| 1 | import json |
| 2 | from typing import Dict, List, Optional, Any |
| 3 | |
| 1 | 4 | class RestAPI: |
| 2 | 5 | def __init__(self, database: dict | None = None): |
| 3 | | pass |
| 4 | | |
| 6 | """ |
| 7 | Initialize the REST API with a database of users. |
| 8 | |
| 9 | Args: |
| 10 | database: A dictionary containing user data with the structure: |
| 11 | {"users": [{"name": str, "owes": dict, "owed_by": dict, "balance": float}]} |
| 12 | """ |
| 13 | if database is None: |
| 14 | self.database = {"users": []} |
| 15 | else: |
| 16 | self.database = database |
| 17 | |
| 5 | 18 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 19 | """ |
| 20 | Handle GET requests to the API. |
| 21 | |
| 22 | Args: |
| 23 | url: The endpoint URL (e.g., "/users") |
| 24 | payload: Optional JSON payload containing request parameters |
| 25 | |
| 26 | Returns: |
| 27 | JSON string response |
| 28 | """ |
| 29 | if url == "/users": |
| 30 | if payload is None: |
| 31 | # Return all users sorted by name |
| 32 | users = sorted(self.database["users"], key=lambda x: x["name"]) |
| 33 | return json.dumps({"users": users}) |
| 34 | else: |
| 35 | # Return only specified users sorted by name |
| 36 | payload_data = json.loads(payload) |
| 37 | user_names = payload_data.get("users", []) |
| 38 | |
| 39 | # Edge Case: Empty users list in payload |
| 40 | if not user_names: |
| 41 | return json.dumps({"users": []}) |
| 42 | |
| 43 | # Filter users by name |
| 44 | filtered_users = [user for user in self.database["users"] if user["name"] in user_names] |
| 45 | # Sort by name |
| 46 | filtered_users.sort(key=lambda x: x["name"]) |
| 47 | return json.dumps({"users": filtered_users}) |
| 48 | |
| 49 | # Edge Case: Invalid URL |
| 50 | return json.dumps({"error": "Invalid URL"}) |
| 51 | |
| 8 | 52 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 53 | """ |
| 54 | Handle POST requests to the API. |
| 55 | |
| 56 | Args: |
| 57 | url: The endpoint URL (e.g., "/add", "/iou") |
| 58 | payload: JSON payload containing request data |
| 59 | |
| 60 | Returns: |
| 61 | JSON string response |
| 62 | """ |
| 63 | if payload is None: |
| 64 | # Edge Case: Missing payload |
| 65 | return json.dumps({"error": "Payload required"}) |
| 66 | |
| 67 | try: |
| 68 | payload_data = json.loads(payload) |
| 69 | except json.JSONDecodeError: |
| 70 | # Edge Case: Invalid JSON payload |
| 71 | return json.dumps({"error": "Invalid JSON payload"}) |
| 72 | |
| 73 | if url == "/add": |
| 74 | user_name = payload_data.get("user") |
| 75 | |
| 76 | # Edge Case: Missing user name |
| 77 | if not user_name: |
| 78 | return json.dumps({"error": "User name required"}) |
| 79 | |
| 80 | # Edge Case: User already exists |
| 81 | if any(user["name"] == user_name for user in self.database["users"]): |
| 82 | return json.dumps({"error": "User already exists"}) |
| 83 | |
| 84 | # Create new user |
| 85 | new_user = { |
| 86 | "name": user_name, |
| 87 | "owes": {}, |
| 88 | "owed_by": {}, |
| 89 | "balance": 0.0 |
| 90 | } |
| 91 | self.database["users"].append(new_user) |
| 92 | return json.dumps(new_user) |
| 93 | |
| 94 | elif url == "/iou": |
| 95 | lender_name = payload_data.get("lender") |
| 96 | borrower_name = payload_data.get("borrower") |
| 97 | amount = payload_data.get("amount") |
| 98 | |
| 99 | # Edge Case: Missing required fields |
| 100 | if not lender_name or not borrower_name or amount is None: |
| 101 | return json.dumps({"error": "Lender, borrower, and amount are required"}) |
| 102 | |
| 103 | # Edge Case: Invalid amount type |
| 104 | if not isinstance(amount, (int, float)): |
