@@ -1,9 +1,32 @@
1+-- | This module provides 'Context's which are used to expand expressions in
2+-- templates and allow for arbitrary customisation.
3+--
4+-- 'Template's define a small expression DSL which consists of strings,
5+-- identifiers and function application. There is no type system, every value is
6+-- a string and on the top level they get substituted verbatim into the page.
7+--
8+-- For example, you can build a context that contains
9+--
10+-- > … <> functionField "concat" (const . concat) <> …
11+--
12+-- which will allow you to use the @concat@ identifier as a function that takes
13+-- arbitrarily many stings and concatenates them to a new string:
14+--
15+-- > $partial(concat("templates/categories/", category))$
16+--
17+-- This will evaluate the @category@ field in the context, then prepend he path,
18+-- and include the referenced file as a template.
19+
20+
121--------------------------------------------------------------------------------
22+{-# LANGUAGE CPP #-}
223{-# LANGUAGE ExistentialQuantification #-}
24+{-# LANGUAGE RankNTypes #-}
325module Hakyll.Web.Template.Context
426 ( ContextField (..)
527 , Context (..)
628 , field
29+ , boolField
730 , constField
831 , listField
932 , listFieldWith
@@ -16,43 +39,49 @@ module Hakyll.Web.Template.Context
1639 , urlField
1740 , pathField
1841 , titleField
42+ , snippetField
1943 , dateField
2044 , dateFieldWith
2145 , getItemUTC
46+ , getItemModificationTime
2247 , modificationTimeField
2348 , modificationTimeFieldWith
2449 , teaserField
50+ , teaserFieldWithSeparator
2551 , missingField
52+ , bindItem
2653 ) where
2754
2855
2956--------------------------------------------------------------------------------
30−import Control.Applicative (Alternative (..), (<$>))
57+import Control.Applicative (Alternative (..))
3158import Control.Monad (msum)
32−import Data.List (intercalate)
33−import qualified Data.Map as M
34−import Data.Monoid (Monoid (..))
59+import Data.List (intercalate, tails)
60+#if MIN_VERSION_base(4,9,0)
61+import Data.Semigroup (Semigroup (..))
62+#endif
3563import Data.Time.Clock (UTCTime (..))
36−import Data.Time.Format (formatTime, parseTime)
37−import System.FilePath (takeBaseName, splitDirectories)
38−import System.Locale (TimeLocale, defaultTimeLocale)
39−
40−
41−--------------------------------------------------------------------------------
64+import Data.Time.Format (formatTime)
65+import qualified Data.Time.Format as TF
66+import Data.Time.Locale.Compat (TimeLocale, defaultTimeLocale)
4267import Hakyll.Core.Compiler
4368import Hakyll.Core.Compiler.Internal
4469import Hakyll.Core.Identifier
4570import Hakyll.Core.Item
4671import Hakyll.Core.Metadata
4772import Hakyll.Core.Provider
48−import Hakyll.Core.Util.String (splitAll, needlePrefix)
73+import Hakyll.Core.Util.String (needlePrefix, splitAll)
4974import Hakyll.Web.Html
75+import Prelude hiding (id)
76+import System.FilePath (dropExtension, splitDirectories,
77+ takeBaseName)
5078
5179
5280--------------------------------------------------------------------------------
5381-- | Mostly for internal usage
5482data ContextField
55− = StringField String
83+ = EmptyField
84+ | StringField String
5685 | forall a. ListField (Context a) [Item a]
5786
5887
@@ -77,61 +106,140 @@ newtype Context a = Context
77106
78107
79108--------------------------------------------------------------------------------
109+-- | Tries to find a key in the left context,
110+-- or when that fails in the right context.
111+#if MIN_VERSION_base(4,9,0)
112+instance Semigroup (Context a) where
113+ (<>) (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
114+
115+instance Monoid (Context a) where
116+ mempty = missingField
117+ mappend = (<>)
118+#else
80119instance Monoid (Context a) where
81120 mempty = missingField
82121 mappend (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
122+#endif
83123
84124
85125--------------------------------------------------------------------------------
86126field' :: String -> (Item a -> Compiler ContextField) -> Context a
87−field' key value = Context $ \k _ i -> if k == key then value i else empty
127+field' key value = Context $ \k _ i ->
128+ if k == key
129+ then value i
130+ else noResult $ "Tried field " ++ key
88131
89132
90133--------------------------------------------------------------------------------
91−-- | Constructs a new field in the 'Context.'
