#!/usr/bin/python
#
# mailer.py: send email describing a commit
#
# $HeadURL: http://svn.collab.net/repos/svn/trunk/tools/hook-scripts/mailer/mailer.py $
# $LastChangedDate: 2003-09-01 00:21:42 +0200 (Mon, 01 Sep 2003) $
# $LastChangedBy: striker $
# $LastChangedRevision: 6940 $
#
# USAGE: mailer.py REPOS-DIR REVISION [CONFIG-FILE]
#
#   Using CONFIG-FILE, deliver an email describing the changes between
#   REV and REV-1 for the repository REPOS.
#

import os
import sys
import string
import ConfigParser
import time
import popen2
import cStringIO
import smtplib
import re

import svn.fs
import svn.core
import svn.delta
import svn.repos

SEPARATOR = '=' * 78


def main(pool, config_fname, repos_dir, rev):
  repos = Repository(repos_dir, rev, pool)

  cfg = Config(config_fname, repos)

  editor = ChangeCollector(repos, rev-1)

  e_ptr, e_baton = svn.delta.make_editor(editor, pool)
  svn.repos.svn_repos_replay(repos.root_this, e_ptr, e_baton, pool)

  # get all the changes and sort by path
  changelist = editor.changes.items()
  changelist.sort()

  ### hunh. this code isn't actually needed for StandardOutput. refactor?
  # collect the set of groups and the unique sets of params for the options
  groups = { }
  for path, change in changelist:
    for (group, params) in cfg.which_groups(path):
      # turn the params into a hashable object and stash it away
      param_list = params.items()
      param_list.sort()
      groups[group, tuple(param_list)] = params

  output = determine_output(cfg, repos, changelist)
  output.generate(groups, pool)


def determine_output(cfg, repos, changelist):
  if cfg.is_set('general.mail_command'):
    cls = PipeOutput
  elif cfg.is_set('general.smtp_hostname'):
    cls = SMTPOutput
  else:
    cls = StandardOutput

  return cls(cfg, repos, changelist)


class MailedOutput:
  def __init__(self, cfg, repos, changelist):
    self.cfg = cfg
    self.repos = repos
    self.changelist = changelist

    # figure out the changed files/directories
    paths = { }
    modules = { }
    for path, change in changelist:
      modules[(path.split('/'))[0]] = None
      paths[path] = None

    self.modules = modules.keys()

    pathlist = paths.keys()
    
    # FIXME: use os.path.commonprefix()

    # figure out the common portion of all the paths. note that there is
    # no "common" if only a single path was changed, or the root was changed.
    if len(pathlist) == 1 or paths.has_key(''):
      commondir = ''
    else:
      common = string.split(pathlist.pop(), '/')
      for d in pathlist:
        parts = string.split(d, '/')
        for i in range(len(common)):
          if i == len(parts) or common[i] != parts[i]:
            del common[i:]
            break
      commondir = string.join(common, '/')
      if commondir:
        # strip the common portion from each path
        l = len(commondir) + 1
        pathlist = [ ]
        for d in paths.keys():
          if d == commondir:
            pathlist.append('.')
          else:
            pathlist.append(d[l:])
      else:
        # nothing in common, so reset the list of files
        pathlist = paths.keys()

    # compose the basic subject line. later, we can prefix it.
    pathlist.sort()
    pathlist = string.join(pathlist)
    if commondir:
      self.subject = 'r%d: %s: %s' % (repos.rev, commondir, pathlist)
    else:
      self.subject = 'r%d: %s' % (repos.rev, pathlist)

  def generate(self, groups, pool):
    "Generate email for the various groups and option-params."

    ### these groups need to be further compressed. if the headers and
    ### body are the same across groups, then we can have multiple To:
    ### addresses. SMTPOutput holds the entire message body in memory,
    ### so if the body doesn't change, then it can be sent N times
    ### rather than rebuilding it each time.

    subpool = svn.core.svn_pool_create(pool)

    for (group, param_tuple), params in groups.items():
      self.start(group, params)

