code.delx.au - offlineimap/blob - src/Data/Syncable.hs

   1 {- offlineimap component
   2 Copyright (C) 2002-2008 John Goerzen <jgoerzen@complete.org>
   3
   4 This program is free software; you can redistribute it and/or modify
   5 it under the terms of the GNU General Public License as published by
   6 the Free Software Foundation; either version 2 of the License, or
   7 (at your option) any later version.
   8
   9 This program is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 GNU General Public License for more details.
  13
  14 You should have received a copy of the GNU General Public License
  15 along with this program; if not, write to the Free Software
  16 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  17 -}
  18
  19 {-
  20 The OfflineIMAP v6 algorithm worked like this:
  21
  22 call remoterepos.syncfoldersto(localrepos, [statusrepos])
  23
  24 for each folder, call
  25  syncfolder(remotename, remoterepos, remotefolder, localrepos, statusrepos, quick)
  26    this:
  27    sets localfolder = local folder
  28    adds localfolder to mbnames
  29    sets statusfolder = status folder
  30    if localfolder.getuidvalidity() == None, removes anything in statusfolder
  31
  32    statusfolder.cachemessagelist()
  33
  34    localfolder.cachemessagelist()
  35
  36    Check UID validity
  37    Save UID validity
  38
  39    remotefolder.cachemessagelist()
  40
  41    if not statusfolder.isnewfolder():
  42         # Delete local copies of remote messages.  This way,
  43         # if a message's flag is modified locally but it has been
  44         # deleted remotely, we'll delete it locally.  Otherwise, we
  45         # try to modify a deleted message's flags!  This step
  46         # need only be taken if a statusfolder is present; otherwise,
  47         # there is no action taken *to* the remote repository.
  48         remotefolder.syncmessagesto_delete(localfolder, [localfolder,
  49                                                          statusfolder])
  50         localfolder.syncmessagesto(statusfolder, [remotefolder, statusfolder])
  51
  52    # Synchroonize remote changes
  53    remotefolder.syncmessagesto(localfolder, [localfolder, statusfolder])
  54
  55    # Make sure the status folder is up-to-date.
  56    ui.syncingmessages(localrepos, localfolder, statusrepos, statusfolder)
  57    localfolder.syncmessagesto(statusfolder)
  58    statusfolder.save()
  59    localrepos.restore_atime()
  60
  61
  62
  63 call forgetfolders on local and remote
  64 -}
  65
  66 module Data.Syncable where
  67 import qualified Data.Map as Map
  68
  69 type SyncCollection k v = Map.Map k v
  70
  71 data (Eq k, Ord k, Show k, Show v) =>
  72     SyncCommand k v =
  73            DeleteItem k
  74          | CopyItem k v
  75          | ModifyContent k v
  76     deriving (Eq, Ord, Show)
  77
  78 pairToFunc :: (a -> b -> c) -> (a, b) -> c
  79 pairToFunc func (a, b) = func a b
  80
  81 {- | Perform a bi-directional sync.  Compared to the last known state of
  82 the child, evaluate the new states of the master and child.  Return a list of
  83 changes to make to the master and list of changes to make to the child to
  84 bring them into proper sync.
  85
  86 In the event that both master and child previously had an item, and the payload
  87 of the item has changed on both ends, the payload as given in the child
  88 will take precedence.
  89
  90 This relationship should hold:
  91
  92 >let (masterCmds, childCmds) = syncBiDir masterState childState lastChildState
  93 >unaryApplyChanges masterState masterCmds ==
  94 > unaryApplyChanges childState childCmds
  95
  96 This relationship is validated in the test suite that accompanies this
  97 software.
  98
  99 -}
 100 syncBiDir :: (Ord k, Show k, Show v, Eq v) =>
 101             SyncCollection k v  -- ^ Present state of master
 102          -> SyncCollection k v  -- ^ Present state of child
 103          -> SyncCollection k v  -- ^ Last state of child
 104          -> ([SyncCommand k v], [SyncCommand k v]) -- ^ Changes to make to (master, child)
 105 syncBiDir masterstate childstate lastchildstate =
 106     (masterchanges, childchanges)
 107     where masterchanges = (map DeleteItem .
