| 1 | import json |
| 2 | |
| 1 | 3 | class RestAPI: |
| 2 | 4 | def __init__(self, database: dict | None = None): |
| 3 | | pass |
| 4 | | |
| 5 | """ |
| 6 | Initialize the REST API with an optional database. |
| 7 | |
| 8 | Args: |
| 9 | database: A dictionary containing initial user data. |
| 10 | """ |
| 11 | # Edge Case: Handle None database by initializing empty users dict |
| 12 | if database is None: |
| 13 | self.users = {} |
| 14 | else: |
| 15 | self.users = database.get('users', {}) |
| 16 | |
| 17 | # Convert list of users to dictionary for easier access |
| 18 | if isinstance(self.users, list): |
| 19 | self.users = {user['name']: user for user in self.users} |
| 20 | |
| 21 | # Ensure all users have the required fields |
| 22 | for user in self.users.values(): |
| 23 | if 'owes' not in user: |
| 24 | user['owes'] = {} |
| 25 | if 'owed_by' not in user: |
| 26 | user['owed_by'] = {} |
| 27 | if 'balance' not in user: |
| 28 | user['balance'] = 0.0 |
| 29 | |
| 30 | def _net_debts(self, user1, user2): |
| 31 | """ |
| 32 | Net debts between two users by offsetting mutual debts. |
| 33 | |
| 34 | Args: |
| 35 | user1: First user dictionary |
| 36 | user2: Second user dictionary |
| 37 | """ |
| 38 | name1 = user1['name'] |
| 39 | name2 = user2['name'] |
| 40 | |
| 41 | # Check if user1 owes user2 and user2 owes user1 |
| 42 | user1_owes_user2 = user1['owes'].get(name2, 0) |
| 43 | user2_owes_user1 = user2['owes'].get(name1, 0) |
| 44 | |
| 45 | if user1_owes_user2 > 0 and user2_owes_user1 > 0: |
| 46 | # Net the amounts |
| 47 | net_amount = abs(user1_owes_user2 - user2_owes_user1) |
| 48 | |
| 49 | if user1_owes_user2 > user2_owes_user1: |
| 50 | # User1 owes more to user2 |
| 51 | user1['owes'][name2] = net_amount |
| 52 | user2['owed_by'][name1] = net_amount |
| 53 | # Remove the opposite debt |
| 54 | del user2['owes'][name1] |
| 55 | del user1['owed_by'][name2] |
| 56 | elif user2_owes_user1 > user1_owes_user2: |
| 57 | # User2 owes more to user1 |
| 58 | user2['owes'][name1] = net_amount |
| 59 | user1['owed_by'][name2] = net_amount |
| 60 | # Remove the opposite debt |
| 61 | del user1['owes'][name2] |
| 62 | del user2['owed_by'][name1] |
| 63 | else: |
| 64 | # Debts cancel out completely |
| 65 | del user1['owes'][name2] |
| 66 | del user2['owed_by'][name1] |
| 67 | del user2['owes'][name1] |
| 68 | del user1['owed_by'][name2] |
| 69 | |
| 70 | def _calculate_balance(self, user): |
| 71 | """ |
| 72 | Calculate the balance for a user based on what they owe and are owed. |
| 73 | |
| 74 | Args: |
| 75 | user: The user dictionary to calculate balance for. |
| 76 | |
| 77 | Returns: |
| 78 | float: The calculated balance. |
| 79 | """ |
| 80 | total_owed_by_others = sum(user['owed_by'].values()) |
| 81 | total_owed_to_others = sum(user['owes'].values()) |
| 82 | return round(total_owed_by_others - total_owed_to_others, 2) |
| 83 | |
| 84 | def _get_user(self, name): |
| 85 | """ |
| 86 | Get a user by name, creating them if they don't exist. |
| 87 | |
| 88 | Args: |
| 89 | name: The name of the user to retrieve. |
| 90 | |
| 91 | Returns: |
| 92 | dict: The user object. |
| 93 | """ |
| 94 | # Edge Case: Create user if they don't exist |
| 95 | if name not in self.users: |
| 96 | self.users[name] = { |
| 97 | 'name': name, |
| 98 | 'owes': {}, |
| 99 | 'owed_by': {}, |
| 100 | 'balance': 0.0 |
| 101 | } |
| 102 | return self.users[name] |
| 103 | |
| 5 | 104 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 105 | """ |
| 106 | Handle GET requests to the API. |
| 107 | |
| 108 | Args: |
| 109 | url: The endpoint URL. |
| 110 | payload: Optional JSON payload. |
| 111 | |
| 112 | Returns: |
| 113 | str: JSON response. |
| 114 | """ |
| 115 | # Edge Case: Handle /users endpoint |
| 116 | if url == '/users': |
| 117 | # If payload exists, filter users |
| 118 | if payload: |
| 119 | data = json.loads(payload) |
| 120 | user_names = data.get('users', []) |
| 121 | # Edge Case: Handle empty users list in payload |
| 122 | if not user_names: |
| 123 | return json.dumps({'users': []}) |
| 124 | |
| 125 | # Edge Case: Filter only existing users |
| 126 | filtered_users = [] |
| 127 | for name in user_names: |
| 128 | if name in self.users: |
| 129 | user = self.users[name].copy() |
| 130 | user['balance'] = self._calculate_balance(user) |
| 131 | filtered_users.append(user) |
| 132 | |
| 133 | # Sort by name |
| 134 | filtered_users.sort(key=lambda x: x['name']) |
