 | | pass |
| 4 | | |
| 6 | """ |
| 7 | Initialize the REST API with a database of users. |
| 8 | |
| 9 | Args: |
| 10 | database: A dictionary containing user data with IOUs |
| 11 | """ |
| 12 | if database is None: |
| 13 | self.database = {"users": []} |
| 14 | else: |
| 15 | self.database = database |
| 16 | |
| 5 | 17 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 18 | """ |
| 19 | Handle GET requests to the API. |
| 20 | |
| 21 | Args: |
| 22 | url: The endpoint URL |
| 23 | payload: Optional JSON payload |
| 24 | |
| 25 | Returns: |
| 26 | JSON string response |
| 27 | """ |
| 28 | if url == "/users": |
| 29 | if payload is None: |
| 30 | # Return all users |
| 31 | return json.dumps({"users": [self._format_user(user) for user in self.database["users"]]}) |
| 32 | else: |
| 33 | # Return specific users |
| 34 | data = json.loads(payload) |
| 35 | user_names = data.get("users", []) |
| 36 | |
| 37 | # Edge Case: Empty users list in payload |
| 38 | if not user_names: |
| 39 | return json.dumps({"users": []}) |
| 40 | |
| 41 | # Filter users by name and sort |
| 42 | filtered_users = [user for user in self.database["users"] if user["name"] in user_names] |
| 43 | filtered_users.sort(key=lambda x: x["name"]) |
| 44 | |
| 45 | # Edge Case: User not found |
| 46 | if len(filtered_users) != len(user_names): |
| 47 | # Some users were not found, but we still return what we have |
| 48 | pass |
| 49 | |
| 50 | return json.dumps({"users": [self._format_user(user) for user in filtered_users]}) |
| 51 | |
| 52 | # Edge Case: Invalid URL |
| 53 | return json.dumps({"error": "Invalid URL"}) |
| 54 | |
| 8 | 55 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 56 | """ |
| 57 | Handle POST requests to the API. |
| 58 | |
| 59 | Args: |
| 60 | url: The endpoint URL |
| 61 | payload: JSON payload |
| 62 | |
| 63 | Returns: |
| 64 | JSON string response |
| 65 | """ |
| 66 | if payload is None: |
| 67 | # Edge Case: Missing payload |
| 68 | return json.dumps({"error": "Payload required"}) |
| 69 | |
| 70 | try: |
| 71 | data = json.loads(payload) |
| 72 | except json.JSONDecodeError: |
| 73 | # Edge Case: Invalid JSON payload |
| 74 | return json.dumps({"error": "Invalid JSON payload"}) |
| 75 | |
| 76 | if url == "/add": |
| 77 | user_name = data.get("user") |
| 78 | |
| 79 | # Edge Case: Missing user name |
| 80 | if not user_name: |
| 81 | return json.dumps({"error": "User name required"}) |
| 82 | |
| 83 | # Check if user already exists |
| 84 | for user in self.database["users"]: |
| 85 | if user["name"] == user_name: |
| 86 | # Return existing user instead of error |
| 87 | return json.dumps(self._format_user(user)) |
| 88 | |
| 89 | # Create new user |
| 90 | new_user = { |
| 91 | "name": user_name, |
| 92 | "owes": {}, |
| 93 | "owed_by": {}, |
| 94 | "balance": 0.0 |
| 95 | } |
| 96 | self.database["users"].append(new_user) |
| 97 | |
| 98 | return json.dumps(self._format_user(new_user)) |
| 99 | |
| 100 | elif url == "/iou": |
| 101 | lender_name = data.get("lender") |
| 102 | borrower_name = data.get("borrower") |
| 103 | amount = data.get("amount") |
| 104 | |
| 105 | # Edge Case: Missing required fields |
| 106 | if not lender_name or not borrower_name or amount is None: |
| 107 | return json.dumps({"error": "Lender, borrower, and amount required"}) |
| 108 | |
| 109 | # Edge Case: Invalid amount type |
| 110 | if not isinstance(amount, (int, float)): |
| 111 | return json.dumps({"error": "Amount must be a number"}) |
| 112 | |
| 113 | # Edge Case: Negative amount |
| 114 | if amount < 0: |
| 115 | return json.dumps({"error": "Amount must be positive"}) |
| 116 | |
| 117 | # Edge Case: Lender and borrower are the same |
| 118 | if lender_name == borrower_name: |
| 119 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 120 | |
| 121 | # Find users or create them if they don't exist |
| 122 | lender = None |
| 123 | borrower = None |
| 124 | for user in self.database["users"]: |
| 125 | if user["name"] == lender_name: |
| 126 | lender = user |
| 127 | elif user["name"] == borrower_name: |
| 128 | borrower = user |
