from mercurial import error
from mercurial import util
from mercurial import destutil
from mercurial import extensions
from mercurial.i18n import _

def _destmergebranch(orig, repo):
    p1 = repo['.']
    top = p1.topic()
    if top:
        heads = repo.revs('heads(topic(.)::topic(.))')
        if p1.rev() not in heads:
            raise error.Abort(_("not at topic head, update or explicit"))
        elif 1 == len(heads):
            # should look at all branch involved but... later
            bhead = ngtip(repo, p1.branch(), all=True)
            if not bhead:
                raise error.Abort(_("nothing to merge"))
            elif 1 == len(bhead):
                return bhead.first()
            else:
                raise error.Abort(_("branch '%s' has %d heads - "
                                   "please merge with an explicit rev")
                                 % (p1.branch(), len(bhead)),
                                 hint=_("run 'hg heads .' to see heads"))
        elif 2 == len(heads):
            heads = [r for r in heads if r != p1.rev()]
            # XXX: bla bla bla bla bla
            if 1 < len(heads):
                raise error.Abort(_('working directory not at a head revision'),
                                 hint=_("use 'hg update' or merge with an "
                                        "explicit revision"))
            return heads[0]
        elif 2 < len(heads):
            raise error.Abort(_("topic '%s' has %d heads - "
                                "please merge with an explicit rev")
                              % (top, len(heads)))
        else:
            assert False # that's impossible
    return orig(repo)

def setupdest():
    if util.safehasattr(destutil, '_destmergebranch'):
        extensions.wrapfunction(destutil, '_destmergebranch', _destmergebranch)

def ngtip(repo, branch, all=False):
    """tip new generation"""
    ## search for untopiced heads of branch
    # could be heads((::branch(x) - topic()))
    # but that is expensive
    #
    # we should write plain code instead
    subquery = '''heads(
                    parents(
                       ancestor(
                         (head() and branch(%s)
                         or (topic() and branch(%s)))))
                   ::(head() and branch(%s))
                   - topic())'''
    if not all:
        subquery = 'max(%s)' % subquery
    return repo.revs(subquery, branch, branch, branch)