      # generate the content for this group and set of params
      generate_content(self, self.cfg, self.repos, self.changelist,
                       group, params, subpool)

      self.finish()
      svn.core.svn_pool_clear(subpool)

    svn.core.svn_pool_destroy(subpool)

  def start(self, group, params):
    self.to_addr = self.cfg.get('to_addr', group, params)
    self.from_addr = self.cfg.get('from_addr', group, params) or \
                     self.repos.author or 'no_author'
    self.from_hdr = "%s <%s>" % (self.repos.author, \
                                 self.cfg.get('from_addr', group, params))
    self.reply_to = self.cfg.get('reply_to', group, params)

  def mail_headers(self, group, params):
    prefix = self.cfg.get('subject_prefix', group, params)
    if prefix:
      subject = prefix + ' ' + self.subject
    else:
      subject = self.subject
    if len(subject) > 100:
      subject = subject[0:100] + "..."
    hdrs = 'From: %s\n'    \
           'To: %s\n'      \
           'Subject: %s\n' \
           'X-SVN-Repo-Revision: %d\n' \
           'Message-ID: <%d@svn.nemerle.org>\n' \
	   'Mime-Version: 1.0\n' \
	   'Content-Type: text/plain;\n' \
	   '  charset=utf-8\n' \
	   'Content-Disposition: inline\n' \
	   'Content-Transfer-Encoding: 8bit\n' \
           % (self.from_hdr, self.to_addr, subject, \
              self.repos.rev, self.repos.rev)
    if len(self.modules) == 0:
      hdrs += 'X-SVN-Module: \n' # append empty, just in case
    else:
      for m in self.modules:
        hdrs += 'X-SVN-Module: %s\n' % m
    if self.reply_to:
      hdrs += 'Reply-To: %s\n' % self.reply_to
    return hdrs + '\n'


class SMTPOutput(MailedOutput):
  "Deliver a mail message to an MTA using SMTP."

  def __init__(self, cfg, repos, changelist):
    MailedOutput.__init__(self, cfg, repos, changelist)

  def start(self, group, params):
    MailedOutput.start(self, group, params)

    self.buffer = cStringIO.StringIO()
    self.write = self.buffer.write

    self.write(self.mail_headers(group, params))

  def run_diff(self, cmd):
    # we're holding everything in memory, so we may as well read the
    # entire diff into memory and stash that into the buffer
    pipe_ob = popen2.Popen3(cmd)
    self.write(pipe_ob.fromchild.read())

    # wait on the child so we don't end up with a billion zombies
    pipe_ob.wait()

  def finish(self):
    server = smtplib.SMTP(self.cfg.general.smtp_hostname)
    server.sendmail(self.from_addr, [ self.to_addr ], self.buffer.getvalue())
    server.quit()


class StandardOutput:
  "Print the commit message to stdout."

  def __init__(self, cfg, repos, changelist):
    self.cfg = cfg
    self.repos = repos
    self.changelist = changelist

    self.write = sys.stdout.write

  def generate(self, groups, pool):
    "Generate the output; the groups are ignored."

    # use the default group and no parameters
    ### is that right?
    generate_content(self, self.cfg, self.repos, self.changelist,
                     None, { }, pool)

  def run_diff(self, cmd):
    # flush our output to keep the parent/child output in sync
    sys.stdout.flush()
    sys.stderr.flush()

    # we can simply fork and exec the diff, letting it generate all the
    # output to our stdout (and stderr, if necessary).
    pid = os.fork()
    if pid:
      # in the parent. we simply want to wait for the child to finish.
      ### should we deal with the return values?
      os.waitpid(pid, 0)
    else:
      # in the child. run the diff command.
      try:
        os.execvp(cmd[0], cmd)
      finally:
        os._exit(1)


class PipeOutput(MailedOutput):
  "Deliver a mail message to an MDA via a pipe."

  def __init__(self, cfg, repos, changelist):
    MailedOutput.__init__(self, cfg, repos, changelist)

    # figure out the command for delivery
    self.cmd = string.split(cfg.general.mail_command)

    # we want a descriptor to /dev/null for hooking up to the diffs' stdin
    self.null = os.open('/dev/null', os.O_RDONLY)

  def start(self, group, params):
    MailedOutput.start(self, group, params)

    ### gotta fix this. this is pretty specific to sendmail and qmail's
    ### mailwrapper program. should be able to use option param substitution
    cmd = self.cmd + [ '-f', self.from_addr, self.to_addr ]

    # construct the pipe for talking to the mailer
    self.pipe = popen2.Popen3(cmd)
    self.write = self.pipe.tochild.write

