| 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 a database. |
| 7 | |
| 8 | Args: |
| 9 | database: A dictionary containing user data. |
| 10 | """ |
| 11 | # Edge Case: Handle None database by initializing empty users list |
| 12 | self.database = database if database is not None else {"users": []} |
| 13 | |
| 5 | 14 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 15 | """ |
| 16 | Handle GET requests to the API. |
| 17 | |
| 18 | Args: |
| 19 | url: The endpoint URL. |
| 20 | payload: Optional JSON payload. |
| 21 | |
| 22 | Returns: |
| 23 | JSON string response. |
| 24 | """ |
| 25 | if url == "/users": |
| 26 | # Edge Case: Handle missing payload by returning all users |
| 27 | if payload is None: |
| 28 | # Sort users by name |
| 29 | sorted_users = sorted(self.database["users"], key=lambda u: u["name"]) |
| 30 | users = [self._create_user_object(user) for user in sorted_users] |
| 31 | return json.dumps({"users": users}) |
| 32 | else: |
| 33 | # Edge Case: Handle invalid JSON payload |
| 34 | try: |
| 35 | data = json.loads(payload) |
| 36 | except json.JSONDecodeError: |
| 37 | return json.dumps({"error": "Invalid JSON payload"}) |
| 38 | |
| 39 | # Edge Case: Handle missing 'users' key in payload |
| 40 | if "users" not in data: |
| 41 | return json.dumps({"error": "Missing 'users' key in payload"}) |
| 42 | |
| 43 | # Edge Case: Handle non-list 'users' value in payload |
| 44 | if not isinstance(data["users"], list): |
| 45 | return json.dumps({"error": "'users' must be a list"}) |
| 46 | |
| 47 | # Filter users based on payload |
| 48 | requested_users = data["users"] |
| 49 | filtered_users = [user for user in self.database["users"] if user["name"] in requested_users] |
| 50 | |
| 51 | # Instead of returning an error for non-existent users, just return existing ones |
| 52 | # Sort users by name |
| 53 | sorted_users = sorted(filtered_users, key=lambda u: u["name"]) |
| 54 | user_objects = [self._create_user_object(user) for user in sorted_users] |
| 55 | |
| 56 | return json.dumps({"users": user_objects}) |
| 57 | |
| 58 | # Edge Case: Handle unknown URL |
| 59 | return json.dumps({"error": "Unknown endpoint"}) |
| 60 | |
| 8 | 61 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 62 | """ |
| 63 | Handle POST requests to the API. |
| 64 | |
| 65 | Args: |
| 66 | url: The endpoint URL. |
| 67 | payload: JSON payload. |
| 68 | |
| 69 | Returns: |
| 70 | JSON string response. |
| 71 | """ |
| 72 | # Edge Case: Handle missing payload |
| 73 | if payload is None: |
| 74 | return json.dumps({"error": "Payload required"}) |
| 75 | |
| 76 | # Edge Case: Handle invalid JSON payload |
| 77 | try: |
| 78 | data = json.loads(payload) |
| 79 | except json.JSONDecodeError: |
| 80 | return json.dumps({"error": "Invalid JSON payload"}) |
| 81 | |
| 82 | if url == "/add": |
| 83 | # Edge Case: Handle missing 'user' key |
| 84 | if "user" not in data: |
| 85 | return json.dumps({"error": "Missing 'user' key"}) |
| 86 | |
| 87 | # Edge Case: Handle non-string user name |
| 88 | if not isinstance(data["user"], str): |
| 89 | return json.dumps({"error": "User name must be a string"}) |
| 90 | |
| 91 | # Edge Case: Handle empty user name |
| 92 | if not data["user"]: |
| 93 | return json.dumps({"error": "User name cannot be empty"}) |
| 94 | |
| 95 | # Edge Case: Handle duplicate user - return existing user instead of error |
| 96 | for user in self.database["users"]: |
| 97 | if user["name"] == data["user"]: |
| 98 | return json.dumps(self._create_user_object(user)) |
| 99 | |
| 100 | # Create new user |
| 101 | new_user = { |
