| 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 an optional database. |
| 8 | |
| 9 | Args: |
| 10 | database: A dictionary containing initial user data. |
| 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._get_all_users()}) |
| 32 | else: |
| 33 | # Return specific users |
| 34 | data = json.loads(payload) |
| 35 | user_names = data.get("users", []) |
| 36 | # If users list is not provided or is empty, return all users |
| 37 | if not user_names: |
| 38 | return json.dumps({"users": self._get_all_users()}) |
| 39 | return json.dumps({"users": self._get_users_by_names(user_names)}) |
| 40 | return json.dumps({"error": "Invalid URL"}) |
| 41 | |
| 8 | 42 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 43 | """ |
| 44 | Handle POST requests to the API. |
| 45 | |
| 46 | Args: |
| 47 | url: The endpoint URL. |
| 48 | payload: JSON payload. |
| 49 | |
| 50 | Returns: |
| 51 | JSON string response. |
| 52 | """ |
| 53 | if payload is None: |
| 54 | return json.dumps({"error": "Payload required"}) |
| 55 | |
| 56 | data = json.loads(payload) |
| 57 | |
| 58 | if url == "/add": |
| 59 | user_name = data.get("user") |
| 60 | if not user_name: |
| 61 | return json.dumps({"error": "User name required"}) |
| 62 | |
| 63 | # Edge Case: Check if user already exists |
| 64 | if self._find_user(user_name): |
| 65 | return json.dumps({"error": "User already exists"}) |
| 66 | |
| 67 | new_user = { |
| 68 | "name": user_name, |
| 69 | "owes": {}, |
| 70 | "owed_by": {}, |
| 71 | "balance": 0.0 |
| 72 | } |
| 73 | self.database["users"].append(new_user) |
| 74 | return json.dumps(new_user) |
| 75 | |
| 76 | elif url == "/iou": |
| 77 | lender_name = data.get("lender") |
| 78 | borrower_name = data.get("borrower") |
| 79 | amount = data.get("amount") |
| 80 | |
| 81 | # Edge Case: Validate required fields |
| 82 | if not lender_name or not borrower_name or amount is None: |
| 83 | return json.dumps({"error": "Lender, borrower, and amount are required"}) |
| 84 | |
| 85 | # Edge Case: Validate amount is a number |
| 86 | if not isinstance(amount, (int, float)): |
| 87 | return json.dumps({"error": "Amount must be a number"}) |
| 88 | |
| 89 | # Edge Case: Check if lender and borrower are the same person |
| 90 | if lender_name == borrower_name: |
| 91 | return json.dumps({"error": "Lender and borrower cannot be the same person"}) |
| 92 | |
| 93 | lender = self._find_user(lender_name) |
| 94 | borrower = self._find_user(borrower_name) |
| 95 | |
| 96 | # Edge Case: Check if users exist |
| 97 | if not lender or not borrower: |
| 98 | return json.dumps({"error": "Both lender and borrower must exist"}) |
| 99 | |
| 100 | # Handle the IOU transaction properly, considering existing debts |
| 101 | self._handle_iou_transaction(lender, borrower, amount) |
| 102 | |
| 103 | # Recalculate balances |
| 104 | self._recalculate_balance(lender) |
| 105 | self._recalculate_balance(borrower) |
| 106 | |
| 107 | # Return updated users sorted by name |
| 108 | users = [lender, borrower] |
| 109 | users.sort(key=lambda u: u["name"]) |
| 110 | return json.dumps({"users": users}) |
| 111 | |
| 112 | return json.dumps({"error": "Invalid URL"}) |
| 113 | |
| 114 | def _find_user(self, name: str) -> Optional[Dict]: |
| 115 | """ |
| 116 | Find a user by name in the database. |
| 117 | |
| 118 | Args: |
| 119 | name: The name of the user to find. |
| 120 | |
| 121 | Returns: |
| 122 | The user dictionary if found, None otherwise. |
| 123 | """ |
| 124 | for user in self.database["users"]: |
| 125 | if user["name"] == name: |
| 126 | return user |
| 127 | return None |
| 128 | |
| 129 | def _recalculate_balance(self, user: Dict) -> None: |
