new git working strategy, using worktrees now for easier parallel development

common/general/shell/branch.func.sh

@@ -0,0 +1,105 @@
+branch() {
+  local branch_name=${1:-}
+  if [ -z "$branch_name" ]; then
+    echo "Usage: branch <name>" >&2
+    return 2
+  fi
+
+  # branch <name> — create or open a worktree for <name>
+  # This function will change directory into the selected worktree so the
+  # caller's shell is moved into it.
+
+  local xdg=${XDG_DATA_HOME:-$HOME/.local/share}
+
+  local common_dir
+  if ! common_dir=$(git rev-parse --git-common-dir 2>/dev/null); then
+    echo "Not inside a git repository." >&2
+    return 1
+  fi
+  if [ "${common_dir#/}" = "$common_dir" ]; then
+    common_dir="$(pwd)/$common_dir"
+  fi
+  local repo_dir="${common_dir%%/.git*}"
+  if [ -z "$repo_dir" ]; then
+    echo "Unable to determine repository root." >&2
+    return 1
+  fi
+
+  local repo_base repo_hash default_branch
+  repo_base=$(basename "$repo_dir")
+  repo_hash=$(printf "%s" "$repo_dir" | sha1sum | awk '{print $1}')
+
+  default_branch=$(getdefault)
+
+  # Special-case: jump to the main working tree on the default branch
+  if [ "$branch_name" = "default" ] || [ "$branch_name" = "master" ] || [ "$branch_name" = "$default_branch" ]; then
+    if [ "$repo_dir" = "$PWD" ]; then
+      echo "Already in the main working tree on branch '$default_branch'."
+      return 0
+    fi
+    echo "Switching to main working tree on branch '$default_branch'."
+    cd "$repo_dir" || return 1
+    return 0
+  fi
+
+  # If a worktree for this branch is already registered elsewhere, open a shell there
+  local existing
+  existing=$(git -C "$repo_dir" worktree list --porcelain 2>/dev/null | awk -v b="$branch_name" 'BEGIN{RS="";FS="\n"} $0 ~ "refs/heads/"b{for(i=1;i<=NF;i++) if ($i ~ /^worktree /){ sub(/^worktree /,"",$i); print $i }}')
+  if [ -n "$existing" ]; then
+    echo "Opening existing worktree for branch '$branch_name' at '$existing'."
+    cd "$existing" || return 1
+    return 0
+  fi
+
+  # Ensure we have up-to-date remote info
+  git -C "$repo_dir" fetch --all --prune || true
+
+  local wt_root wt_path
+  wt_root="$xdg/git_worktrees/${repo_base}_${repo_hash}"
+  wt_path="$wt_root/$branch_name"
+
+  # If worktree already exists at our expected path, open a shell there
+  if [ -d "$wt_path" ]; then
+    echo "Opening existing worktree at '$wt_path'."
+    cd "$wt_path" || return 1
+    return 0
+  fi
+
+  local branch_exists branch_from
+  branch_exists=$(git -C "$repo_dir" ls-remote --heads origin "$branch_name" | wc -l)
+  branch_from="$default_branch"
+  if [ "$branch_exists" -eq 0 ]; then
+    echo "Branch '$branch_name' does not exist on remote; creating from '$branch_from'."
+  else
+    branch_from="origin/$branch_name"
+    echo "Branch '$branch_name' exists on remote; creating worktree tracking it."
+  fi
+
+  echo "Creating new worktree for branch '$branch_name' at '$wt_path'."
+
+  # Try to add or update worktree from the resolved ref. Use a fallback path if needed.
+  if git -C "$repo_dir" worktree add -b "$branch_name" "$wt_path" "$branch_from" 2>/dev/null; then
+    cd "$wt_path" || return 1
+    return 0
+  fi
+
+  # Fallback: try to resolve a concrete SHA and create the branch ref locally, then add worktree
+  local start_sha
+  if start_sha=$(git -C "$repo_dir" rev-parse --verify "$branch_from" 2>/dev/null); then
+    if git -C "$repo_dir" branch "$branch_name" "$start_sha" 2>/dev/null; then
+      if git -C "$repo_dir" worktree add "$wt_path" "$branch_name" 2>/dev/null; then
+        cd "$wt_path" || return 1
+        return 0
+      else
+        git -C "$repo_dir" branch -D "$branch_name" 2>/dev/null || true
+        rmdir "$wt_path" 2>/dev/null || true
+        echo "Failed to add worktree after creating branch ref." >&2
+        return 1
+      fi
+    fi
+  fi
+
+  echo "Failed to add worktree for branch '$branch_name'." >&2
+  rmdir "$wt_path" 2>/dev/null || true
+  return 1
+}