| 105 | return json.dumps({"error": "Amount must be a number"}) |
| 106 | |
| 107 | # Edge Case: Negative amount |
| 108 | if amount < 0: |
| 109 | return json.dumps({"error": "Amount must be positive"}) |
| 110 | |
| 111 | # Edge Case: Lender and borrower are the same |
| 112 | if lender_name == borrower_name: |
| 113 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 114 | |
| 115 | # Find lender and borrower |
| 116 | lender = next((user for user in self.database["users"] if user["name"] == lender_name), None) |
| 117 | borrower = next((user for user in self.database["users"] if user["name"] == borrower_name), None) |
| 118 | |
| 119 | # Edge Case: Lender or borrower does not exist |
| 120 | if not lender or not borrower: |
| 121 | return json.dumps({"error": "Lender or borrower does not exist"}) |
| 122 | |
| 123 | # Handle debt offsetting - check if borrower owes lender |
| 124 | # This happens when there's an existing debt in the opposite direction |
| 125 | if lender_name in borrower["owes"]: |
| 126 | # Borrower owes lender, so we need to offset |
| 127 | existing_debt = borrower["owes"][lender_name] |
| 128 | if existing_debt == amount: |
| 129 | # Debts cancel out completely |
| 130 | del borrower["owes"][lender_name] |
| 131 | if borrower_name in lender["owed_by"]: |
| 132 | del lender["owed_by"][borrower_name] |
| 133 | elif existing_debt > amount: |
| 134 | # Borrower still owes lender, reduce the debt |
| 135 | borrower["owes"][lender_name] = existing_debt - amount |
| 136 | if borrower_name in lender["owed_by"]: |
| 137 | del lender["owed_by"][borrower_name] |
| 138 | else: |
| 139 | # New loan is larger, reverse the debt direction |
| 140 | del borrower["owes"][lender_name] |
| 141 | if borrower_name in lender["owed_by"]: |
| 142 | del lender["owed_by"][borrower_name] |
| 143 | # Now lender owes borrower the difference |
| 144 | lender["owes"][borrower_name] = amount - existing_debt |
| 145 | borrower["owed_by"][lender_name] = amount - existing_debt |
| 146 | else: |
| 147 | # No existing debt in opposite direction, just add the new debt |
| 148 | # Update lender's owed_by (borrower owes lender) |
| 149 | if borrower_name in lender["owed_by"]: |
| 150 | lender["owed_by"][borrower_name] += amount |
| 151 | else: |
| 152 | lender["owed_by"][borrower_name] = amount |
| 153 | |
| 154 | # Update borrower's owes (borrower owes lender) |
| 155 | if lender_name in borrower["owes"]: |
| 156 | borrower["owes"][lender_name] += amount |
| 157 | else: |
| 158 | borrower["owes"][lender_name] = amount |
| 159 | |
| 160 | # Recalculate balances |
| 161 | lender_total_owed = sum(lender["owed_by"].values()) |
| 162 | lender_total_owes = sum(lender["owes"].values()) |
| 163 | lender["balance"] = lender_total_owed - lender_total_owes |
| 164 | |
| 165 | borrower_total_owed = sum(borrower["owed_by"].values()) |
| 166 | borrower_total_owes = sum(borrower["owes"].values()) |
| 167 | borrower["balance"] = borrower_total_owed - borrower_total_owes |
| 168 | |
| 169 | # Return updated users sorted by name |
| 170 | updated_users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 171 | return json.dumps({"users": updated_users}) |
| 172 | |
| 173 | # Edge Case: Invalid URL |
| 174 | return json.dumps({"error": "Invalid URL"}) |
| 175 | |
| 176 | # Handled Edge Cases: Invalid URL, Missing payload, Invalid JSON payload, Missing user name, |
| 177 | # User already exists, Missing required fields, Invalid amount type, Negative amount, |
| 178 | # Lender and borrower are the same, Lender or borrower does not exist, Empty users list in payload |