| 102 | "name": data["user"], |
| 103 | "owes": {}, |
| 104 | "owed_by": {}, |
| 105 | "balance": 0.0 |
| 106 | } |
| 107 | self.database["users"].append(new_user) |
| 108 | |
| 109 | return json.dumps(self._create_user_object(new_user)) |
| 110 | |
| 111 | elif url == "/iou": |
| 112 | # Edge Case: Handle missing required keys |
| 113 | required_keys = ["lender", "borrower", "amount"] |
| 114 | for key in required_keys: |
| 115 | if key not in data: |
| 116 | return json.dumps({"error": f"Missing '{key}' key"}) |
| 117 | |
| 118 | lender_name = data["lender"] |
| 119 | borrower_name = data["borrower"] |
| 120 | amount = data["amount"] |
| 121 | |
| 122 | # Edge Case: Handle non-string lender/borrower names |
| 123 | if not isinstance(lender_name, str) or not isinstance(borrower_name, str): |
| 124 | return json.dumps({"error": "Lender and borrower must be strings"}) |
| 125 | |
| 126 | # Edge Case: Handle empty lender/borrower names |
| 127 | if not lender_name or not borrower_name: |
| 128 | return json.dumps({"error": "Lender and borrower names cannot be empty"}) |
| 129 | |
| 130 | # Edge Case: Handle non-numeric amount |
| 131 | if not isinstance(amount, (int, float)): |
| 132 | return json.dumps({"error": "Amount must be a number"}) |
| 133 | |
| 134 | # Edge Case: Handle negative amount |
| 135 | if amount < 0: |
| 136 | return json.dumps({"error": "Amount cannot be negative"}) |
| 137 | |
| 138 | # Edge Case: Handle lender and borrower being the same person |
| 139 | if lender_name == borrower_name: |
| 140 | return json.dumps({"error": "Lender and borrower cannot be the same person"}) |
| 141 | |
| 142 | # Find lender and borrower, create them if they don't exist |
| 143 | lender = None |
| 144 | borrower = None |
| 145 | |
| 146 | for user in self.database["users"]: |
| 147 | if user["name"] == lender_name: |
| 148 | lender = user |
| 149 | elif user["name"] == borrower_name: |
| 150 | borrower = user |
| 151 | |
| 152 | # Create users if they don't exist |
| 153 | if lender is None: |
| 154 | lender = { |
| 155 | "name": lender_name, |
| 156 | "owes": {}, |
| 157 | "owed_by": {}, |
| 158 | "balance": 0.0 |
| 159 | } |
| 160 | self.database["users"].append(lender) |
| 161 | |
| 162 | if borrower is None: |
| 163 | borrower = { |
| 164 | "name": borrower_name, |
| 165 | "owes": {}, |
| 166 | "owed_by": {}, |
| 167 | "balance": 0.0 |
| 168 | } |
| 169 | self.database["users"].append(borrower) |
| 170 | |
| 171 | # Handle IOU with proper debt netting |
| 172 | # Check if there's an existing debt in the same direction |
| 173 | # (lender is owed by borrower) |
| 174 | if borrower_name in lender["owed_by"]: |
| 175 | # Add to existing debt |
| 176 | lender["owed_by"][borrower_name] += amount |
| 177 | borrower["owes"][lender_name] += amount |
| 178 | # Check if there's an existing debt in the opposite direction |
| 179 | # (borrower owes lender) |
| 180 | elif lender_name in borrower["owes"]: |
| 181 | existing_debt = borrower["owes"][lender_name] |
| 182 | |
| 183 | if amount == existing_debt: |
| 184 | # Exact offset - remove both debts |
| 185 | del borrower["owes"][lender_name] |
| 186 | if borrower_name in lender["owed_by"]: |
| 187 | del lender["owed_by"][borrower_name] |
| 188 | elif amount > existing_debt: |
| 189 | # New IOU is larger - create reverse debt |
| 190 | del borrower["owes"][lender_name] |
| 191 | if borrower_name in lender["owed_by"]: |
| 192 | del lender["owed_by"][borrower_name] |
| 193 | |
| 194 | # Create reverse debt: lender now owes borrower |
| 195 | reverse_amount = amount - existing_debt |
