| 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 or {"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 | 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 x: x["name"]) |
| 29 | return json.dumps({"users": users}) |
| 30 | else: |
| 31 | # Return specified users sorted by name |
| 32 | data = json.loads(payload) |
| 33 | user_names = data.get("users", []) |
| 34 | |
| 35 | # Edge Case: Empty user list in payload - return all users |
| 36 | if not user_names: |
| 37 | users = [self._create_user_object(user) for user in self.database["users"]] |
| 38 | users.sort(key=lambda x: x["name"]) |
| 39 | return json.dumps({"users": users}) |
| 40 | |
| 41 | # Edge Case: Non-existent users in payload |
| 42 | users = [] |
| 43 | for user_name in user_names: |
| 44 | user = self._get_user(user_name) |
| 45 | if user: |
| 46 | users.append(self._create_user_object(user)) |
| 47 | |
| 48 | users.sort(key=lambda x: x["name"]) |
| 49 | return json.dumps({"users": users}) |
| 50 | |
| 51 | # Edge Case: Invalid URL |
| 52 | return json.dumps({"error": "Invalid URL"}) |
| 53 | |
| 8 | 54 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 55 | """ |
| 56 | Handle POST requests to the API. |
| 57 | |
| 58 | Args: |
| 59 | url: The endpoint URL. |
| 60 | payload: JSON payload. |
| 61 | |
| 62 | Returns: |
| 63 | JSON string response. |
| 64 | """ |
| 65 | if payload is None: |
| 66 | # Edge Case: Missing payload |
| 67 | return json.dumps({"error": "Payload required"}) |
| 68 | |
| 69 | data = json.loads(payload) |
| 70 | |
| 71 | if url == "/add": |
| 72 | user_name = data.get("user") |
| 73 | |
| 74 | # Edge Case: Missing user name |
| 75 | if not user_name: |
| 76 | return json.dumps({"error": "User name required"}) |
| 77 | |
| 78 | # Edge Case: User already exists - return existing user |
| 79 | existing_user = self._get_user(user_name) |
| 80 | if existing_user: |
| 81 | return json.dumps(self._create_user_object(existing_user)) |
| 82 | |
| 83 | new_user = { |
| 84 | "name": user_name, |
| 85 | "owes": {}, |
| 86 | "owed_by": {}, |
| 87 | "balance": 0.0 |
| 88 | } |
| 89 | self.database["users"].append(new_user) |
| 90 | return json.dumps(self._create_user_object(new_user)) |
| 91 | |
| 92 | elif url == "/iou": |
| 93 | lender_name = data.get("lender") |
| 94 | borrower_name = data.get("borrower") |
| 95 | amount = data.get("amount") |
| 96 | |
| 97 | # Edge Case: Missing required fields |
| 98 | if not lender_name or not borrower_name or amount is None: |
| 99 | return json.dumps({"error": "Lender, borrower, and amount required"}) |
| 100 | |
| 101 | # Edge Case: Invalid amount type |
| 102 | if not isinstance(amount, (int, float)): |
| 103 | return json.dumps({"error": "Amount must be a number"}) |
| 104 | |
| 105 | # Edge Case: Negative amount |
| 106 | if amount < 0: |
| 107 | return json.dumps({"error": "Amount must be positive"}) |
| 108 | |
| 109 | lender = self._get_user(lender_name) |
| 110 | borrower = self._get_user(borrower_name) |
| 111 | |
| 112 | # Edge Case: Non-existent lender or borrower |
| 113 | if not lender or not borrower: |
| 114 | return json.dumps({"error": "Lender or borrower does not exist"}) |
| 115 | |
| 116 | # Edge Case: Lender and borrower are the same person |
| 117 | if lender_name == borrower_name: |
| 118 | return json.dumps({"error": "Cannot create IOU between same user"}) |
| 119 | |
| 120 | # Check if there's already an IOU in the opposite direction |
| 121 | existing_lender_owes = lender["owes"].get(borrower_name, 0) |
| 122 | existing_borrower_owed_by = borrower["owed_by"].get(lender_name, 0) |
| 123 | |
| 124 | if existing_lender_owes > 0 or existing_borrower_owed_by > 0: |
| 125 | # There's an existing IOU in opposite direction, need to net them |
| 126 | net_amount = amount - existing_lender_owes |
| 127 | |
| 128 | if net_amount > 0: |
| 129 | # New IOU is larger, update in the new direction |
| 130 | # Remove old opposite direction entries |
| 131 | if borrower_name in lender["owes"]: |
| 132 | del lender["owes"][borrower_name] |
