#!/usr/bin/env bash

set -eEou pipefail

die() {
	printf "%s\n" "${*}"
	exit 1
}

usage() {
	local script
	script="$(basename "${0}")"
	cat <<-__EOS__
		==== USAGE ====

		Provide a file:
		    ${script} ./some/path/to/a/file
		Pipe from stdin:
		    echo "hello\nworld!" | ${script}
		Redirect from stdin:
		    ${script} < ./some/path/to/a/file

		==== USAGE ====
	__EOS__
}

handle_lines() {
	local input="${1}"
	local line_count=0
	while read -r line; do
		# To satisfy the `set -u` incantation at the top, we have to assign the variable instead of
		# a simple ((line_count++))
		line_count=$((line_count + 1))
		if ((line_count % 2 == 0)); then
			printf "%s\n" "$line"
		fi
	done <"$input"

	if ((line_count > 10)); then
		printf "big\n"
	else
		printf "small\n"
	fi
}

main() {
	# Check if we should read from stdin or a given file
	if [[ -t 0 ]]; then
		# Input should be a path to a file
		set +u
		if [[ -z "${1}" ]]; then
			usage
			die "No input received!"
		fi
		set -u
		local fpath="${1}"

		if ! [[ -r "$fpath" ]]; then
			die "Unable to read a file at: ${fpath}"
		fi
		handle_lines "$fpath"
	else
		# Read from stdin
		handle_lines "/dev/stdin"
	fi
}

main "${@}"