#!/bin/sh -e
#
# Breaks simple captchas.
#
# deps: gocr, imagemagick, multicrop, textcleaner
#

# -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
NUM_CHARS=4
CHARSET="[0-9A-z]"

# lower number = more dense to search = more rigorous detection
DENSITY=3

# 0-100, higher numbers will force strict matches
CERTAINTY=0

# 16: not dot divide overlapping chars
# 32: do not context correct
MODE='-m 16 -m 32'

IMAGE_PROG=mpvimg
# -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*

usage() {
    >&2 printf "Usage: %s [-d] [-v] [file]\n" "${0##*/}"
    exit 1
}

init() {
    random() { r=$(($(date +%s) / $$ - $$)) ; echo ${r#-} ; }
    dir=/tmp/$(random) # dir to store tmp files
    tmp=$dir/$(random) # image created
    unset -f random

    clean
    mkdir -p "$dir"
}

clean() {
    rm -r "${dir:-?}" 2>/dev/null ||:
}

check() {
    if [ ! -f "$1" ] ; then
        >&2 echo "No such image: $1"
        exit 1
    fi
}

jpg2png() {
    case $(file "$1") in
        *jpg*|*JPG*|*jpeg*|*JPEG*)
            convert "$1" "${1%.*}.png"
            rm "$1"
            image=${image%.*}.png
            ;;
    esac
}

main() {
    image=$1
    check "$image"

    init
    # trap 'clean' INT TERM EXIT

    # convert to png if necessary
    jpg2png "image"

    # clean up text and $IM<Plug> black on white background
    # text will be evenly spaced but not aligned
    convert \
        -quality 100 \
        -shave 1x1 \
        -resize 500%x500% \
        -threshold 50% \
        -deskew 50 \
        -trim \
        -bordercolor white \
        -border 20 \
        "$image" "$tmp"

    [ "$DEBUG" = true ] && $IMAGE_PROG "$tmp" &


    # IMPORTANT: multicrop reads from top-to-bottom, while
    # we need to read left-to-right as we are reading text.
    #
    # Without rotation the resulting letters are mixed at random.
    convert -rotate 90 "$tmp" "$tmp"
    multicrop -u 1 -f 20 -g "${DENSITY:-5}" \
        -b white "$tmp" "$dir/multicut.png" >/dev/null

    # expand borders a little to help with ocr
    for i in "$dir"/multicut-*.png ; do
        {
            # and rotate 270 to put us back where we were
            convert -rotate 270 "$i" "$i"

            textcleaner -g -e stretch -f 25 -o 10 -s 1 "$i" "$i"

            convert \
                -quality 100 \
                -monochrome \
                -trim \
                -bordercolor white \
                -border 100 \
                "$i" "$i"
        } &
    done
    wait

    if [ "$DEBUG" = true ] ; then
        for i in "$dir/multicut-"*.png ; do
            $IMAGE_PROG "$i" &
        done
    fi

    montage "$dir/multicut-*.png" -tile "${NUM_CHARS:-4}"x1 "$dir/out.png"

    if [ "$DEBUG" = true ] || [ "$DISPLAY_RESULT" = true ] ; then
        $IMAGE_PROG "$dir/out.png" &
    fi

    # shellcheck disable=2086
    gocr -u '?' $MODE \
        -a ${CERTAINTY:-0} \
        -c ${CHARSET:-'[0-9A-z]'} \
        "$dir/out.png" 2>/dev/null | \
    sed 's/ //g' | tr '[:lower:]' '[:upper:]'
}

while [ "$1" ] ; do
    case $1 in
        -h) usage ;;
        -v) DEBUG=true ; shift ;;
        -d) DISPLAY_RESULT=true ; shift ;;
         *) break
    esac
done

main "$@"