134+-- | Constructs a new field for a 'Context'.
135+-- If the key matches, the compiler is run and its result is substituted in the
136+-- template.
137+--
138+-- If the compiler fails, the field will be considered non-existent
139+-- in an @$if()$@ macro or ultimately break the template application
140+-- (unless the key is found in another context when using '<>').
141+-- Use 'empty' or 'noResult' for intentional failures of fields used in
142+-- @$if()$@, to distinguish them from exceptions thrown with 'fail'.
92143field
93144 :: String -- ^ Key
94145 -> (Item a -> Compiler String) -- ^ Function that constructs a value based
95− -- on the item
146+ -- on the item (e.g. accessing metadata)
96147 -> Context a
97148field key value = field' key (fmap StringField . value)
98149
99150
100151--------------------------------------------------------------------------------
101−-- | Creates a 'field' that does not depend on the 'Item'
102−constField :: String -> String -> Context a
152+-- | Creates a 'field' to use with the @$if()$@ template macro.
153+-- Attempting to substitute the field into the template will cause an error.
154+boolField
155+ :: String
156+ -> (Item a -> Bool)
157+ -> Context a
158+boolField name f = field' name (\i -> if f i
159+ then return EmptyField
160+ else noResult $ "Field " ++ name ++ " is false")
161+
162+
163+--------------------------------------------------------------------------------
164+-- | Creates a 'field' that does not depend on the 'Item' but always yields
165+-- the same string
166+constField :: String -- ^ Key
167+ -> String -- ^ Value
168+ -> Context a
103169constField key = field key . const . return
104170
105171
106172--------------------------------------------------------------------------------
173+-- | Creates a list field to be consumed by a @$for(…)$@ expression.
174+-- The compiler returns multiple items which are rendered in the loop body
175+-- with the supplied context.
107176listField :: String -> Context a -> Compiler [Item a] -> Context b
108177listField key c xs = listFieldWith key c (const xs)
109178
110179
111180--------------------------------------------------------------------------------
181+-- | Produces a new 'Context' which has list field 'key'. All fields from
182+-- 'c' are also accessible from the produced context.
183+-- Be careful when doing @listFieldWith k ca f <> cb@ as any fields in @ca@
184+-- will override fields in @cb@ with the same name.
185+-- Creates a list field like 'listField', but supplies the current page
186+-- to the compiler.
112187listFieldWith
113188 :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
114189listFieldWith key c f = field' key $ fmap (ListField c) . f
115190
116191
117192--------------------------------------------------------------------------------
118−functionField :: String -> ([String] -> Item a -> Compiler String) -> Context a
193+-- | Creates a variadic function field.
194+--
195+-- The function will be called with the dynamically evaluated string arguments
196+-- from the template as well as the page that is currently rendered.
197+functionField :: String -- ^ Key
198+ -> ([String] -> Item a -> Compiler String) -- ^ Function
199+ -> Context a
119200functionField name value = Context $ \k args i ->
120201 if k == name
121202 then StringField <$> value args i
122− else empty
203+ else noResult $ "Tried function field " ++ name
123204
124205
125206--------------------------------------------------------------------------------
207+-- | Transform the respective string results of all fields in a context.
208+-- For example,
209+--
210+-- > mapContext (++"c") (constField "x" "a" <> constField "y" "b")
211+--
212+-- is equivalent to
213+--
214+-- > constField "x" "ac" <> constField "y" "bc"
215+--
126216mapContext :: (String -> String) -> Context a -> Context a
127217mapContext f (Context c) = Context $ \k a i -> do
128218 fld <- c k a i
129219 case fld of
220+ EmptyField -> wrongType "boolField"
130221 StringField str -> return $ StringField (f str)
131− ListField _ _ -> fail $
132− "Hakyll.Web.Template.Context.mapContext: " ++
133− "can't map over a ListField!"
222+ _ -> wrongType "ListField"
223+ where
224+ wrongType typ = fail $ "Hakyll.Web.Template.Context.mapContext: " ++
225+ "can't map over a " ++ typ ++ "!"
134226
227+--------------------------------------------------------------------------------
228+-- | A context that allows snippet inclusion. In processed file, use as:
229+--
230+-- > ...
231+-- > $snippet("path/to/snippet/")$
232+-- > ...
233+--
234+-- The contents of the included file will not be interpolated like @partial@
235+-- does it.
