| 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 | self.database = database if database is not None else {"users": []} |
| 12 | |
| 5 | 13 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 14 | """ |
| 15 | Handle GET requests to the API. |
| 16 | |
| 17 | Args: |
| 18 | url: The endpoint URL. |
| 19 | payload: Optional JSON payload. |
| 20 | |
| 21 | Returns: |
| 22 | A JSON string response. |
| 23 | """ |
| 24 | if url == "/users": |
| 25 | if payload is None: |
| 26 | # Return all users sorted by name |
| 27 | users = [self._create_user_object(user) for user in self.database["users"]] |
| 28 | users.sort(key=lambda u: u["name"]) |
| 29 | return json.dumps({"users": users}) |
| 30 | else: |
| 31 | # Return specific users |
| 32 | data = json.loads(payload) |
| 33 | user_names = data.get("users", []) |
| 34 | |
| 35 | # Edge Case: Empty user list in payload |
| 36 | if not user_names: |
| 37 | return json.dumps({"users": []}) |
| 38 | |
| 39 | # Edge Case: Non-existent users in payload |
| 40 | users = [] |
| 41 | for name in user_names: |
| 42 | user = self._find_user(name) |
| 43 | if user is not None: |
| 44 | users.append(self._create_user_object(user)) |
| 45 | |
| 46 | # Sort users by name |
| 47 | users.sort(key=lambda u: u["name"]) |
| 48 | return json.dumps({"users": users}) |
| 49 | |
| 50 | # Edge Case: Invalid URL |
| 51 | return json.dumps({"error": "Invalid URL"}) |
| 52 | |
| 8 | 53 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 54 | """ |
| 55 | Handle POST requests to the API. |
| 56 | |
| 57 | Args: |
| 58 | url: The endpoint URL. |
| 59 | payload: JSON payload. |
| 60 | |
| 61 | Returns: |
| 62 | A JSON string response. |
| 63 | """ |
| 64 | if payload is None: |
| 65 | # Edge Case: Missing payload |
| 66 | return json.dumps({"error": "Payload required"}) |
| 67 | |
| 68 | data = json.loads(payload) |
| 69 | |
| 70 | if url == "/add": |
| 71 | user_name = data.get("user") |
| 72 | |
| 73 | # Edge Case: Missing user name |
| 74 | if user_name is None: |
| 75 | return json.dumps({"error": "User name required"}) |
| 76 | |
| 77 | # Edge Case: User already exists |
| 78 | if self._find_user(user_name) is not None: |
| 79 | return json.dumps({"error": "User already exists"}) |
| 80 | |
| 81 | # Create new user |
| 82 | new_user = { |
| 83 | "name": user_name, |
| 84 | "owes": {}, |
| 85 | "owed_by": {}, |
| 86 | "balance": 0.0 |
| 87 | } |
| 88 | self.database["users"].append(new_user) |
| 89 | return json.dumps(self._create_user_object(new_user)) |
| 90 | |
| 91 | elif url == "/iou": |
| 92 | lender_name = data.get("lender") |
| 93 | borrower_name = data.get("borrower") |
| 94 | amount = data.get("amount") |
| 95 | |
| 96 | # Edge Case: Missing required fields |
| 97 | if lender_name is None or borrower_name is None or amount is None: |
| 98 | return json.dumps({"error": "Lender, borrower, and amount required"}) |
| 99 | |
| 100 | # Edge Case: Lender and borrower are the same |
| 101 | if lender_name == borrower_name: |
| 102 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 103 | |
| 104 | lender = self._find_user(lender_name) |
| 105 | borrower = self._find_user(borrower_name) |
| 106 | |
| 107 | # Edge Case: Non-existent lender or borrower |
| 108 | if lender is None or borrower is None: |
| 109 | return json.dumps({"error": "Lender or borrower does not exist"}) |
| 110 | |
| 111 | # Update the IOU transaction by properly netting debts |
| 112 | # Calculate the net amount that borrower owes lender after this transaction |
