chore(usbgadget): update usbgadget config only when needed (#474)

internal/usbgadget/changeset_resolver.go

@@ -0,0 +1,183 @@
+package usbgadget
+
+import (
+	"fmt"
+
+	"github.com/rs/zerolog"
+	"github.com/sourcegraph/tf-dag/dag"
+)
+
+type ChangeSetResolver struct {
+	changeset *ChangeSet
+
+	l *zerolog.Logger
+	g *dag.AcyclicGraph
+
+	changesMap            map[string]*FileChange
+	conditionalChangesMap map[string]*FileChange
+
+	orderedChanges            []dag.Vertex
+	resolvedChanges           []*FileChange
+	additionalResolveRequired bool
+}
+
+func (c *ChangeSetResolver) toOrderedChanges() error {
+	for key, change := range c.changesMap {
+		v := c.g.Add(key)
+
+		for _, dependsOn := range change.DependsOn {
+			c.g.Connect(dag.BasicEdge(dependsOn, v))
+		}
+		for _, dependsOn := range change.resolvedDeps {
+			c.g.Connect(dag.BasicEdge(dependsOn, v))
+		}
+	}
+
+	cycles := c.g.Cycles()
+	if len(cycles) > 0 {
+		return fmt.Errorf("cycles detected: %v", cycles)
+	}
+
+	orderedChanges := c.g.TopologicalOrder()
+	c.orderedChanges = orderedChanges
+	return nil
+}
+
+func (c *ChangeSetResolver) doResolveChanges(initial bool) error {
+	resolvedChanges := make([]*FileChange, 0)
+
+	for _, key := range c.orderedChanges {
+		change := c.changesMap[key.(string)]
+		if !initial {
+			change.ResetActionResolution()
+		}
+
+		resolvedAction := change.Action()
+
+		resolvedChanges = append(resolvedChanges, change)
+		// no need to check the triggers if there's no change
+		if resolvedAction == FileChangeResolvedActionDoNothing {
+			continue
+		}
+
+		if !initial {
+			continue
+		}
+
+		if change.BeforeChange != nil {
+			change.resolvedDeps = append(change.resolvedDeps, change.BeforeChange...)
+			c.additionalResolveRequired = true
+
+			// add the dependencies to the changes map
+			for _, dep := range change.BeforeChange {
+				depChange, ok := c.conditionalChangesMap[dep]
+				if !ok {
+					return fmt.Errorf("dependency %s not found", dep)
+				}
+
+				c.changesMap[dep] = depChange
+			}
+		}
+	}
+
+	c.resolvedChanges = resolvedChanges
+	return nil
+}
+
+func (c *ChangeSetResolver) resolveChanges(initial bool) error {
+	// get the ordered changes
+	err := c.toOrderedChanges()
+	if err != nil {
+		return err
+	}
+
+	// resolve the changes
+	err = c.doResolveChanges(initial)
+	if err != nil {
+		return err
+	}
+
+	for _, change := range c.resolvedChanges {
+		c.l.Trace().Str("change", change.String()).Msg("resolved change")
+	}
+
+	if !c.additionalResolveRequired || !initial {
+		return nil
+	}
+
+	return c.resolveChanges(false)
+}
+
+func (c *ChangeSetResolver) applyChanges() error {
+	for _, change := range c.resolvedChanges {
+		change.ResetActionResolution()
+		action := change.Action()
+		actionStr := FileChangeResolvedActionString[action]
+
+		l := c.l.Info()
+		if action == FileChangeResolvedActionDoNothing {
+			l = c.l.Trace()
+		}
+
+		l.Str("action", actionStr).Str("change", change.String()).Msg("applying change")
+
+		err := c.changeset.applyChange(change)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (c *ChangeSetResolver) GetChanges() ([]*FileChange, error) {
+	localChanges := c.changeset.Changes
+	changesMap := make(map[string]*FileChange)
+	conditionalChangesMap := make(map[string]*FileChange)
+
+	// build the map of the changes
+	for _, change := range localChanges {
+		key := change.Key
+		if key == "" {
+			key = change.Path
+		}
+
+		// remove it from the map first
+		if change.When != "" {
+			conditionalChangesMap[key] = &change
+			continue
+		}
+
+		if _, ok := changesMap[key]; ok {
+			if changesMap[key].IsSame(&change.RequestedFileChange) {
+				continue
+			}
+			return nil, fmt.Errorf(
+				"duplicate change: %s, current: %s, requested: %s",
+				key,
+				changesMap[key].String(),
+				change.String(),
+			)
+		}
+
+		changesMap[key] = &change
+	}
+
+	c.changesMap = changesMap
+	c.conditionalChangesMap = conditionalChangesMap
+
+	err := c.resolveChanges(true)
+	if err != nil {
+		return nil, err
+	}
+
+	return c.resolvedChanges, nil
+}
+
+func (c *ChangeSetResolver) Apply() error {
+	if _, err := c.GetChanges(); err != nil {
+		return err
+	}
+
+	return c.applyChanges()
+}