    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Simple.Program.Types
    -- Copyright   :  Isaac Jones 2006, Duncan Coutts 2007-2009
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- This provides an abstraction which deals with configuring and running
    -- programs. A 'Program' is a static notion of a known program. A
    -- 'ConfiguredProgram' is a 'Program' that has been found on the current
    -- machine and is ready to be run (possibly with some user-supplied default
    -- args). Configuring a program involves finding its location and if necessary
    -- finding its version. There's reasonable default behavior for trying to find
    -- \"foo\" in PATH, being able to override its location, etc.
    --
    module Distribution.Simple.Program.Types (
        -- * Program and functions for constructing them
        Program(..),
        simpleProgram,

        -- * Configured program and related functions
        ConfiguredProgram(..),
        programPath,
        ProgArg,
        ProgramLocation(..),
      ) where

    import Distribution.Simple.Utils
             ( findProgramLocation )
    import Distribution.Version
             ( Version )
    import Distribution.Verbosity
             ( Verbosity )

    -- | Represents a program which can be configured.
    data Program = Program {
           -- | The simple name of the program, eg. ghc
           programName :: String,

           -- | A function to search for the program if it's location was not
           -- specified by the user. Usually this will just be a
           programFindLocation :: Verbosity -> IO (Maybe FilePath),

           -- | Try to find the version of the program. For many programs this is
           -- not possible or is not necessary so it's ok to return Nothing.
           programFindVersion :: Verbosity -> FilePath -> IO (Maybe Version),

           -- | A function to do any additional configuration after we have
           -- located the program (and perhaps identified its version). It is
           -- allowed to return additional flags that will be passed to the
           -- program on every invocation.
           programPostConf :: Verbosity -> ConfiguredProgram -> IO [ProgArg]
         }

    type ProgArg = String

    data ConfiguredProgram = ConfiguredProgram {
           -- | Just the name again
           programId :: String,

           -- | The version of this program, if it is known.
           programVersion :: Maybe Version,

           -- | Default command-line args for this program.
           -- These flags will appear first on the command line, so they can be
           -- overridden by subsequent flags.
           programDefaultArgs :: [String],

           -- | Override command-line args for this program.
           -- These flags will appear last on the command line, so they override
           -- all earlier flags.
           programOverrideArgs :: [String],

           -- | Location of the program. eg. @\/usr\/bin\/ghc-6.4@
           programLocation :: ProgramLocation
         } deriving (Read, Show, Eq)

    -- | Where a program was found. Also tells us whether it's specifed by user or
    -- not.  This includes not just the path, but the program as well.
    data ProgramLocation
        = UserSpecified { locationPath :: FilePath }
          -- ^The user gave the path to this program,
          -- eg. --ghc-path=\/usr\/bin\/ghc-6.6
        | FoundOnSystem { locationPath :: FilePath }
          -- ^The location of the program, as located by searching PATH.
          deriving (Read, Show, Eq)

    -- | The full path of a configured program.
    programPath :: ConfiguredProgram -> FilePath
    programPath = locationPath . programLocation

    -- | Make a simple named program.
    --
    -- By default we'll just search for it in the path and not try to find the
    -- version name. You can override these behaviours if necessary, eg:
    --
    -- > simpleProgram "foo" { programFindLocation = ... , programFindVersion ... }
    --
    simpleProgram :: String -> Program
    simpleProgram name = Program {
        programName         = name,
        programFindLocation = \v   -> findProgramLocation v name,
        programFindVersion  = \_ _ -> return Nothing,
        programPostConf     = \_ _ -> return []
      }