Flesh out pyproject.toml to allow properly installing

Mostly because I'd like to be able to install it with uv, so it's
entirely for selfish reasons.

git_tidy.py

@@ -0,0 +1,169 @@
+#!/usr/bin/env python3
+# Copyright 2023-2025 James Smith
+# git-tidy is free software: you can redistribute it and/or modify it under the terms of the GNU
+# General Public License as published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+# git-tidy is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
+# the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+# Public License for more details.
+# You should have received a copy of the GNU General Public License along with git-tidy. If not, see
+# <https://www.gnu.org/licenses/>.
+"""git-tidy utility."""
+
+import argparse
+import subprocess
+import sys
+from typing import List, Tuple, Union
+
+try:
+    from importlib.metadata import version
+except ImportError:
+    # Python < 3.8
+    from importlib_metadata import version
+
+common_default_branches = [
+    "main",
+    "master",
+    "devel",
+    "dev",
+]
+
+
+def run(command: Union[List[str], str]) -> Tuple[int, str]:
+    """Run a subprocess.
+
+    The subprocess is checked for whether it returns successfully, and its
+    stdout or stderr is captured for the caller to make use of.
+
+    Parameters
+    ----------
+    command
+        The command to run as a subprocess.
+
+    Returns
+    -------
+    returncode
+        The (integer) return code from the completed subprocess.
+    stdout / stderr
+        In the case of a zero return code, the stdout from the subprocess is
+        returned. In all other cases, the stderr is returned. In both cases,
+        the bytes are converted to str and stripped of whitespace on either
+        side.
+    """
+    try:
+        process = subprocess.run(command, check=True, capture_output=True)
+    except subprocess.CalledProcessError as exception:
+        return exception.returncode, exception.stderr.decode().strip()
+
+    return process.returncode, process.stdout.decode().strip()
+
+
+def get_default_branch() -> str:
+    """Return the name of the repo's default branch.
+
+    First try the config, if that doesn't work, check existing branches for
+    some common defaults. If there aren't any or they're ambiguous, ask the
+    user.
+
+    Returns
+    -------
+    str
+        The name of the default branch with which we'll work for the rest of
+        the exercise.
+    """
+    returncode, configured_default_branch = run(["git", "config", "--get", "--local", "tidy.defaultbranch"])
+    if returncode == 128:
+        # The --local flag caused this to fail because we're not in a git repository.
+        print("fatal: not inside a repository", file=sys.stderr)
+        sys.exit(returncode)
+
+    # If we're in a repository, we need a list of branches, either as a
+    # sanity check that the configured branch is there, or to choose one
+    # if it's not configured.
+    _, branch_list_raw = run(["git", "branch", "--list"])
+    branch_list = [
+        branch.strip("*").strip()  # Remove the indicator of current branch.
+        for branch in branch_list_raw.split("\n")
+        if len(branch)  # Ignore empty lines.
+    ]
+
+    if returncode == 0:  # The config entry was successfully returned.
+        # But it's worth checking that the branch exists nonetheless.
+        if configured_default_branch in branch_list:
+            return configured_default_branch
+
+        print(
+            f"{configured_default_branch} configured as default branch for tidying purposes, but it doesn't exist! "
+            "Attempting to reconfigure....",
+            file=sys.stderr,
+        )
+
+    else:
+        print("No default branch for git-tidy configured, will try to figure out which to use...")
+
+    candidates = []
+
+    # Check whether any branches match our list of common defaults.
+    for branch in branch_list:
+        if branch in common_default_branches:
+            candidates.append(branch)
+
+    if len(candidates) == 1:
+        # Only one branch name matches, so we'll go with that one.
+        print(f"Using branch {candidates[0]}...")
+        run(["git", "config", "--add", "tidy.defaultbranch", candidates[0]])
+        return candidates[0]
+
+    # If there's no clear default, let the user select which one to use:
+    selection = -1
+    while (selection < 0) or (selection >= len(branch_list)):
+        print("Unable to determine default branch automatically. Please select one:")
+        for n, branch in enumerate(branch_list):
+            print(f"{n}: {branch}")
+
+        raw_input = input("Which to choose? ")
+        try:
+            selection = int(raw_input)
+        except ValueError:
+            continue
+        print(selection)
+
+    return branch_list[selection]
+
+def main():
+    """Main function."""
+    parser = argparse.ArgumentParser(description="A time-saving device for a developer using git.")
+    parser.add_argument("--version", action="version", version=f"git-tidy {version('git-tidy-python')}")
+    parser.parse_args()
+    
+    default_branch = get_default_branch()
+    print(f"Switching to {default_branch}")
+    run(["git", "checkout", default_branch])
+
+    # Check which remote it's configured with.
+    _, remote = run(["git", "config", "--get", f"branch.{default_branch}.remote"])
+    print(f"{default_branch} is connected to {remote}")
+
+    # Get latest changes from remote, clear up unnecessary stuff.
+    returncode, output = run(["git", "fetch", "--all", "--prune"])
+    if returncode != 0:  # possibly a problem in contacting the remote?
+        print(output, file=sys.stderr)
+        sys.exit(returncode)
+    print(output)  # I like to see what `git fetch` has accomplished.
+
+    returncode, output = run(["git", "merge", "--ff-only", f"{remote}/{default_branch}", default_branch])
+    if returncode != 0:  # Probably fast-forwarding won't work.
+        print(output, file=sys.stderr)
+        sys.exit(returncode)
+
+    # Check which branches are `--merged` and clean them up.
+    _, merged_branches_raw = run(["git", "branch", "--merged"])
+    merged_branches = [
+        branch for branch in merged_branches_raw.split("\n") if len(branch)  # Remove zero-length elements.
+    ]
+    for branch in merged_branches:
+        if branch[0] != "*":  # This time we want to explicitly exclude the checked-out branch.
+            subprocess.run(["git", "branch", "-d", branch.strip()], check=True)
+
+if __name__ == "__main__":
+    main()