diff --git a/migration/action.go b/migration/action.go
index ae4a58d..cb4a6d1 100644
--- a/migration/action.go
+++ b/migration/action.go
@@ -2,22 +2,22 @@ package migration
 
 import "fmt"
 
-// Action is an interface of terraform command for state migration.
-type Action interface {
+// StateAction is an interface of terraform command for state migration.
+type StateAction interface {
 	// MigrationAction returns a string of terraform command for state migration.
 	MigrationAction() string
 }
 
-// StateImportAction implements the Action interface.
+// StateImportAction implements the StateAction interface.
 type StateImportAction struct {
 	address string
 	id      string
 }
 
-var _ Action = (*StateImportAction)(nil)
+var _ StateAction = (*StateImportAction)(nil)
 
 // NewStateImportAction returns a new instance of StateImportAction.
-func NewStateImportAction(address string, id string) Action {
+func NewStateImportAction(address string, id string) StateAction {
 	return &StateImportAction{
 		address: address,
 		id:      id,
diff --git a/migration/analyzer.go b/migration/analyzer.go
index e7f0a88..559994f 100644
--- a/migration/analyzer.go
+++ b/migration/analyzer.go
@@ -1,29 +1,43 @@
 package migration
 
-type Analyzer interface {
+// PlanAnalyzer is an interface that abstracts the analysis rules of plan.
+type PlanAnalyzer interface {
+	// Analyze analyzes a given plan and generates a state migration so that
+	// the plan results in no changes.
 	Analyze(plan *Plan) *StateMigration
 }
 
-type defaultAnalyzer struct {
+// defaultPlanAnalyzer is a default implementation for PlanAnalyzer.
+// This is a predefined rule-based analyzer.
+type defaultPlanAnalyzer struct {
+	// A list of rules used for analysis.
 	resolvers []Resolver
 }
 
-var _ Analyzer = (*defaultAnalyzer)(nil)
+var _ PlanAnalyzer = (*defaultPlanAnalyzer)(nil)
 
-func NewDefaultAnalyzer() Analyzer {
-	return &defaultAnalyzer{
+// NewDefaultPlanAnalyzer returns a new instance of defaultPlanAnalyzer.
+// The current implementation only supports import, but allows us to compose
+// multiple resolvers for future extension.
+func NewDefaultPlanAnalyzer() PlanAnalyzer {
+	return &defaultPlanAnalyzer{
 		resolvers: []Resolver{
 			&StateImportResolver{},
 		},
 	}
 }
 
-func (a *defaultAnalyzer) Analyze(plan *Plan) *StateMigration {
-	var migration StateMigration
+// Analyze analyzes a given plan and generates a state migration so that
+// the plan results in no changes.
+func (a *defaultPlanAnalyzer) Analyze(plan *Plan) *StateMigration {
+	subject := NewSubject(plan)
 
+	var migration StateMigration
+	current := subject
 	for _, r := range a.resolvers {
-		actions := r.Resolve(plan)
+		next, actions := r.Resolve(current)
 		migration.AppendActions(actions...)
+		current = next
 	}
 
 	return &migration
diff --git a/migration/conflict.go b/migration/conflict.go
new file mode 100644
index 0000000..736a9a5
--- /dev/null
+++ b/migration/conflict.go
@@ -0,0 +1,68 @@
+package migration
+
+import (
+	tfjson "github.com/hashicorp/terraform-json"
+	"github.com/minamijoyo/tfedit/migration/schema"
+)
+
+// Conflict is a planned resource change.
+// It also has a status of whether it has already been resolved.
+type Conflict struct {
+	// A planned resource change.
+	rc *tfjson.ResourceChange
+	// A flag indicating that it has already been resolved.
+	// The state mv operation reduces two conflicts to a single state migration
+	// action, so we need a flag to see if it has already been processed.
+	resolved bool
+}
+
+// NewConflict returns a new instalce of Conflict.
+func NewConflict(rc *tfjson.ResourceChange) *Conflict {
+	return &Conflict{
+		rc:       rc,
+		resolved: false,
+	}
+}
+
+// MarkAsResolved marks the conflict as resolved.
+func (c *Conflict) MarkAsResolved() {
+	c.resolved = true
+}
+
+// IsResolved return true if the conflict has already been resolved.
+func (c *Conflict) IsResolved() bool {
+	return c.resolved
+}
+
+// PlannedActionType returns a string that represents the type of action.
+// Currently some actions that may be included in the plan are not supported.
+// It returns "unknown" if not supported.
+// The valid values are:
+//   - create
+//   - unknown
+func (c *Conflict) PlannedActionType() string {
+	switch {
+	case c.rc.Change.Actions.Create():
+		return "create"
+	default:
+		return "unknown"
+	}
+
+}
+
+// ResourceType returns a resource type. (e.g. aws_s3_bucket_acl)
+func (c *Conflict) ResourceType() string {
+	return c.rc.Type
+}
+
+// Address returns an absolute address. (e.g. aws_s3_bucket_acl.example)
+func (c *Conflict) Address() string {
+	return c.rc.Address
+}
+
+// ResourceAfter retruns a planned resource after change.
+// It doesn't contains attributes known after apply.
+func (c *Conflict) ResourceAfter() schema.Resource {
+	after := c.rc.Change.After.(map[string]interface{})
+	return schema.Resource(after)
+}
diff --git a/migration/generate.go b/migration/generate.go
index 8ed277c..601662b 100644
--- a/migration/generate.go
+++ b/migration/generate.go
@@ -1,12 +1,13 @@
 package migration
 