    # we don't need the read-from-mailer descriptor, so close it
    self.pipe.fromchild.close()

    # start writing out the mail message
    self.write(self.mail_headers(group, params))

  def run_diff(self, cmd):
    # flush the buffers that write to the mailer. we're about to fork, and
    # we don't want data sitting in both copies of the buffer. we also
    # want to ensure the parts are delivered to the mailer in the right order.
    self.pipe.tochild.flush()

    pid = os.fork()
    if pid:
      # in the parent

      # wait for the diff to finish
      ### do anything with the return value?
      os.waitpid(pid, 0)

      return

    # in the child

    # duplicate the write-to-mailer descriptor to our stdout and stderr
    os.dup2(self.pipe.tochild.fileno(), 1)
    os.dup2(self.pipe.tochild.fileno(), 2)

    # hook up stdin to /dev/null
    os.dup2(self.null, 0)

    ### do we need to bother closing self.null and self.pipe.tochild ?

    # run the diff command, now that we've hooked everything up
    try:
      os.execvp(cmd[0], cmd)
    finally:
      os._exit(1)

  def finish(self):
    # signal that we're done sending content
    self.pipe.tochild.close()

    # wait to avoid zombies
    self.pipe.wait()


def generate_content(output, cfg, repos, changelist, group, params, pool):

  svndate = repos.get_rev_prop(svn.core.SVN_PROP_REVISION_DATE)
  ### pick a different date format?
  date = time.ctime(svn.core.secs_from_timestr(svndate, pool))

  log = repos.get_rev_prop(svn.core.SVN_PROP_REVISION_LOG) or ''
  try:
      log = unicode(log, 'utf8')
      #log = unicode(log, 'utf8').encode('iso-8859-2')
  except UnicodeError:
      pass
  output.write('Log:\n%s\n\n' % log)

  output.write('Author: %s\nDate: %s\nNew Revision: %s\n\n'
               % (repos.author, date, repos.rev))

  # print summary sections
  generate_list(output, 'Added', changelist, _select_adds)
  generate_list(output, 'Removed', changelist, _select_deletes)
  generate_list(output, 'Modified', changelist, _select_modifies)

  # these are sorted by path already
  for path, change in changelist:
    generate_diff(output, cfg, repos, date, change, group, params, pool)


def _select_adds(change):
  return change.added
def _select_deletes(change):
  return change.path is None
def _select_modifies(change):
  return not change.added and change.path is not None


def generate_list(output, header, changelist, selection):
  items = [ ]
  for path, change in changelist:
    if selection(change):
      items.append((path, change))
  if items:
    output.write('%s:\n' % header)
    for fname, change in items:
      if change.item_type == ChangeCollector.DIR:
        is_dir = '/'
      else:
        is_dir = ''
      if change.prop_changes:
        if change.text_changed:
          props = '   (contents, props changed)'
        else:
          props = '   (props changed)'
      else:
        props = ''
      output.write('   %s%s%s\n' % (fname, is_dir, props))
      if change.added and change.base_path:
        if is_dir:
          text = ''
        elif change.text_changed:
          text = ', changed'
        else:
          text = ' unchanged'
        output.write('      - copied%s from rev %d, %s%s\n'
                     % (text, change.base_rev, change.base_path[1:], is_dir))


def generate_diff(output, cfg, repos, date, change, group, params, pool):

  if change.item_type == ChangeCollector.DIR:
    # all changes were printed in the summary. nothing to do.
    return

  if not change.path:
    ### params is a bit silly here
    suppress = cfg.get('suppress_deletes', group, params)
    if suppress == 'yes':
      # a record of the deletion is in the summary. no need to write
      # anything further here.
      return

    output.write('\nDeleted: %s\n' % change.base_path)
    diff = svn.fs.FileDiff(repos.get_root(change.base_rev),
                           change.base_path, None, None, pool)

    label1 = '%s\t%s' % (change.base_path, date)
    label2 = '(empty file)'
    singular = True
  elif change.added:
    if change.base_path and (change.base_rev != -1):
      # this file was copied.

