| 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 | # Edge Case: Handle /users endpoint |
| 26 | if url == "/users": |
| 27 | # Edge Case: Handle payload with specific users |
| 28 | if payload is not None: |
| 29 | data = json.loads(payload) |
| 30 | if "users" in data: |
| 31 | # Filter users and sort by name |
| 32 | users = [user for user in self.database["users"] if user["name"] in data["users"]] |
| 33 | users.sort(key=lambda x: x["name"]) |
| 34 | return json.dumps({"users": users}) |
| 35 | # Edge Case: Handle request for all users |
| 36 | else: |
| 37 | # Return all users sorted by name |
| 38 | users = sorted(self.database["users"], key=lambda x: x["name"]) |
| 39 | return json.dumps({"users": users}) |
| 40 | |
| 41 | # Handled Edge Cases: /users endpoint with and without payload |
| 42 | return json.dumps({"error": "Invalid endpoint"}) |
| 43 | |
| 8 | 44 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 45 | """ |
| 46 | Handle POST requests to the API. |
| 47 | |
| 48 | Args: |
| 49 | url: The endpoint URL. |
| 50 | payload: JSON payload. |
| 51 | |
| 52 | Returns: |
| 53 | JSON string response. |
| 54 | """ |
| 55 | # Edge Case: Handle None payload |
| 56 | if payload is None: |
| 57 | return json.dumps({"error": "Payload required"}) |
| 58 | |
| 59 | data = json.loads(payload) |
| 60 | |
| 61 | # Edge Case: Handle /add endpoint |
| 62 | if url == "/add": |
| 63 | # Edge Case: Check if user field exists in payload |
| 64 | if "user" not in data: |
| 65 | return json.dumps({"error": "User field required"}) |
| 66 | |
| 67 | user_name = data["user"] |
| 68 | |
| 69 | # Edge Case: Check if user already exists |
| 70 | for user in self.database["users"]: |
| 71 | if user["name"] == user_name: |
| 72 | return json.dumps({"error": "User already exists"}) |
| 73 | |
| 74 | # Create new user |
| 75 | new_user = { |
| 76 | "name": user_name, |
| 77 | "owes": {}, |
| 78 | "owed_by": {}, |
| 79 | "balance": 0.0 |
| 80 | } |
| 81 | |
| 82 | self.database["users"].append(new_user) |
| 83 | return json.dumps(new_user) |
| 84 | |
| 85 | # Edge Case: Handle /iou endpoint |
| 86 | elif url == "/iou": |
| 87 | # Edge Case: Validate required fields |
| 88 | required_fields = ["lender", "borrower", "amount"] |
| 89 | for field in required_fields: |
| 90 | if field not in data: |
| 91 | return json.dumps({"error": f"Missing field: {field}"}) |
| 92 | |
| 93 | lender_name = data["lender"] |
| 94 | borrower_name = data["borrower"] |
| 95 | amount = data["amount"] |
| 96 | |
| 97 | # Edge Case: Validate amount is positive |
| 98 | if amount <= 0: |
| 99 | return json.dumps({"error": "Amount must be positive"}) |
| 100 | |
| 101 | # Edge Case: Validate lender and borrower are different |
| 102 | if lender_name == borrower_name: |
| 103 | return json.dumps({"error": "Lender and borrower must be different"}) |
| 104 | |
| 105 | # Edge Case: Validate both users exist |
| 106 | lender = None |
| 107 | borrower = None |
| 108 | for user in self.database["users"]: |
| 109 | if user["name"] == lender_name: |
| 110 | lender = user |
| 111 | elif user["name"] == borrower_name: |
| 112 | borrower = user |
| 113 | |
| 114 | # Edge Case: Handle user not found |
| 115 | if lender is None or borrower is None: |
| 116 | return json.dumps({"error": "User not found"}) |
| 117 | |
| 118 | # Handle debt relationships - check if there's existing debt between users |
| 119 | |
| 120 | # Case 1: Lender already owes borrower |
| 121 | if borrower_name in lender["owes"]: |
| 122 | # Check if new IOU is in the same direction (lender lending to borrower) |
| 123 | # If so, add to existing debt; otherwise, offset debts |
| 124 | if lender_name == data["lender"] and borrower_name == data["borrower"]: |
| 125 | # Same direction - accumulate debt |
| 126 | lender["owes"][borrower_name] += amount |
| 127 | borrower["owed_by"][lender_name] += amount |
| 128 | else: |
| 129 | # Opposite direction - offset debts |
| 130 | existing_debt = lender["owes"][borrower_name] |
| 131 | |
| 132 | if existing_debt == amount: |
| 133 | # Exact cancellation - remove the debt |
| 134 | del lender["owes"][borrower_name] |
