gotta-patch-em-all: Add options to simplify patcher testing

[why]
When working on the font-patcher the developer needs to test the changes
on a number of fonts. This is usually a manual call of `font-patcher`
and afterwards a 'diff' of the newly created font with the 'old' font in
the patched-fonts/ directory with fontforge (which has a font-compare
option).

If you run gotta-patch-em-all normally the newly generated font will
replace the existing font and git will ALWAYS show it as different. The
reason is that at least the timestamp in the generated font has changed.
Far more easy would be if the new gotta-patch-em-all run could keep the
previous timestamps, in that way one can immediately see that the old
and new fonts are bitwise equal (via git).

Furthermore if you expect a change and want to show the differences of
old and new font in fontforge you need both fonts in the filesystem.
But a normal gotta-patch-em-all run replaces the font. A different
destination folder would help here.

[how]
Introduce two new (independent) options to
a) keep the timestamp equal to previous patch run
b) generate the fonts in a different directory

While b) is straight forward, a) is a bit more complicated, esp because
filenames can change and so on. So the script examines just one (1)
random font in the specific font directory and uses its timestamp. In
most cases this is correct enough if the developer uses gotta-patch-em-all
consequently.

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

.gitignore

@@ -1,6 +1,7 @@
 temp-glyph-source-fonts/*
 temp/*
 patched-fonts/Input*
+check-fonts/*
 unpatched-sample-fonts/Input*
 casks/*
 archives/*

bin/scripts/gotta-patch-em-all-font-patcher!.sh

@@ -32,40 +32,80 @@ total_count=0
 last_parent_dir=""
 unpatched_parent_dir="bin/scripts/../../src/unpatched-fonts"
 patched_parent_dir="patched-fonts"
+timestamp_parent_dir=${patched_parent_dir}
 max_parallel_process=64
 
-while getopts ":h-:" option; do
+function activate_keeptime {
+  type ttfdump >/dev/null 2>&1 || {
+    echo >&2 "$LINE_PREFIX ttfdump must be installed for option --keeptime"
+    exit 1
+  }
+  keeptime=TRUE
+}
+
+function activate_checkfont {
+  patched_parent_dir="check-fonts"
+}
+
+function activate_info {
+  info_only=$2
+  echo "${LINE_PREFIX} 'Info Only' option given, only generating font info (not patching)"
+}
+
+function show_help {
+  echo "Usage: $0 [OPTION] [FILTER]"
+  echo
+  echo "    OPTION:"
+  echo "        -c, --checkfont     Create the font(s) in check-fonts/ instead"
+  echo "        -t, --keeptime      Try to preserve timestamp of previously patched"
+  echo "                            font in patched-fonts/ directory"
+  echo "        -i, --info          Rebuild JUST the readmes"
+  echo "        -h, --help          Show this help"
+  echo
+  echo "    FILTER:"
+  echo "        The filter argument to this script is a filter for the fonts to patch."
+  echo "        The filter is a regex (glob "*" is expressed as "[^/]*", see \`man 7 glob\`)"
+  echo "        All font files that start with that filter (and are ttf, otf, or sfd files) will"
+  echo "        be processed only."
+  echo "          Example ./gotta-patch-em-all-font-patcher\!.sh \"iosevka\""
+  echo "          Process all font files that start with \"iosevka\""
+  echo "        If the argument starts with a '/' all font files in a directory that matches"
+  echo "        the filter are processed only."
+  echo "          Example ./gotta-patch-em-all-font-patcher\!.sh \"/iosevka\""
+  echo "          Process all font files that are in directory \"iosevka\""
+}
+
+while getopts ":chit-:" option; do
   case "${option}" in
+    c)
+      activate_checkfont
+      ;;
     h)
-      echo "Usage: $0 [OPTION] [FILTER]"
-      echo
-      echo "    OPTION:"
-      echo "        --info              Rebuild JUST the readmes"
-      echo
-      echo "    FILTER:"
-      echo "        The filter argument to this script is a filter for the fonts to patch."
-      echo "        The filter is a regex (glob "*" is expressed as "[^/]*", see \`man 7 glob\`)"
-      echo "        All font files that start with that filter (and are ttf, otf, or sfd files) will"
-      echo "        be processed only."
-      echo "          Example ./gotta-patch-em-all-font-patcher\!.sh \"iosevka\""
-      echo "          Process all font files that start with \"iosevka\""
-      echo "        If the argument starts with a '/' all font files in a directory that matches"
-      echo "        the filter are processed only."
-      echo "          Example ./gotta-patch-em-all-font-patcher\!.sh \"/iosevka\""
-      echo "          Process all font files that are in directory \"iosevka\""
+      show_help
       exit 0;;
+    i)
+      activate_info
+      ;;
+    t)
+      activate_keeptime
+      ;;
     -)
       case "${OPTARG}" in
         info)
-          info_only=$2
-          echo "${LINE_PREFIX} 'Info Only' option given, only generating font info (not patching)"
+          activate_info
+          ;;
+        keeptime)
+          activate_keeptime
+          ;;
+        checkfont)
+          activate_checkfont
           ;;
         *)
-          echo >&2 "Option '${OPTARG}' unknown"
+          echo >&2 "Option '--${OPTARG}' unknown"
           exit 1;;
       esac;;
     *)
-      echo >&2 "Option '${OPTARG}' unknown"
+      echo >&2 "Option '-${OPTARG}' unknown"
       exit 1;;
   esac
 done
@@ -73,7 +113,7 @@ shift $((${OPTIND}-1))
 
 if [ $# -gt 1 ]
 then
-  echo >&2 "Unknown parameter(s): $2.."
+  echo >&2 "Unknown parameter(s): $2 ..."
   exit 1
 fi
 
@@ -114,6 +154,23 @@ function patch_font {
   local f=$1; shift
   local i=$1; shift
   local purge=$1; shift
+
+  # Try to copy the release date from the 'original' patch
+  if [ -n "${keeptime}" ]
+  then
+    # take everything before the last slash (/) to start building the full path
+    local ts_font_dir="${f%/*}/"
+    local ts_font_dir="${ts_font_dir/$unpatched_parent_dir/$timestamp_parent_dir}"
+    local one_font=$(find ${ts_font_dir} -name '*.[ot]tf' | head -n 1)
+    if [ -n "${one_font}" ]
+    then
+      orig_font_date=$(ttfdump -t head "${one_font}" | \
+        grep -E '[^a-z]modified:.*0x' | sed 's/.*x//' | tr 'a-f' 'A-F')
+      SOURCE_DATE_EPOCH=$(dc -e "16i ${orig_font_date} Ai 86400 24107 * - p")
+      echo "$LINE_PREFIX Release timestamp adjusted to $(date -R --date=@${SOURCE_DATE_EPOCH})"
+    fi
+  fi
+
   # take everything before the last slash (/) to start building the full path
   local patched_font_dir="${f%/*}/"
   # find replace unpatched parent dir with patched parent dir: