How to Build a Flow Control Credit Window in Python

class CreditWindow:
    def __init__(self, max_credit=1000):
        self.max_credit = max_credit
        self.used_credit = 0
        self.pending_credit = 0
    
    def try_reserve(self, amount):
        available = self.max_credit - self.used_credit - self.pending_credit
        if available >= amount:
            self.pending_credit += amount
            return True
        return False
    
    def confirm(self, amount):
        self.pending_credit -= amount
        self.used_credit += amount
    
    def release(self, amount):
        self.pending_credit -= amount
    
    def settle(self, amount):
        self.used_credit = max(0, self.used_credit - amount)
    
    def available(self):
        return self.max_credit - self.used_credit - self.pending_credit
    
    def __repr__(self):
        return (f"CreditWindow(max={self.max_credit}, used={self.used_credit}, "
                f"pending={self.pending_credit}, available={self.available()})")


if __name__ == "__main__":
    window = CreditWindow(max_credit=1000)
    print(f"Initial: {window}")
    
    print(f"Reserve 300: {window.try_reserve(300)}")
    window.confirm(300)
    print(f"After confirm: {window}")
    
    print(f"Reserve 700: {window.try_reserve(700)}")
    print(f"Reserve 500: {window.try_reserve(500)}")
    window.release(500)
    print(f"After release: {window}")
    
    window.settle(200)
    print(f"After settle: {window}")