Engine/GCTScript: Refactor script manager (#580)

* refactor script manager

* remove singleton GCTScriptConfig
* create constant for ".gct" extension
* move GctScriptManager into vm package
* reduce script manager global dependencies
* use manager struct to store runtime override values
* enable/disable scripting subsystem now doesn't store the setting in
config (aligned with other subsystems)
* setting max VMs via start option doesn't change config

* instantiate scriptmanager as part of creating a new Engine

    * script manager config is now set during instantiation
    * run script manager when enabled in conf or explicitly enabled
    * use the Started() method to check if script manager is running

* in tests set script manager as running

* script manager adjustments

* create manager before attempting overrides
* check for nil config when creating script manager

* fix script manager waitgroup counter increased too late

* move autoload() function to autoload.go
* add tests to script manager

gctscript/vm/manager.go

@@ -0,0 +1,99 @@
+package vm
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+	"sync/atomic"
+
+	"github.com/thrasher-corp/gocryptotrader/engine/subsystem"
+	"github.com/thrasher-corp/gocryptotrader/log"
+)
+
+const gctscriptManagerName = "GCTScript"
+
+// GctScriptManager loads and runs GCT Tengo scripts
+type GctScriptManager struct {
+	config   *Config
+	started  int32
+	stopped  int32
+	shutdown chan struct{}
+	// Optional values to override stored config ('nil' if not overridden)
+	MaxVirtualMachines *uint8
+}
+
+// NewManager creates a new instance of script manager
+func NewManager(config *Config) (*GctScriptManager, error) {
+	if config == nil {
+		return nil, errors.New("config must be provided for script manager")
+	}
+	return &GctScriptManager{
+		config: config,
+	}, nil
+}
+
+// Started returns if gctscript manager subsystem is started
+func (g *GctScriptManager) Started() bool {
+	return atomic.LoadInt32(&g.started) == 1
+}
+
+// Start starts gctscript subsystem and creates shutdown channel
+func (g *GctScriptManager) Start(wg *sync.WaitGroup) (err error) {
+	if atomic.AddInt32(&g.started, 1) != 1 {
+		return fmt.Errorf("%s %s", gctscriptManagerName, subsystem.ErrSubSystemAlreadyStarted)
+	}
+
+	defer func() {
+		if err != nil {
+			atomic.CompareAndSwapInt32(&g.started, 1, 0)
+		}
+	}()
+	log.Debugln(log.Global, gctscriptManagerName, subsystem.MsgSubSystemStarting)
+
+	g.shutdown = make(chan struct{})
+	wg.Add(1)
+	go g.run(wg)
+	return nil
+}
+
+// Stop stops gctscript subsystem along with all running Virtual Machines
+func (g *GctScriptManager) Stop() error {
+	if atomic.LoadInt32(&g.started) == 0 {
+		return fmt.Errorf("%s %s", gctscriptManagerName, subsystem.ErrSubSystemNotStarted)
+	}
+
+	if atomic.AddInt32(&g.stopped, 1) != 1 {
+		return fmt.Errorf("%s %s", gctscriptManagerName, subsystem.ErrSubSystemAlreadyStopped)
+	}
+
+	log.Debugln(log.GCTScriptMgr, gctscriptManagerName, subsystem.MsgSubSystemShuttingDown)
+	close(g.shutdown)
+	err := g.ShutdownAll()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func (g *GctScriptManager) run(wg *sync.WaitGroup) {
+	log.Debugln(log.Global, gctscriptManagerName, subsystem.MsgSubSystemStarted)
+
+	SetDefaultScriptOutput()
+	g.autoLoad()
+	defer func() {
+		atomic.CompareAndSwapInt32(&g.stopped, 1, 0)
+		atomic.CompareAndSwapInt32(&g.started, 1, 0)
+		wg.Done()
+		log.Debugln(log.GCTScriptMgr, gctscriptManagerName, subsystem.MsgSubSystemShutdown)
+	}()
+
+	<-g.shutdown
+}
+
+// GetMaxVirtualMachines returns the max number of VMs to create
+func (g *GctScriptManager) GetMaxVirtualMachines() uint8 {
+	if g.MaxVirtualMachines != nil {
+		return *g.MaxVirtualMachines
+	}
+	return g.config.MaxVirtualMachines
+}