function __block_in_file__help() {
    local func="$1"
    if [[ "$func" = "update" ]]
    then
    echo "block_in_file [<OPTIONS>] <FILE> <ID> <BLOCK>"
    else
    echo "block_in_file_remove [<OPTIONS>] <FILE> <ID>"
    fi
    echo "$func [<OPTIONS>] <FILE> <ID> <BLOCK>"
    echo
    echo "OPTIONS:"
    if [[ "$func" = "update" ]]
    then
    echo "  --before <MATCH>       insert block before matched line"
    echo "  --after <MATCH>        insert block after matched line"
    fi
    echo "  --id-start-pre <str>   set id-start-pre to str"
    echo "  --id-start-post <str>  set id-start-post to str"
    echo "  --id-end-pre <str>     set id-end-pre to str"
    echo "  --id-end-post <str>    set id-end-post to str"
    echo
    echo "ID:"
    echo "  an identifier string to regonise the block."
    if [[ "$func" = "update" ]]
    then
    echo
    echo "MATCH:"
    echo "  line search/match string in grep format"
    fi
    echo
    echo "block fomat:"
    echo "  <id-start-pre><id><id-start-post>"
    echo "  <block>"
    echo "  <id-end-pre><id><id-end-post>"
}

function block_in_file() {
    __block_in_file__inner "update" $*
}

function block_in_file_remove() {
    __block_in_file__inner "remove" $*
}

function __block_in_file__inner() {
    local FN="$1"
    local BEFORE="EOF"
    local AFTER="SOF"
    local ID_START_PRE="#START manged by elf_packages: "
    local ID_START_POST=""
    local ID_END_PRE="#END "
    local ID_END_POST=""
    while [[ $1 == \-* ]]
    do
        case "$1" in
            "--before")
                if [[ "$FN" = "update" ]]
                then
                    shift
                    BEFORE="$1"
                    shift
                else
                    echo "ERROR: invalid options $1"
                    __block_in_file__help "$FN"
                    exit 1
                fi
                ;;
            "--after")
                if [[ "$FN" = "update" ]]
                then
                    shift
                    AFTER="$1"
                    shift
                else
                    echo "ERROR: invalid options $1"
                    __block_in_file__help "$FN"
                    exit 1
                fi
                ;;
            "--id-start-pre")
                shift
                ID_START_PRE="$1"
                shift
                ;;
            "--id-start-post")
                shift
                ID_START_POST="$1"
                shift
                ;;
            "--id-end-pre")
                shift
                ID_END_PRE="$1"
                shift
                ;;
            "--id-end-post")
                shift
                ID_END_POST="$1"
                shift
                ;;
            "--")
                shift
                break
                ;;
            *)
                echo "ERROR: invalid options $1"
                __block_in_file__help "$FN"
                exit 1
                ;;
        esac
    done
    local FILE="$1"
    local ID="$2"
    local BLOCK="$3"

    if [[ ! -f "$FILE" ]]
    then
        echo "ERROR: file not found: $FILE"
        exit 1
    fi

    local id_start_line="${ID_START_PRE}${ID}${ID_START_POST}"
    local id_end_line="${ID_END_PRE}${ID}${ID_END_POST}"

    if [[ "$func" = "update" ]]
    then
        block_in_file "$FILE" "$id_start_line" "$id_end_line" "$BEFORE" "$AFTER" "$BLOCK"
    else
        block_in_file_remove "$FILE" "$id_start_line" "$id_end_line" "$BLOCK"
    fi
}

function __block_in_file__inner_update() {
    local file="$1"
    local id_start_line="$2"
    local id_end_line="$3"
    local before="$4"
    local after="$5"
    local block="$6"

    if [[ -z "$(grep "^$id_start_line\$" "$file")" ]]
    then
        # no existing block. add a new one
        if [ "$before" == "EOF" ]
        then
            before="$(($(cat "$file" | wc --lines) + 1))"
        else
            before="$(grep --line-number -e "$before" "$file" | head --lines=1 | awk -F: '{{print $1}}')"
        fi
        if [ "$after" == "SOF" ]
        then
            after="0"
        else
            after="$(grep --line-number -e "$after" "$file" | head --lines=1 | awk -F: '{{print $1}}')"
        fi
        
        if [[ $after > $before ]]; then
            echo "ERROR: after is bigger than before, no place to put the block"
            exit 1
        fi

        tmp_file=$(mktemp)
        head --lines=$AFTER "$file"           >"$tmp_file"
        echo "$id_start_line"                 >>"$tmp_file"
        echo "$block"                         >>"$tmp_file"
        echo "$id_end_line"                   >>"$tmp_file"
        tail --lines=+$(($AFTER + 1)) "$file" >>"$tmp_file"
        mv "$tmp_file" "$file"
    else
        # update existing block
        local start="$(grep --line-number -e "^$id_start_line\$" "$file" | head --lines=1 | awk -F: '{{print $1}}')"
        local end="$(grep --line-number -e "^$id_end_line\$" "$file" | head --lines=1 | awk -F: '{{print $1}}')"

        local tmp_file=$(mktemp)
        head --lines=$start "$file" >"$tmp_file"
        echo "$block"               >>"$tmp_file"
        tail --lines=+$end "$file"  >>"$tmp_file"
        mv "$tmp_file" "$file"
    fi
}

function __block_in_file__inner_remove() {
    local file="$1"
    local id_start_line="$2"
    local id_end_line="$3"
    local block="$4"

    local start="$(grep --line-number -e "^$id_start_line\$" "$file" | head --lines=1 | awk -F: '{{print $1}}')"
    local end="$(grep --line-number -e "^$id_end_line\$" "$file" | head --lines=1 | awk -F: '{{print $1}}')"

    local tmp_file=$(mktemp)
    head --lines=$(($start - 1)) "$file"   >"$tmp_file"
    tail --lines=+$(($start + 1)) "$file"  >>"$tmp_file"
    mv "$tmp_file" "$file"
}