| 133 | if lender_name in borrower["owed_by"]: |
| 134 | del borrower["owed_by"][lender_name] |
| 135 | |
| 136 | # Add new direction entries |
| 137 | lender["owed_by"][borrower_name] = net_amount |
| 138 | borrower["owes"][lender_name] = net_amount |
| 139 | |
| 140 | # Update balances - lender gains amount, borrower loses amount |
| 141 | lender["balance"] += amount |
| 142 | borrower["balance"] -= amount |
| 143 | |
| 144 | elif net_amount < 0: |
| 145 | # Old IOU is larger, update in the old direction |
| 146 | # Remove any entries that might exist in new direction |
| 147 | if borrower_name in lender["owed_by"]: |
| 148 | del lender["owed_by"][borrower_name] |
| 149 | if lender_name in borrower["owes"]: |
| 150 | del borrower["owes"][lender_name] |
| 151 | |
| 152 | # Update old direction entries |
| 153 | lender["owes"][borrower_name] = abs(net_amount) |
| 154 | borrower["owed_by"][lender_name] = abs(net_amount) |
| 155 | |
| 156 | # Update balances - lender loses amount, borrower gains amount |
| 157 | lender["balance"] -= amount |
| 158 | borrower["balance"] += amount |
| 159 | |
| 160 | else: |
| 161 | # Net to zero, remove all entries |
| 162 | if borrower_name in lender["owes"]: |
| 163 | del lender["owes"][borrower_name] |
| 164 | if lender_name in borrower["owed_by"]: |
| 165 | del borrower["owed_by"][lender_name] |
| 166 | if borrower_name in lender["owed_by"]: |
| 167 | del lender["owed_by"][borrower_name] |
| 168 | if lender_name in borrower["owes"]: |
| 169 | del borrower["owes"][lender_name] |
| 170 | |
| 171 | # Update balances - lender gains existing_lender_owes, borrower loses existing_lender_owes |
| 172 | lender["balance"] += existing_lender_owes |
| 173 | borrower["balance"] -= existing_lender_owes |
| 174 | else: |
| 175 | # No existing IOU in opposite direction, add new IOU |
| 176 | # Update lender's owed_by |
| 177 | if borrower_name in lender["owed_by"]: |
| 178 | lender["owed_by"][borrower_name] += amount |
| 179 | else: |
| 180 | lender["owed_by"][borrower_name] = amount |
| 181 | |
| 182 | # Update borrower's owes |
| 183 | if lender_name in borrower["owes"]: |
| 184 | borrower["owes"][lender_name] += amount |
| 185 | else: |
| 186 | borrower["owes"][lender_name] = amount |
| 187 | |
| 188 | # Update balances |
| 189 | lender["balance"] += amount |
| 190 | borrower["balance"] -= amount |
| 191 | |
| 192 | # Return updated user objects sorted by name |
| 193 | users = [self._create_user_object(lender), self._create_user_object(borrower)] |
| 194 | users.sort(key=lambda x: x["name"]) |
| 195 | return json.dumps({"users": users}) |
| 196 | |
| 197 | # Edge Case: Invalid URL |
| 198 | return json.dumps({"error": "Invalid URL"}) |
| 199 | |
| 200 | def _get_user(self, name: str): |
| 201 | """ |
| 202 | Find a user by name in the database. |
| 203 | |
| 204 | Args: |
| 205 | name: The name of the user to find. |
| 206 | |
| 207 | Returns: |
| 208 | The user dictionary if found, None otherwise. |
| 209 | """ |
| 210 | for user in self.database["users"]: |
| 211 | if user["name"] == name: |
| 212 | return user |
| 213 | return None |
| 214 | |
| 215 | def _create_user_object(self, user: dict) -> dict: |
| 216 | """ |
| 217 | Create a user object with calculated balance. |
| 218 | |
| 219 | Args: |
| 220 | user: The user dictionary from the database. |
| 221 | |
| 222 | Returns: |
| 223 | A user object with calculated balance. |
| 224 | """ |
| 225 | # Calculate balance from owes and owed_by |
| 226 | total_owed = sum(user["owes"].values()) |
| 227 | total_owed_by = sum(user["owed_by"].values()) |
| 228 | balance = total_owed_by - total_owed |
| 229 | |
| 230 | return { |
| 231 | "name": user["name"], |
| 232 | "owes": user["owes"], |
| 233 | "owed_by": user["owed_by"], |
| 234 | "balance": balance |
| 235 | } |
| 236 | # Handled Edge Cases: Invalid URL, Missing payload, Missing user name, User already exists, Missing required fields, Invalid amount type, Negative amount, Non-existent lender or borrower, Lender and borrower are the same person, Empty user list in payload, Non-existent users in payload |