| 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 = sorted(self.database["users"], key=lambda x: x["name"]) |
| 28 | return json.dumps({"users": users}) |
| 29 | else: |
| 30 | # Return specific users sorted by name |
| 31 | data = json.loads(payload) |
| 32 | user_names = data.get("users", []) |
| 33 | |
| 34 | # Edge Case: Empty user list in payload |
| 35 | if not user_names: |
| 36 | return json.dumps({"users": []}) |
| 37 | |
| 38 | # Filter users by name |
| 39 | users = [user for user in self.database["users"] if user["name"] in user_names] |
| 40 | users = sorted(users, key=lambda x: x["name"]) |
| 41 | |
| 42 | # Edge Case: User in payload not found in database |
| 43 | if len(users) != len(user_names): |
| 44 | return json.dumps({"users": []}) |
| 45 | |
| 46 | return json.dumps({"users": users}) |
| 47 | |
| 48 | # Edge Case: Invalid URL |
| 49 | return json.dumps({"error": "Invalid URL"}) |
| 50 | |
| 8 | 51 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 52 | """ |
| 53 | Handle POST requests to the API. |
| 54 | |
| 55 | Args: |
| 56 | url: The endpoint URL. |
| 57 | payload: JSON payload. |
| 58 | |
| 59 | Returns: |
| 60 | A JSON string response. |
| 61 | """ |
| 62 | if payload is None: |
| 63 | # Edge Case: Missing payload |
| 64 | return json.dumps({"error": "Missing payload"}) |
| 65 | |
| 66 | data = json.loads(payload) |
| 67 | |
| 68 | if url == "/add": |
| 69 | user_name = data.get("user") |
| 70 | |
| 71 | # Edge Case: Missing user name |
| 72 | if not user_name: |
| 73 | return json.dumps({"error": "Missing user name"}) |
| 74 | |
| 75 | # Edge Case: User already exists - return the existing user |
| 76 | for user in self.database["users"]: |
| 77 | if user["name"] == user_name: |
| 78 | return json.dumps(user) |
| 79 | |
| 80 | # Create new user |
| 81 | new_user = { |
| 82 | "name": user_name, |
| 83 | "owes": {}, |
| 84 | "owed_by": {}, |
| 85 | "balance": 0.0 |
| 86 | } |
| 87 | self.database["users"].append(new_user) |
| 88 | |
| 89 | return json.dumps(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 not lender_name or not borrower_name or amount is None: |
| 98 | return json.dumps({"error": "Missing required fields"}) |
| 99 | |
| 100 | # Edge Case: Invalid amount type |
| 101 | if not isinstance(amount, (int, float)): |
| 102 | return json.dumps({"error": "Invalid amount"}) |
| 103 | |
| 104 | # Edge Case: Negative amount |
| 105 | if amount < 0: |
| 106 | return json.dumps({"error": "Amount must be positive"}) |
| 107 | |
| 108 | # Edge Case: Lender and borrower are the same |
| 109 | if lender_name == borrower_name: |
| 110 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 111 | |
| 112 | # Find lender and borrower, create if they don't exist |
| 113 | lender = None |
| 114 | borrower = None |
| 115 | |
| 116 | for user in self.database["users"]: |
| 117 | if user["name"] == lender_name: |
| 118 | lender = user |
| 119 | elif user["name"] == borrower_name: |
| 120 | borrower = user |
| 121 | |
| 122 | # Create lender if not found |
| 123 | if lender is None: |
| 124 | lender = { |
| 125 | "name": lender_name, |
| 126 | "owes": {}, |
| 127 | "owed_by": {}, |
| 128 | "balance": 0.0 |
| 129 | } |
| 130 | self.database["users"].append(lender) |
| 131 | |
| 132 | # Create borrower if not found |
| 133 | if borrower is None: |
| 134 | borrower = { |
| 135 | "name": borrower_name, |
| 136 | "owes": {}, |
| 137 | "owed_by": {}, |
| 138 | "balance": 0.0 |
| 139 | } |
| 140 | self.database["users"].append(borrower) |
| 141 | |
| 142 | # Update owes and owed_by with proper handling of reverse transactions |
| 143 | |
| 144 | # Handle the case where the borrower already owes the lender |
| 145 | # This creates a net effect where debts can cancel out or reduce |
| 146 | |
| 147 | # If borrower already owes lender, reduce that amount first |
| 148 | if borrower_name in lender["owes"]: |
| 149 | existing_owes = lender["owes"][borrower_name] |
| 150 | if amount > existing_owes: |
| 151 | # New IOU is larger than existing debt, remove the debt and create new owed amount |
| 152 | del lender["owes"][borrower_name] |
| 153 | del borrower["owed_by"][lender_name] |
| 154 | |
| 155 | # Add the remaining amount to owed_by |
| 156 | lender["owed_by"][borrower_name] = amount - existing_owes |
| 157 | borrower["owes"][lender_name] = amount - existing_owes |
| 158 | else: |
| 159 | # New IOU is smaller or equal to existing debt, just reduce the debt |
| 160 | lender["owes"][borrower_name] -= amount |
| 161 | borrower["owed_by"][lender_name] -= amount |
| 162 | |
| 163 | # Remove entries if they become zero |
| 164 | if lender["owes"][borrower_name] == 0: |
| 165 | del lender["owes"][borrower_name] |
| 166 | del borrower["owed_by"][lender_name] |
| 167 | else: |
| 168 | # Normal case - update lender's owed_by |
| 169 | if borrower_name in lender["owed_by"]: |
| 170 | lender["owed_by"][borrower_name] += amount |
| 171 | else: |
| 172 | lender["owed_by"][borrower_name] = amount |
| 173 | |
| 174 | # Update borrower's owes |
| 175 | if lender_name in borrower["owes"]: |
| 176 | borrower["owes"][lender_name] += amount |
| 177 | else: |
| 178 | borrower["owes"][lender_name] = amount |
| 179 | |
| 180 | # Recalculate balances |
| 181 | lender_total_owed = sum(lender["owed_by"].values()) |
| 182 | lender_total_owes = sum(lender["owes"].values()) |
| 183 | lender["balance"] = lender_total_owed - lender_total_owes |
| 184 | |
| 185 | borrower_total_owed = sum(borrower["owed_by"].values()) |
| 186 | borrower_total_owes = sum(borrower["owes"].values()) |
| 187 | borrower["balance"] = borrower_total_owed - borrower_total_owes |
| 188 | |
| 189 | # Return updated users sorted by name |
| 190 | users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 191 | return json.dumps({"users": users}) |
| 192 | |
| 193 | # Edge Case: Invalid URL |
| 194 | return json.dumps({"error": "Invalid URL"}) |
| 195 | |
| 196 | # Handled Edge Cases: Invalid URL, Missing payload, Missing user name, User already exists, Missing required fields, Invalid amount type, Negative amount, Lender and borrower are the same, Lender or borrower not found |