summaryrefslogtreecommitdiff
path: root/src/Hakyll/Core/Routes.hs
blob: 34a613d62112da8dfcd1841bc9611f4914365fd0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
--------------------------------------------------------------------------------
-- | Once a target is compiled, the user usually wants to save it to the disk.
-- This is where the 'Routes' type comes in; it determines where a certain
-- target should be written.
--
-- Suppose we have an item @foo\/bar.markdown@. We can render this to
-- @foo\/bar.html@ using:
--
-- > route "foo/bar.markdown" (setExtension ".html")
--
-- If we do not want to change the extension, we can use 'idRoute', the simplest
-- route available:
--
-- > route "foo/bar.markdown" idRoute
--
-- That will route @foo\/bar.markdown@ to @foo\/bar.markdown@.
--
-- Note that the extension says nothing about the content! If you set the
-- extension to @.html@, it is your own responsibility to ensure that the
-- content is indeed HTML.
--
-- Finally, some special cases:
--
-- * If there is no route for an item, this item will not be routed, so it will
--   not appear in your site directory.
--
-- * If an item matches multiple routes, the first rule will be chosen.
{-# LANGUAGE Rank2Types #-}
module Hakyll.Core.Routes
    ( UsedMetadata
    , Routes
    , runRoutes
    , idRoute
    , setExtension
    , matchRoute
    , customRoute
    , constRoute
    , gsubRoute
    , metadataRoute
    , composeRoutes
    ) where


--------------------------------------------------------------------------------
import           Data.Monoid                    (Monoid, mappend, mempty)
import           System.FilePath                (replaceExtension)


--------------------------------------------------------------------------------
import           Hakyll.Core.Identifier
import           Hakyll.Core.Identifier.Pattern
import           Hakyll.Core.Metadata
import           Hakyll.Core.Provider
import           Hakyll.Core.Util.String


--------------------------------------------------------------------------------
-- | When you ran a route, it's useful to know whether or not this used
-- metadata. This allows us to do more granular dependency analysis.
type UsedMetadata = Bool


--------------------------------------------------------------------------------
-- | Type used for a route
newtype Routes = Routes
    { unRoutes :: Provider -> Identifier -> IO (Maybe FilePath, UsedMetadata)
    }


--------------------------------------------------------------------------------
instance Monoid Routes where
    mempty = Routes $ \_ _ -> return (Nothing, False)
    mappend (Routes f) (Routes g) = Routes $ \p id' -> do
        (mfp, um) <- f p id'
        case mfp of
            Nothing -> g p id'
            Just _  -> return (mfp, um)


--------------------------------------------------------------------------------
-- | Apply a route to an identifier
runRoutes :: Routes -> Provider -> Identifier
          -> IO (Maybe FilePath, UsedMetadata)
runRoutes = unRoutes


--------------------------------------------------------------------------------
-- | A route that uses the identifier as filepath. For example, the target with
-- ID @foo\/bar@ will be written to the file @foo\/bar@.
idRoute :: Routes
idRoute = customRoute toFilePath


--------------------------------------------------------------------------------
-- | Set (or replace) the extension of a route.
--
-- Example:
--
-- > runRoutes (setExtension "html") "foo/bar"
--
-- Result:
--
-- > Just "foo/bar.html"
--
-- Example:
--
-- > runRoutes (setExtension "html") "posts/the-art-of-trolling.markdown"
--
-- Result:
--
-- > Just "posts/the-art-of-trolling.html"
setExtension :: String -> Routes
setExtension extension = customRoute $
    (`replaceExtension` extension) . toFilePath


--------------------------------------------------------------------------------
-- | Apply the route if the identifier matches the given pattern, fail
-- otherwise
matchRoute :: Pattern -> Routes -> Routes
matchRoute pattern (Routes route) = Routes $ \p id' ->
    if matches pattern id' then route p id' else return (Nothing, False)


--------------------------------------------------------------------------------
-- | Create a custom route. This should almost always be used with
-- 'matchRoute'
customRoute :: (Identifier -> FilePath) -> Routes
customRoute f = Routes $ const $ \id' -> return (Just (f id'), False)


--------------------------------------------------------------------------------
-- | A route that always gives the same result. Obviously, you should only use
-- this for a single compilation rule.
constRoute :: FilePath -> Routes
constRoute = customRoute . const


--------------------------------------------------------------------------------
-- | Create a gsub route
--
-- Example:
--
-- > runRoutes (gsubRoute "rss/" (const "")) "tags/rss/bar.xml"
--
-- Result:
--
-- > Just "tags/bar.xml"
gsubRoute :: String              -- ^ Pattern
          -> (String -> String)  -- ^ Replacement
          -> Routes              -- ^ Resulting route
gsubRoute pattern replacement = customRoute $
    replaceAll pattern replacement . toFilePath


--------------------------------------------------------------------------------
-- | Get access to the metadata in order to determine the route
metadataRoute :: (Metadata -> Routes) -> Routes
metadataRoute f = Routes $ \p i -> do
    metadata <- resourceMetadata p i
    unRoutes (f metadata) p i


--------------------------------------------------------------------------------
-- | Compose routes so that @f \`composeRoutes\` g@ is more or less equivalent
-- with @g . f@.
--
-- Example:
--
-- > let routes = gsubRoute "rss/" (const "") `composeRoutes` setExtension "xml"
-- > in runRoutes routes "tags/rss/bar"
--
-- Result:
--
-- > Just "tags/bar.xml"
--
-- If the first route given fails, Hakyll will not apply the second route.
composeRoutes :: Routes  -- ^ First route to apply
              -> Routes  -- ^ Second route to apply
              -> Routes  -- ^ Resulting route
composeRoutes (Routes f) (Routes g) = Routes $ \p i -> do
    (mfp, um) <- f p i
    case mfp of
        Nothing -> return (Nothing, um)
        Just fp -> do
            (mfp', um') <- g p (fromFilePath fp)
            return (mfp', um || um')