diff --git a/src/photools3/metadata_writer.py b/src/photools3/metadata_writer.py
index e2d8b8f..253193d 100644
--- a/src/photools3/metadata_writer.py
+++ b/src/photools3/metadata_writer.py
@@ -22,14 +22,14 @@ SIDECAR_EXTENSIONS = {".dng", ".nef", ".cr2", ".cr3", ".arw", ".raf", ".orf", ".
 
 XmpKey = Annotated[str, StringConstraints(pattern=r"^\w+\:\w+")]
 
-type Caption = str | None
+type Caption = str
 type Keywords = list[str] | None
 type Color = str | None
 type XmpMetadata = dict[str, Any]
 
-XMO_KEYS_CAPTION: list[XmpKey] = [
-    "EXIF:ImageDescription",
+XMP_KEYS_CAPTION: list[XmpKey] = [
     "XMP:Description",
+    "EXIF:ImageDescription",
     "IPTC:Caption-Abstract",
 ]
 
@@ -44,12 +44,8 @@ def _prefixed(txt: str) -> str:
     return f"{settings.metadata_prefix} {txt}"
 
 
-def read_metadata(path: Path) -> XmpMetadata | None:
-    try:
-        with exiftool.ExifToolHelper() as exif:
-            return exif.get_metadata([str(path)])[0]
-    except Exception as exc:  # noqa: BLE001
-        log.error(f"Could not read metadata from {path}: {exc}")
+def _is_prefixed(txt: str) -> bool:
+    return txt.startswith(settings.metadata_prefix)
 
 
 class MetadataWriter:
@@ -59,28 +55,64 @@ class MetadataWriter:
     """
 
     def __init__(
-        self, force_sidecar: bool = False, append: bool = True, prefix: str = "photools"
+        self,
+        path: Path,
+        force_sidecar: bool = False,
+        append: bool = True,
     ):
+        self.path = Path
         self.force_sidecar = force_sidecar
         self.append = append
-        self.prefix = prefix
 
-    def write_caption(self, path: Path, caption: Caption): ...
+        self._metadata: XmpMetadata | None = None
 
-    def write_keywords(self, path: Path, keywords: Keywords): ...
+    @property
+    def sidecar_path(self) -> Path:
+        ...
+        return Path()
 
-    def write_color(self, path: Path, color: Color): ...
+    @property
+    def metadata(self) -> XmpMetadata:
+        try:
+            with exiftool.ExifToolHelper() as exif:
+                metadata = exif.get_metadata([str(self.path)])[0]
+        except Exception as exc:  # noqa: BLE001
+            log.error(f"Could not read metadata from {self.path}: {exc}")
+        assert metadata
+        return metadata
+
+    def set_metadata(self):
+        if self.sidecar_path.exists():
+            params=["-overwrite_original"]
+        else:
+            params=["-o", "%f.xmp"]
+        # TODO
+        ...
+
+    def write_caption(self, caption: Caption):
+        existing = self.metadata.get(XMP_KEYS_CAPTION[0], "")
+        is_existing_prefixed = _is_prefixed(existing)
+        if existing and is_existing_prefixed:
+            return
+        elif existing and not is_existing_prefixed:
+            caption = f"{existing}. {_prefixed(caption)}"
+        metadata_tags = {key: caption for key in XMP_KEYS_CAPTION}
+        # TODO
+        ...
+
+    def write_keywords(self, keywords: Keywords): ...
+
+    def write_color(self, color: Color): ...
 
     def write(
         self,
-        path: Path,
-        caption: Caption = None,
+        caption: Caption | None = None,
         keywords: Keywords = None,
         color: Color = None,
     ):
         if caption is not None:
-            self.write_caption(path, caption)
+            self.write_caption(caption)
         if keywords is not None:
-            self.write_keywords(path, keywords)
+            self.write_keywords(keywords)
         if color is not None:
-            self.write_color(path, color)
+            self.write_color(color)