| 129 | |
| 130 | # Create lender if not found |
| 131 | if lender is None: |
| 132 | lender = { |
| 133 | "name": lender_name, |
| 134 | "owes": {}, |
| 135 | "owed_by": {}, |
| 136 | "balance": 0.0 |
| 137 | } |
| 138 | self.database["users"].append(lender) |
| 139 | |
| 140 | # Create borrower if not found |
| 141 | if borrower is None: |
| 142 | borrower = { |
| 143 | "name": borrower_name, |
| 144 | "owes": {}, |
| 145 | "owed_by": {}, |
| 146 | "balance": 0.0 |
| 147 | } |
| 148 | self.database["users"].append(borrower) |
| 149 | |
| 150 | # Update IOUs with proper debt resolution |
| 151 | # When a lender lends to a borrower, we need to consider existing debts |
| 152 | |
| 153 | # Check if there's an existing reverse debt (lender owes borrower) |
| 154 | if borrower_name in lender["owes"]: |
| 155 | # Lender already owes borrower - this new lending reduces that debt |
| 156 | existing_debt = lender["owes"][borrower_name] |
| 157 | if existing_debt >= amount: |
| 158 | # The new lending amount is less than or equal to existing debt |
| 159 | # Reduce the existing debt |
| 160 | new_debt = existing_debt - amount |
| 161 | if new_debt > 0: |
| 162 | lender["owes"][borrower_name] = new_debt |
| 163 | borrower["owed_by"][lender_name] = new_debt |
| 164 | else: |
| 165 | # Debt is completely resolved |
| 166 | del lender["owes"][borrower_name] |
| 167 | del borrower["owed_by"][lender_name] |
| 168 | else: |
| 169 | # The new lending amount exceeds existing debt |
| 170 | # Resolve the existing debt and create reverse debt |
| 171 | del lender["owes"][borrower_name] |
| 172 | del borrower["owed_by"][lender_name] |
| 173 | # Create reverse debt for the remaining amount |
| 174 | remaining_amount = amount - existing_debt |
| 175 | if remaining_amount > 0: |
| 176 | lender["owed_by"][borrower_name] = remaining_amount |
| 177 | borrower["owes"][lender_name] = remaining_amount |
| 178 | else: |
| 179 | # No existing reverse debt - simply add the new debt |
| 180 | if borrower_name in lender["owed_by"]: |
| 181 | lender["owed_by"][borrower_name] += amount |
| 182 | else: |
| 183 | lender["owed_by"][borrower_name] = amount |
| 184 | |
| 185 | if lender_name in borrower["owes"]: |
| 186 | borrower["owes"][lender_name] += amount |
| 187 | else: |
| 188 | borrower["owes"][lender_name] = amount |
| 189 | |
| 190 | # Update balances |
| 191 | self._update_balance(lender) |
| 192 | self._update_balance(borrower) |
| 193 | |
| 194 | # Return updated users sorted by name |
| 195 | updated_users = [lender, borrower] |
| 196 | updated_users.sort(key=lambda x: x["name"]) |
| 197 | |
| 198 | return json.dumps({ |
| 199 | "users": [self._format_user(user) for user in updated_users] |
| 200 | }) |
| 201 | |
| 202 | # Edge Case: Invalid URL |
| 203 | return json.dumps({"error": "Invalid URL"}) |
| 204 | |
| 205 | def _format_user(self, user: Dict[str, Any]) -> Dict[str, Any]: |
| 206 | """ |
| 207 | Format a user object for output, ensuring balance is a number. |
| 208 | |
| 209 | Args: |
| 210 | user: User dictionary |
| 211 | |
| 212 | Returns: |
| 213 | Formatted user dictionary |
| 214 | """ |
| 215 | # Make a copy to avoid modifying the original |
| 216 | formatted = user.copy() |
| 217 | # Ensure balance is a float |
| 218 | formatted["balance"] = float(formatted["balance"]) |
| 219 | return formatted |
| 220 | |
| 221 | def _update_balance(self, user: Dict[str, Any]) -> None: |
| 222 | """ |
| 223 | Update the balance for a user based on their owes and owed_by. |
| 224 | |
| 225 | Args: |
| 226 | user: User dictionary to update |
| 227 | """ |
| 228 | total_owed_by = sum(user["owed_by"].values()) |
| 229 | total_owes = sum(user["owes"].values()) |
| 230 | user["balance"] = total_owed_by - total_owes |
| 231 | |
| 232 | # Handled Edge Cases: Invalid URL, Missing payload, Invalid JSON payload, Missing user name, |
| 233 | # User already exists, Missing required fields, Invalid amount type, Negative amount, |
| 234 | # Lender and borrower are the same, Lender not found, Borrower not found, Empty users list in payload, |
| 235 | # User not found |