#!/usr/bin/env bash
# Long options parsing using while and case

usage() {
    printf 'Usage: %s [--verbose] [--output FILE] [--] INPUT\n' "$0"
}

verbose=false
output_file=''
positional=()

while [ $# -gt 0 ]; do
    case $1 in
        --verbose)
            verbose=true
            shift
            ;;
        --output)
            if [ $# -lt 2 ] || [ -z "$2" ]; then
                printf 'Error: --output requires a value\n' >&2
                usage >&2
                exit 2
            fi
            output_file=$2
            shift 2
            ;;
        --output=*)
            output_file=${1#*=}
            if [ -z "$output_file" ]; then
                printf 'Error: --output requires a value\n' >&2
                usage >&2
                exit 2
            fi
            shift
            ;;
        --)
            shift
            positional+=("$@")
            break
            ;;
        -*)
            printf 'Error: unknown option: %s\n' "$1" >&2
            usage >&2
            exit 2
            ;;
        *)
            positional+=("$1")
            shift
            ;;
    esac
done

if [ ${#positional[@]} -ne 1 ]; then
    usage >&2
    exit 2
fi

input_file=${positional[0]}

if [ "$verbose" = "true" ]; then
    printf 'Input: %s\nOutput: %s\n' \
        "$input_file" "${output_file:-stdout}"
fi