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1from fastapi import FastAPI, HTTPException, Header
2from pydantic import BaseModel
3from typing import Optional
4import secrets
5import datetime
6 
7app = FastAPI()
8 
9users = {}
10expenses = {}
11budgets = {}
12tokens = {}
13next_user_id = 1
14next_expense_id = 1
15next_budget_id = 1
16 
17class SignupRequest(BaseModel):
18    username: str
19    password: str
20 
21class LoginRequest(BaseModel):
22    username: str
23    password: str
24 
25class ExpenseCreate(BaseModel):
26    category: str
27    amount: float
28    description: Optional[str] = None
29 
30class BudgetCreate(BaseModel):
31    category: str
32    limit: float
33 
34def get_current_user(authorization: str = Header(None)):
35    if not authorization:
36        raise HTTPException(status_code=401, detail="Missing auth header")
37    token = authorization.replace("Bearer ", "")
38    if token not in tokens:
39        raise HTTPException(status_code=401, detail="Invalid token")
40    return tokens[token]
41 
42@app.post("/signup")
43def signup(req: SignupRequest):
44    global next_user_id
45    for u in users.values():
46        if u["username"] == req.username:
47            raise HTTPException(status_code=400, detail="User exists")
48    user_id = next_user_id
49    next_user_id += 1
50    users[user_id] = {
51        "id": user_id,
52        "username": req.username,
53        "password": req.password
54    }
55    return {"id": user_id, "username": req.username}
56 
57@app.post("/login")
58def login(req: LoginRequest):
59    for u in users.values():
60        if u["username"] == req.username and u["password"] == req.password:
61            token = secrets.token_hex(16)
62            tokens[token] = u["id"]
63            return {"token": token}
64    raise HTTPException(status_code=401, detail="Invalid credentials")
65 
66@app.get("/expenses/{expense_id}")
67def get_expense(expense_id: int, authorization: str = Header(None)):
68    user_id = get_current_user(authorization)
69    if expense_id not in expenses:
70        raise HTTPException(status_code=404, detail="Expense not found")
71    return expenses[expense_id]
72 
73@app.post("/expenses")
74def create_expense(expense: ExpenseCreate, authorization: str = Header(None)):
75    global next_expense_id
76    user_id = get_current_user(authorization)
77    expense_id = next_expense_id
78    next_expense_id += 1
79    expenses[expense_id] = {
80        "id": expense_id,
81        "user_id": user_id,
82        "category": expense.category,
83        "amount": expense.amount,
84        "description": expense.description,
85        "created_at": datetime.datetime.utcnow().isoformat()
86    }
87    return expenses[expense_id]
88 
89@app.get("/budgets/{budget_id}")
90def get_budget(budget_id: int, authorization: str = Header(None)):
91    user_id = get_current_user(authorization)
92    if budget_id not in budgets:
93        raise HTTPException(status_code=404, detail="Budget not found")
94    return budgets[budget_id]
95 
96@app.post("/budgets")
97def create_budget(budget: BudgetCreate, authorization: str = Header(None)):
98    global next_budget_id
99    user_id = get_current_user(authorization)
100    budget_id = next_budget_id
101    next_budget_id += 1
102    budgets[budget_id] = {
103        "id": budget_id,
104        "user_id": user_id,
105        "category": budget.category,
106        "limit": budget.limit
107    }
108    return budgets[budget_id]
109 
110@app.get("/budget")
111def get_budget_summary(authorization: str = Header(None)):
112    user_id = get_current_user(authorization)
113    user_expenses = [e for e in expenses.values() if e["user_id"] == user_id]
114    user_budgets = [b for b in budgets.values() if b["user_id"] == user_id]
115 
116    spending_by_category = {}
117    for e in user_expenses:
118        cat = e["category"]
119        spending_by_category[cat] = spending_by_category.get(cat, 0) + e["amount"]
120 
121    result = []
122    for b in user_budgets:
123        cat = b["category"]
124        spent = spending_by_category.get(cat, 0)
125        remaining = b["limit"] - spent
126        result.append({
127            "category": cat,
128            "limit": b["limit"],
129            "spent": spent,
130            "remaining": remaining
131        })
132    return result

1fastapi
2uvicorn