engine: Resources package rewrite

This giant patch makes some much needed improvements to the code base.

* The engine has been rewritten and lives within engine/graph/
* All of the common interfaces and code now live in engine/
* All of the resources are in one package called engine/resources/
* The Res API can use different "traits" from engine/traits/
* The Res API has been simplified to hide many of the old internals
* The Watch & Process loops were previously inverted, but is now fixed
* The likelihood of package cycles has been reduced drastically
* And much, much more...

Unfortunately, some code had to be temporarily removed. The remote code
had to be taken out, as did the prometheus code. We hope to have these
back in new forms as soon as possible.

engine/traits/autogroup.go

@@ -0,0 +1,89 @@
+// Mgmt
+// Copyright (C) 2013-2018+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package traits
+
+import (
+	"fmt"
+
+	"github.com/purpleidea/mgmt/engine"
+)
+
+// Groupable contains a general implementation with most of the properties and
+// methods needed to support autogrouping on resources. It may be used as a
+// starting point to avoid re-implementing the straightforward methods.
+type Groupable struct {
+	meta *engine.AutoGroupMeta
+
+	isGrouped bool                  // am i contained within a group?
+	grouped   []engine.GroupableRes // list of any grouped resources
+
+	// Bug5819 works around issue https://github.com/golang/go/issues/5819
+	Bug5819 interface{} // XXX: workaround
+}
+
+// AutoGroupMeta lets you get or set meta params for the automatic grouping
+// trait.
+func (obj *Groupable) AutoGroupMeta() *engine.AutoGroupMeta {
+	if obj.meta == nil { // set the defaults if previously empty
+		obj.meta = &engine.AutoGroupMeta{
+			Disabled: false,
+		}
+	}
+	return obj.meta
+}
+
+// GroupCmp compares two resources and decides if they're suitable for grouping.
+// You'll probably want to override this method when implementing a resource...
+// This base implementation assumes not, so override me!
+func (obj *Groupable) GroupCmp(res engine.GroupableRes) error {
+	return fmt.Errorf("the default grouping compare is not nil")
+}
+
+// GroupRes groups resource argument (res) into self.
+func (obj *Groupable) GroupRes(res engine.GroupableRes) error {
+	if l := len(res.GetGroup()); l > 0 {
+		return fmt.Errorf("the `%s` resource already contains %d grouped resources", res, l)
+	}
+	if res.IsGrouped() {
+		return fmt.Errorf("the `%s` resource is already grouped", res)
+	}
+
+	obj.grouped = append(obj.grouped, res)
+	res.SetGrouped(true) // i am contained _in_ a group
+	return nil
+}
+
+// IsGrouped determines if we are grouped.
+func (obj *Groupable) IsGrouped() bool { // am I grouped?
+	return obj.isGrouped
+}
+
+// SetGrouped sets a flag to tell if we are grouped.
+func (obj *Groupable) SetGrouped(b bool) {
+	obj.isGrouped = b
+}
+
+// GetGroup returns everyone grouped inside me.
+func (obj *Groupable) GetGroup() []engine.GroupableRes {
+	return obj.grouped
+}
+
+// SetGroup sets the grouped resources into me.
+func (obj *Groupable) SetGroup(grouped []engine.GroupableRes) {
+	obj.grouped = grouped
+}