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/graph/autogroup/nonreachability.go

@@ -0,0 +1,73 @@
+// 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 autogroup
+
+import (
+	"github.com/purpleidea/mgmt/pgraph"
+
+	errwrap "github.com/pkg/errors"
+)
+
+// NonReachabilityGrouper is the most straight-forward algorithm for grouping.
+// TODO: this algorithm may not be correct in all cases. replace if needed!
+type NonReachabilityGrouper struct {
+	baseGrouper // "inherit" what we want, and reimplement the rest
+}
+
+// Name returns the name for the grouper algorithm.
+func (ag *NonReachabilityGrouper) Name() string {
+	return "NonReachabilityGrouper"
+}
+
+// VertexNext iteratively finds vertex pairs with simple graph reachability...
+// This algorithm relies on the observation that if there's a path from a to b,
+// then they *can't* be merged (b/c of the existing dependency) so therefore we
+// merge anything that *doesn't* satisfy this condition or that of the reverse!
+func (ag *NonReachabilityGrouper) VertexNext() (v1, v2 pgraph.Vertex, err error) {
+	for {
+		v1, v2, err = ag.baseGrouper.VertexNext() // get all iterable pairs
+		if err != nil {
+			return nil, nil, errwrap.Wrapf(err, "error running autoGroup(vertexNext)")
+		}
+
+		// ignore self cmp early (perf optimization)
+		if v1 != v2 && v1 != nil && v2 != nil {
+			// if NOT reachable, they're viable...
+			out1, e1 := ag.graph.Reachability(v1, v2)
+			if e1 != nil {
+				return nil, nil, e1
+			}
+			out2, e2 := ag.graph.Reachability(v2, v1)
+			if e2 != nil {
+				return nil, nil, e2
+			}
+			if len(out1) == 0 && len(out2) == 0 {
+				return // return v1 and v2, they're viable
+			}
+		}
+
+		// if we got here, it means we're skipping over this candidate!
+		if ok, err := ag.baseGrouper.VertexTest(false); err != nil {
+			return nil, nil, errwrap.Wrapf(err, "error running autoGroup(vertexTest)")
+		} else if !ok {
+			return nil, nil, nil // done!
+		}
+
+		// the vertexTest passed, so loop and try with a new pair...
+	}
+}