236+--
237+snippetField :: Context String
238+snippetField = functionField "snippet" f
239+ where
240+ f [contentsPath] _ = loadBody (fromFilePath contentsPath)
241+ f [] _ = fail "No argument to function 'snippet()'"
242+ f _ _ = fail "Too many arguments to function 'snippet()'"
135243
136244--------------------------------------------------------------------------------
137245-- | A context that contains (in that order)
@@ -151,8 +259,7 @@ defaultContext =
151259 metadataField `mappend`
152260 urlField "url" `mappend`
153261 pathField "path" `mappend`
154− titleField "title" `mappend`
155− missingField
262+ titleField "title"
156263
157264
158265--------------------------------------------------------------------------------
@@ -170,15 +277,20 @@ bodyField key = field key $ return . itemBody
170277-- | Map any field to its metadata value, if present
171278metadataField :: Context a
172279metadataField = Context $ \k _ i -> do
173− value <- getMetadataField (itemIdentifier i) k
174− maybe empty (return . StringField) value
280+ let id = itemIdentifier i
281+ empty' = noResult $ "No '" ++ k ++ "' field in metadata " ++
282+ "of item " ++ show id
283+ value <- getMetadataField id k
284+ maybe empty' (return . StringField) value
175285
176286
177287--------------------------------------------------------------------------------
178288-- | Absolute url to the resulting item
179289urlField :: String -> Context a
180−urlField key = field key $
181− fmap (maybe empty toUrl) . getRoute . itemIdentifier
290+urlField key = field key $ \i -> do
291+ let id = itemIdentifier i
292+ empty' = fail $ "No route url found for item " ++ show id
293+ fmap (maybe empty' toUrl) $ getRoute id
182294
183295
184296--------------------------------------------------------------------------------
@@ -225,10 +337,16 @@ titleField = mapContext takeBaseName . pathField
225337-- Alternatively, when the metadata has a field called @path@ in a
226338-- @folder/yyyy-mm-dd-title.extension@ format (the convention for pages)
227339-- and no @published@ metadata field set, this function can render
228−-- the date. This pattern matches the file name or directory names
340+-- the date. This pattern matches the file name or directory names
229341-- that begins with @yyyy-mm-dd@ . For example:
230342-- @folder//yyyy-mm-dd-title//dist//main.extension@ .
231343-- In case of multiple matches, the rightmost one is used.
344+--
345+-- As another alternative, if none of the above matches, and the file has a
346+-- path which contains nested directories specifying a date, then that date
347+-- will be used. In other words, if the path is of the form
348+-- @**//yyyy//mm//dd//**//main.extension@ .
349+-- As above, in case of multiple matches, the rightmost one is used.
232350
233351dateField :: String -- ^ Key in which the rendered date should be placed
234352 -> String -- ^ Format to use on the date
@@ -239,7 +357,7 @@ dateField = dateFieldWith defaultTimeLocale
239357--------------------------------------------------------------------------------
240358-- | This is an extended version of 'dateField' that allows you to
241359-- specify a time locale that is used for outputting the date. For more
242−-- details, see 'dateField'.
360+-- details, see 'dateField' and 'formatTime'.
243361dateFieldWith :: TimeLocale -- ^ Output time locale
244362 -> String -- ^ Destination key
245363 -> String -- ^ Format to use on the date
@@ -259,17 +377,18 @@ getItemUTC :: MonadMetadata m
259377 -> m UTCTime -- ^ Parsed UTCTime
260378getItemUTC locale id' = do
261379 metadata <- getMetadata id'
262− let tryField k fmt = M.lookup k metadata >>= parseTime' fmt
263− paths = splitDirectories $ toFilePath id'
380+ let tryField k fmt = lookupString k metadata >>= parseTime' fmt
381+ paths = splitDirectories $ (dropExtension . toFilePath) id'
264382
265383 maybe empty' return $ msum $
266384 [tryField "published" fmt | fmt <- formats] ++
267385 [tryField "date" fmt | fmt <- formats] ++
268− [parseTime' "%Y-%m-%d" $ intercalate "-" $ take 3 $ splitAll "-" fnCand | fnCand <- reverse paths]
386+ [parseTime' "%Y-%m-%d" $ intercalate "-" $ take 3 $ splitAll "-" fnCand | fnCand <- reverse paths] ++
387+ [parseTime' "%Y-%m-%d" $ intercalate "-" $ fnCand | fnCand <- map (take 3) $ reverse . tails $ paths]
269388 where
270389 empty' = fail $ "Hakyll.Web.Template.Context.getItemUTC: " ++
271390 "could not parse time for " ++ show id'
272− parseTime' = parseTime locale
391+ parseTime' = parseTimeM True locale
273392 formats =
274393 [ "%a, %d %b %Y %H:%M:%S %Z"
275394 , "%Y-%m-%dT%H:%M:%S%Z"
@@ -282,20 +401,33 @@ getItemUTC locale id' = do
282401
283402
284403--------------------------------------------------------------------------------
404+-- | Get the time on which the actual file was last modified. This only works if
405+-- there actually is an underlying file, of couse.
