package client

import (
	"math/rand"
	"sync"
	"time"

	"github.com/aws/aws-sdk-go/aws/request"
)

// DefaultRetryer implements basic retry logic using exponential backoff for
// most services. If you want to implement custom retry logic, implement the
// request.Retryer interface or create a structure type that composes this
// struct and override the specific methods. For example, to override only
// the MaxRetries method:
//
//		type retryer struct {
//      client.DefaultRetryer
//    }
//
//    // This implementation always has 100 max retries
//    func (d retryer) MaxRetries() int { return 100 }
type DefaultRetryer struct {
	NumMaxRetries int
}

// MaxRetries returns the number of maximum returns the service will use to make
// an individual API request.
func (d DefaultRetryer) MaxRetries() int {
	return d.NumMaxRetries
}

var seededRand = rand.New(&lockedSource{src: rand.NewSource(time.Now().UnixNano())})

// RetryRules returns the delay duration before retrying this request again
func (d DefaultRetryer) RetryRules(r *request.Request) time.Duration {
	// Set the upper limit of delay in retrying at ~five minutes
	minTime := 30
	throttle := d.shouldThrottle(r)
	if throttle {
		minTime = 500
	}

	retryCount := r.RetryCount
	if retryCount > 13 {
		retryCount = 13
	} else if throttle && retryCount > 8 {
		retryCount = 8
	}

	delay := (1 << uint(retryCount)) * (seededRand.Intn(minTime) + minTime)
	return time.Duration(delay) * time.Millisecond
}

// ShouldRetry returns true if the request should be retried.
func (d DefaultRetryer) ShouldRetry(r *request.Request) bool {
	// If one of the other handlers already set the retry state
	// we don't want to override it based on the service's state
	if r.Retryable != nil {
		return *r.Retryable
	}

	if r.HTTPResponse.StatusCode >= 500 {
		return true
	}
	return r.IsErrorRetryable() || d.shouldThrottle(r)
}

// ShouldThrottle returns true if the request should be throttled.
func (d DefaultRetryer) shouldThrottle(r *request.Request) bool {
	if r.HTTPResponse.StatusCode == 502 ||
		r.HTTPResponse.StatusCode == 503 ||
		r.HTTPResponse.StatusCode == 504 {
		return true
	}
	return r.IsErrorThrottle()
}

// lockedSource is a thread-safe implementation of rand.Source
type lockedSource struct {
	lk  sync.Mutex
	src rand.Source
}

func (r *lockedSource) Int63() (n int64) {
	r.lk.Lock()
	n = r.src.Int63()
	r.lk.Unlock()
	return
}

func (r *lockedSource) Seed(seed int64) {
	r.lk.Lock()
	r.src.Seed(seed)
	r.lk.Unlock()
}
