from zope.interface import implements
from allmydata.interfaces import IRepairResults, ICheckResults

class RepairResults:
    implements(IRepairResults)

    def __init__(self, smap):
        self.servermap = smap

    def to_string(self):
        return ""

class MustForceRepairError(Exception):
    pass

class Repairer:
    def __init__(self, node, check_results):
        self.node = node
        self.check_results = ICheckResults(check_results)
        assert check_results.storage_index == self.node.get_storage_index()

    def start(self, force=False):
        # download, then re-publish. If a server had a bad share, try to
        # replace it with a good one of the same shnum.

        # The normal repair operation should not be used to replace
        # application-specific merging of alternate versions: i.e if there
        # are multiple highest seqnums with different roothashes. In this
        # case, the application must use node.upload() (referencing the
        # servermap that indicates the multiple-heads condition), or
        # node.overwrite(). The repair() operation will refuse to run in
        # these conditions unless a force=True argument is provided. If
        # force=True is used, then the highest root hash will be reinforced.

        # Likewise, the presence of an unrecoverable latest version is an
        # unusual event, and should ideally be handled by retrying a couple
        # times (spaced out over hours or days) and hoping that new shares
        # will become available. If repair(force=True) is called, data will
        # be lost: a new seqnum will be generated with the same contents as
        # the most recent recoverable version, skipping over the lost
        # version. repair(force=False) will refuse to run in a situation like
        # this.

        # Repair is designed to fix the following injuries:
        #  missing shares: add new ones to get at least N distinct ones
        #  old shares: replace old shares with the latest version
        #  bogus shares (bad sigs): replace the bad one with a good one

        smap = self.check_results.get_servermap()

        if smap.unrecoverable_newer_versions():
            if not force:
                raise MustForceRepairError("There were unrecoverable newer "
                                           "versions, so force=True must be "
                                           "passed to the repair() operation")
            # continuing on means that node.upload() will pick a seqnum that
            # is higher than everything visible in the servermap, effectively
            # discarding the unrecoverable versions.
        if smap.needs_merge():
            if not force:
                raise MustForceRepairError("There were multiple recoverable "
                                           "versions with identical seqnums, "
                                           "so force=True must be passed to "
                                           "the repair() operation")
            # continuing on means that smap.best_recoverable_version() will
            # pick the one with the highest roothash, and then node.upload()
            # will replace all shares with its contents

        # missing shares are handled during upload, which tries to find a
        # home for every share

        # old shares are handled during upload, which will replace any share
        # that was present in the servermap

        # bogus shares need to be managed here. We might notice a bogus share
        # during mapupdate (whether done for a filecheck or just before a
        # download) by virtue of it having an invalid signature. We might
        # also notice a bad hash in the share during verify or download. In
        # either case, the problem will be noted in the servermap, and the
        # bad share (along with its checkstring) will be recorded in
        # servermap.bad_shares . Publish knows that it should try and replace
        # these.

        # I chose to use the retrieve phase to ensure that the privkey is
        # available, to avoid the extra roundtrip that would occur if we,
        # say, added an smap.get_privkey() method.

        assert self.node.get_writekey() # repair currently requires a writecap

        best_version = smap.best_recoverable_version()
        d = self.node.download_version(smap, best_version, fetch_privkey=True)
        d.addCallback(self.node.upload, smap)
        d.addCallback(self.get_results, smap)
        return d

    def get_results(self, res, smap):
        return RepairResults(smap)