init commit

optimizetka/app.py

@@ -0,0 +1,77 @@
+from fastapi import FastAPI
+from pydantic import BaseModel
+from typing import List
+from collections import defaultdict
+
+app = FastAPI(openapi_url="/optimizetka/openapi.json", docs_url="/optimizetka/docs")
+
+
+class Participant(BaseModel):
+    id: int
+
+
+class Position(BaseModel):
+    price: float
+    assigned_to_ids: List[int]
+
+
+class Transaction(BaseModel):
+    owner_id: int
+    positions: List[Position]
+
+
+class InputData(BaseModel):
+    participants: List[Participant]
+    transactions: List[Transaction]
+
+
+class Debt(BaseModel):
+    from_user_id: int
+    to_user_id: int
+    amount: float
+
+
+@app.post("/optimizetka/api/calculate-debts", response_model=List[Debt])
+def calculate_debts(data: InputData) -> List[Debt]:
+    balances = defaultdict(float)
+
+    for transaction in data.transactions:
+        owner_id = transaction.owner_id
+        for position in transaction.positions:
+            price = position.price
+            assigned_to_ids = position.assigned_to_ids
+            share = price / len(assigned_to_ids)
+
+            for participant_id in assigned_to_ids:
+                if participant_id != owner_id:
+                    balances[participant_id] -= share
+                    balances[owner_id] += share
+
+    debts = []
+    creditors = [(p, amount) for p, amount in balances.items() if amount > 0]
+    debtors = [(p, -amount) for p, amount in balances.items() if amount < 0]
+
+    i, j = 0, 0
+    while i < len(creditors) and j < len(debtors):
+        creditor_id, credit_amount = creditors[i]
+        debtor_id, debt_amount = debtors[j]
+
+        payment = min(credit_amount, debt_amount)
+
+        debts.append(
+            {
+                "from_user_id": debtor_id,
+                "to_user_id": creditor_id,
+                "amount": round(payment, 2),
+            }
+        )
+
+        creditors[i] = (creditor_id, credit_amount - payment)
+        debtors[j] = (debtor_id, debt_amount - payment)
+
+        if creditors[i][1] == 0:
+            i += 1
+        if debtors[j][1] == 0:
+            j += 1
+
+    return debts