| 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 with 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 | sorted_users = sorted(self.database["users"], key=lambda x: x["name"]) |
| 33 | return json.dumps({"users": sorted_users}) |
| 34 | else: |
| 35 | # Return specific users |
| 36 | payload_data = json.loads(payload) |
| 37 | requested_users = payload_data.get("users", []) |
| 38 | |
| 39 | # Edge Case: Handle when users list is empty |
| 40 | if not requested_users: |
| 41 | return json.dumps({"users": []}) |
| 42 | |
| 43 | # Filter users |
| 44 | result_users = [user for user in self.database["users"] if user["name"] in requested_users] |
| 45 | |
| 46 | # Edge Case: Handle when requested users don't exist |
| 47 | # Sort by name |
| 48 | result_users.sort(key=lambda x: x["name"]) |
| 49 | return json.dumps({"users": result_users}) |
| 50 | |
| 51 | # Edge Case: Handle unknown URL |
| 52 | return json.dumps({"error": "Not found"}) |
| 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 (e.g., "/add", "/iou") |
| 60 | payload: JSON payload with request data |
| 61 | |
| 62 | Returns: |
| 63 | JSON string response |
| 64 | """ |
| 65 | if payload is None: |
| 66 | # Edge Case: Handle missing payload |
| 67 | return json.dumps({"error": "Payload required"}) |
| 68 | |
| 69 | try: |
| 70 | payload_data = json.loads(payload) |
| 71 | except json.JSONDecodeError: |
| 72 | # Edge Case: Handle invalid JSON |
| 73 | return json.dumps({"error": "Invalid JSON"}) |
| 74 | |
| 75 | if url == "/add": |
| 76 | user_name = payload_data.get("user") |
| 77 | |
| 78 | # Edge Case: Handle missing user name |
| 79 | if not user_name: |
| 80 | return json.dumps({"error": "User name required"}) |
| 81 | |
| 82 | # Edge Case: Handle duplicate user - return existing user |
| 83 | for user in self.database["users"]: |
| 84 | if user["name"] == user_name: |
| 85 | return json.dumps(user) |
| 86 | |
| 87 | # Create new user |
| 88 | new_user = { |
| 89 | "name": user_name, |
| 90 | "owes": {}, |
| 91 | "owed_by": {}, |
| 92 | "balance": 0.0 |
| 93 | } |
| 94 | self.database["users"].append(new_user) |
| 95 | return json.dumps(new_user) |
| 96 | |
| 97 | elif url == "/iou": |
| 98 | lender_name = payload_data.get("lender") |
| 99 | borrower_name = payload_data.get("borrower") |
| 100 | amount = payload_data.get("amount") |
| 101 | |
| 102 | # Edge Case: Handle missing fields |
| 103 | if not lender_name or not borrower_name or amount is None: |
| 104 | return json.dumps({"error": "Lender, borrower, and amount are required"}) |
| 105 | |
| 106 | # Edge Case: Handle invalid amount type |
| 107 | if not isinstance(amount, (int, float)): |
| 108 | return json.dumps({"error": "Amount must be a number"}) |
| 109 | |
| 110 | # Edge Case: Handle negative amount |
| 111 | if amount < 0: |
| 112 | return json.dumps({"error": "Amount must be positive"}) |
| 113 | |
| 114 | # Edge Case: Handle same lender and borrower |
| 115 | if lender_name == borrower_name: |
| 116 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 117 | |
| 118 | # Check if users exist |
| 119 | lender = None |
| 120 | borrower = None |
| 121 | for user in self.database["users"]: |
| 122 | if user["name"] == lender_name: |
| 123 | lender = user |
| 124 | elif user["name"] == borrower_name: |
| 125 | borrower = user |
| 126 | |
| 127 | # Edge Case: Handle non-existent lender or borrower |
| 128 | if lender is None or borrower is None: |
| 129 | return json.dumps({"error": "Both lender and borrower must exist"}) |
| 130 | |
| 131 | # Handle IOU transaction - when lender "lends" to borrower, lender actually owes borrower |
