#! /usr/bin/env bash

# Commit and push an update to an existing note.
#
# -c
#   Commit only, don't push.
#
usage="usage: $0 [-c]"

owd=`pwd`
trap "{ cd $owd; exit 1; }" ERR
set -o errtrace # Trap in functions.

function info () { echo "$*" 1>&2; }
function error () { info "$*"; exit 1; }

push="y"

while [ $# -gt 0 ]; do
  case $1 in
    -c)
      push="n"
      shift
      ;;
    *)
      error "$usage"
      ;;
  esac
done

if git status --porcelain | grep -q '^M '; then
  error "error: repository already has staged changes"
fi

# @@ We could probably handle the case where extra files are added to the
# note. We just need to make sure they are not changes to other notes.
#
if git status --porcelain | grep -q '^?? '; then
  error "error: repository has untracked files"
fi

modified="$(git status --porcelain  | sed -n -e 's/^ M \(.*\)/\1/p')"

mc="$(echo "$modified" | wc -w)"

if [ "$mc" -eq 0 ]; then
  error "error: nothing modified"
fi

if [ "$mc" -gt 1 ]; then
  error "error: multiple modified files"
fi

# Extract the start line and count from the changeset header.
#
# The format is:
#
# @@ [+-]FROM-START,FROM-COUNT [+-]TO-START,TO-COUNT @@
#
# Note that if the changeset has only one line then the count is omitted.
#
function changeset_start ()
{
  echo "$1" | sed -e 's/^@@ [^ ]* [+-]\([^, ]*\).*$/\1/'
}

function changeset_count ()
{
  local r
  r="$(echo "$1" | sed -n -e 's/^@@ [^ ]* [+-][^,]*,\([^ ]*\) @@$/\1/p')"
  if [ -z "$r" ]; then
    r="1"
  fi
  echo "$r"
}

#changeset_start "@@ -12,3 +13,11 @@"
#changeset_count "@@ -12,3 +13,11 @@"
#changeset_start "@@ -12 +13 @@"
#changeset_count "@@ -12 +13 @@"

h=
if [ "$(basename "$modified")" = "list" ]; then
  #
  # This is a list of notes. The plan is to get the start line numbers for the
  # first and last change set. We then scan the list line by line looking for
  # headers until we hit the start of the first change set: the last header
  # that we see should be our header. We also continue scanning until we hit
  # the end of the last changeset: if we see any headers then we are updating
  # multiple notes.
  #

  # Get the diff output as a list of change set headers.
  #
  diff="$(git diff -U0 | sed -n -e '/^@@ /p')"

  fc="$(echo "$diff" | head -n 1)"
  lc="$(echo "$diff" | tail -n 1)"

  sl="$(changeset_start "$fc")"
  el="$(($(changeset_start "$lc") + $(changeset_count "$lc") - 1))"

  # Scan the list looking for headers.
  #
  l=
  c="0"
  while read l || [ -n "$l" ]; do

    # Stop if we are past the end line.
    #
    c="$(($c + 1))"
    if [ "$c" -gt "$el" ]; then
      break
    fi

    # See if this is a header.
    #
    if echo "$l" | grep -q '^[-?!] '; then

      # If we are past the start line then we are modifying multiple notes.
      #
      if [ "$c" -gt "$sl" ]; then
	error "error: multiple modified notes in $modified:${sl}-${el}"
      fi

      # This is the last header.
      #
      h="$l"
    fi
  done < <(cat "$modified")

  if [ -z "$h" ]; then
    error "error: unable to find note header for $modified:${sl}-${el}"
  fi
else
  # This is a file note. All we need to do is get its header (the first line).
  #
  h="$(head -n 1 "$modified")"
fi

# Header should start with one of [-?!].
#
sum="$(echo "$h" | sed -n -re 's/^[-?!] ([^[]*)( \[.*\])?$/\1/p')"

if [ -z "$sum" ]; then
  error "error: unable to parse note header '$h'"
fi

# By convention the first label is a note type (bug, feature, etc).
#
type="$(echo "$h" | sed -n -re 's/^[^[]*\[([^ ]*).*\]$/\1/p')"

if [ -z "$type" ]; then
  error "error: note header does not include note type as first label"
fi

# Ok, all looks good so add, commit and push the change.
#
git add "$modified"
git ci -m "Update $type: $sum"

if [ "$push" = "y" ]; then
  git push
fi