    -- | Module used for generating HTML redirect pages. This allows renaming pages
    -- to avoid breaking existing links without requiring server-side support for
    -- formal 301 Redirect error codes
    module Hakyll.Web.Redirect
        ( Redirect (..)
        , createRedirects
        ) where

    import           Control.Applicative    ((<$>))
    import           Control.Monad          (forM_, when)
    import           Data.Binary            (Binary (..))
    import           Data.List              (sort, group)
    import           Hakyll.Core.Compiler
    import           Hakyll.Core.Identifier
    import           Hakyll.Core.Routes
    import           Hakyll.Core.Rules
    import           Hakyll.Core.Writable   (Writable (..))

    -- | This function exposes a higher-level interface compared to using the
    -- 'Redirect' type manually.
    --
    -- This creates, using a database mapping broken URLs to working ones, HTML
    -- files which will do HTML META tag redirect pages (since, as a static site, we
    -- can't use web-server-level 301 redirects, and using JS is gross).
    --
    -- This is useful for sending people using old URLs to renamed versions, dealing
    -- with common typos etc, and will increase site traffic.  Such broken URLs can
    -- be found by looking at server logs or by using Google Webmaster Tools.
    -- Broken URLs must be valid Haskell strings, non-URL-escaped valid POSIX
    -- filenames, and relative links, since they will be defined in a @hakyll.hs@
    -- and during generation, written to disk with the filename corresponding to the
    -- broken URLs.  (Target URLs can be absolute or relative, but should be
    -- URL-escaped.) So broken incoming links like <http://www.gwern.net/foo/> which
    -- should be <http://www.gwern.net/foobar> cannot be fixed (since you cannot
    -- create a HTML file named @"foo/"@ on disk, as that would be a directory).
    --
    -- An example of a valid association list would be:
    --
    -- > brokenLinks =
    -- >     [ ("projects.html", "http://github.com/gwern")
    -- >     , ("/Black-market archive", "Black-market%20archives")
    -- >     ]
    --
    -- In which case the functionality can then be used in `main` with a line like:
    --
    -- > version "redirects" $ createRedirects brokenLinks
    --
    -- The 'version' is recommended to separate these items from your other pages.
    --
    -- The on-disk files can then be uploaded with HTML mimetypes
    -- (either explicitly by generating and uploading them separately, by
    -- auto-detection of the filetype, or an upload tool defaulting to HTML
    -- mimetype, such as calling @s3cmd@ with @--default-mime-type=text/html@) and
    -- will redirect browsers and search engines going to the old/broken URLs.
    --
    -- See also <https://groups.google.com/d/msg/hakyll/sWc6zxfh-uM/fUpZPsFNDgAJ>.
    createRedirects :: [(Identifier, String)] -> Rules ()
    createRedirects :: [(Identifier, String)] -> Rules ()
    createRedirects redirects :: [(Identifier, String)]
    redirects =
     do -- redirects are many-to-fewer; keys must be unique, and must point somewhere else:
        let gkeys :: [[Identifier]]
    gkeys = [Identifier] -> [[Identifier]]
    forall a. Eq a => [a] -> [[a]]
    group ([Identifier] -> [[Identifier]]) -> [Identifier] -> [[Identifier]]
    forall a b. (a -> b) -> a -> b
    $ [Identifier] -> [Identifier]
    forall a. Ord a => [a] -> [a]
    sort ([Identifier] -> [Identifier]) -> [Identifier] -> [Identifier]
    forall a b. (a -> b) -> a -> b
    $ ((Identifier, String) -> Identifier)
    -> [(Identifier, String)] -> [Identifier]
    forall a b. (a -> b) -> [a] -> [b]
    map (Identifier, String) -> Identifier
    forall a b. (a, b) -> a
    fst [(Identifier, String)]
    redirects
        [[Identifier]] -> ([Identifier] -> Rules ()) -> Rules ()
    forall (t :: * -> *) (m :: * -> *) a b.
    (Foldable t, Monad m) =>
    t a -> (a -> m b) -> m ()
    forM_ [[Identifier]]
    gkeys (([Identifier] -> Rules ()) -> Rules ())
    -> ([Identifier] -> Rules ()) -> Rules ()
    forall a b. (a -> b) -> a -> b
    $ \gkey :: [Identifier]
    gkey -> case [Identifier]
    gkey of
            (k :: Identifier
    k : _ : _) -> String -> Rules ()
    forall (m :: * -> *) a. MonadFail m => String -> m a
    fail (String -> Rules ()) -> String -> Rules ()
    forall a b. (a -> b) -> a -> b
    $
                "Duplicate 301 redirects; " String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ Identifier -> String
    forall a. Show a => a -> String
    show Identifier
    k String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ " is ambiguous."
            _           -> () -> Rules ()
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()