| 135 | del borrower["owed_by"][lender_name] |
| 136 | elif existing_debt > amount: |
| 137 | # Lender owes more than new loan - reduce existing debt |
| 138 | lender["owes"][borrower_name] -= amount |
| 139 | borrower["owed_by"][lender_name] -= amount |
| 140 | else: |
| 141 | # Lender owes less than new loan - convert the debt |
| 142 | remaining_amount = amount - existing_debt |
| 143 | del lender["owes"][borrower_name] |
| 144 | del borrower["owed_by"][lender_name] |
| 145 | # Now borrower owes lender the remaining amount |
| 146 | if lender_name in borrower["owes"]: |
| 147 | borrower["owes"][lender_name] += remaining_amount |
| 148 | else: |
| 149 | borrower["owes"][lender_name] = remaining_amount |
| 150 | |
| 151 | if borrower_name in lender["owed_by"]: |
| 152 | lender["owed_by"][borrower_name] += remaining_amount |
| 153 | else: |
| 154 | lender["owed_by"][borrower_name] = remaining_amount |
| 155 | # Case 2: Borrower already owes lender |
| 156 | elif lender_name in borrower["owes"]: |
| 157 | # Check if new IOU is in the same direction (borrower lending to lender) |
| 158 | # If so, add to existing debt; otherwise, offset debts |
| 159 | if borrower_name == data["lender"] and lender_name == data["borrower"]: |
| 160 | # Same direction - accumulate debt |
| 161 | borrower["owes"][lender_name] += amount |
| 162 | lender["owed_by"][borrower_name] += amount |
| 163 | else: |
| 164 | # Opposite direction - offset debts |
| 165 | existing_debt = borrower["owes"][lender_name] |
| 166 | |
| 167 | if existing_debt == amount: |
| 168 | # Exact cancellation - remove the debt |
| 169 | del borrower["owes"][lender_name] |
| 170 | del lender["owed_by"][borrower_name] |
| 171 | elif existing_debt > amount: |
| 172 | # Borrower owes more than new loan - reduce existing debt |
| 173 | borrower["owes"][lender_name] -= amount |
| 174 | lender["owed_by"][borrower_name] -= amount |
| 175 | else: |
| 176 | # Borrower owes less than new loan - convert the debt |
| 177 | remaining_amount = amount - existing_debt |
| 178 | del borrower["owes"][lender_name] |
| 179 | del lender["owed_by"][borrower_name] |
| 180 | # Now lender owes borrower the remaining amount |
| 181 | if borrower_name in lender["owes"]: |
| 182 | lender["owes"][borrower_name] += remaining_amount |
| 183 | else: |
| 184 | lender["owes"][borrower_name] = remaining_amount |
| 185 | |
| 186 | if lender_name in borrower["owed_by"]: |
| 187 | borrower["owed_by"][lender_name] += remaining_amount |
| 188 | else: |
| 189 | borrower["owed_by"][lender_name] = remaining_amount |
| 190 | else: |
| 191 | # Normal case - no existing debt |
| 192 | # Update lender's owed_by |
| 193 | if borrower_name in lender["owed_by"]: |
| 194 | lender["owed_by"][borrower_name] += amount |
| 195 | else: |
| 196 | lender["owed_by"][borrower_name] = amount |
| 197 | |
| 198 | # Update borrower's owes |
| 199 | if lender_name in borrower["owes"]: |
| 200 | borrower["owes"][lender_name] += amount |
| 201 | else: |
| 202 | borrower["owes"][lender_name] = amount |
| 203 | |
| 204 | # Recalculate balances |
| 205 | lender_total_owed = sum(lender["owed_by"].values()) |
| 206 | lender_total_owes = sum(lender["owes"].values()) |
| 207 | lender["balance"] = lender_total_owed - lender_total_owes |
| 208 | |
| 209 | borrower_total_owed = sum(borrower["owed_by"].values()) |
| 210 | borrower_total_owes = sum(borrower["owes"].values()) |
| 211 | borrower["balance"] = borrower_total_owed - borrower_total_owes |
| 212 | |
| 213 | # Return updated users sorted by name |
| 214 | updated_users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 215 | return json.dumps({"users": updated_users}) |
| 216 | |
| 217 | # Handled Edge Cases: /add and /iou endpoints with all validation checks |
| 218 | return json.dumps({"error": "Invalid endpoint"}) |
| 219 | |
| 220 | # Handled Edge Cases: None database initialization, None payload handling, user already exists, |
| 221 | # missing user field, invalid endpoints, missing IOU fields, negative amounts, |
| 222 | # same lender/borrower, user not found, /users endpoint with and without payload |