Implement basic throttle library

.gitignore

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+/.idea

LICENSE

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+MIT License
+
+Copyright (c) 2021 ChronosX88
+
+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.

README.md

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+# go-throttle
+
+The Go library for throttling some actions, for example, API requests to some network service.
+
+## Install
+
+Using Go Modules:
+
+```
+go get github.com/ChronosX88/go-throttle
+```
+
+## Usage
+
+TBD
+
+## License
+
+This project is licensed under the MIT license, Copyright (c) 2021 ChronosX88. For more information see [LICENSE](LICENSE) file.
+

config.go

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+package throttle
+
+import "time"
+
+type Config struct {
+	NumTokens   float64
+	Delay       time.Duration
+	RefillRate  float64
+	DefaultCost float64
+	Capacity    float64
+	MaxCapacity int
+}

go.mod

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+module github.com/ChronosX88/go-throttle
+
+go 1.15
+
+require github.com/reactivex/rxgo/v2 v2.4.0

go.sum

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throttle.go

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+package throttle
+
+import (
+	"context"
+	"github.com/reactivex/rxgo/v2"
+	"math"
+	"sync"
+	"time"
+)
+
+type Throttle struct {
+	lastTimestamp int64
+	queueChan chan *req
+	config Config
+	cfgMut sync.Mutex
+	running bool
+	ctx context.Context
+}
+
+func NewThrottle(ctx context.Context, cfg *Config) *Throttle {
+	if cfg == nil {
+		cfg = &Config{
+			NumTokens:   0,
+			Delay:       0.001,
+			RefillRate:  0.001,
+			DefaultCost: 1.000,
+			Capacity:    1.000,
+		}
+	}
+
+	return &Throttle{
+		lastTimestamp: -1,
+		queueChan: make(chan *req, cfg.MaxCapacity),
+		config: *cfg,
+		running: false,
+		ctx: ctx,
+	}
+}
+
+func (t *Throttle) run() {
+	go func() {
+		for {
+			select {
+			case <-t.ctx.Done(): {
+				return
+			}
+			case r:=<-t.queueChan: {
+				for {
+					if t.config.NumTokens > 0 || t.config.RefillRate == 0 {
+						r.resolveChan <- rxgo.Of(true)
+						close(r.resolveChan)
+						var cost float64 = 0
+						if r.cost != -1 {
+							cost = r.cost
+						} else {
+							cost = t.config.DefaultCost
+						}
+						t.config.NumTokens -= cost
+						break
+					}
+					if t.lastTimestamp == -1 {
+						t.lastTimestamp = time.Now().Unix()
+					}
+					now := time.Now().Unix()
+					elapsed := now - t.lastTimestamp
+					t.lastTimestamp = now
+					t.config.NumTokens = math.Min(t.config.Capacity, t.config.NumTokens+float64(elapsed)*t.config.RefillRate)
+					time.Sleep(t.config.Delay)
+				}
+			}
+			}
+		}
+	}()
+
+}
+
+func (t *Throttle) Take(rateLimit float64, cost float64) rxgo.Observable {
+	t.cfgMut.Lock()
+	defer t.cfgMut.Unlock()
+	ch := make(chan rxgo.Item)
+	t.queueChan <- &req{
+		cost: cost,
+		resolveChan: ch,
+	}
+	if rateLimit == 0 {
+		t.config.RefillRate = 0
+	} else {
+		t.config.RefillRate = 1/rateLimit
+	}
+	return rxgo.FromChannel(ch)
+}
+
+type req struct {
+	cost float64
+	resolveChan chan rxgo.Item
+}
+