#!/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}"

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"

    # Revert the patch

    popd >/dev/null 2>&1

    printf "  restoring '${base}'..."

    rm -f "diffstat.tmp"

    rm -rf "${base}"

    mv "${base}.orig" "${base}"

    printf " done\n\n"

    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"

    cat "patch.out" |(IFS=$(printf "\n"); while read line; do printf "  ${line}\n"; done)

    rm -f "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 -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"

  fi

done

printf "  done.\n"