#!/usr/bin/env python3

import subprocess
import webbrowser


def git(*args: str) -> str:
    """
    Run a Git command and return the output.
    """
    cmd = ["git"] + list(args)
    return subprocess.check_output(cmd, text=True).strip()


def get_parent(commit_id: str) -> str:
    """
    Return the commit ID of the parent of this commit.
    """
    return git("log", "--pretty=%P", "-n", "1", commit_id)


def get_remote_branches(commit_id: str) -> list[str]:
    """
    Return a list of remote branches where this commit is the tip.
    """
    branches = git(
        "for-each-ref",
        "--format=%(refname:short)",
        "refs/remotes/",
        "--points-at",
        commit_id,
    ).splitlines()
    return [b for b in branches if b != "origin"]


def get_local_branches(commit_id: str) -> list[str]:
    """
    Return a list of local branches where this commit is the tip.
    """
    return git(
        "for-each-ref",
        "--format=%(refname:short)",
        "refs/heads/",
        "--points-at",
        commit_id,
    ).splitlines


if __name__ == "__main__":
    current_branch = git("rev-parse", "--abbrev-ref", "HEAD")
    base_branch = "main"

    commit = git("rev-parse", "HEAD")
    for _ in range(5):
        parent = get_parent(commit)

        if rb := get_remote_branches(parent):
            base_branch = rb[0].replace("origin/", "")
            break

        if lb := get_local_branches(parent):
            if lb[0] == "main":
                break

    github_url = subprocess.check_output("_get_github_url", text=True).strip()

    url = f"{github_url}/compare/{base_branch}...{current_branch}?expand=1"
    webbrowser.open(url)