From edd9918fe20836b3644869f81f4998c460f1f54b Mon Sep 17 00:00:00 2001
From: Fritz Durchardt <fritz.duchardt.ext@gec.io>
Date: Mon, 7 Aug 2023 08:57:07 +0200
Subject: [PATCH] feat: added lazy sync functionality to only do a sync, if the
 config has changed since the last sync. Added extra field to lock file in
 order to keep track of config changes.

---
 pkg/vendir/cmd/sync.go              | 50 +++++++++++++++++++++++++++--
 pkg/vendir/config/lock_config.go    |  7 ++++
 pkg/vendir/config/lock_directory.go |  1 +
 pkg/vendir/directory/directory.go   | 15 ++++++++-
 4 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/pkg/vendir/cmd/sync.go b/pkg/vendir/cmd/sync.go
index c60882b9..62259e92 100644
--- a/pkg/vendir/cmd/sync.go
+++ b/pkg/vendir/cmd/sync.go
@@ -4,7 +4,10 @@
 package cmd
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
+	"gopkg.in/yaml.v3"
 	"os"
 	"path/filepath"
 	"strings"
@@ -30,6 +33,7 @@ type SyncOptions struct {
 
 	Directories []string
 	Locked      bool
+	Lazy        bool
 
 	Chdir                       string
 	AllowAllSymlinkDestinations bool
@@ -50,6 +54,7 @@ func NewSyncCmd(o *SyncOptions) *cobra.Command {
 
 	cmd.Flags().StringSliceVarP(&o.Directories, "directory", "d", nil, "Sync specific directory (format: dir/sub-dir[=local-dir])")
 	cmd.Flags().BoolVarP(&o.Locked, "locked", "l", false, "Consult lock file to pull exact references (e.g. use git sha instead of branch name)")
+	cmd.Flags().BoolVar(&o.Lazy, "lazy", false, "Only fetch remote if vendir.yaml diverges from lock file")
 
 	cmd.Flags().StringVar(&o.Chdir, "chdir", "", "Set current directory for process")
 	cmd.Flags().BoolVar(&o.AllowAllSymlinkDestinations, "dangerous-allow-all-symlink-destinations", false, "Symlinks to all destinations are allowed")
@@ -57,6 +62,37 @@ func NewSyncCmd(o *SyncOptions) *cobra.Command {
 	return cmd
 }
 
+func configUnchanged(vendirConfig ctlconf.Config, lockConfig ctlconf.LockConfig) bool {
+	for _, dir := range vendirConfig.Directories {
+		for _, content := range dir.Contents {
+			if !matchesLockConfig(dir.Path, content, lockConfig) {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+func matchesLockConfig(dir string, content ctlconf.DirectoryContents, lockConfig ctlconf.LockConfig) bool {
+	for _, lockDir := range lockConfig.Directories {
+		for _, lockContent := range lockDir.Contents {
+			if lockDir.Path == dir && lockContent.Path == content.Path {
+				yaml, err := yaml.Marshal(content)
+				if err != nil {
+					return false
+				}
+				hash := sha256.Sum256(yaml)
+				hashStr := hex.EncodeToString(hash[:])
+
+				if hashStr == lockContent.Hash {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
 func (o *SyncOptions) Run() error {
 	if len(o.Chdir) > 0 {
 		err := os.Chdir(o.Chdir)
@@ -95,13 +131,21 @@ func (o *SyncOptions) Run() error {
 		o.ui.PrintBlock(configBs)
 	}
 
-	// If syncing against a lock file, apply lock information
-	// on top of existing config
-	if o.Locked {
+	if o.Lazy && ctlconf.LockFileExists(o.LockFile) {
 		existingLockConfig, err := ctlconf.NewLockConfigFromFile(o.LockFile)
 		if err != nil {
 			return err
 		}
+		if configUnchanged(conf, existingLockConfig) {
+			o.ui.PrintLinef("No changes in vendir.yaml since last sync. No need to sync.")
+			return nil
+		}
+	}
+
+	// If syncing against a lock file, apply lock information
+	// on top of existing config
+	if o.Locked {
+		existingLockConfig, err := ctlconf.NewLockConfigFromFile(o.LockFile)
 
 		err = conf.Lock(existingLockConfig)
 		if err != nil {
diff --git a/pkg/vendir/config/lock_config.go b/pkg/vendir/config/lock_config.go
index d2a0c2cb..e50e517e 100644
--- a/pkg/vendir/config/lock_config.go
+++ b/pkg/vendir/config/lock_config.go
@@ -28,6 +28,13 @@ func NewLockConfig() LockConfig {
 	}
 }
 
+func LockFileExists(path string) bool {
+	if _, err := os.Stat(path); err != nil {
+		return false
+	}
+	return true
+}
+
 func NewLockConfigFromFile(path string) (LockConfig, error) {
 	bs, err := os.ReadFile(path)
 	if err != nil {
diff --git a/pkg/vendir/config/lock_directory.go b/pkg/vendir/config/lock_directory.go
index 41651e47..52811206 100644
--- a/pkg/vendir/config/lock_directory.go
+++ b/pkg/vendir/config/lock_directory.go
@@ -10,6 +10,7 @@ type LockDirectory struct {
 
 type LockDirectoryContents struct {
 	Path string `json:"path"`
+	Hash string `json:"hash"`
 
 	Git           *LockDirectoryContentsGit           `json:"git,omitempty"`
 	Hg            *LockDirectoryContentsHg            `json:"hg,omitempty"`
diff --git a/pkg/vendir/directory/directory.go b/pkg/vendir/directory/directory.go
index 8baf5b07..5ea59daf 100644
--- a/pkg/vendir/directory/directory.go
+++ b/pkg/vendir/directory/directory.go
@@ -4,7 +4,10 @@
 package directory
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
+	"gopkg.in/yaml.v3"
 	"os"
 	"path/filepath"
 
@@ -57,7 +60,17 @@ func (d *Directory) Sync(syncOpts SyncOpts) (ctlconf.LockDirectory, error) {
 			return lockConfig, err
 		}
 
-		lockDirContents := ctlconf.LockDirectoryContents{Path: contents.Path}
+		yaml, err := yaml.Marshal(contents)
+		if err != nil {
+			return lockConfig, err
+		}
+		hash := sha256.Sum256(yaml)
+		hashStr := hex.EncodeToString(hash[:])
+
+		lockDirContents := ctlconf.LockDirectoryContents{
+			Path: contents.Path,
+			Hash: hashStr,
+		}
 
 		skipFileFilter := false
 		skipNewRootPath := false