      # copies with no changes are reported in the header, so we can just
      # skip them here.
      if not change.text_changed:
        return

      # note that we strip the leading slash from the base (copyfrom) path
      output.write('\nCopied: %s (from rev %d, %s)\n'
                   % (change.path, change.base_rev, change.base_path[1:]))
      diff = svn.fs.FileDiff(repos.get_root(change.base_rev),
                             change.base_path[1:],
                             repos.root_this, change.path,
                             pool)
      label1 = change.base_path[1:] + '\t(original)'
      label2 = '%s\t%s' % (change.path, date)
      singular = False
    else:
      output.write('\nAdded: %s\n' % change.path)
      diff = svn.fs.FileDiff(None, None, repos.root_this, change.path, pool)
      label1 = '(empty file)'
      label2 = '%s\t%s' % (change.path, date)
      singular = True
  elif not change.text_changed:
    # don't bother to show an empty diff. prolly just a prop change.
    return
  else:
    output.write('\nModified: %s\n' % change.path)
    diff = svn.fs.FileDiff(repos.get_root(change.base_rev),
                           change.base_path[1:],
                           repos.root_this, change.path,
                           pool)
    label1 = change.base_path[1:] + '\t(original)'
    label2 = '%s\t%s' % (change.path, date)
    singular = False

  output.write(SEPARATOR + '\n')

  if diff.either_binary():
    if singular:
      output.write('Binary file. No diff available.\n')
    else:
      output.write('Binary files. No diff available.\n')
    return

  ### do something with change.prop_changes

  src_fname, dst_fname = diff.get_files()

  output.run_diff(cfg.get_diff_cmd({
    'label_from' : label1,
    'label_to' : label2,
    'from' : src_fname,
    'to' : dst_fname,
    }))


class Repository:
  "Hold roots and other information about the repository."

  def __init__(self, repos_dir, rev, pool):
    self.repos_dir = repos_dir
    self.rev = rev
    self.pool = pool

    db_path = svn.repos.svn_repos_find_root_path(repos_dir, pool)
    if not db_path:
      db_path = repos_dir

    self.fs_ptr = svn.repos.svn_repos_fs(svn.repos.svn_repos_open(db_path, pool))
    
    self.roots = { }

    self.root_this = self.get_root(rev)

    self.author = self.get_rev_prop(svn.core.SVN_PROP_REVISION_AUTHOR)

  def get_rev_prop(self, propname):
    return svn.fs.revision_prop(self.fs_ptr, self.rev, propname, self.pool)

  def get_root(self, rev):
    try:
      return self.roots[rev]
    except KeyError:
      pass
    root = self.roots[rev] = svn.fs.revision_root(self.fs_ptr, rev, self.pool)
    return root


class ChangeCollector(svn.delta.Editor):
  DIR = 'DIR'
  FILE = 'FILE'

  # BATON FORMAT: [path, base_path, base_rev]
  
  def __init__(self, repos, rev_prev):
    self.repos = repos
    self.rev_prev = rev_prev

    # path -> _change()
    self.changes = { }

  def open_root(self, base_revision, dir_pool):
    return ('', '', self.rev_prev)  # dir_baton

  def delete_entry(self, path, revision, parent_baton, pool):
    base_path = _svn_join(parent_baton[1], _svn_basename(path))
    if svn.fs.is_dir(self.repos.get_root(parent_baton[2]), base_path, pool):
      item_type = ChangeCollector.DIR
    else:
      item_type = ChangeCollector.FILE
    self.changes[path] = _change(item_type,
                                 False,
                                 False,
                                 base_path,
                                 parent_baton[2], # base_rev
                                 None,            # (new) path
                                 False,           # added
                                 )

  def add_directory(self, path, parent_baton,
                    copyfrom_path, copyfrom_revision, dir_pool):
    self.changes[path] = _change(ChangeCollector.DIR,
                                 False,
                                 False,
                                 copyfrom_path,     # base_path
                                 copyfrom_revision, # base_rev
                                 path,              # path
                                 True,              # added
                                 )
    if copyfrom_path and (copyfrom_revision != -1):
      base_path = copyfrom_path
    else:
      base_path = path
    base_rev = copyfrom_revision
    return (path, base_path, base_rev)  # dir_baton

  def open_directory(self, path, parent_baton, base_revision, dir_pool):
    base_path = _svn_join(parent_baton[1], _svn_basename(path))
    return (path, base_path, parent_baton[2])  # dir_baton

  def change_dir_prop(self, dir_baton, name, value, pool):
    dir_path = dir_baton[0]
    if self.changes.has_key(dir_path):
      self.changes[dir_path].prop_changes = True
    else:
      # can't be added or deleted, so this must be CHANGED
      self.changes[dir_path] = _change(ChangeCollector.DIR,
                                       True,
                                       False,
                                       dir_baton[1], # base_path
                                       dir_baton[2], # base_rev
                                       dir_path,     # path
                                       False,        # added
                                       )