| 130 | """ |
| 131 | Recalculate the balance for a user based on their owes and owed_by. |
| 132 | |
| 133 | Args: |
| 134 | user: The user dictionary to update. |
| 135 | """ |
| 136 | total_owed_by = sum(user["owed_by"].values()) |
| 137 | total_owes = sum(user["owes"].values()) |
| 138 | user["balance"] = round(total_owed_by - total_owes, 2) |
| 139 | |
| 140 | def _get_all_users(self) -> List[Dict]: |
| 141 | """ |
| 142 | Get all users from the database, sorted by name. |
| 143 | |
| 144 | Returns: |
| 145 | A list of all user dictionaries sorted by name. |
| 146 | """ |
| 147 | return sorted(self.database["users"], key=lambda u: u["name"]) |
| 148 | |
| 149 | def _handle_iou_transaction(self, lender: Dict, borrower: Dict, amount: float) -> None: |
| 150 | """ |
| 151 | Handle an IOU transaction between a lender and borrower, properly accounting for existing debts. |
| 152 | |
| 153 | Args: |
| 154 | lender: The user who is lending money. |
| 155 | borrower: The user who is borrowing money. |
| 156 | amount: The amount of money being lent (can be negative). |
| 157 | """ |
| 158 | # Handle negative amounts by reversing lender/borrower relationship |
| 159 | if amount < 0: |
| 160 | # Swap lender and borrower |
| 161 | lender, borrower = borrower, lender |
| 162 | amount = -amount |
| 163 | |
| 164 | # Simplified approach: net the debts |
| 165 | # If Adam owes Bob 3.0, and Bob lends 1.0 to Adam, |
| 166 | # then Adam should owe Bob 2.0 |
| 167 | |
| 168 | # Get current debts |
| 169 | amount_borrower_owes_lender = borrower["owes"].get(lender["name"], 0.0) |
| 170 | amount_lender_owes_borrower = lender["owes"].get(borrower["name"], 0.0) |
| 171 | |
| 172 | # Net the amounts |
| 173 | net_debt = amount_borrower_owes_lender - amount_lender_owes_borrower + amount |
| 174 | |
| 175 | # Update the records based on net debt |
| 176 | if net_debt > 0: |
| 177 | # Borrower owes lender |
| 178 | borrower["owes"][lender["name"]] = net_debt |
| 179 | borrower["owed_by"].pop(lender["name"], None) |
| 180 | lender["owed_by"][borrower["name"]] = net_debt |
| 181 | lender["owes"].pop(borrower["name"], None) |
| 182 | elif net_debt < 0: |
| 183 | # Lender owes borrower |
| 184 | absolute_debt = abs(net_debt) |
| 185 | lender["owes"][borrower["name"]] = absolute_debt |
| 186 | lender["owed_by"].pop(borrower["name"], None) |
| 187 | borrower["owed_by"][lender["name"]] = absolute_debt |
| 188 | borrower["owes"].pop(lender["name"], None) |
| 189 | else: |
| 190 | # No debt |
| 191 | borrower["owes"].pop(lender["name"], None) |
| 192 | borrower["owed_by"].pop(lender["name"], None) |
| 193 | lender["owes"].pop(borrower["name"], None) |
| 194 | lender["owed_by"].pop(borrower["name"], None) |
| 195 | |
| 196 | def _get_users_by_names(self, names: List[str]) -> List[Dict]: |
| 197 | """ |
| 198 | Get specific users by their names. |
| 199 | |
| 200 | Args: |
| 201 | names: A list of user names to retrieve. |
| 202 | |
| 203 | Returns: |
| 204 | A list of user dictionaries sorted by name. |
| 205 | """ |
| 206 | users = [] |
| 207 | for name in names: |
| 208 | user = self._find_user(name) |
| 209 | if user: |
| 210 | users.append(user) |
| 211 | return sorted(users, key=lambda u: u["name"]) |
| 212 | |
| 213 | # Handled Edge Cases: User already exists, missing required fields, invalid amount, lender and borrower are the same, users don't exist |
| 214 | # Handled Edge Cases: Missing payload, invalid URL |
| 215 | # Handled Edge Cases: Missing user name, user already exists |
| 216 | # Handled Edge Cases: Missing required fields, invalid amount type, negative amount, lender equals borrower, users don't exist, invalid URL |