| 135 | return json.dumps({'users': filtered_users}) |
| 136 | else: |
| 137 | # Return all users |
| 138 | all_users = [] |
| 139 | for user in self.users.values(): |
| 140 | user_copy = user.copy() |
| 141 | user_copy['balance'] = self._calculate_balance(user_copy) |
| 142 | all_users.append(user_copy) |
| 143 | |
| 144 | # Sort by name |
| 145 | all_users.sort(key=lambda x: x['name']) |
| 146 | return json.dumps({'users': all_users}) |
| 147 | |
| 148 | # Edge Case: Handle unknown endpoints |
| 149 | return json.dumps({'error': 'Not found'}) |
| 150 | |
| 8 | 151 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 152 | """ |
| 153 | Handle POST requests to the API. |
| 154 | |
| 155 | Args: |
| 156 | url: The endpoint URL. |
| 157 | payload: JSON payload. |
| 158 | |
| 159 | Returns: |
| 160 | str: JSON response. |
| 161 | """ |
| 162 | # Edge Case: Handle missing payload |
| 163 | if not payload: |
| 164 | return json.dumps({'error': 'Payload required'}) |
| 165 | |
| 166 | data = json.loads(payload) |
| 167 | |
| 168 | # Edge Case: Handle /add endpoint |
| 169 | if url == '/add': |
| 170 | user_name = data.get('user') |
| 171 | # Edge Case: Handle missing user in payload |
| 172 | if not user_name: |
| 173 | return json.dumps({'error': 'User name required'}) |
| 174 | |
| 175 | # Edge Case: Handle duplicate user - return existing user |
| 176 | if user_name in self.users: |
| 177 | return json.dumps(self.users[user_name]) |
| 178 | |
| 179 | new_user = { |
| 180 | 'name': user_name, |
| 181 | 'owes': {}, |
| 182 | 'owed_by': {}, |
| 183 | 'balance': 0.0 |
| 184 | } |
| 185 | self.users[user_name] = new_user |
| 186 | return json.dumps(new_user) |
| 187 | |
| 188 | # Edge Case: Handle /iou endpoint |
| 189 | elif url == '/iou': |
| 190 | lender_name = data.get('lender') |
| 191 | borrower_name = data.get('borrower') |
| 192 | amount = data.get('amount') |
| 193 | |
| 194 | # Edge Case: Handle missing required fields |
| 195 | if not lender_name or not borrower_name or amount is None: |
| 196 | return json.dumps({'error': 'Lender, borrower, and amount required'}) |
| 197 | |
| 198 | # Edge Case: Handle invalid amount type |
| 199 | if not isinstance(amount, (int, float)): |
| 200 | return json.dumps({'error': 'Amount must be a number'}) |
| 201 | |
| 202 | # Edge Case: Handle negative amount |
| 203 | if amount < 0: |
| 204 | return json.dumps({'error': 'Amount must be positive'}) |
| 205 | |
| 206 | # Edge Case: Handle same lender and borrower |
| 207 | if lender_name == borrower_name: |
| 208 | return json.dumps({'error': 'Lender and borrower cannot be the same'}) |
| 209 | |
| 210 | # Get or create users |
| 211 | lender = self._get_user(lender_name) |
| 212 | borrower = self._get_user(borrower_name) |
| 213 | |
| 214 | # Update debts with proper netting |
| 215 | # Add to lender's owed_by and borrower's owes |
| 216 | if borrower_name in lender['owed_by']: |
| 217 | lender['owed_by'][borrower_name] += amount |
| 218 | else: |
| 219 | lender['owed_by'][borrower_name] = amount |
| 220 | |
| 221 | if lender_name in borrower['owes']: |
| 222 | borrower['owes'][lender_name] += amount |
| 223 | else: |
| 224 | borrower['owes'][lender_name] = amount |
| 225 | |
| 226 | # Net the debts if both users have debts to each other |
| 227 | self._net_debts(lender, borrower) |
| 228 | |
| 229 | # Recalculate balances |
| 230 | lender['balance'] = self._calculate_balance(lender) |
| 231 | borrower['balance'] = self._calculate_balance(borrower) |
| 232 | |
| 233 | # Return updated users, sorted by name |
| 234 | updated_users = [lender, borrower] |
| 235 | updated_users.sort(key=lambda x: x['name']) |
| 236 | |
| 237 | # Create copies without modifying the originals |
| 238 | result_users = [] |
| 239 | for user in updated_users: |
| 240 | user_copy = user.copy() |
| 241 | user_copy['balance'] = self._calculate_balance(user_copy) |
| 242 | result_users.append(user_copy) |
| 243 | |
| 244 | return json.dumps({'users': result_users}) |
| 245 | |
| 246 | # Edge Case: Handle unknown endpoints |
| 247 | return json.dumps({'error': 'Not found'}) |
| 248 | |
| 249 | # Handled Edge Cases: None database, missing payload, unknown endpoints, /users filtering, |
| 250 | # empty users list, non-existing users in filter, /add missing user, duplicate user, |
| 251 | # /iou missing fields, invalid amount type, negative amount, same lender/borrower |