        [(Identifier, String)]
    -> ((Identifier, String) -> Rules ()) -> Rules ()
    forall (t :: * -> *) (m :: * -> *) a b.
    (Foldable t, Monad m) =>
    t a -> (a -> m b) -> m ()
    forM_ [(Identifier, String)]
    redirects (((Identifier, String) -> Rules ()) -> Rules ())
    -> ((Identifier, String) -> Rules ()) -> Rules ()
    forall a b. (a -> b) -> a -> b
    $ \(r :: Identifier
    r, t :: String
    t) ->
            Bool -> Rules () -> Rules ()
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
    when (Identifier -> String
    toFilePath Identifier
    r String -> String -> Bool
    forall a. Eq a => a -> a -> Bool
    == String
    t) (Rules () -> Rules ()) -> Rules () -> Rules ()
    forall a b. (a -> b) -> a -> b
    $ String -> Rules ()
    forall (m :: * -> *) a. MonadFail m => String -> m a
    fail (String -> Rules ()) -> String -> Rules ()
    forall a b. (a -> b) -> a -> b
    $
                "Self-redirect detected: " String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ Identifier -> String
    forall a. Show a => a -> String
    show Identifier
    r String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ " points to itself."

        [(Identifier, String)]
    -> ((Identifier, String) -> Rules ()) -> Rules ()
    forall (t :: * -> *) (m :: * -> *) a b.
    (Foldable t, Monad m) =>
    t a -> (a -> m b) -> m ()
    forM_ [(Identifier, String)]
    redirects (((Identifier, String) -> Rules ()) -> Rules ())
    -> ((Identifier, String) -> Rules ()) -> Rules ()
    forall a b. (a -> b) -> a -> b
    $ \(ident :: Identifier
    ident, to :: String
    to) ->
            [Identifier] -> Rules () -> Rules ()
    create [Identifier
    ident] (Rules () -> Rules ()) -> Rules () -> Rules ()
    forall a b. (a -> b) -> a -> b
    $ do
                Routes -> Rules ()
    route Routes
    idRoute
                Compiler (Item Redirect) -> Rules ()
    forall a.
    (Binary a, Typeable a, Writable a) =>
    Compiler (Item a) -> Rules ()
    compile (Compiler (Item Redirect) -> Rules ())
    -> Compiler (Item Redirect) -> Rules ()
    forall a b. (a -> b) -> a -> b
    $ Redirect -> Compiler (Item Redirect)
    forall a. a -> Compiler (Item a)
    makeItem (Redirect -> Compiler (Item Redirect))
    -> Redirect -> Compiler (Item Redirect)
    forall a b. (a -> b) -> a -> b
    $! String -> Redirect
    Redirect String
    to

