Add init nix shell command

home/bin/init-nix-shell

@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+
+"""
+Create a shell.nix with default settings in the current directory, and set the .envrc file to "use nix"
+"""
+
+import argparse
+import logging
+from pathlib import Path
+import sys
+
+logging.basicConfig(level=logging.WARNING)
+LOG = logging.getLogger(__name__)
+
+
+SHELL_NIX_TEMPLATE = """{ pkgs ? import <nixpkgs> { } }:
+with pkgs;
+mkShell {
+  packages = [
+  ];
+}
+"""
+
+
+def init_shell_nix(path: Path):
+    with path.open("w") as outfile:
+        print(SHELL_NIX_TEMPLATE, file=outfile)
+
+
+def init_envrc(path: Path):
+    with path.open("w") as outfile:
+        print("use nix", file=outfile)
+
+
+def init_dir(root: Path, force: bool):
+    LOG.info(f"initialising {root}")
+
+    shell_nix_path = root.joinpath("shell.nix")
+    envrc_path = root.joinpath(".envrc")
+
+    if shell_nix_path.is_file() and not force:
+        raise ValueError(f"file exists at {shell_nix_path}")
+
+    if envrc_path.is_file() and not force:
+        raise ValueError(f"file exists at {envrc_path}")
+
+    init_shell_nix(shell_nix_path)
+    init_envrc(envrc_path)
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-v", "--verbose", action="store_true", default=False)
+    parser.add_argument("-r", "--root-dir", required=False, default=Path.cwd(), type=Path)
+    parser.add_argument("-f", "--force", action="store_true", default=False)
+    args = parser.parse_args()
+
+    if args.verbose:
+        LOG.setLevel(logging.DEBUG)
+
+    try:
+        init_dir(args.root_dir.resolve(), args.force)
+    except Exception as e:
+        print(f"Error: {e}", file=sys.stderr)
+        raise SystemExit(1)