Templates: migrate clan templates to flake identifiers

pkgs/clan-cli/clan_lib/templates/handler.py

@@ -99,3 +99,73 @@ def machine_template(
     finally:
         # If no error occurred, the machine directory is kept
         pass
+
+
+@contextmanager
+def clan_template(flake: Flake, template_ident: str, dst_dir: Path) -> Iterator[Path]:
+    """
+    Create a clan from a template.
+    This function will copy the template files to a new clan directory
+
+    :param flake: The flake to create the machine in.
+    :param template_ident: The identifier of the template to use. Example ".#template_name"
+    :param dst: The name of the directory to create.
+
+
+    Example usage:
+
+    >>> with clan_template(
+    ...     Flake("/home/johannes/git/clan-core"), ".#new-machine", "my-machine"
+    ... ) as clan_dir:
+    ...     # Use `clan_dir` here if you want to access the created directory
+
+    ... The directory is removed if the context raised any errors.
+    ... Only if the context is exited without errors, it is kept.
+    """
+
+    # Get the clan template from the specifier
+    [flake_ref, template_selector] = transform_url("clan", template_ident, flake=flake)
+    # For pretty error messages
+    printable_template_ref = f"{flake_ref}#{template_selector}"
+
+    template_flake = Flake(flake_ref)
+
+    try:
+        template = template_flake.select(template_selector)
+    except ClanError as e:
+        msg = f"Failed to select template '{template_ident}' from flake '{flake_ref}' (via attribute path: {printable_template_ref})"
+        raise ClanError(msg) from e
+
+    src = template.get("path")
+    if not src:
+        msg = f"Malformed template: {printable_template_ref} does not have a 'path' attribute"
+        raise ClanError(msg)
+
+    src_path = Path(src).resolve()
+
+    realize_nix_path(template_flake, str(src_path))
+
+    if not src_path.exists():
+        msg = f"Template {printable_template_ref} does not exist at {src_path}"
+        raise ClanError(msg)
+
+    if not src_path.is_dir():
+        msg = f"Template {printable_template_ref} is not a directory at {src_path}"
+        raise ClanError(msg)
+
+    if dst_dir.exists():
+        msg = f"Destination directory {dst_dir} already exists"
+        raise ClanError(msg)
+
+    copy_from_nixstore(src_path, dst_dir)
+
+    try:
+        yield dst_dir
+    except Exception as e:
+        log.error(f"An error occurred inside the 'clan_template' context: {e}")
+        log.info(f"Removing left-over directory: {dst_dir}")
+        shutil.rmtree(dst_dir, ignore_errors=True)
+        raise
+    finally:
+        # If no error occurred, the directory is kept
+        pass