gapi: Split out graph generation into a proper graph API

This is a monster patch that splits out the yaml and puppet based graph
generation and pushes them behind a common API. In addition alternate
pluggable GAPI's can be easily added! The important side benefit is that
you can now write a custom GAPI for embedding mgmt!

This also includes some slight clean ups that I didn't find it worth
splitting into separate patches.

yamlgraph/gapi.go

@@ -0,0 +1,120 @@
+// Mgmt
+// Copyright (C) 2013-2016+ 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 Affero 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package yamlgraph
+
+import (
+	"fmt"
+	"log"
+	"sync"
+
+	"github.com/purpleidea/mgmt/gapi"
+	"github.com/purpleidea/mgmt/pgraph"
+	"github.com/purpleidea/mgmt/recwatch"
+)
+
+// GAPI implements the main yamlgraph GAPI interface.
+type GAPI struct {
+	File *string // yaml graph definition to use; nil if undefined
+
+	data        gapi.Data
+	initialized bool
+	closeChan   chan struct{}
+	wg          sync.WaitGroup // sync group for tunnel go routines
+}
+
+// NewGAPI creates a new yamlgraph GAPI struct and calls Init().
+func NewGAPI(data gapi.Data, file *string) (*GAPI, error) {
+	obj := &GAPI{
+		File: file,
+	}
+	return obj, obj.Init(data)
+}
+
+// Init initializes the yamlgraph GAPI struct.
+func (obj *GAPI) Init(data gapi.Data) error {
+	if obj.initialized {
+		return fmt.Errorf("Already initialized!")
+	}
+	if obj.File == nil {
+		return fmt.Errorf("The File param must be specified!")
+	}
+	obj.data = data // store for later
+	obj.closeChan = make(chan struct{})
+	obj.initialized = true
+	return nil
+}
+
+// Graph returns a current Graph.
+func (obj *GAPI) Graph() (*pgraph.Graph, error) {
+	if !obj.initialized {
+		return nil, fmt.Errorf("yamlgraph: GAPI is not initialized")
+	}
+
+	config := ParseConfigFromFile(*obj.File)
+	if config == nil {
+		return nil, fmt.Errorf("yamlgraph: ParseConfigFromFile returned nil")
+	}
+
+	g, err := config.NewGraphFromConfig(obj.data.Hostname, obj.data.EmbdEtcd, obj.data.Noop)
+	return g, err
+}
+
+// SwitchStream returns nil errors every time there could be a new graph.
+func (obj *GAPI) SwitchStream() chan error {
+	if obj.data.NoWatch {
+		return nil
+	}
+	ch := make(chan error)
+	obj.wg.Add(1)
+	go func() {
+		defer obj.wg.Done()
+		defer close(ch) // this will run before the obj.wg.Done()
+		if !obj.initialized {
+			ch <- fmt.Errorf("yamlgraph: GAPI is not initialized")
+			return
+		}
+		configChan := recwatch.ConfigWatch(*obj.File)
+		for {
+			select {
+			case err, ok := <-configChan: // returns nil events on ok!
+				if !ok { // the channel closed!
+					return
+				}
+				log.Printf("yamlgraph: Generating new graph...")
+				ch <- err // trigger a run
+				if err != nil {
+					return
+				}
+			case <-obj.closeChan:
+				return
+			}
+		}
+	}()
+	return ch
+}
+
+// Close shuts down the yamlgraph GAPI.
+func (obj *GAPI) Close() error {
+	if !obj.initialized {
+		return fmt.Errorf("yamlgraph: GAPI is not initialized")
+	}
+	close(obj.closeChan)
+	obj.wg.Wait()
+	obj.initialized = false // closed = true
+	return nil
+}