from node import bin, hex, nullid, nullrev

def read(repo):

    partial = {}

    try:

        f = repo.opener("cache/branchheads")

        lines = f.read().split('\n')

        f.close()

    except (IOError, OSError):

        return {}, nullid, nullrev

    try:

        last, lrev = lines.pop(0).split(" ", 1)

        last, lrev = bin(last), int(lrev)

        if lrev >= len(repo) or repo[lrev].node() != last:

            # invalidate the cache

            raise ValueError('invalidating branch cache (tip differs)')

        for l in lines:

            if not l:

                continue

            node, label = l.split(" ", 1)

            label = encoding.tolocal(label.strip())

            if not node in repo:

                raise ValueError('invalidating branch cache because node '+

                                 '%s does not exist' % node)

            partial.setdefault(label, []).append(bin(node))

    except KeyboardInterrupt:

        raise

    except Exception, inst:

        if repo.ui.debugflag:

            repo.ui.warn(str(inst), '\n')

        partial, last, lrev = {}, nullid, nullrev

    return partial, last, lrev