// Copyright © 2023 OpenIM open source community. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package middleware

import (
	"sync"
	"time"

	"github.com/gin-gonic/gin"
)

// define rate limit struct.
type frequencyControlByTokenBucket struct {
	refreshRate float64    // token refresh rate
	capacity    int64      // bucket capacity
	tokens      float64    // token count
	lastToken   time.Time  // latest time token stored
	mtx         sync.Mutex // mutex
}

// allow frequency.
func (tb *frequencyControlByTokenBucket) Allow() bool {
	tb.mtx.Lock()
	defer tb.mtx.Unlock()
	now := time.Now()
	// compute tokens which needs
	tb.tokens = tb.tokens + tb.refreshRate*now.Sub(tb.lastToken).Seconds()
	if tb.tokens > float64(tb.capacity) {
		tb.tokens = float64(tb.capacity)
	}
	// judge weather to pass through
	if tb.tokens >= 1 {
		tb.tokens--
		tb.lastToken = now

		return true
	}

	return false
}

// LimitHandler registried a middle ware to use.
func LimitHandler(maxConn int, refreshRate float64) gin.HandlerFunc {
	tb := &frequencyControlByTokenBucket{
		capacity:    int64(maxConn),
		refreshRate: refreshRate,
		tokens:      0,
		lastToken:   time.Now(),
	}

	return func(c *gin.Context) {
		if !tb.Allow() {
			c.String(503, "Too many request")
			c.Abort()

			return
		}
		c.Next()
	}
}