| 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 structure |
| 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 being accessed. |
| 23 | payload: Optional JSON payload with request parameters. |
| 24 | |
| 25 | Returns: |
| 26 | JSON string response. |
| 27 | |
| 28 | Raises: |
| 29 | ValueError: If the URL is not recognized. |
| 30 | """ |
| 31 | # Edge Case: Handle /users endpoint |
| 32 | if url == "/users": |
| 33 | # Edge Case: Handle payload with specific users |
| 34 | if payload is not None: |
| 35 | data = json.loads(payload) |
| 36 | if "users" in data: |
| 37 | # Filter users by the provided list |
| 38 | user_names = set(data["users"]) |
| 39 | users = [user for user in self.database["users"] if user["name"] in user_names] |
| 40 | # Recalculate balances for all users |
| 41 | for user in users: |
| 42 | total_owed = sum(user["owed_by"].values()) |
| 43 | total_owes = sum(user["owes"].values()) |
| 44 | user["balance"] = total_owed - total_owes |
| 45 | # Sort by name |
| 46 | users.sort(key=lambda x: x["name"]) |
| 47 | return json.dumps({"users": users}) |
| 48 | |
| 49 | # Edge Case: Return all users when no payload or no users specified |
| 50 | users = sorted(self.database["users"], key=lambda x: x["name"]) |
| 51 | # Recalculate balances for all users |
| 52 | for user in users: |
| 53 | total_owed = sum(user["owed_by"].values()) |
| 54 | total_owes = sum(user["owes"].values()) |
| 55 | user["balance"] = total_owed - total_owes |
| 56 | return json.dumps({"users": users}) |
| 57 | |
| 58 | # Edge Case: Handle unknown URLs |
| 59 | raise ValueError(f"Unknown GET endpoint: {url}") |
| 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 being accessed. |
| 67 | payload: JSON payload with request data. |
| 68 | |
| 69 | Returns: |
| 70 | JSON string response. |
| 71 | |
| 72 | Raises: |
| 73 | ValueError: If the URL is not recognized or if required data is missing. |
| 74 | """ |
| 75 | # Edge Case: Handle missing payload |
| 76 | if payload is None: |
| 77 | raise ValueError("Payload is required for POST requests") |
| 78 | |
| 79 | data = json.loads(payload) |
| 80 | |
| 81 | # Edge Case: Handle /add endpoint |
| 82 | if url == "/add": |
| 83 | # Edge Case: Handle missing user field |
| 84 | if "user" not in data: |
| 85 | raise ValueError("Missing 'user' field in payload") |
| 86 | |
| 87 | user_name = data["user"] |
| 88 | |
| 89 | # Edge Case: Handle duplicate user - return existing user instead of raising error |
| 90 | for user in self.database["users"]: |
| 91 | if user["name"] == user_name: |
| 92 | return json.dumps(user) |
| 93 | |
| 94 | # Create new user |
| 95 | new_user = { |
| 96 | "name": user_name, |
| 97 | "owes": {}, |
| 98 | "owed_by": {}, |
| 99 | "balance": 0.0 |
| 100 | } |
| 101 | |
| 102 | self.database["users"].append(new_user) |
| 103 | return json.dumps(new_user) |
| 104 | |
| 105 | # Edge Case: Handle /iou endpoint |
| 106 | elif url == "/iou": |
| 107 | # Edge Case: Handle missing required fields |
| 108 | required_fields = ["lender", "borrower", "amount"] |
| 109 | for field in required_fields: |
| 110 | if field not in data: |
| 111 | raise ValueError(f"Missing '{field}' field in payload") |
| 112 | |
| 113 | lender_name = data["lender"] |
| 114 | borrower_name = data["borrower"] |
| 115 | amount = data["amount"] |
| 116 | |
| 117 | # Edge Case: Handle negative or zero amount |
| 118 | if amount <= 0: |
| 119 | raise ValueError("Amount must be positive") |
| 120 | |
| 121 | # Edge Case: Handle lender and borrower being the same person |