  def add_file(self, path, parent_baton,
               copyfrom_path, copyfrom_revision, file_pool):
    self.changes[path] = _change(ChangeCollector.FILE,
                                 False,
                                 False,
                                 copyfrom_path,     # base_path
                                 copyfrom_revision, # base_rev
                                 path,              # path
                                 True,              # added
                                 )
    if copyfrom_path and (copyfrom_revision != -1):
      base_path = copyfrom_path
    else:
      base_path = path
    base_rev = copyfrom_revision
    return (path, base_path, base_rev)  # file_baton

  def open_file(self, path, parent_baton, base_revision, file_pool):
    base_path = _svn_join(parent_baton[1], _svn_basename(path))
    return (path, base_path, parent_baton[2])  # file_baton

  def apply_textdelta(self, file_baton, base_checksum):
    file_path = file_baton[0]
    if self.changes.has_key(file_path):
      self.changes[file_path].text_changed = True
    else:
      # an add would have inserted a change record already, and it can't
      # be a delete with a text delta, so this must be a normal change.
      self.changes[file_path] = _change(ChangeCollector.FILE,
                                        False,
                                        True,
                                        file_baton[1], # base_path
                                        file_baton[2], # base_rev
                                        file_path,     # path
                                        False,         # added
                                        )

    # no handler
    return None

  def change_file_prop(self, file_baton, name, value, pool):
    file_path = file_baton[0]
    if self.changes.has_key(file_path):
      self.changes[file_path].prop_changes = True
    else:
      # an add would have inserted a change record already, and it can't
      # be a delete with a prop change, so this must be a normal change.
      self.changes[file_path] = _change(ChangeCollector.FILE,
                                        True,
                                        False,
                                        file_baton[1], # base_path
                                        file_baton[2], # base_rev
                                        file_path,     # path
                                        False,         # added
                                        )


class _change:
  __slots__ = [ 'item_type', 'prop_changes', 'text_changed',
                'base_path', 'base_rev', 'path',
                'added',
                ]
  def __init__(self,
               item_type, prop_changes, text_changed, base_path, base_rev,
               path, added):
    self.item_type = item_type
    self.prop_changes = prop_changes
    self.text_changed = text_changed
    self.base_path = base_path
    self.base_rev = base_rev
    self.path = path

    ### it would be nice to avoid this flag. however, without it, it would
    ### be quite difficult to distinguish between a change to the previous
    ### revision (which has a base_path/base_rev) and a copy from some
    ### other path/rev. a change in path is obviously add-with-history,
    ### but the same path could be a change to the previous rev or a restore
    ### of an older version. when it is "change to previous", I'm not sure
    ### if the rev is always repos.rev - 1, or whether it represents the
    ### created or time-of-checkout rev. so... we use a flag (for now)
    self.added = added


class Config:

  # The predefined configuration sections. These are omitted from the
  # set of groups.
  _predefined = ('general', 'defaults')

  def __init__(self, fname, repos):
    cp = ConfigParser.ConfigParser()
    cp.read(fname)

    # record the (non-default) groups that we find
    self._groups = [ ]

    for section in cp.sections():
      if not hasattr(self, section):
        section_ob = _sub_section()
        setattr(self, section, section_ob)
        if section not in self._predefined:
          self._groups.append((section, section_ob))
      else:
        section_ob = getattr(self, section)
      for option in cp.options(section):
        # get the raw value -- we use the same format for *our* interpolation
        value = cp.get(section, option, raw=1)
        setattr(section_ob, option, value)

    ### do some better splitting to enable quoting of spaces
    self._diff_cmd = string.split(self.general.diff)

    # these params are always available, although they may be overridden
    self._global_params = {
      'author' : repos.author,
      }

    self._prep_groups(repos)

  def get_diff_cmd(self, args):
    cmd = [ ]
    for part in self._diff_cmd:
      cmd.append(part % args)
    return cmd

  def is_set(self, option):
    """Return None if the option is not set; otherwise, its value is returned.

