    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Package
    -- Copyright   :  Isaac Jones 2003-2004
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- Defines a package identifier along with a parser and pretty printer for it.
    -- 'PackageIdentifier's consist of a name and an exact version. It also defines
    -- a 'Dependency' data type. A dependency is a package name and a version
    -- range, like @\"foo >= 1.2 && < 2\"@.

    {- All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are
    met:

        * Redistributions of source code must retain the above copyright
          notice, this list of conditions and the following disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials provided
          with the distribution.

        * Neither the name of Isaac Jones nor the names of other
          contributors may be used to endorse or promote products derived
          from this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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    module Distribution.Package (
            -- * Package ids
            PackageName(..),
            PackageIdentifier(..),
            PackageId,

            -- * Installed package identifiers
            InstalledPackageId(..),

            -- * Package source dependencies
            Dependency(..),
            thisPackageVersion,
            notThisPackageVersion,
            simplifyDependency,

            -- * Package classes
            Package(..), packageName, packageVersion,
            PackageFixedDeps(..),
      ) where

    import Distribution.Version
             ( Version(..), VersionRange, anyVersion, thisVersion
             , notThisVersion, simplifyVersionRange )

    import Distribution.Text (Text(..))
    import qualified Distribution.Compat.ReadP as Parse
    import Distribution.Compat.ReadP ((<++))
    import qualified Text.PrettyPrint as Disp
    import Text.PrettyPrint ((<>), (<+>), text)
    import qualified Data.Char as Char ( isDigit, isAlphaNum )
    import Data.List ( intersperse )

    newtype PackageName = PackageName String
        deriving (Read, Show, Eq, Ord)

    instance Text PackageName where
      disp (PackageName n) = Disp.text n
      parse = do
        ns <- Parse.sepBy1 component (Parse.char '-')
        return (PackageName (concat (intersperse "-" ns)))
        where
          component = do
            cs <- Parse.munch1 Char.isAlphaNum
            if all Char.isDigit cs then Parse.pfail else return cs
            -- each component must contain an alphabetic character, to avoid
            -- ambiguity in identifiers like foo-1 (the 1 is the version number).

    -- | Type alias so we can use the shorter name PackageId.
    type PackageId = PackageIdentifier

    -- | The name and version of a package.
    data PackageIdentifier
        = PackageIdentifier {
            pkgName    :: PackageName, -- ^The name of this package, eg. foo
            pkgVersion :: Version -- ^the version of this package, eg 1.2
         }
         deriving (Read, Show, Eq, Ord)

    instance Text PackageIdentifier where
      disp (PackageIdentifier n v) = case v of
        Version [] _ -> disp n -- if no version, don't show version.
        _            -> disp n <> Disp.char '-' <> disp v

      parse = do
        n <- parse
        v <- (Parse.char '-' >> parse) <++ return (Version [] [])
        return (PackageIdentifier n v)

    -- ------------------------------------------------------------
    -- * Installed Package Ids
    -- ------------------------------------------------------------

    -- | An InstalledPackageId uniquely identifies an instance of an installed package.
    -- There can be at most one package with a given 'InstalledPackageId'
    -- in a package database, or overlay of databases.
    --
    newtype InstalledPackageId = InstalledPackageId String
     deriving (Read,Show,Eq,Ord)

    instance Text InstalledPackageId where
      disp (InstalledPackageId str) = text str

      parse = InstalledPackageId `fmap` Parse.munch1 abi_char
       where abi_char c = Char.isAlphaNum c || c `elem` ":-_."

    -- ------------------------------------------------------------
    -- * Package source dependencies
    -- ------------------------------------------------------------

    -- | Describes a dependency on a source package (API)
    --
    data Dependency = Dependency PackageName VersionRange
                      deriving (Read, Show, Eq)

    instance Text Dependency where
      disp (Dependency name ver) =
        disp name <+> disp ver

      parse = do name <- parse
                 Parse.skipSpaces
                 ver <- parse <++ return anyVersion
                 Parse.skipSpaces
                 return (Dependency name ver)

    thisPackageVersion :: PackageIdentifier -> Dependency
    thisPackageVersion (PackageIdentifier n v) =
      Dependency n (thisVersion v)

    notThisPackageVersion :: PackageIdentifier -> Dependency
    notThisPackageVersion (PackageIdentifier n v) =
      Dependency n (notThisVersion v)

    -- | Simplify the 'VersionRange' expression in a 'Dependency'.
    -- See 'simplifyVersionRange'.
    --
    simplifyDependency :: Dependency -> Dependency
    simplifyDependency (Dependency name range) =
      Dependency name (simplifyVersionRange range)

    -- | Class of things that have a 'PackageIdentifier'
    --
    -- Types in this class are all notions of a package. This allows us to have
    -- different types for the different phases that packages go though, from
    -- simple name\/id, package description, configured or installed packages.
    --
    -- Not all kinds of packages can be uniquely identified by a
    -- 'PackageIdentifier'. In particular, installed packages cannot, there may be
    -- many installed instances of the same source package.
    --
    class Package pkg where
      packageId :: pkg -> PackageIdentifier

    packageName    :: Package pkg => pkg -> PackageName
    packageName     = pkgName    . packageId

    packageVersion :: Package pkg => pkg -> Version
    packageVersion  = pkgVersion . packageId

    instance Package PackageIdentifier where
      packageId = id

    -- | Subclass of packages that have specific versioned dependencies.
    --
    -- So for example a not-yet-configured package has dependencies on version
    -- ranges, not specific versions. A configured or an already installed package
    -- depends on exact versions. Some operations or data structures (like
    --  dependency graphs) only make sense on this subclass of package types.
    --
    class Package pkg => PackageFixedDeps pkg where
      depends :: pkg -> [PackageIdentifier]