| 132 | # This is the confusing part - the lender is the one who ends up owing money |
| 133 | |
| 134 | # Get existing amounts |
| 135 | existing_lender_owes_borrower = 0 |
| 136 | existing_borrower_owes_lender = 0 |
| 137 | |
| 138 | if borrower_name in lender["owes"]: |
| 139 | existing_lender_owes_borrower = lender["owes"][borrower_name] |
| 140 | |
| 141 | if borrower_name in lender["owed_by"]: |
| 142 | existing_borrower_owes_lender = lender["owed_by"][borrower_name] |
| 143 | |
| 144 | # Calculate new total debt (lender owes borrower) |
| 145 | # When lender "lends" to borrower, lender actually owes borrower the amount |
| 146 | # Handle existing debts properly |
| 147 | if existing_borrower_owes_lender > 0: |
| 148 | # Borrower already owes lender, so this reduces that debt |
| 149 | if amount > existing_borrower_owes_lender: |
| 150 | # New loan is larger than existing debt, reverse the debt |
| 151 | new_debt = amount - existing_borrower_owes_lender |
| 152 | else: |
| 153 | # New loan is smaller than or equal to existing debt, reduce the debt |
| 154 | new_debt = existing_lender_owes_borrower - (existing_borrower_owes_lender - amount) |
| 155 | else: |
| 156 | # No existing debt from borrower to lender, add to lender's debt to borrower |
| 157 | new_debt = existing_lender_owes_borrower + amount |
| 158 | |
| 159 | # Clear existing relationships |
| 160 | if borrower_name in lender["owes"]: |
| 161 | del lender["owes"][borrower_name] |
| 162 | del borrower["owed_by"][lender_name] |
| 163 | |
| 164 | if borrower_name in lender["owed_by"]: |
| 165 | del lender["owed_by"][borrower_name] |
| 166 | del borrower["owes"][lender_name] |
| 167 | |
| 168 | # Set new relationship |
| 169 | if new_debt > 0: |
| 170 | # Lender owes borrower |
| 171 | lender["owes"][borrower_name] = new_debt |
| 172 | borrower["owed_by"][lender_name] = new_debt |
| 173 | elif new_debt < 0: |
| 174 | # Borrower owes lender |
| 175 | lender["owed_by"][borrower_name] = -new_debt |
| 176 | borrower["owes"][lender_name] = -new_debt |
| 177 | # If new_debt == 0, no debts remain |
| 178 | |
| 179 | # Recalculate balances |
| 180 | lender_total_owed = sum(lender["owed_by"].values()) |
| 181 | lender_total_owes = sum(lender["owes"].values()) |
| 182 | lender["balance"] = lender_total_owed - lender_total_owes |
| 183 | |
| 184 | borrower_total_owed = sum(borrower["owed_by"].values()) |
| 185 | borrower_total_owes = sum(borrower["owes"].values()) |
| 186 | borrower["balance"] = borrower_total_owed - borrower_total_owes |
| 187 | |
| 188 | # Recalculate balances |
| 189 | lender_total_owed = sum(lender["owed_by"].values()) |
| 190 | lender_total_owes = sum(lender["owes"].values()) |
| 191 | lender["balance"] = lender_total_owed - lender_total_owes |
| 192 | |
| 193 | borrower_total_owed = sum(borrower["owed_by"].values()) |
| 194 | borrower_total_owes = sum(borrower["owes"].values()) |
| 195 | borrower["balance"] = borrower_total_owed - borrower_total_owes |
| 196 | |
| 197 | # Return updated users sorted by name |
| 198 | result_users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 199 | return json.dumps({"users": result_users}) |
| 200 | |
| 201 | # Edge Case: Handle unknown URL |
| 202 | return json.dumps({"error": "Not found"}) |
| 203 | |
| 204 | # Handled Edge Cases: Missing payload, Invalid JSON, Missing user name, Duplicate user, Missing fields, |
| 205 | # Invalid amount type, Negative amount, Same lender and borrower, Non-existent lender or borrower, Unknown URL |
| 206 | # Handled Edge Cases: Unknown URL, Missing payload |