#!/bin/bash
# vi: et sts=4 sw=4 ts=4

PRESERVE_TIMESTAMP=0

TEMP_FILES=()
cleanup() {
    rm -f -- "${TEMP_FILES[@]}"
}
trap 'cleanup' EXIT

file_size() {
    stat \
        --format='%s' \
        --dereference \
        -- \
        "$@" \
        2>/dev/null
}

# copies $2 over to $1 if $2 is smaller than $1
use_smaller() {
    # if `$TEMP' isn't empty and it's of a smaller size than `$FILE',
    # preserve every attribute and replace `$FILE' with `$TEMP'
    local \
        FILE=$1 \
        TEMP=$2 \
        ORIGSIZE \
        TEMPSIZE

    ORIGSIZE=$(file_size "$FILE")
    TEMPSIZE=$(file_size "$TEMP")

    if [[ -f $TEMP &&
        $TEMPSIZE -gt 0 &&
        $TEMPSIZE -lt $ORIGSIZE
    ]]; then

        # Preserve attributes by copying them from the original file to the
        # temporary one
        chmod \
            --reference="$FILE" \
            -- \
            "$TEMP" &&

        if [[ $PRESERVE_TIMESTAMP -ne 0 ]]; then
            touch \
                --reference="$FILE" \
                -- \
                "$TEMP"
        fi &&

        if [[ $UID -eq 0 ]]; then
            # We are root, so we can chown(1) things
            chown \
                --reference="$FILE" \
                -- \
                "$TEMP"
        fi &&

        cp \
            --preserve=mode,ownership,timestamps \
            -- \
            "$TEMP" \
            "$FILE"

        local ERR=$?
        case "$ERR" in
            '0')
                printf 'Optimized "%s"\n' \
                    "$FILE" \
                    >&2
                ;;
            *)
                printf 'Failed to optimize "%s"!\n' \
                    "$FILE" \
                    >&2
                ;;
        esac

    fi

    # Protect against unsuccessful following file writes to our TEMP file
    rm -f -- "$TEMP"

}

TEMP0=$(mktemp -t "${0##*/}.XXXXXX")
TEMP1=$(mktemp -t "${0##*/}.XXXXXX")
TEMP_FILES+=("$TEMP0" "$TEMP0")

ERRORS=0
for FILE; do
    rm -f -- "$TEMP0" "$TEMP1"
    if !
        qpdf --stream-data=uncompress -- "$FILE" "$TEMP0" &&
        qpdf --stream-data=compress -- "$TEMP0" "$TEMP1" &&
        use_smaller "$FILE" "$TEMP1"; then
        (( ++ERRORS ))
    fi
done

if [[ $ERRORS -gt 0 ]]; then
    exit 1
fi