file-output

#!/usr/bin/env bash

set -euo pipefail

function change_mode() {
    if [ -n "${MODE}" ]
    then
        update_trap MODE_FAILED_TO_CHANGE
        if chmod -c "${MODE}" "${FILE}" 2>&1 | grep -q '.'
        then
            update_result MODE_CHANGED
        fi
        update_trap OK
    fi
}

function clear_trap() {
    trap '' INT EXIT TERM
}

function create_file() {
    if [ ! -e "${FILE}" ]
    then
        update_trap FILE_FAILED_TO_CREATE
        touch "${FILE}"
        update_result FILE_CREATED
        update_trap OK
    fi
}

function create_parents() {
    if [ ! -e "$(dirname "${FILE}")" ]
    then
        update_trap PARENTS_FAILED_TO_CREATE
        mkdir -p "$(dirname "${FILE}")"
        update_result PARENTS_CREATED
        update_trap OK
    fi
}

function help() {
    cat << EOF >&2
Usage:
    ${0} [OPTION]... [--] FILE

Write Options:
    -A          append
    -N          do not write any contents
    -R          replace (default)

Overwrite Options:
    -a          abort if already file exists (default)
    -f          overwrite
    -n          do not overwrite

Miscellaneous Options:
    -c          do not create any files
    -h          show help
    -m MODE     set file mode
    -p          create parent directories
EOF
}

function ignore_contents() {
    update_trap CONTENTS_FAILED_TO_READ
    cat - > /dev/null
    update_trap OK
    update_result CONTENTS_IGNORED_TO_OVERWRITE
}

function print_error() {
    local file="$(relative_path "${FILE}")"
    local message="${ERROR_MESSAGES[${1}]}"
    local severity="${ERROR_SEVERITIES[${1}]}"
    if which echo-with-color > /dev/null 2>&1
    then
        if [ ${severity} -ge 100 ]
        then
            echo-with-color -0 "${file}:" -R "${message}" >&2
        elif [ ${severity} -ge 10 ]
        then
            echo-with-color -0 "${file}:" -Y "${message}" >&2
        else
            echo-with-color -0 "${file}:" -G "${message}" >&2
        fi
    else
        echo "${file}: ${message}" >&2
    fi
}

function print_result() {
    print_error "${RESULT}"
}

function relative_path() {
    realpath -ms "--relative-to=$(pwd)" "${1}"
}

function update_result() {
    local cur_severity="${ERROR_SEVERITIES[${RESULT}]}"
    local new_severity="${ERROR_SEVERITIES[${1}]}"
    if [ ${cur_severity} -lt ${new_severity} ]
    then
        RESULT="${1}"
    fi
}

function update_trap() {
    trap "update_result '${1}'; print_result" INT EXIT TERM
}

function write_contents() {
    update_trap CONTENTS_FAILED_TO_WRITE
    local old_checksum="$(sha256sum "${FILE}")"
    case "${WRITE_POLICY}" in
        append)
            cat - >> "${FILE}"
            ;;
        no-write)
            ;;
        replace)
            cat - > "${FILE}"
            ;;
        *)
            clear_trap
            echo "${WRITE_POLICY}: invalid write policy" >&2
            exit 1
            ;;
    esac
    local new_checksum="$(sha256sum "${FILE}")"
    if [ "${old_checksum}" != "${new_checksum}" ]
    then
        update_result CONTENTS_CHANGED
    fi
    update_trap OK
}

declare -A ERROR_MESSAGES=(
  ["CONTENTS_ABORTED_TO_OVERWRITE"]="already exists"
  ["CONTENTS_CHANGED"]="changed"
  ["CONTENTS_FAILED_TO_READ"]="failed to read from standard input"
  ["CONTENTS_FAILED_TO_WRITE"]="failed to write file"
  ["CONTENTS_IGNORED_TO_OVERWRITE"]="already exists, but ignored"
  ["FILE_CREATED"]="file created"
  ["FILE_FAILED_TO_CREATE"]="failed to create file"
  ["MODE_CHANGED"]="mode changed"
  ["MODE_FAILED_TO_CHANGED"]="failed to change mode"
  ["OK"]="OK"
  ["PARENTS_CREATED"]="parent directories created"
  ["PARENTS_FAILED_TO_CREATE"]="failed to create parent directories"
)
declare -A ERROR_SEVERITIES=(
  ["CONTENTS_ABORTED_TO_OVERWRITE"]=100
  ["CONTENTS_CHANGED"]=12
  ["CONTENTS_FAILED_TO_READ"]=100
  ["CONTENTS_FAILED_TO_WRITE"]=100
  ["CONTENTS_IGNORED_TO_OVERWRITE"]=1
  ["FILE_CREATED"]=13
  ["FILE_FAILED_TO_CREATE"]=100
  ["MODE_CHANGED"]=11
  ["MODE_FAILED_TO_CHANGED"]=100
  ["OK"]=0
  ["PARENTS_CREATED"]=10
  ["PARENTS_FAILED_TO_CREATE"]=100
)

CREATE_FILE=yes
CREATE_PARENTS=
FILE=
MODE=
OVERWRITE_POLICY=abort
RESULT=OK
WRITE_POLICY=replace

while getopts 'ANRacfhm:np' OPT
do
    case "${OPT}" in
        A)
            WRITE_POLICY=append
            ;;
        N)
            WRITE_POLICY=no-write
            ;;
        R)
            WRITE_POLICY=replace
            ;;
        a)
            OVERWRITE_POLICY=abort
            ;;
        c)
            CREATE_FILE=
            ;;
        f)
            OVERWRITE_POLICY=force
            ;;
        h)
            help
            exit 1
            ;;
        m)
            MODE="${OPTARG}"
            ;;
        n)
            OVERWRITE_POLICY=ignore
            ;;
        p)
            CREATE_PARENTS=yes
            ;;
        *)
            exit 1
            ;;
    esac
done

shift $(($OPTIND - 1))

if [ ${#@} -ne 1 ]
then
    help
    exit 1
fi

FILE="${1}"

update_trap OK

if [ -e "${FILE}" ]
then
    change_mode

    if [ "${WRITE_POLICY}" == replace ]
    then
        case "${OVERWRITE_POLICY}" in
            abort)
                update_result CONTENTS_ABORTED_TO_OVERWRITE
                exit 1
                ;;
            force)
                ;;
            ignore)
                ignore_contents
                exit 0
                ;;
            *)
                clear_trap
                echo "${OVERWRITE_POLICY}: invalid overwrite policy" >&2
                exit 1
                ;;
        esac
    fi
else
    if [ -n "${CREATE_FILE}" ]
    then
        [ -n "${CREATE_PARENTS}" ] && create_parents
        create_file
    fi

    change_mode
fi

write_contents