Rackspace Auto Scale: Add policies Update()
diff --git a/rackspace/autoscale/v1/policies/fixtures.go b/rackspace/autoscale/v1/policies/fixtures.go
index 587c5e7..a66d6d1 100644
--- a/rackspace/autoscale/v1/policies/fixtures.go
+++ b/rackspace/autoscale/v1/policies/fixtures.go
@@ -117,6 +117,16 @@
 }
 `
 
+// PolicyUpdateRequest contains the canned body of a policies.Update request.
+const PolicyUpdateRequest = `
+{
+  "name": "updated webhook policy",
+  "type": "webhook",
+  "cooldown": 600,
+  "changePercent": 6.6
+}
+`
+
 var (
 	// WebhookPolicy is a Policy corresponding to the first result in PolicyListBody.
 	WebhookPolicy = Policy{
@@ -199,3 +209,20 @@
 		fmt.Fprintf(w, PolicyGetBody)
 	})
 }
+
+// HandlePolicyUpdateSuccessfully sets up the test server to respond to a policies Update request.
+func HandlePolicyUpdateSuccessfully(t *testing.T) {
+	groupID := "60b15dad-5ea1-43fa-9a12-a1d737b4da07"
+	policyID := "2b48d247-0282-4b9d-8775-5c4b67e8e649"
+
+	path := fmt.Sprintf("/groups/%s/policies/%s", groupID, policyID)
+
+	th.Mux.HandleFunc(path, func(w http.ResponseWriter, r *http.Request) {
+		th.TestMethod(t, r, "PUT")
+		th.TestHeader(t, r, "X-Auth-Token", client.TokenID)
+
+		th.TestJSONRequest(t, r, PolicyUpdateRequest)
+
+		w.WriteHeader(http.StatusNoContent)
+	})
+}
diff --git a/rackspace/autoscale/v1/policies/requests.go b/rackspace/autoscale/v1/policies/requests.go
index ab3d5eb..9cc6c34 100644
--- a/rackspace/autoscale/v1/policies/requests.go
+++ b/rackspace/autoscale/v1/policies/requests.go
@@ -129,3 +129,78 @@
 
 	return result
 }
+
+// UpdateOptsBuilder is the interface responsible for generating the map
+// structure for producing JSON for an Update operation.
+type UpdateOptsBuilder interface {
+	ToPolicyUpdateMap() (map[string]interface{}, error)
+}
+
+// UpdateOpts represents the options for updating an existing policy.
+//
+// Update operations completely replace the configuration being updated. Empty
+// values in the update are accepted and overwrite previously specified
+// parameters.
+type UpdateOpts struct {
+	// Name [required] is a name for the policy.
+	Name string
+
+	// Type [required] of policy, i.e. either "webhook" or "schedule".
+	Type Type
+
+	// Cooldown [required] period in seconds.  If you don't specify a cooldown,
+	// it will default to zero, and the policy will be configured as such.
+	Cooldown int
+
+	// Adjustment [requried] type and value for the policy.
+	Adjustment Adjustment
+
+	// Additional configuration options for some types of policy.
+	Args map[string]interface{}
+}
+
+// ToPolicyUpdateMap converts an UpdateOpts struct into a map for use as the
+// request body in an Update request.
+func (opts UpdateOpts) ToPolicyUpdateMap() (map[string]interface{}, error) {
+	if opts.Name == "" {
+		return nil, ErrNoName
+	}
+
+	if opts.Type == Schedule && opts.Args == nil {
+		return nil, ErrNoArgs
+	}
+
+	policy := make(map[string]interface{})
+
+	policy["name"] = opts.Name
+	policy["type"] = opts.Type
+	policy["cooldown"] = opts.Cooldown
+
+	// TODO: Function to validate and cast key + value?
+	policy[string(opts.Adjustment.Type)] = opts.Adjustment.Value
+
+	if opts.Args != nil {
+		policy["args"] = opts.Args
+	}
+
+	return policy, nil
+}
+
+// Update requests the configuration of the given policy be updated.
+func Update(client *gophercloud.ServiceClient, groupID, policyID string, opts UpdateOptsBuilder) UpdateResult {
+	var result UpdateResult
+
+	url := updateURL(client, groupID, policyID)
+	reqBody, err := opts.ToPolicyUpdateMap()
+
+	if err != nil {
+		result.Err = err
+		return result
+	}
+
+	_, result.Err = client.Put(url, reqBody, nil, &gophercloud.RequestOpts{
+		OkCodes: []int{204},
+	})
+
+	return result
+}
diff --git a/rackspace/autoscale/v1/policies/requests_test.go b/rackspace/autoscale/v1/policies/requests_test.go
index b600377..8ee90f3 100644
--- a/rackspace/autoscale/v1/policies/requests_test.go
+++ b/rackspace/autoscale/v1/policies/requests_test.go
@@ -108,3 +108,24 @@
 	th.AssertNoErr(t, err)
 	th.CheckDeepEquals(t, WebhookPolicy, *policy)
 }
+
+func TestUpdate(t *testing.T) {
+	th.SetupHTTP()
+	defer th.TeardownHTTP()
+	HandlePolicyUpdateSuccessfully(t)
+
+	client := client.ServiceClient()
+	opts := UpdateOpts{
+		Name:     "updated webhook policy",
+		Type:     Webhook,
+		Cooldown: 600,
+		Adjustment: Adjustment{
+			Type:  ChangePercent,
+			Value: 6.6,
+		},
+	}
+
+	err := Update(client, groupID, webhookPolicyID, opts).ExtractErr()
+
+	th.AssertNoErr(t, err)
+}
diff --git a/rackspace/autoscale/v1/policies/results.go b/rackspace/autoscale/v1/policies/results.go
index e92d636..f63b1a7 100644
--- a/rackspace/autoscale/v1/policies/results.go
+++ b/rackspace/autoscale/v1/policies/results.go
@@ -47,6 +47,11 @@
 	policyResult
 }
 
+// UpdateResult represents the result of an update operation.
+type UpdateResult struct {
+	gophercloud.ErrResult
+}
+
 // Policy represents a scaling policy.
 type Policy struct {
 	// UUID for the policy.
diff --git a/rackspace/autoscale/v1/policies/urls.go b/rackspace/autoscale/v1/policies/urls.go
index ebbd154..7203ccf 100644
--- a/rackspace/autoscale/v1/policies/urls.go
+++ b/rackspace/autoscale/v1/policies/urls.go
@@ -13,3 +13,7 @@
 func getURL(c *gophercloud.ServiceClient, groupID, policyID string) string {
 	return c.ServiceURL("groups", groupID, "policies", policyID)
 }
+
+func updateURL(c *gophercloud.ServiceClient, groupID, policyID string) string {
+	return getURL(c, groupID, policyID)
+}