| 113 | # Net debt = (borrower's existing debt to lender) + amount - (lender's existing debt to borrower) |
| 114 | |
| 115 | # Get current amounts |
| 116 | lender_owes_borrower = lender["owes"].get(borrower_name, 0.0) |
| 117 | borrower_owes_lender = borrower["owes"].get(lender_name, 0.0) |
| 118 | |
| 119 | # Calculate net debt (positive means borrower owes lender, negative means lender owes borrower) |
| 120 | net_debt = (borrower_owes_lender + amount) - lender_owes_borrower |
| 121 | |
| 122 | # Remove all existing debt entries between these users |
| 123 | # Clean up lender's records |
| 124 | if borrower_name in lender["owes"]: |
| 125 | del lender["owes"][borrower_name] |
| 126 | if borrower_name in lender["owed_by"]: |
| 127 | del lender["owed_by"][borrower_name] |
| 128 | |
| 129 | # Clean up borrower's records |
| 130 | if lender_name in borrower["owes"]: |
| 131 | del borrower["owes"][lender_name] |
| 132 | if lender_name in borrower["owed_by"]: |
| 133 | del borrower["owed_by"][lender_name] |
| 134 | |
| 135 | # Set new netted amounts |
| 136 | if net_debt > 0: |
| 137 | # Borrower owes lender |
| 138 | lender["owed_by"][borrower_name] = net_debt |
| 139 | borrower["owes"][lender_name] = net_debt |
| 140 | elif net_debt < 0: |
| 141 | # Lender owes borrower |
| 142 | lender["owes"][borrower_name] = -net_debt |
| 143 | borrower["owed_by"][lender_name] = -net_debt |
| 144 | # If net_debt is 0, no entries are needed (no debt between them) |
| 145 | |
| 146 | # Recalculate balances for both users |
| 147 | lender_total_owed = sum(lender["owes"].values()) |
| 148 | lender_total_owed_by = sum(lender["owed_by"].values()) |
| 149 | lender["balance"] = lender_total_owed_by - lender_total_owed |
| 150 | |
| 151 | borrower_total_owed = sum(borrower["owes"].values()) |
| 152 | borrower_total_owed_by = sum(borrower["owed_by"].values()) |
| 153 | borrower["balance"] = borrower_total_owed_by - borrower_total_owed |
| 154 | |
| 155 | # Return updated users |
| 156 | users = [self._create_user_object(lender), self._create_user_object(borrower)] |
| 157 | users.sort(key=lambda u: u["name"]) |
| 158 | return json.dumps({"users": users}) |
| 159 | |
| 160 | # Edge Case: Invalid URL |
| 161 | return json.dumps({"error": "Invalid URL"}) |
| 162 | |
| 163 | def _find_user(self, name: str): |
| 164 | """ |
| 165 | Find a user by name in the database. |
| 166 | |
| 167 | Args: |
| 168 | name: The name of the user to find. |
| 169 | |
| 170 | Returns: |
| 171 | The user object if found, None otherwise. |
| 172 | """ |
| 173 | for user in self.database["users"]: |
| 174 | if user["name"] == name: |
| 175 | return user |
| 176 | return None |
| 177 | |
| 178 | def _create_user_object(self, user): |
| 179 | """ |
| 180 | Create a user object for API response. |
| 181 | |
| 182 | Args: |
| 183 | user: The user data from the database. |
| 184 | |
| 185 | Returns: |
| 186 | A user object for API response. |
| 187 | """ |
| 188 | # Calculate balance from owes and owed_by |
| 189 | total_owed = sum(user["owes"].values()) |
| 190 | total_owed_by = sum(user["owed_by"].values()) |
| 191 | balance = float(total_owed_by - total_owed) |
| 192 | |
| 193 | return { |
| 194 | "name": user["name"], |
| 195 | "owes": user["owes"], |
| 196 | "owed_by": user["owed_by"], |
| 197 | "balance": balance |
| 198 | } |
| 199 | # Handled Edge Cases: Invalid URL, Missing payload, Missing user name, User already exists, Missing required fields, Lender and borrower are the same, Non-existent lender or borrower |