# shellcheck shell=dash
# vim: ft=sh

# substitute replaces all occurances of one string with another in the provided
# file, writing to the specified output file.
substitute() {
    local input="$1"
    local output="$2"

    shift 2

    # TODO: real parsing
    local search="$1"
    local replace="$2"

        #-v RS="$(printf "\0")" \
    awk \
        -v srch="$search" \
        -v repl="$replace" \
        -v RS="" \
        -v ORS="" \
        '{ gsub(srch, repl, $0); print $0 }' \
        < "$input" > "$output"
}

# substituteInPlace works like substitute but operates in-place on the provided
# file
substituteInPlace() {
    local fpath="$1"
    shift

    local tmpfile
    tmpfile="$(mktemp)"
    
    if ! substitute "$fpath" "$tmpfile" "$@"; then
        rm "$tmpfile"
        return $?
    fi

    # Overwrite now that we've succeeded
    mv "$tmpfile" "$fpath"
}

# Shell-quotes an arbitrary string.
#
# From: http://www.etalabs.net/sh_tricks.html
#
#     This function simply replaces every instance of «'» (single quote) within
#     the string with «'\''» (single quote, backslash, single quote, single
#     quote), then puts single quotes at the beginning and end of the string.
#     Since the only character whose meaning is special within single quotes is
#     the single quote character itself, this is totally safe. Trailing
#     newlines are handled correctly, and the single quote at the end doubles
#     as a safety character to prevent command substitution from clobbering the
#     trailing newlines, should one want to do something like:
#         quoted=$(quote "$var")
quote() {
    printf "%s\n" "$1" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/'/"
}


# Returns whether or not a string matches a glob; similar to the bash [[ test,
# but portable.
fnmatch() {
    # We explicitly want this to act as a glob
    # shellcheck disable=SC2254
    case "$2" in
        $1) return 0 ;;
        *)  return 1 ;;
    esac
}

# Portable equivalent to GNU's `date +"%s"`
#
# From: http://www.etalabs.net/sh_tricks.html
epochseconds() {
    # This is horrible, but... it tells 'date' to generate a string that
    # contains shell math to generate the actual epoch date.
    #
    # TODO(andrew-d): break down and verify the math here
    echo $(( $(TZ=GMT0 date +"((%Y-1600)*365+(%Y-1600)/4-(%Y-1600)/100+(%Y-1600)/400+1%j-1000-135140)*86400+(1%H-100)*3600+(1%M-100)*60+(1%S-100)") ))
}

# user_homedir returns the home directory for the provided user
user_homedir() {
    local user="$1"

    awk \
        -v u="$user" \
        -v FS=':' \
        '$1==u {print $6}' \
        /etc/passwd
}

# sponge acts like sponge(1) from moreutils, but is portable.
#
# It "soaks up" all input from stdin before writing it to the specified output;
# helpful for modifying a file in-place with a utility that does not support
# it.
sponge() {
    local append=false

    while getopts 'a' opt; do
        case $opt in
            a) append=true ;;
            *) echo "unknown option: $opt" >&2; exit 1;;
        esac
    done
    shift "$(( OPTIND - 1 ))"

    local outfile="$1"
    local tmpfile

    tmpfile="$(mktemp "$(dirname "$outfile")/tmp-sponge.XXXXXXXX")" &&
    cat >"$tmpfile" &&
    if "$append"; then
        cat "$tmpfile" >>"$outfile"
    else
        if [ -f "$outfile" ]; then
            # NOTE: the stat() call here isn't exactly portable, but both GNU
            # coreutils and busybox support it, so close enough? Let's
            # double-check that it returns something sensible just to be sure.
            local oldperms
            oldperms="$(stat -c '%a' "$outfile")"

            # Should be a string of length 3 with only digits
            if [ "${#oldperms}" = "3" ] && [ -z "$(echo "$oldperms" | tr -d '0-9')" ]; then
                chmod "$oldperms" "$tmpfile"
            else
                printf "warning (bad: %s): not setting permssions on: %s\n" "${oldperms}" "$outfile" >&2
            fi
        fi
        if [ -f "$outfile" ]; then
            mv "$tmpfile" "$outfile"
        elif [ -n "$outfile" ] && [ ! -e "$outfile" ]; then
            cat "$tmpfile" >"$outfile"
        else
            cat "$tmpfile"
        fi
    fi &&
    rm -f "$tmpfile"
}