| 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 | if database is None: |
| 12 | self.database = {"users": []} |
| 13 | else: |
| 14 | self.database = database |
| 15 | |
| 5 | 16 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 17 | """ |
| 18 | Handle GET requests to the API. |
| 19 | |
| 20 | Args: |
| 21 | url: The endpoint URL. |
| 22 | payload: Optional JSON payload. |
| 23 | |
| 24 | Returns: |
| 25 | JSON string response. |
| 26 | """ |
| 27 | if url == "/users": |
| 28 | if payload is None: |
| 29 | # Return all users |
| 30 | return json.dumps({"users": self._get_all_users()}) |
| 31 | else: |
| 32 | # Return specific users |
| 33 | data = json.loads(payload) |
| 34 | user_names = data.get("users", []) |
| 35 | return json.dumps({"users": self._get_users_by_names(user_names)}) |
| 36 | return json.dumps({"error": "Not found"}) |
| 37 | |
| 8 | 38 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 39 | """ |
| 40 | Handle POST requests to the API. |
| 41 | |
| 42 | Args: |
| 43 | url: The endpoint URL. |
| 44 | payload: JSON payload. |
| 45 | |
| 46 | Returns: |
| 47 | JSON string response. |
| 48 | """ |
| 49 | if payload is None: |
| 50 | return json.dumps({"error": "Payload required"}) |
| 51 | |
| 52 | data = json.loads(payload) |
| 53 | |
| 54 | if url == "/add": |
| 55 | user_name = data.get("user") |
| 56 | if not user_name: |
| 57 | return json.dumps({"error": "User name required"}) |
| 58 | |
| 59 | # Edge Case: Check if user already exists |
| 60 | if self._find_user(user_name): |
| 61 | return json.dumps({"error": "User already exists"}) |
| 62 | |
| 63 | new_user = { |
| 64 | "name": user_name, |
| 65 | "owes": {}, |
| 66 | "owed_by": {}, |
| 67 | "balance": 0.0 |
| 68 | } |
| 69 | self.database["users"].append(new_user) |
| 70 | return json.dumps(new_user) |
| 71 | |
| 72 | elif url == "/iou": |
| 73 | lender_name = data.get("lender") |
| 74 | borrower_name = data.get("borrower") |
| 75 | amount = data.get("amount") |
| 76 | |
| 77 | # Edge Case: Validate required fields |
| 78 | if not lender_name or not borrower_name or amount is None: |
| 79 | return json.dumps({"error": "Missing required fields"}) |
| 80 | |
| 81 | # Edge Case: Validate amount is a positive number |
| 82 | if not isinstance(amount, (int, float)) or amount <= 0: |
| 83 | return json.dumps({"error": "Amount must be a positive number"}) |
| 84 | |
| 85 | # Edge Case: Check if lender and borrower are the same person |
| 86 | if lender_name == borrower_name: |
| 87 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 88 | |
| 89 | lender = self._find_user(lender_name) |
| 90 | borrower = self._find_user(borrower_name) |
| 91 | |
| 92 | # Edge Case: Check if users exist |
| 93 | if not lender or not borrower: |
| 94 | return json.dumps({"error": "User not found"}) |
| 95 | |
| 96 | # Handle debt netting properly |
| 97 | # Check if there's an existing debt in the opposite direction |
| 98 | if borrower_name in lender["owes"]: |
| 99 | # Lender already owes borrower - net the debts |
| 100 | existing_debt = lender["owes"][borrower_name] |
| 101 | if amount > existing_debt: |
| 102 | # New IOU is larger than existing debt |
| 103 | # Remove the existing debt and create a new one in opposite direction |
| 104 | del lender["owes"][borrower_name] |
| 105 | del borrower["owed_by"][lender_name] |
| 106 | # Add the remaining amount to lender's owed_by |
| 107 | remaining = amount - existing_debt |
| 108 | lender["owed_by"][borrower_name] = remaining |
| 109 | borrower["owes"][lender_name] = remaining |
| 110 | elif amount == existing_debt: |
| 111 | # Debts exactly cancel out |
| 112 | del lender["owes"][borrower_name] |
| 113 | del borrower["owed_by"][lender_name] |
| 114 | else: |
| 115 | # New IOU is smaller than existing debt |
| 116 | # Reduce the existing debt |
| 117 | lender["owes"][borrower_name] -= amount |
| 118 | borrower["owed_by"][lender_name] -= amount |
| 119 | elif lender_name in borrower["owes"]: |
| 120 | # Borrower already owes lender - add to existing debt |
| 121 | existing_debt = borrower["owes"][lender_name] |
| 122 | borrower["owes"][lender_name] = existing_debt + amount |
| 123 | lender["owed_by"][borrower_name] = existing_debt + amount |
| 124 | else: |
| 125 | # No existing debt, create new entries |
| 126 | lender["owed_by"][borrower_name] = amount |
| 127 | borrower["owes"][lender_name] = amount |
| 128 | |
| 129 | # Recalculate balances |
| 130 | self._recalculate_balance(lender) |
| 131 | self._recalculate_balance(borrower) |
| 132 | |
| 133 | # Return updated users sorted by name |
| 134 | users = [lender, borrower] |
| 135 | users.sort(key=lambda u: u["name"]) |
| 136 | return json.dumps({"users": users}) |
| 137 | |
| 138 | return json.dumps({"error": "Not found"}) |
| 139 | |
| 140 | def _find_user(self, name: str): |
| 141 | """ |
| 142 | Find a user by name in the database. |
| 143 | |
| 144 | Args: |
| 145 | name: The name of the user to find. |
| 146 | |
| 147 | Returns: |
| 148 | The user object if found, None otherwise. |
| 149 | """ |
| 150 | for user in self.database["users"]: |
| 151 | if user["name"] == name: |
| 152 | return user |
| 153 | return None |
| 154 | |
| 155 | def _get_all_users(self): |
| 156 | """ |
| 157 | Get all users from the database, sorted by name. |
| 158 | |
| 159 | Returns: |
| 160 | List of all user objects sorted by name. |
| 161 | """ |
| 162 | return sorted(self.database["users"], key=lambda u: u["name"]) |
| 163 | |
| 164 | def _get_users_by_names(self, names: list): |
| 165 | """ |
| 166 | Get specific users by their names. |
| 167 | |
| 168 | Args: |
| 169 | names: List of user names to retrieve. |
| 170 | |
| 171 | Returns: |
| 172 | List of user objects sorted by name. |
| 173 | """ |
| 174 | users = [] |
| 175 | for name in names: |
| 176 | user = self._find_user(name) |
| 177 | if user: |
| 178 | users.append(user) |
| 179 | return sorted(users, key=lambda u: u["name"]) |
| 180 | |
| 181 | def _recalculate_balance(self, user): |
| 182 | """ |
| 183 | Recalculate the balance for a user based on their owes and owed_by. |
| 184 | |
| 185 | Args: |
| 186 | user: The user object to update. |
| 187 | """ |
| 188 | total_owed_by = sum(user["owed_by"].values()) |
| 189 | total_owes = sum(user["owes"].values()) |
| 190 | user["balance"] = round(total_owed_by - total_owes, 2) |
| 191 | |
| 192 | # Handled Edge Cases: Invalid payload, missing user name, duplicate user, missing required fields, |
| 193 | # invalid amount, lender equals borrower, user not found |