git-main

#!/bin/zsh
# vim:ft=zsh
#
# git-main - git switch to main branch
#
#================================================== 

show_help() {
  printf -- "
git-main - git switch to main branch

Usage:  git main [OPTIONS]

Options:
  -h, --help    Show this help message

Description:
  Switch to the main branch of the current git repository. The default branch 
  is determined based on common branch names or fallback to remote HEAD. 
  Switches the main branch in the main worktree if the current directory is 
  a linked worktree (does not change shell directory).
"
  exit 0
}

find_main_branch() {
  command git rev-parse --git-dir &>/dev/null || return 1
  
  local ref remote
  local -a branches=(main trunk mainline default stable master)
  local -a remotes=(origin upstream)
  
  # 1. Check local branches
  for ref in refs/heads/$^branches; do
    if command git show-ref -q --verify "$ref"; then
      echo "${ref:t}"
      return 0
    fi
  done
  
  # 2. Try to get default branch from remote HEAD
  for remote in $remotes; do
    if ref=$(command git symbolic-ref "refs/remotes/$remote/HEAD" 2>/dev/null); then
      echo "${ref:t}"
      return 0
    fi
  done

  # 3. Fallback to common remote branch names
  for remote in $remotes; do
    for ref in refs/remotes/$remote/$^branches; do
      if command git show-ref -q --verify "$ref"; then
        echo "${ref:t}"
        return 0
      fi
    done
  done

  # Ultimate fallback
  echo "master"
  return 1
}

switch_to_main() {
  local main_branch
  if ! main_branch=$(find_main_branch); then
    echo "Error: Not a git repository or could not determine main branch." >&2
    return 1
  fi

  local curr_wt main_wt
  curr_wt=$(command git rev-parse --show-toplevel 2>/dev/null)
  main_wt=$(command git worktree list --porcelain | awk '/^worktree / {sub(/^worktree /, ""); print; exit}')

  if [[ "$curr_wt" != "$main_wt" ]]; then
    echo "Switch to main worktree branch (you are in a linked worktree)."
    echo "To work in the main worktree, run: cd \"$main_wt\""
    return 0
  fi

  # Switch branch
  command git switch "$main_branch"
}

main() {
  case "$1" in
    -h|--help)
      show_help
      ;;
    *)
      switch_to_main
      ;;
  esac
}

main "$@"