 108                           findDeleted childstate masterstate $ lastchildstate)
 109                           ++
 110                           (map (pairToFunc CopyItem) .
 111                            findAdded childstate masterstate $ lastchildstate)
 112                           ++ (map (pairToFunc ModifyContent) . Map.toList $ masterPayloadChanges)
 113           childchanges = (map DeleteItem .
 114                           findDeleted masterstate childstate $ lastchildstate)
 115                          ++
 116                          (map (pairToFunc CopyItem) .
 117                           findAdded masterstate childstate $ lastchildstate)
 118                          ++ (map (pairToFunc ModifyContent) . Map.toList $ childPayloadChanges)
 119           masterPayloadChanges =
 120               findModified childstate lastchildstate
 121           -- The child's payload takes precedence, so we are going to
 122           -- calculate the changes made on the master to apply to the client,
 123           -- then subtract out any items in the master changes that have the
 124           -- same key.
 125           childPayloadChanges =
 126               foldl (flip Map.delete) (findModified masterstate lastchildstate)
 127                     (Map.keys masterPayloadChanges)
 128
 129
 130 {- | Compares two SyncCollections, and returns the commands that, when
 131 applied to the first collection, would yield the second. -}
 132 diffCollection :: (Ord k, Show k, Show v) =>
 133                   SyncCollection k v
 134                -> SyncCollection k v
 135                -> [SyncCommand k v]
 136 diffCollection coll1 coll2 =
 137     (map DeleteItem . findDeleted coll2 coll1 $ coll1) ++
 138     (map (pairToFunc CopyItem) . findAdded coll2 coll1 $ coll1)
 139
 140 {- | Returns a list of keys that exist in state2 and lastchildstate
 141 but not in state1 -}
 142 findDeleted :: Ord k =>
 143                SyncCollection k v -> SyncCollection k v -> SyncCollection k v ->
 144                [k]
 145 findDeleted state1 state2 lastchildstate =
 146     Map.keys . Map.difference (Map.intersection state2 lastchildstate) $ state1
 147
 148 {- | Returns a list of keys that exist in state1 but in neither
 149 state2 nor lastchildstate -}
 150 findAdded :: (Ord k, Eq k) =>
 151                SyncCollection k v -> SyncCollection k v -> SyncCollection k v ->
 152                [(k, v)]
 153 findAdded state1 state2 lastchildstate =
 154     Map.toList . Map.difference state1 . Map.union state2 $ lastchildstate
 155
 156 {- Finds all items that exist in both state1 and lastchildstate in which the payload
 157 is different in state1 than it was in lastchildstate.  Returns the key and new
 158 payload for each such item found. -}
 159 findModified :: (Ord k, Eq v) =>
 160                 SyncCollection k v -> SyncCollection k v -> SyncCollection k v
 161 findModified state1 lastchildstate =
 162     Map.mapMaybe id .
 163     Map.intersectionWith (\v1 v2 -> if v1 /= v2 then Just v1 else Nothing)
 164        state1 $ lastchildstate
 165
 166 {- | Apply the specified changes to the given SyncCollection.  Returns
 167 a new SyncCollection with the changes applied.  If changes are specified
 168 that would apply to UIDs that do not exist in the source list, these changes
 169 are silently ignored. -}
 170 unaryApplyChanges :: (Eq k, Ord k, Show k, Show v) =>
 171                      SyncCollection k v -> [SyncCommand k v] -> SyncCollection k v
 172 unaryApplyChanges collection commands =
 173     let makeChange collection (DeleteItem key) =
 174             Map.delete key collection
 175         makeChange collection (CopyItem key val) =
 176             Map.insert key val collection
 177     in foldl makeChange collection commands