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1from fastapi import FastAPI, HTTPException, Header
2from pydantic import BaseModel
3from typing import Optional, List
4import secrets
5import datetime
6 
7app = FastAPI()
8 
9# In-memory stores
10users = {}
11tokens = {}
12bills = {}
13bill_items = {}
14payments = {}
15collectors = {}
16 
17# ID counters
18user_id_counter = 1
19bill_id_counter = 1
20bill_item_id_counter = 1
21payment_id_counter = 1
22 
23# Models
24class SignupRequest(BaseModel):
25    username: str
26    password: str
27 
28class LoginRequest(BaseModel):
29    username: str
30    password: str
31 
32class BillCreate(BaseModel):
33    title: str
34    total_amount: float
35    split_among: List[int]  # user IDs
36 
37class BillItemCreate(BaseModel):
38    bill_id: int
39    user_id: int
40    amount: float
41    description: Optional[str] = None
42 
43class PaymentCreate(BaseModel):
44    bill_id: int
45    from_user_id: int
46    amount: float
47 
48class CollectorPromote(BaseModel):
49    bill_id: int
50    collector_user_id: int
51    fee_percentage: float = 0.0
52 
53def get_current_user(authorization: Optional[str] = Header(None)):
54    if not authorization:
55        raise HTTPException(status_code=401, detail="No auth header")
56    token = authorization.replace("Bearer ", "")
57    if token not in tokens:
58        raise HTTPException(status_code=401, detail="Invalid token")
59    return tokens[token]
60 
61# Auth endpoints
62@app.post("/signup")
63def signup(req: SignupRequest):
64    global user_id_counter
65    for uid, u in users.items():
66        if u["username"] == req.username:
67            raise HTTPException(status_code=400, detail="Username taken")
68    user_id = user_id_counter
69    user_id_counter += 1
70    users[user_id] = {
71        "id": user_id,
72        "username": req.username,
73        "password": req.password  # plaintext, we said no security
74    }
75    return {"user_id": user_id, "message": "User created"}
76 
77@app.post("/login")
78def login(req: LoginRequest):
79    for uid, u in users.items():
80        if u["username"] == req.username and u["password"] == req.password:
81            token = secrets.token_hex(16)
82            tokens[token] = uid
83            return {"token": token, "user_id": uid}
84    raise HTTPException(status_code=401, detail="Invalid credentials")
85 
86# Resource endpoints
87@app.get("/bills/{bill_id}")
88def get_bill(bill_id: int, authorization: Optional[str] = Header(None)):
89    get_current_user(authorization)
90    if bill_id not in bills:
91        raise HTTPException(status_code=404, detail="Bill not found")
92    return bills[bill_id]
93 
94@app.post("/bills")
95def create_bill(bill: BillCreate, authorization: Optional[str] = Header(None)):
96    current_user = get_current_user(authorization)
97    global bill_id_counter
98    bill_id = bill_id_counter
99    bill_id_counter += 1
100    bills[bill_id] = {
101        "id": bill_id,
102        "title": bill.title,
103        "total_amount": bill.total_amount,
104        "split_among": bill.split_among,
105        "created_by": current_user,
106        "created_at": datetime.datetime.now().isoformat()
107    }
108    return {"bill_id": bill_id, "message": "Bill created"}
109 
110@app.get("/bill_items/{item_id}")
111def get_bill_item(item_id: int, authorization: Optional[str] = Header(None)):
112    get_current_user(authorization)
113    if item_id not in bill_items:
114        raise HTTPException(status_code=404, detail="Bill item not found")
115    return bill_items[item_id]
116 
117@app.post("/bill_items")
118def create_bill_item(item: BillItemCreate, authorization: Optional[str] = Header(None)):
119    get_current_user(authorization)
120    if item.bill_id not in bills:
121        raise HTTPException(status_code=404, detail="Bill not found")
122    global bill_item_id_counter
123    item_id = bill_item_id_counter
124    bill_item_id_counter += 1
125    bill_items[item_id] = {
126        "id": item_id,
127        "bill_id": item.bill_id,
128        "user_id": item.user_id,
129        "amount": item.amount,
130        "description": item.description
131    }
132    return {"item_id": item_id, "message": "Bill item created"}
133 
134@app.get("/payments/{payment_id}")
135def get_payment(payment_id: int, authorization: Optional[str] = Header(None)):
136    get_current_user(authorization)
137    if payment_id not in payments:
138        raise HTTPException(status_code=404, detail="Payment not found")
139    return payments[payment_id]
140 
141@app.post("/payments")
142def create_payment(payment: PaymentCreate, authorization: Optional[str] = Header(None)):
143    current_user = get_current_user(authorization)
144    if payment.bill_id not in bills:
145        raise HTTPException(status_code=404, detail="Bill not found")
146    global payment_id_counter
147    payment_id = payment_id_counter
148    payment_id_counter += 1
149    payments[payment_id] = {
150        "id": payment_id,
151        "bill_id": payment.bill_id,
152        "from_user_id": payment.from_user_id,
153        "amount": payment.amount,
154        "paid_by": current_user,
155        "timestamp": datetime.datetime.now().isoformat()
156    }
157    return {"payment_id": payment_id, "message": "Payment recorded"}
158 
159# Collector endpoints
160@app.post("/collectors/promote")
161def promote_collector(req: CollectorPromote, authorization: Optional[str] = Header(None)):
162    current_user = get_current_user(authorization)
163    if req.bill_id not in bills:
164        raise HTTPException(status_code=404, detail="Bill not found")
165    if req.collector_user_id not in users:
166        raise HTTPException(status_code=404, detail="User not found")
167    collectors[req.bill_id] = {
168        "bill_id": req.bill_id,
169        "collector_user_id": req.collector_user_id,
170        "fee_percentage": req.fee_percentage,
171        "promoted_by": current_user
172    }
173    return {"message": f"User {req.collector_user_id} is now collector for bill {req.bill_id}"}
174 
175@app.post("/collectors/chase/{bill_id}")
176def chase_payments(bill_id: int, authorization: Optional[str] = Header(None)):
177    current_user = get_current_user(authorization)
178    if bill_id not in bills:
179        raise HTTPException(status_code=404, detail="Bill not found")
180    if bill_id not in collectors:
181        raise HTTPException(status_code=400, detail="No collector for this bill")
182    collector = collectors[bill_id]
183    if collector["collector_user_id"] != current_user:
184        raise HTTPException(status_code=403, detail="You are not the collector")
185    bill = bills[bill_id]
186    total_paid = sum(p["amount"] for p in payments.values() if p["bill_id"] == bill_id)
187    outstanding = bill["total_amount"] - total_paid
188    fee = outstanding * (collector["fee_percentage"] / 100)
189    return {
190        "bill_id": bill_id,
191        "outstanding": outstanding,
192        "collector_fee": fee,
193        "total_due": outstanding + fee,
194        "message": "Chase sent (simulated)"
195    }
196 
197@app.get("/users/{user_id}")
198def get_user(user_id: int, authorization: Optional[str] = Header(None)):
199    get_current_user(authorization)
200    if user_id not in users:
201        raise HTTPException(status_code=404, detail="User not found")
202    u = users[user_id]
203    return {"id": u["id"], "username": u["username"]}
204 
205@app.get("/collectors/{bill_id}")
206def get_collector(bill_id: int, authorization: Optional[str] = Header(None)):
207    get_current_user(authorization)
208    if bill_id not in collectors:
209        raise HTTPException(status_code=404, detail="No collector for this bill")
210    return collectors[bill_id]

1fastapi
2uvicorn