// Copyright (c) 2019 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package quotas

// MultiStageRateLimiter indicates a domain specific rate limit policy
type MultiStageRateLimiter struct {
	domainLimiters ICollection
	globalLimiter  Limiter
}

// NewMultiStageRateLimiter returns a new domain quota rate limiter. This is about
// an order of magnitude slower than
func NewMultiStageRateLimiter(global Limiter, domainLimiters ICollection) *MultiStageRateLimiter {
	return &MultiStageRateLimiter{
		domainLimiters: domainLimiters,
		globalLimiter:  global,
	}
}

// Allow attempts to allow a request to go through. The method returns
// immediately with a true or false indicating if the request can make
// progress
func (d *MultiStageRateLimiter) Allow(info Info) (allowed bool) {
	domain := info.Domain
	if len(domain) == 0 {
		return d.globalLimiter.Allow()
	}

	// take a reservation with the domain limiter first
	rsv := d.domainLimiters.For(domain).Reserve()
	defer func() {
		rsv.Used(allowed) // returns the token if allowed but not used
	}()

	if !rsv.Allow() {
		return false
	}

	// ensure that the reservation does not break the global rate limit, if it
	// does, cancel the reservation and do not allow to proceed.
	if !d.globalLimiter.Allow() {
		return false
	}
	return true
}
