Start API refactor to remove separate Tree

We want trees to just be notes. We want to reference notes
by Path instead of object ids. Stop thinking about the
fs implementation and the fuse service with the same terms -
they will be different backends.

trovedb/trove.py

@@ -1,14 +1,39 @@
-from typing import Protocol, runtime_checkable, Optional, Dict, List, Self, NamedTuple, Iterable, TypedDict
+from typing import Protocol, runtime_checkable, Optional, Dict, List, Self, NamedTuple, Iterable, TypedDict, Iterator
 from uuid import UUID
-from pathlib import PurePosixPath
 import datetime as dt
-
+import errno
 
 type ObjectId = int | str | UUID
 
 class TroveError(Exception):
     """Base class for all Trove errors."""
 
+class ErrorWithErrno(TroveError):
+    """Raised when an error occurs with an errno."""
+
+    def __init__(self, error: int, *args):
+        super().__init__(*args)
+        self.errno = error
+
+class ErrorExists(ErrorWithErrno):
+    """Raised when a note already exists."""
+
+    def __init__(self, *args):
+        super().__init__(errno.EEXIST, *args)
+
+class ErrorNotFound(ErrorWithErrno):
+    """Raised when a note is not found."""
+
+    def __init__(self, *args):
+        super().__init__(errno.ENOENT, *args)
+
+class ErrorNotEmpty(ErrorWithErrno):
+    """Raised when a directory is not empty."""
+
+    def __init__(self, *args):
+        super().__init__(errno.ENOTEMPTY, *args)
+
+
 class BadNoteType(TypeError):
     """Raised when an invalid note type is encountered."""
 
@@ -21,6 +46,12 @@ class NoteNotFound(KeyError):
 class OpenArguments(TypedDict):
     create: bool
 
+class TreeEntry(NamedTuple):
+    name: str
+    object_id: ObjectId
+
+DEFAULT_MIME = "application/octet-stream"
+
 @runtime_checkable
 class Note(Protocol):
     """
@@ -64,10 +95,30 @@ class Note(Protocol):
         """Write the raw content of the note."""
         ...
 
+    def children(self) -> Iterator[TreeEntry]:
+        """Get all children of this note."""
+        ...
+
+    def child(self, name: str) -> 'Note':
+        """Retrieve a child note by name."""
+        ...
+
+    def new_child(self, name: str, mime: str, content: bytes | None, executable: bool, hidden: bool) -> 'Note':
+        """Create a new child note."""
+        ...
+
+    def rm_child(self, name: str, recurse: bool):
+        """Remove a child note."""
+        ...
+
+    def has_children(self) -> bool:
+        """Check if note has children."""
+        return next(self.children(), None) is not None
+
+
+def new_child(note: Note, name: str, mime: str = DEFAULT_MIME, content: bytes | None = None, executable: bool = False, hidden: bool = False) -> Note:
+    return note.new_child(name=name, mime=mime, content=content, executable=executable, hidden=hidden)
 
-class TreeEntry(NamedTuple):
-    name: str
-    object_id: ObjectId
 
 @runtime_checkable
 class Tree(Protocol):
@@ -87,17 +138,10 @@ class Tree(Protocol):
         """Remove a directory from the tree."""
         ...
 
-    def child(self, name: str) -> Note:
-        """Retrieve a child note by name."""
-        ...
-
     def entries(self) -> Iterable[TreeEntry]:
         """Return all entries in the directory"""
         ...
 
-    def list(self) -> dict[str, int]:
-        """Return all entries as {name: object_id}."""
-        ...
 
 @runtime_checkable
 class TreeNote(Note, Tree, Protocol):