repo2html/hashcache

#!/bin/bash
#
# Hash cache storage and retrieval operations
#
#  Copyright (C) 2012  Mike Gerwitz
#
#  This file is part of repo2html.
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.
# #

# intended to be configured from a configuration file; lowercase to help
# mitigate global env var conflicts
cachefile="${hashcache:-${path_root:+$path_root/}.hashcache}"

# 'cause it rhymes and 'cause it's useful
_cache()
{
  hash="$1"
  value="$2"
  title="$3"

  echo "$hash $value $title" >>"$cachefile"
}

# retrieves the value associated with the given hash
_retrieve()
{
  hash="$1"

  # if multiple identical hashes exist, then the last one takes precedence
  # (ideally, such a thing should never happen, but it's best to be prepared);
  # note that we *do not* check for a space after the hash, which allows for
  # partial hashes to be matched (common practice for Git due to its long
  # hashes); this may cause problems with other version control systems---such
  # as SVN---that use revision numbers, in which case this implementation will
  # have to be changed to accept a flag for whether or not to accept partial
  # matches, or it must operate under the assumption that the commits are always
  # processed in reverse order and (as such) the tail in this pipeline will
  # always return the intended result
  grep "^$hash" "$cachefile" \
    | tail -n1 \
    | cut -d' ' -f2-
}

# clears the cache file
_wipe()
{
  >"$cachefile"
}


# the hash is required, but the value to set it to is optional
hash="${1?No hash provided}"
set="$2"
title="$3"

# poor man's argument parsing (we don't need no stinkin' options [yet]); "clear"
# is not a valid hash currently, though I suppose a sadistic repository could
# allow such, and we're supposed to be repo-agnostic
if [ "$hash" == 'clear' ]; then
  _wipe
elif [ "$set" ]; then
  _cache "$hash" "$set" "$title"
else
  result="$( _retrieve "$hash" "$set" )"
  echo "$result"

  # exit with negative status if we have no result
  [ -n "$result" ]
fi