%  Copyright (C) 2002-2004 David Roundy
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\section{darcs rollback}
\begin{code}
module Rollback ( rollback ) where
import Directory hiding ( getCurrentDirectory )
import Workaround ( getCurrentDirectory )
import Control.Exception ( block )

import DarcsCommands ( DarcsCommand(..), nodefaults )
import DarcsArguments ( DarcsFlag,
                        verbose, working_repo_dir, nocompress,
                        match_one_nontag,
                      )
import Repository ( am_in_repo, slurp_recorded, read_pending,
                    write_patch, write_pending, add_to_inventory,
                    sift_for_pending,
                  )
import Patch ( join_patches, apply_to_slurpy, invert,
               patch2patchinfo,
             )
import Depends ( is_tag )
import PatchInfo ( is_inverted )
import SlurpDirectory ( slurp_write_dirty )
import Lock ( withLock )
import SelectChanges ( with_selected_patch_from_repo )
#include "impossible.h"
\end{code}

\begin{code}
rollback_description :: String
rollback_description =
 "Roll back a named patch."
\end{code}

\options{rollback}

\haskell{rollback_help} If you decide you didn't want to roll back a patch
after all, you probably should use unrecord to undo the rollback, since
like rollback, unrecord doesn't affect the working directory.

\begin{code}
rollback_help :: String
rollback_help =
 "Rollback is used to undo the effects of a single patch without actually\n"++
 "deleting that patch.  Instead, it applies the inverse patch as a new patch.\n"++
 "Unlike unpull and unrecord (which accomplish a similar goal) rollback is\n"++
 "perfectly safe, since it leaves in the repository a record of the patch it\n"++
 "is removing.\n"
\end{code}
\begin{code}
rollback :: DarcsCommand
rollback = DarcsCommand {command_name = "rollback",
                         command_help = rollback_help,
                         command_description = rollback_description,
                         command_extra_args = 0,
                         command_extra_arg_help = [],
                         command_command = rollback_cmd,
                         command_prereq = am_in_repo,
                         command_get_arg_possibilities = return [],
                         command_argdefaults = nodefaults,
                         command_darcsoptions = [match_one_nontag,
                                                 nocompress,verbose,
                                                 working_repo_dir]}
\end{code}
\begin{code}
rollback_cmd :: [DarcsFlag] -> [String] -> IO ()
rollback_cmd opts _ = withLock "./_darcs/lock" $ do
  recorded <- slurp_recorded "."
  mpend <- read_pending
  let pend = case mpend of
             Nothing -> join_patches []
             Just p -> p
  with_selected_patch_from_repo "rollback" opts False $
    \ (p, _) ->
      case apply_to_slurpy (invert p) recorded of
      Nothing -> bug "Rollback:  Unable to apply inverse patch!\n"
      Just rec' ->
        case patch2patchinfo (invert p) of
        Nothing -> impossible
        Just pinfo | is_tag pinfo ->
            fail "cannot roll back a 'tag' patch."
        Just pinfo | not (is_inverted pinfo) ->
            fail "cannot roll back a 'rollback' patch."
        Just pinfo -> do write_patch opts $ invert p
                         former_dir <- getCurrentDirectory
                         setCurrentDirectory "_darcs/current"
                         block $ do slurp_write_dirty rec'
                                    setCurrentDirectory former_dir
                                    write_pending $ sift_for_pending $
                                                  join_patches [p, pend]
                                    add_to_inventory "." pinfo
                         putStr $ "Finished rolling back.\n"
\end{code}