406+getItemModificationTime
407+ :: Identifier
408+ -> Compiler UTCTime
409+getItemModificationTime identifier = do
410+ provider <- compilerProvider <$> compilerAsk
411+ return $ resourceModificationTime provider identifier
412+
413+
414+--------------------------------------------------------------------------------
415+-- | Creates a field with the last modification date of the underlying item.
285416modificationTimeField :: String -- ^ Key
286417 -> String -- ^ Format
287− -> Context a -- ^ Resuting context
418+ -> Context a -- ^ Resulting context
288419modificationTimeField = modificationTimeFieldWith defaultTimeLocale
289420
290421
291422--------------------------------------------------------------------------------
423+-- | Creates a field with the last modification date of the underlying item
424+-- in a custom localisation format (see 'formatTime').
292425modificationTimeFieldWith :: TimeLocale -- ^ Time output locale
293426 -> String -- ^ Key
294427 -> String -- ^ Format
295428 -> Context a -- ^ Resulting context
296429modificationTimeFieldWith locale key fmt = field key $ \i -> do
297− provider <- compilerProvider <$> compilerAsk
298− let mtime = resourceModificationTime provider $ itemIdentifier i
430+ mtime <- getItemModificationTime $ itemIdentifier i
299431 return $ formatTime locale fmt mtime
300432
301433
@@ -306,9 +438,21 @@ modificationTimeFieldWith locale key fmt = field key $ \i -> do
306438teaserField :: String -- ^ Key to use
307439 -> Snapshot -- ^ Snapshot to load
308440 -> Context String -- ^ Resulting context
309−teaserField key snapshot = field key $ \item -> do
441+teaserField = teaserFieldWithSeparator teaserSeparator
442+
443+
444+--------------------------------------------------------------------------------
445+-- | A context with "teaser" key which contain a teaser of the item, defined as
446+-- the snapshot content before the teaser separator. The item is loaded from the
447+-- given snapshot (which should be saved in the user code before any templates
448+-- are applied).
449+teaserFieldWithSeparator :: String -- ^ Separator to use
450+ -> String -- ^ Key to use
451+ -> Snapshot -- ^ Snapshot to load
452+ -> Context String -- ^ Resulting context
453+teaserFieldWithSeparator separator key snapshot = field key $ \item -> do
310454 body <- itemBody <$> loadSnapshot (itemIdentifier item) snapshot
311− case needlePrefix teaserSeparator body of
455+ case needlePrefix separator body of
312456 Nothing -> fail $
313457 "Hakyll.Web.Template.Context: no teaser defined for " ++
314458 show (itemIdentifier item)
@@ -316,7 +460,22 @@ teaserField key snapshot = field key $ \item -> do
316460
317461
318462--------------------------------------------------------------------------------
463+-- | Constantly reports any field as missing. Mostly for internal usage,
464+-- it is the last choice in every context used in a template application.
319465missingField :: Context a
320−missingField = Context $ \k _ i -> fail $
321− "Missing field $" ++ k ++ "$ in context for item " ++
322− show (itemIdentifier i)
466+missingField = Context $ \k _ _ -> noResult $
467+ "Missing field '" ++ k ++ "' in context"
468+
469+parseTimeM :: Bool -> TimeLocale -> String -> String -> Maybe UTCTime
470+#if MIN_VERSION_time(1,5,0)
471+parseTimeM = TF.parseTimeM
472+#else
473+parseTimeM _ = TF.parseTime
474+#endif
475+
476+--------------------------------------------------------------------------------
477+
478+-- | Binds an 'Item' to a given 'Context', allowing it to be combined with any
479+-- other 'Context' of any type.
480+bindItem :: Context a -> Item a -> forall b. Context b
481+bindItem (Context ctx) ia = Context $ \k args _ -> ctx k args ia