#!/bin/sh

 # Get our required options

 base="$1"

 src="$2"

 dst="$3"

 shift 3

 # The remainder is for diff

 diff="$@"

 # This function checks that the files listed in the file in "$1"

 # do exist, at the given depth-stripping level (aka diff -p#)

 do_check_files_at_depth() {

   local flist="$1"

   local depth="$2"

   local ok=0  # 0: OK,  !0: KO

   exec 6<&0

   exec 7<"${flist}"

   while read -u7 f; do

     f="$( echo "${f}" |sed -r -e "s:^([^/]+/){${depth}}::;" )"

     [ -f "${f}" ] || ok=1

   done

   exec 7<&-

   exec <&6

   return ${ok}

 }

 mkdir -p "${dst}"

 base="${base%%/}"

 src="$( cd "${src}"; pwd )"

 dst="$( cd "${dst}"; pwd )"

 # Iterate through patches

 for p in "${src}/"*.patch; do

   pname="$( basename "${p}" )"

   printf "Handling patch '${pname}'...\n"

   printf "  creating reference..."

   cp -a "${base}" "${base}.orig"

   printf " done\n"

   printf "  retrieving patch comment..."

   comment="$( awk '

 BEGIN { mark=0; }

 $0~/^diff --/ { nextfile; }

 $1=="---" { mark=1; next; }

 $1=="+++" && mark==1 { nextfile; }

 { mark=0; print; }

 ' "${p}" )"

   printf " done\n"

   printf "  creating patched file list..."

   diffstat -f 4 -r 2 -u -p 0 "${p}"                         \

   |head -n -1                                               \

   |awk '{ for(i=NF;i>=NF-5;i--) { $(i) = ""; } print; }'    \

   |sort                                                     \

   >"diffstat.orig"

   printf " done\n"

   pushd "${base}" >/dev/null 2>&1

   # Check all files exist, up to depth 3

   printf "  checking depth:"

   for((d=0;d<4;d++)); do

     printf " ${d}"

     if do_check_files_at_depth "../diffstat.orig" ${d}; then

       printf " ok, using depth '${d}'\n"

       break

     fi

   done

   if [ ${d} -ge 4 ]; then

     printf "\n"

     printf "  checking depth failed\n"

     read -p "  --> enter patch depth (or Ctrl-C to abort): " d

   fi

   # Store the original list of fiels touched by the patch,

   # removing the $d leading components

   sed -r -e "s:^([^/]+/){${d}}::;" "../diffstat.orig" >"${dst}/${pname}.diffstat.orig"

   # Apply the patch proper, and check it applied cleanly.

   # We can't check with --dry-run because of patches that

   # contain multiple accumulated patches onto a single file.

   printf "  applying patch..."

   if ! patch -g0 -F1 -f -p${d} <"${p}" >"../patch.out" 2>&1; then

     printf " ERROR\n\n"

     popd >/dev/null 2>&1

     printf "There was an error while applying:\n  -->  ${p}  <--\n"

     printf "'${base}' was restored to the state it was prior to applying this faulty patch.\n"

     printf "Here's the 'patch' command, and its output:\n"

     printf "  ----8<----\n"

     printf "  patch -g0 -F1 -f -p${d} <'${p}'\n"

     sed -r -e 's/^/  /;' "patch.out"

     printf "  ----8<----\n"

     exit 1

   fi

   printf " done\n"

   printf "  removing '.orig' files..."

   find . -type f -name '*.orig' -exec rm -f {} +

   printf " done\n"

   popd >/dev/null 2>&1

   printf "  re-diffing the patch..."

   printf "%s\n\n" "${comment}" >"${dst}/${pname}"

   diff -durN "${base}.orig" "${base}" >>"${dst}/${pname}"

   printf " done\n"

   if [ -n "${diff}" ]; then

     printf "  applying diff filter..."

     filterdiff -x "${diff}" "${dst}/${pname}" >"tmp-diff"

     mv "tmp-diff" "${dst}/${pname}"

     printf " done\n"

   fi

   printf "  creating new patched file list..."

   diffstat -f 4 -r 2 -u -p 1 "${dst}/${pname}"              \

   |head -n -1                                               \

   |awk '{ for(i=NF;i>=NF-5;i--) { $(i) = ""; } print; }'    \

   |sort                                                     \

   >"${dst}/${pname}.diffstat.new"

   printf " done\n"

   printf "  removing temporary files/dirs..."

   rm -f "patch.out"

   rm -f "diffstat.tmp"

   rm -f "diffstat.orig"

   rm -rf "${base}.orig"

   printf " done\n"

 done

 # Scan all new patches to see if they touch

 # more files than the original patches

 printf "\nChecking resulting patchset:\n"

 for p in "${dst}/"*.patch; do

   pname="$( basename "${p}" )"

   if ! cmp "${p}.diffstat.orig" "${p}.diffstat.new" >/dev/null; then

     printf "  --> '${pname}' differ in touched files <--\n"

   else

     rm -f "${p}.diffstat.orig" "${p}.diffstat.new"

   fi

 done

 printf "  done.\n"