#!/bin/bash
set -e -u -C

# Assume all arguments except the last one are git-format-patch options.
options=("${@:1:($#-1)}")

# Assume the last argument is the one operand for git-format-patch: the revision
# set.
revisions=${@:(-1)}

# Fetch the array of revisions (with abbreviated hashes) in increasing order.
rev_list=($(git log --reverse --format=tformat:%h "$revisions"))

# Create temporary directory.
tmpd=$(mktemp -d)
trap 'rm -r -- "$tmpd"' EXIT

# If the Notes section of a patch contains "context:-U3", "context:-U8" etc, or
# "context:-W" lines, return those lines. The "git notes show" output is
# expected on stdin.
filter_context_opts()
{
  sed -n -r -e 's/^context:(-U[0-9]+|-W)$/\1/p'
}

# In the directory given by $1, expand * into an array, then print the element
# with subscript $2 to stdout. The printed element will be qualified with the
# containing directory $1.
get_nth_file()
{
  local dir=$1
  local ofs=$2
  local flist=("$dir"/*)

  printf '%s\n' ${flist["$ofs"]}
}

# Collect all the context options used over the series into an array. The
# default "-U3" context option will be forcibly generated.
all_context_opts=($(
  (
    for rev in "${rev_list[@]}"; do
      git notes show "$rev" 2>/dev/null || true
    done \
    | filter_context_opts

    printf '%s\n' -U3
  ) \
  | sort -u
))

# For each found context option, format the entire series, into a dedicated
# subdirectory, using the caller-specified options and revision set. (Format a
# cover letter as well.) Unfortunately, this is necessary because the "/m" part
# in "[PATCH v3 n/m]" depends on *all* patches being formatted in one go.
for context_opt in "${all_context_opts[@]}"; do
  mkdir -- "$tmpd/context$context_opt"
  git format-patch --notes --cover-letter --numbered --stat=1000 \
      --stat-graph-width=20 --output-directory "$tmpd/context$context_opt" \
      "$context_opt" "${options[@]}" "$revisions" >/dev/null
done

# Iterate over the cover letter and all the revisions. For each, determine the
# context option. (For the cover letter, and for revisions without a
# "context:..." line in the Notes section, assume -U3. If a revision has
# multiple "context:..." lines in the Notes section, pick the first one.) Once
# the context option has been determined, *positionally* look up the formatted
# patch email that corresponds to the cover letter or the revision, in the
# subdirectory that corresponds to the context option.
patchnr=0
for rev in cover_letter "${rev_list[@]}"; do
  if test cover_letter = "$rev"; then
    context_opt=
  else
    context_opt=$(
      git notes show "$rev" 2>/dev/null \
      | filter_context_opts \
      | head -1
    )
  fi
  if test -z "$context_opt"; then
    context_opt=-U3
  fi
  file=$(get_nth_file "$tmpd/context$context_opt" "$patchnr")
  cat -- "$file"
  if test $patchnr -gt 0 && test $patchnr -lt ${#rev_list[@]}; then
    printf '\n'
  fi
  patchnr=$(($patchnr + 1))
done