    -- | This datatype can be used directly if you want a lower-level interface to
    -- generate redirects.  For example, if you want to redirect @foo.html@ to
    -- @bar.jpg@, you can use:
    --
    -- > create ["foo.html"] $ do
    -- >     route idRoute
    -- >     compile $ makeItem $ Redirect "bar.jpg"
    data Redirect = Redirect
        { Redirect -> String
    redirectTo :: String
        } deriving (Redirect -> Redirect -> Bool
    (Redirect -> Redirect -> Bool)
    -> (Redirect -> Redirect -> Bool) -> Eq Redirect
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    /= :: Redirect -> Redirect -> Bool
    $c/= :: Redirect -> Redirect -> Bool
    == :: Redirect -> Redirect -> Bool
    $c== :: Redirect -> Redirect -> Bool
    Eq, Eq Redirect
    Eq Redirect =>
    (Redirect -> Redirect -> Ordering)
    -> (Redirect -> Redirect -> Bool)
    -> (Redirect -> Redirect -> Bool)
    -> (Redirect -> Redirect -> Bool)
    -> (Redirect -> Redirect -> Bool)
    -> (Redirect -> Redirect -> Redirect)
    -> (Redirect -> Redirect -> Redirect)
    -> Ord Redirect
    Redirect -> Redirect -> Bool
    Redirect -> Redirect -> Ordering
    Redirect -> Redirect -> Redirect
    forall a.
    Eq a =>
    (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    min :: Redirect -> Redirect -> Redirect
    $cmin :: Redirect -> Redirect -> Redirect
    max :: Redirect -> Redirect -> Redirect
    $cmax :: Redirect -> Redirect -> Redirect
    >= :: Redirect -> Redirect -> Bool
    $c>= :: Redirect -> Redirect -> Bool
    > :: Redirect -> Redirect -> Bool
    $c> :: Redirect -> Redirect -> Bool
    <= :: Redirect -> Redirect -> Bool
    $c<= :: Redirect -> Redirect -> Bool
    < :: Redirect -> Redirect -> Bool
    $c< :: Redirect -> Redirect -> Bool
    compare :: Redirect -> Redirect -> Ordering
    $ccompare :: Redirect -> Redirect -> Ordering
    $cp1Ord :: Eq Redirect
    Ord, Int -> Redirect -> String -> String
    [Redirect] -> String -> String
    Redirect -> String
    (Int -> Redirect -> String -> String)
    -> (Redirect -> String)
    -> ([Redirect] -> String -> String)
    -> Show Redirect
    forall a.
    (Int -> a -> String -> String)
    -> (a -> String) -> ([a] -> String -> String) -> Show a
    showList :: [Redirect] -> String -> String
    $cshowList :: [Redirect] -> String -> String
    show :: Redirect -> String
    $cshow :: Redirect -> String
    showsPrec :: Int -> Redirect -> String -> String
    $cshowsPrec :: Int -> Redirect -> String -> String
    Show)

    instance Binary Redirect where
        put :: Redirect -> Put
    put (Redirect to :: String
    to) = String -> Put
    forall t. Binary t => t -> Put
    put String
    to
        get :: Get Redirect
    get = String -> Redirect
    Redirect (String -> Redirect) -> Get String -> Get Redirect
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> Get String
    forall t. Binary t => Get t
    get

    instance Writable Redirect where
        write :: String -> Item Redirect -> IO ()
    write path :: String
    path = String -> Item String -> IO ()
    forall a. Writable a => String -> Item a -> IO ()
    write String
    path (Item String -> IO ())
    -> (Item Redirect -> Item String) -> Item Redirect -> IO ()
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (Redirect -> String) -> Item Redirect -> Item String
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap Redirect -> String
    redirectToHtml

    redirectToHtml :: Redirect -> String
    redirectToHtml :: Redirect -> String
    redirectToHtml (Redirect working :: String
    working) =
        "<!DOCTYPE html><html><head><meta charset=\"utf-8\"/><meta name=\"generator\" content=\"hakyll\"/>" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++
        "<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++
        "<meta http-equiv=\"refresh\" content=\"0; url=" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    working String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++
        "\"><link rel=\"canonical\" href=\"" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    working String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++
        "\"><title>Permanent Redirect</title></head><body><p>The page has moved to: <a href=\"" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    working String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++
        "\">this page</a></p></body></html>"