Refactor a bit.

mathrand.go

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-package gae
-
-import (
-        "math/rand"
-
-        "github.com/luci/luci-go/common/clock"
-        "golang.org/x/net/context"
-)
-
-// TODO(riannucci): Extract this into its own package. It's used by taskqueue,
-// but otherwise isn't related to gae services at all.
-
-// MathRandFactory is the function signature for factory methods compatible with
-// SetMathRandFactory.
-type MathRandFactory func(context.Context) *rand.Rand
-
-// GetMathRand gets a *"math/rand".Rand from the context. If one hasn't been
-// set, this creates a new Rand object with a Source initialized from the
-// current time clock.Now(c).UnixNano().
-func GetMathRand(c context.Context) *rand.Rand {
-        if f, ok := c.Value(mathRandKey).(MathRandFactory); ok && f != nil {
-                return f(c)
-        }
-        return rand.New(rand.NewSource(clock.Now(c).UnixNano()))
-}
-
-// SetMathRandFactory sets the function to produce *"math/rand".Rand instances,
-// as returned by the GetMathRand method.
-func SetMathRandFactory(c context.Context, mrf MathRandFactory) context.Context {
-        return context.WithValue(c, mathRandKey, mrf)
-}
-
-// SetMathRand sets the current *"math/rand".Rand object in the context. Useful
-// for testing with a quick mock. This is just a shorthand SetMathRandFactory
-// invocation to set a factory which always returns the same object.
-func SetMathRand(c context.Context, r *rand.Rand) context.Context {
-        if r == nil {
-                return SetMathRandFactory(c, nil)
-        }
-        return SetMathRandFactory(c, func(context.Context) *rand.Rand { return r })
-}