    The option is specified as a dotted symbol, such as 'general.mail_command'
    """
    parts = string.split(option, '.')
    ob = self
    for part in string.split(option, '.'):
      if not hasattr(ob, part):
        return None
      ob = getattr(ob, part)
    return ob

  def get(self, option, group, params):
    if group:
      sub = getattr(self, group)
      if hasattr(sub, option):
        return getattr(sub, option) % params
    return getattr(self.defaults, option, '') % params

  def _prep_groups(self, repos):
    self._group_re = [ ]

    repos_dir = os.path.abspath(repos.repos_dir)

    # compute the default repository-based parameters. start with some
    # basic parameters, then bring in the regex-based params.
    default_params = self._global_params.copy()

    try:
      match = re.match(self.defaults.for_repos, repos_dir)
      if match:
        default_params.update(match.groupdict())
    except AttributeError:
      # there is no self.defaults.for_repos
      pass

    # select the groups that apply to this repository
    for group, sub in self._groups:
      params = default_params
      if hasattr(sub, 'for_repos'):
        match = re.match(sub.for_repos, repos_dir)
        if not match:
          continue
        params = self._global_params.copy()
        params.update(match.groupdict())

      # if a matching rule hasn't been given, then use the empty string
      # as it will match all paths
      for_paths = getattr(sub, 'for_paths', '')
      self._group_re.append((group, re.compile(for_paths), params))

    # after all the groups are done, add in the default group
    try:
      self._group_re.append((None,
                             re.compile(self.defaults.for_paths),
                             default_params))
    except AttributeError:
      # there is no self.defaults.for_paths
      pass

  def which_groups(self, path):
    "Return the path's associated groups."
    groups = []
    for group, pattern, repos_params in self._group_re:
      match = pattern.match(path)
      if match:
        params = repos_params.copy()
        params.update(match.groupdict())
        groups.append((group, params))
    if not groups:
      groups.append((None, self._global_params))
    return groups


class _sub_section:
  pass


class MissingConfig(Exception):
  pass


def _svn_basename(path):
  "Compute the basename of an SVN path ('/' separators)."
  idx = string.rfind(path, '/')
  if idx == -1:
    return path
  return path[idx+1:]

def _svn_join(base, relative):
  "Join a relative path onto a base path using the SVN separator ('/')."
  if relative[:1] == '/':
    return relative
  if base[-1:] == '/':
    return base + relative
  return base + '/' + relative


# enable True/False in older vsns of Python
try:
  _unused = True
except NameError:
  True = 1
  False = 0


if __name__ == '__main__':
  if len(sys.argv) < 3 or len(sys.argv) > 4:
    sys.stderr.write('USAGE: %s REPOS-DIR REVISION [CONFIG-FILE]\n'
                     % sys.argv[0])
    sys.exit(1)

  repos_dir = sys.argv[1]
  revision = int(sys.argv[2])

  if len(sys.argv) == 3:
    # default to REPOS-DIR/conf/mailer.conf
    config_fname = os.path.join(repos_dir, 'conf', 'mailer.conf')
    if not os.path.exists(config_fname):
      # okay. look for 'mailer.conf' as a sibling of this script
      config_fname = os.path.join(os.path.dirname(sys.argv[0]), 'mailer.conf')
  else:
    # the config file was explicitly provided
    config_fname = sys.argv[3]

  if not os.path.exists(config_fname):
    raise MissingConfig(config_fname)

  ### run some validation on these params
  svn.core.run_app(main, config_fname, repos_dir, revision)


# ------------------------------------------------------------------------
# TODO
#
# * add configuration options
#   - default options  [DONE]
#   - per-group overrides  [DONE]
#   - group selection based on repos and on path  [DONE]
#   - each group defines delivery info:
#     o how to construct From:  [DONE]
#     o how to construct To:  [DONE]
#     o subject line prefixes  [DONE]
#     o whether to set Reply-To and/or Mail-Followup-To
#       (btw: it is legal do set Reply-To since this is the originator of the
#        mail; i.e. different from MLMs that munge it)
#   - each group defines content construction:
#     o max size of diff before trimming
#     o max size of entire commit message before truncation
#     o flag to disable generation of add/delete diffs
#   - per-repository configuration
#     o extra config living in repos
#     o how to construct a ViewCVS URL for the diff
#     o optional, non-mail log file
#     o look up authors (username -> email; for the From: header) in a
#       file(s) or DBM
#   - put the commit author into the params dict  [DONE]
#   - if the subject line gets too long, then trim it. configurable?
#