#!/bin/bash

# Updates one component (i.e. subdirectory) in static-master/master

# acquires a shared lock on the base directory (so that we know no updates are
# outgoing, as those acquire an exclusive one).  Also acquired an exclusive lock
# on the component directory in question.
#
# The config file is a list of component source-directory pairs.

# Copyright (c) 2012 Peter Palfrader
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

componentlist=/etc/static-components.conf
base=/home/staticsync/static-master/master

set -e
set -u

if [ "`id -u`" != "`stat -c %u "$base"`" ]; then
  echo >&2 "You are probably running this as the wrong user."
  exit 1
fi

lock() {
  local fd="$1"; shift
  local path="$1"; shift
  local exclusive="$1"; shift

  eval "exec $fd< '$path'"

  if [ "$exclusive" -gt 0 ]; then
    locktype="-e"
  else
    locktype="-s"
  fi

  if ! flock "$locktype" "$fd"; then
    echo >&2 "$0: Cannot acquire lock on $path (flock $locktype failed) - Very bad, we should have waited!"
    exit 1
  fi
}

unlock() {
  local fd="$1"; shift

  if ! flock -o "$fd"; then
    echo >&2 "$0: Cannot release lock on fd $fd - This should not have happened!"
    exit 1
  fi
  eval "exec $fd<&-"
}

if [ "$#" != 1 ]; then
  echo >&2 "Usage: $0 <component>"
  exit 1
fi

component="$1"

if [ "${component%/*}" != "$component" ] ; then
  echo >&2 "$0: Invalid component: $component";
  exit 1
fi

srchost="$(awk -v this_host="$(hostname -f)" -v component="$component" '!/^ *(#|$)/ && $1 == this_host && $2 == component {print $3; exit}' "$componentlist")"
srcdir="$(awk -v this_host="$(hostname -f)" -v component="$component" '!/^ *(#|$)/ && $1 == this_host && $2 == component {print $4; exit}' "$componentlist")"
if [ -z "$srchost" ] || [ -z "$srcdir" ]; then
  echo >&2 "$0: Invalid component: $component (not found in $componentlist)";
  exit 1
fi
tgt="$base/$component"
if ! [ -d "$tgt" ]; then
  echo "$0: Creating $tgt for $component";
  mkdir "$tgt"
fi

if [ "$srchost" = "`hostname -f`" ]; then
  src="$srcdir"
else
  src="$srchost:$srcdir"
fi

echo "$0: Acquiring locks..."
lock 201 "$tgt" 1

tmpdir_new="$(mktemp -d --tmpdir="$base" "${component}-updating.incoming-XXXXXX")"
tmpdir_old="$(mktemp -d --tmpdir="$base" "${component}-updating.removing-XXXXXX")"
trap "rm -rf '$tmpdir_new' '$tmpdir_old'" EXIT
chmod 0755 "$tmpdir_new"

lock 202 "$tmpdir_new" 1
echo "$0: Got them."

echo "$0: Updating master copy of $component..."
rsync --delete \
  -trz \
  --links --hard-links --safe-links \
  --link-dest="$tgt" \
  --exclude='/.serial' \
  "$src/." "$tmpdir_new/."
echo "$0: Done.  Committing."

mv "$tgt" "$tmpdir_old/old"
if ! mv "$tmpdir_new" "$tgt"; then
  echo >&2 "$0: WARNING: could not move $tmpdir_new to $tgt.  Trying to recover"
  rm -rf "$tgt"
  mv "$tmpdir_old/old" "$tgt"
  echo >&2 "$0: Rolled back to old tree, maybe even successfully."
  exit 1
fi

rm -rf "$tmpdir_new" "$tmpdir_old"
trap - EXIT

date '+%s' > "$tgt/.serial"
unlock 201
unlock 202
echo "$0: Triggering mirror runs..."
exec static-master-run "$component"

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