+// Generate returns bytes of a migration file which reverts a given planned changes.
 func Generate(planJSON []byte) ([]byte, error) {
 	plan, err := NewPlan(planJSON)
 	if err != nil {
 		return nil, err
 	}
 
-	analyzer := NewDefaultAnalyzer()
+	analyzer := NewDefaultPlanAnalyzer()
 	migration := analyzer.Analyze(plan)
 
 	return migration.Render()
diff --git a/migration/migration.go b/migration/migration.go
index eb0a7c8..078ea58 100644
--- a/migration/migration.go
+++ b/migration/migration.go
@@ -9,13 +9,12 @@ import (
 // StateMigration is a type which is equivalent to tfmigrate.StateMigratorConfig of
 // minamijoyo/tfmigrate.
 // The current implementation doesn't encode migration actions to a file
-// directly with gohcl, so we avoid to depend on tfmigrate's type and we define
-// only what we need here.
+// directly with gohcl, so we define only what we need here.
 type StateMigration struct {
 	// Dir is a working directory for executing terraform command.
 	Dir string
 	// Actions is a list of state action.
-	Actions []Action
+	Actions []StateAction
 }
 
 var migrationTemplate = `migration "state" "awsv4upgrade" {
@@ -30,7 +29,7 @@ var migrationTemplate = `migration "state" "awsv4upgrade" {
 var compiledMigrationTemplate = template.Must(template.New("migration").Parse(migrationTemplate))
 
 // AppendActions appends a list of actions to migration.
-func (m *StateMigration) AppendActions(actions ...Action) {
+func (m *StateMigration) AppendActions(actions ...StateAction) {
 	m.Actions = append(m.Actions, actions...)
 }
 
diff --git a/migration/resolver.go b/migration/resolver.go
index 06853c5..77d38c1 100644
--- a/migration/resolver.go
+++ b/migration/resolver.go
@@ -5,26 +5,37 @@ import (
 	_ "github.com/minamijoyo/tfedit/migration/schema/aws" // Register schema for aws
 )
 
+// Resolver is an interface that abstracts a rule for solving a subject.
 type Resolver interface {
-	Resolve(plan *Plan) []Action
+	// Resolve tries to resolve some conflicts in a given subject and returns the
+	// updated subject and state migration actions.
+	Resolve(s *Subject) (*Subject, []StateAction)
 }
 
+// StateImportResolver is an implementation of Resolver for import.
 type StateImportResolver struct {
 }
 
 var _ Resolver = (*StateImportResolver)(nil)
 
-func (r *StateImportResolver) Resolve(plan *Plan) []Action {
-	actions := []Action{}
-	for _, rc := range plan.ResourceChanges() {
-		if rc.Change.Actions.Create() {
-			address := rc.Address
-			after := rc.Change.After.(map[string]interface{})
-			importID := schema.ImportID(rc.Type, after)
-			action := NewStateImportAction(address, importID)
+// Resolve tries to resolve some conflicts in a given subject and returns the
+// updated subject and state migration actions.
+// It translates a planned create action into an import state migration.
+func (r *StateImportResolver) Resolve(s *Subject) (*Subject, []StateAction) {
+	actions := []StateAction{}
+	for _, c := range s.Conflicts() {
+		if c.IsResolved() {
+			continue
+		}
+
+		switch c.PlannedActionType() {
+		case "create":
+			importID := schema.ImportID(c.ResourceType(), c.ResourceAfter())
+			action := NewStateImportAction(c.Address(), importID)
 			actions = append(actions, action)
+			c.MarkAsResolved()
 		}
 	}
 
-	return actions
+	return s, actions
 }
diff --git a/migration/subject.go b/migration/subject.go
new file mode 100644
index 0000000..f43a34a
--- /dev/null
+++ b/migration/subject.go
@@ -0,0 +1,36 @@
+package migration
+
+// Subject is a problem to be solved. It contains multiple conflicts.
+type Subject struct {
+	// A list of conflicts to be solved.
+	conflicts []*Conflict
+}
+
+// NewSubject finds conflicts contained in a given plan and defines a problem.
+func NewSubject(plan *Plan) *Subject {
+	conflicts := []*Conflict{}
+	for _, rc := range plan.ResourceChanges() {
+		c := NewConflict(rc)
+		conflicts = append(conflicts, c)
+	}
+
+	return &Subject{
+		conflicts: conflicts,
+	}
+}
+
+// Conflicts returns a list of conflicts. It may include already resolved.
+func (s *Subject) Conflicts() []*Conflict {
+	return s.conflicts
+}
+
+// IsResolved returns true if all conflicts have been resolved, otherwise false.
+func (s *Subject) IsResolved() bool {
+	for _, c := range s.conflicts {
+		if !c.IsResolved() {
+			return false
+		}
+	}
+
+	return true
+}