| 196 | lender["owes"][borrower_name] = reverse_amount |
| 197 | borrower["owed_by"][lender_name] = reverse_amount |
| 198 | else: |
| 199 | # New IOU is smaller - reduce existing debt |
| 200 | new_debt = existing_debt - amount |
| 201 | borrower["owes"][lender_name] = new_debt |
| 202 | lender["owed_by"][borrower_name] = new_debt |
| 203 | # Check if there's an existing debt in the reverse direction |
| 204 | # (borrower is owed by lender) |
| 205 | elif borrower_name in lender["owes"]: |
| 206 | existing_debt = lender["owes"][borrower_name] |
| 207 | |
| 208 | if amount == existing_debt: |
| 209 | # Exact offset - remove both debts |
| 210 | del lender["owes"][borrower_name] |
| 211 | if lender_name in borrower["owed_by"]: |
| 212 | del borrower["owed_by"][lender_name] |
| 213 | elif amount > existing_debt: |
| 214 | # New IOU is larger - create reverse debt |
| 215 | del lender["owes"][borrower_name] |
| 216 | if lender_name in borrower["owed_by"]: |
| 217 | del borrower["owed_by"][lender_name] |
| 218 | |
| 219 | # Create reverse debt: borrower now owes lender |
| 220 | reverse_amount = amount - existing_debt |
| 221 | borrower["owes"][lender_name] = reverse_amount |
| 222 | lender["owed_by"][borrower_name] = reverse_amount |
| 223 | else: |
| 224 | # New IOU is smaller - reduce existing debt |
| 225 | new_debt = existing_debt - amount |
| 226 | lender["owes"][borrower_name] = new_debt |
| 227 | borrower["owed_by"][lender_name] = new_debt |
| 228 | else: |
| 229 | # No existing debt, create new IOU |
| 230 | lender["owed_by"][borrower_name] = amount |
| 231 | borrower["owes"][lender_name] = amount |
| 232 | |
| 233 | # Recalculate balances |
| 234 | self._update_balance(lender) |
| 235 | self._update_balance(borrower) |
| 236 | |
| 237 | # Return updated user objects sorted by name |
| 238 | updated_users = sorted([lender, borrower], key=lambda u: u["name"]) |
| 239 | user_objects = [self._create_user_object(user) for user in updated_users] |
| 240 | |
| 241 | return json.dumps({"users": user_objects}) |
| 242 | |
| 243 | # Edge Case: Handle unknown URL |
| 244 | return json.dumps({"error": "Unknown endpoint"}) |
| 245 | |
| 246 | def _create_user_object(self, user: dict) -> dict: |
| 247 | """ |
| 248 | Create a user object for API response. |
| 249 | |
| 250 | Args: |
| 251 | user: User data from database. |
| 252 | |
| 253 | Returns: |
| 254 | Formatted user object. |
| 255 | """ |
| 256 | # Calculate balance as (total owed by others) - (total owed to others) |
| 257 | total_owed_by = sum(user["owed_by"].values()) |
| 258 | total_owes = sum(user["owes"].values()) |
| 259 | balance = round(total_owed_by - total_owes, 2) |
| 260 | |
| 261 | return { |
| 262 | "name": user["name"], |
| 263 | "owes": user["owes"], |
| 264 | "owed_by": user["owed_by"], |
| 265 | "balance": balance |
| 266 | } |
| 267 | |
| 268 | def _update_balance(self, user: dict) -> None: |
| 269 | """ |
| 270 | Update the balance of a user based on their IOUs. |
| 271 | |
| 272 | Args: |
| 273 | user: User data to update. |
| 274 | """ |
| 275 | total_owed_by = sum(user["owed_by"].values()) |
| 276 | total_owes = sum(user["owes"].values()) |
| 277 | user["balance"] = round(total_owed_by - total_owes, 2) |
| 278 | |
| 279 | # Handled Edge Cases: None database, missing payload, invalid JSON, missing 'users' key, non-list 'users', non-existent users, unknown URL, missing 'user' key, non-string user name, empty user name, duplicate user, missing required keys, non-string names, empty names, non-numeric amount, negative amount, same lender/borrower, user not found |