1 files changed, 67 insertions, 0 deletions
diff --git a/internal/resource/file/checksum.go b/internal/resource/file/checksum.go
new file mode 100644
index 0000000..0cbf135
--- /dev/null
+++ b/internal/resource/file/checksum.go
@@ -0,0 +1,67 @@
+package file
+
+import (
+	"crypto/sha256"
+	"log"
+	"os"
+)
+
+func getChecksum(path string) [32]byte {
+	var checksum [32]byte
+	data, err := os.ReadFile(path)
+	if err != nil {
+		log.Printf("reading %s: %v (file does not exist or cannot be read)", path, err)
+		return checksum
+	}
+	checksum = sha256.Sum256(data)
+	log.Printf("computed checksum for %s: %x", path, checksum)
+	return checksum
+}
+
+func (f *File) ensureFile(path string, content []byte) error {
+	existingChecksum := getChecksum(path)
+	newChecksum := sha256.Sum256(content)
+	log.Printf("computed checksum for new content: %x", newChecksum)
+
+	tmpPath := path + ".tmp"
+	if err := writeTmpFile(tmpPath, content, f.mode); err != nil {
+		return err
+	}
+
+	if err := updateFromTmp(tmpPath, path, existingChecksum != newChecksum); err != nil {
+		return err
+	}
+
+	return f.applyAttributesTo(path)
+}
+
+func writeTmpFile(tmpPath string, content []byte, mode os.FileMode) error {
+	log.Printf("writing %d bytes to temporary file %s with mode %v", len(content), tmpPath, mode)
+	if err := os.WriteFile(tmpPath, content, mode); err != nil {
+		log.Printf("failed to write temporary file %s: %v", tmpPath, err)
+		return err
+	}
+	log.Printf("successfully wrote temporary file %s", tmpPath)
+	return nil
+}
+
+func updateFromTmp(tmpPath, path string, checksumChanged bool) error {
+	if !checksumChanged {
+		log.Printf("checksums match, removing temporary file %s", tmpPath)
+		if err := os.Remove(tmpPath); err != nil {
+			log.Printf("failed to remove temporary file %s: %v", tmpPath, err)
+			return err
+		}
+		log.Printf("no changes needed for %s", path)
+		return nil
+	}
+
+	log.Printf("checksums differ, renaming %s to %s", tmpPath, path)
+	if err := os.Rename(tmpPath, path); err != nil {
+		log.Printf("failed to rename %s to %s: %v", tmpPath, path, err)
+		os.Remove(tmpPath)
+		return err
+	}
+	log.Printf("successfully updated %s", path)
+	return nil
+}