#!/usr/bin/env bash
# next_numbered_dir — Compute the next NNNN- prefix for a numbered directory.
#
# Scans the DIRECT subdirectories of <parent_dir> whose names start with a
# numeric prefix of the form `NNNN-` (4+ digits followed by a hyphen), takes
# the maximum number, adds 1, and prints it zero-padded to <width> (default 4).
# If <parent_dir> does not exist or contains no matching subdir, prints the
# first number (0001 at default width).

next_numbered_dir() {
    local parent_dir="${1:-}"
    local width="${2:-4}"

    if [[ -z "$parent_dir" ]]; then
        echo "usage: next_numbered_dir <parent_dir> [width]" >&2
        return 1
    fi

    local max=0
    local entry base num

    if [[ -d "$parent_dir" ]]; then
        # Iterate only over direct subdirectories. The trailing slash in the
        # glob ensures files (e.g. .gitkeep) are skipped — only dirs match.
        for entry in "$parent_dir"/*/; do
            # If the glob matched nothing it stays literal; guard with -d.
            [[ -d "$entry" ]] || continue
            base="$(basename "$entry")"
            # Require a prefix of 4+ digits followed by a hyphen.
            if [[ "$base" =~ ^([0-9]{4,})- ]]; then
                num="${BASH_REMATCH[1]}"
                # Force base 10 so leading zeros (08, 09) are not read as octal.
                num=$((10#$num))
                if (( num > max )); then
                    max=$num
                fi
            fi
        done
    fi

    printf "%0*d\n" "$width" $(( max + 1 ))
}

if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
    next_numbered_dir "$@"
fi