Add a dry run flag

filesystem.go

@@ -0,0 +1,180 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"sync"
+)
+
+var filesystem FileSystem = NewRealFileSystem()
+
+// FileSystem abstracts filesystem operations so we can swap implementations
+type FileSystem interface {
+	Remove(path string) error
+	RemoveAll(path string) error
+	MkdirAll(path string, perm os.FileMode) error
+	Symlink(source, target string) error
+	Link(source, target string) error
+	SummaryLines() []string
+	IsDryRun() bool
+}
+
+const (
+	opRemove    = "remove"
+	opRemoveAll = "remove_all"
+	opMkdirAll  = "mkdir_all"
+	opSymlink   = "symlink"
+	opHardlink  = "hardlink"
+)
+
+type operationRecord struct {
+	kind   string
+	source string
+	target string
+	err    error
+	dryRun bool
+}
+
+func (r operationRecord) summaryLine() (string, bool) {
+	if r.kind != opSymlink && r.kind != opHardlink {
+		return "", false
+	}
+
+	kindLabel := "Symlink"
+	if r.kind == opHardlink {
+		kindLabel = "Hardlink"
+	}
+
+	status := "OK"
+	if r.err != nil {
+		status = fmt.Sprintf("FAIL: %v", r.err)
+	} else if r.dryRun {
+		status = "DRY-RUN"
+	}
+
+	return fmt.Sprintf("%s %s -> %s (%s)", kindLabel, r.source, r.target, status), true
+}
+
+type baseFileSystem struct {
+	mu         sync.Mutex
+	operations []operationRecord
+}
+
+func (b *baseFileSystem) addOperation(kind, source, target string, err error, dryRun bool) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.operations = append(b.operations, operationRecord{
+		kind:   kind,
+		source: source,
+		target: target,
+		err:    err,
+		dryRun: dryRun,
+	})
+}
+
+func (b *baseFileSystem) snapshot() []operationRecord {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	ops := make([]operationRecord, len(b.operations))
+	copy(ops, b.operations)
+	return ops
+}
+
+func summarizeOperations(records []operationRecord) []string {
+	var lines []string
+	for _, record := range records {
+		if line, ok := record.summaryLine(); ok {
+			lines = append(lines, line)
+		}
+	}
+	return lines
+}
+
+type realFileSystem struct {
+	baseFileSystem
+}
+
+// NewRealFileSystem returns a filesystem implementation that writes to disk
+func NewRealFileSystem() FileSystem {
+	return &realFileSystem{}
+}
+
+func (fs *realFileSystem) Remove(path string) error {
+	err := os.Remove(path)
+	fs.addOperation(opRemove, "", path, err, false)
+	return err
+}
+
+func (fs *realFileSystem) RemoveAll(path string) error {
+	err := os.RemoveAll(path)
+	fs.addOperation(opRemoveAll, "", path, err, false)
+	return err
+}
+
+func (fs *realFileSystem) MkdirAll(path string, perm os.FileMode) error {
+	err := os.MkdirAll(path, perm)
+	fs.addOperation(opMkdirAll, "", path, err, false)
+	return err
+}
+
+func (fs *realFileSystem) Symlink(source, target string) error {
+	err := os.Symlink(source, target)
+	fs.addOperation(opSymlink, source, target, err, false)
+	return err
+}
+
+func (fs *realFileSystem) Link(source, target string) error {
+	err := os.Link(source, target)
+	fs.addOperation(opHardlink, source, target, err, false)
+	return err
+}
+
+func (fs *realFileSystem) SummaryLines() []string {
+	return summarizeOperations(fs.snapshot())
+}
+
+func (fs *realFileSystem) IsDryRun() bool {
+	return false
+}
+
+type dryRunFileSystem struct {
+	baseFileSystem
+}
+
+// NewDryRunFileSystem returns a filesystem implementation that only records operations
+func NewDryRunFileSystem() FileSystem {
+	return &dryRunFileSystem{}
+}
+
+func (fs *dryRunFileSystem) Remove(path string) error {
+	fs.addOperation(opRemove, "", path, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) RemoveAll(path string) error {
+	fs.addOperation(opRemoveAll, "", path, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) MkdirAll(path string, perm os.FileMode) error {
+	fs.addOperation(opMkdirAll, "", path, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) Symlink(source, target string) error {
+	fs.addOperation(opSymlink, source, target, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) Link(source, target string) error {
+	fs.addOperation(opHardlink, source, target, nil, true)
+	return nil
+}
+
+func (fs *dryRunFileSystem) SummaryLines() []string {
+	return summarizeOperations(fs.snapshot())
+}
+
+func (fs *dryRunFileSystem) IsDryRun() bool {
+	return true
+}