#!/bin/bash
us=svg-prep-dxf
usage () { cat <<END
usage: $us [--flatness=VALUE] IN.svg OUT.dxf

Turns a stroked path into its outline path; "union"s it (so that it
does not self-intersect); approximates its bezier curves with line
segments; and produces a dxf for openscad.
END
}
# Copyright 2016 Ian Jackson
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation; either version 2 of the License, or (at your option)
# any later version.
#
# As a special exception, you have permission to link this program
# with the CGAL library and distribute executables, as long as you
# follow the requirements of the GNU GPL in regard to all of the
# software in the executable aside from CGAL.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
# more details.

set -e

fail () { echo >&2 "svg-dxf-prep: $*"; exit 1; }
badusage () { usage >&2; exit 1; }

flatness=0.01
# ^ this number seems to work reasonably well
#   although maybe it should be adjusted?

while true; do
    case "$1" in
    --flatness=*)
	flatness="${1#*=}"
	;;
    -*)
	badusage
	;;
    *)
	break
	;;
    esac
    shift
done

case "$#" in
2)  ;;
*)  badusage ;;
esac

source=$1
dest=$2

case "$source" in
*.svg) ;;
*)  badusage ;;
esac

case "$dest" in
*.dxf) ;;
*)  badusage ;;
esac

tmpdir="$(dirname "$dest")/.$(basename "$dest").tmpdir"
rm -rf -- "$tmpdir"
mkdir -- "$tmpdir"

case "$tmpdir" in
/*)  abstmpdir="$tmpdir" ;;
*)   abstmpdir="$PWD/$tmpdir" ;;
esac

cp -- "$source" "$tmpdir/t.svg"

# startx seems to send "client" stdout/stderr somewhere hopeless
exec 4>&2

baseextdir=$(inkscape -x)
ourid=uk.org.greenend.chiark.ijackson.swirly.flatten

# inkscape doesn't provide a way to specify a per-invocation
# extension directory, but it does look in $HOME.
# Anyway, we're going to want a fresh HOME for startx.
ourxd="$tmpdir"/.config/inkscape/extensions
mkdir -p "$ourxd"
mkdir -p "$tmpdir/.local/share" # inkscape complains otherwise, wtf

# Putting the absolute path in the XML doesn't seem to work:
# inkscape complains that this "dependency" (implicit, apparently)
# is not satisfied.
# I'm not sure why this is, but this does work:
ln -s -- "$baseextdir/flatten.py" "$ourxd"

xmlstarlet \
ed \
 -N ie=http://www.inkscape.org/namespace/inkscape/extension \
 -u "/ie:inkscape-extension/ie:_name" -v "Our Flatten Beziers" \
 -u "/ie:inkscape-extension/ie:id" -v $ourid \
 -d '/ie:inkscape-extension/ie:dependency' \
 -u '/ie:inkscape-extension/ie:param[@name="flatness"]' -v $flatness \
 "$baseextdir"/flatten.inx \
 >"$ourxd"/our-flatten.inx
# known bugs with this approach:
#  - we rely on the .inx filename
#  - we rely on flatten.py being in the extensions/ directory
#    and called exactly that
#  - we drop the dependencies rather than editing them

cat <<'END' >"$tmpdir/run-inkscape"
#!/bin/sh
exec >&4 2>&4
echo
printf "running inkscape to transform and clean up..."
cd "$HOME"
inkscape \
 --with-gui \
 t.svg \
 --verb=ToolNode \
 --verb=EditSelectAll \
 --verb=SelectionUnGroup \
 --verb=EditSelectAll \
 --verb=StrokeToPath \
 --verb=ToolNode \
 --verb=EditSelectAll \
 --verb=SelectionUnion \
 --verb=EditSelectAll \
 --verb=uk.org.greenend.chiark.ijackson.swirly.flatten.noprefs \
 --verb=FileSave \
 --verb=FileQuit \

echo done.
echo
END
chmod +x "$tmpdir"/run-inkscape

cat <<END

Expect some complaints from xinit, for example
  about XFree86_VT property
  lost connection
  file descriptors for console
END

HOME="$abstmpdir" \
/usr/bin/startx \
 "$abstmpdir"/run-inkscape \
 -- \
 `type -p Xvfb`

# It's awkward to get inkscape to save as DXF noninteractively.
# And inkscape doesn't seem to like to exit if I try to export
# from the "interactive" one.

# But anyway inkscape DXF is just made with pstoedit.  So save as SVG,
# and then do a separate inkscape run to convert EPS, and run pstoedit
# to make the DXF.

inkscape --export-area-page \
 -f "$tmpdir"/t.svg \
 -E "$tmpdir"/t.eps \

pstoedit -dt -f 'dxf:-polyaslines -mm' \
 "$tmpdir"/t.eps \
 "$tmpdir/"t.dxf

mv -- "$tmpdir"/t.dxf "$dest"

echo
printf "$us: success, wrote %s\n" "$dest"
echo

exit 0