| 122 | if lender_name == borrower_name: |
| 123 | raise ValueError("Lender and borrower cannot be the same person") |
| 124 | |
| 125 | # Find lender and borrower |
| 126 | lender = None |
| 127 | borrower = None |
| 128 | |
| 129 | for user in self.database["users"]: |
| 130 | if user["name"] == lender_name: |
| 131 | lender = user |
| 132 | elif user["name"] == borrower_name: |
| 133 | borrower = user |
| 134 | |
| 135 | # Edge Case: Handle unknown lender or borrower |
| 136 | if lender is None: |
| 137 | raise ValueError(f"Unknown lender: {lender_name}") |
| 138 | if borrower is None: |
| 139 | raise ValueError(f"Unknown borrower: {borrower_name}") |
| 140 | |
| 141 | # Handle IOU netting - check if there's an existing relationship |
| 142 | # Case 1: Borrower already owes lender (same direction as new IOU) |
| 143 | if borrower_name in lender["owed_by"]: |
| 144 | # Add to existing debt in same direction |
| 145 | lender["owed_by"][borrower_name] += amount |
| 146 | borrower["owes"][lender_name] += amount |
| 147 | # Case 2: Lender already owes borrower (opposite direction to new IOU) |
| 148 | elif lender_name in borrower["owed_by"]: |
| 149 | existing_debt = borrower["owed_by"][lender_name] |
| 150 | if amount > existing_debt: |
| 151 | # New IOU is larger, so remove the existing debt and create new IOU in opposite direction |
| 152 | del borrower["owed_by"][lender_name] |
| 153 | del lender["owes"][borrower_name] |
| 154 | remaining_amount = amount - existing_debt |
| 155 | # Lender is now owed by borrower for the remaining amount |
| 156 | lender["owed_by"][borrower_name] = remaining_amount |
| 157 | borrower["owes"][lender_name] = remaining_amount |
| 158 | elif amount == existing_debt: |
| 159 | # New IOU exactly cancels the existing debt |
| 160 | del borrower["owed_by"][lender_name] |
| 161 | del lender["owes"][borrower_name] |
| 162 | else: |
| 163 | # New IOU is smaller, so reduce the existing debt |
| 164 | borrower["owed_by"][lender_name] -= amount |
| 165 | lender["owes"][borrower_name] -= amount |
| 166 | else: |
| 167 | # No existing debt in either direction, just add the new IOU |
| 168 | # Update lender's owed_by |
| 169 | lender["owed_by"][borrower_name] = lender["owed_by"].get(borrower_name, 0) + amount |
| 170 | # Update borrower's owes |
| 171 | borrower["owes"][lender_name] = borrower["owes"].get(lender_name, 0) + amount |
| 172 | |
| 173 | # Recalculate balances |
| 174 | lender_total_owed = sum(lender["owed_by"].values()) |
| 175 | lender_total_owes = sum(lender["owes"].values()) |
| 176 | lender["balance"] = lender_total_owed - lender_total_owes |
| 177 | |
| 178 | borrower_total_owed = sum(borrower["owed_by"].values()) |
| 179 | borrower_total_owes = sum(borrower["owes"].values()) |
| 180 | borrower["balance"] = borrower_total_owed - borrower_total_owes |
| 181 | |
| 182 | # Return updated users sorted by name |
| 183 | users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 184 | return json.dumps({"users": users}) |
| 185 | |
| 186 | # Edge Case: Handle unknown URLs |
| 187 | raise ValueError(f"Unknown POST endpoint: {url}") |
| 188 | |
| 189 | # Handled Edge Cases: None database, /users endpoint, payload with specific users, |
| 190 | # all users when no payload, unknown URLs, missing payload, /add endpoint, |
| 191 | # missing user field, duplicate user, /iou endpoint, missing required fields, |
| 192 | # negative or zero amount, lender and borrower being the same person, |
| 193 | # unknown lender or borrower |