@@ -1,5 +1,27 @@
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 (..)
@@ -17,43 +39,49 @@ module Hakyll.Web.Template.Context
1739 , urlField
1840 , pathField
1941 , titleField
42+ , snippetField
2043 , dateField
2144 , dateFieldWith
2245 , getItemUTC
46+ , getItemModificationTime
2347 , modificationTimeField
2448 , modificationTimeFieldWith
2549 , teaserField
50+ , teaserFieldWithSeparator
2651 , missingField
52+ , bindItem
2753 ) where
2854
2955
3056--------------------------------------------------------------------------------
31−import Control.Applicative (Alternative (..), (<$>), pure)
57+import Control.Applicative (Alternative (..))
3258import Control.Monad (msum)
33−import Data.List (intercalate)
34−import qualified Data.Map as M
35−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
3663import Data.Time.Clock (UTCTime (..))
37−import Data.Time.Format (formatTime, parseTime)
38−import System.FilePath (takeBaseName, splitDirectories)
39−import System.Locale (TimeLocale, defaultTimeLocale)
40−
41−
42−--------------------------------------------------------------------------------
64+import Data.Time.Format (formatTime)
65+import qualified Data.Time.Format as TF
66+import Data.Time.Locale.Compat (TimeLocale, defaultTimeLocale)
4367import Hakyll.Core.Compiler
4468import Hakyll.Core.Compiler.Internal
4569import Hakyll.Core.Identifier
4670import Hakyll.Core.Item
4771import Hakyll.Core.Metadata
4872import Hakyll.Core.Provider
49−import Hakyll.Core.Util.String (splitAll, needlePrefix)
73+import Hakyll.Core.Util.String (needlePrefix, splitAll)
5074import Hakyll.Web.Html
75+import Prelude hiding (id)
76+import System.FilePath (dropExtension, splitDirectories,
77+ takeBaseName)
5178
5279
5380--------------------------------------------------------------------------------
5481-- | Mostly for internal usage
5582data ContextField
56− = StringField String
83+ = EmptyField
84+ | StringField String
5785 | forall a. ListField (Context a) [Item a]
5886
5987
@@ -78,72 +106,140 @@ newtype Context a = Context
78106
79107
80108--------------------------------------------------------------------------------
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
81119instance Monoid (Context a) where
82120 mempty = missingField
83121 mappend (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i
122+#endif
84123
85124
86125--------------------------------------------------------------------------------
87126field' :: String -> (Item a -> Compiler ContextField) -> Context a
88−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
89131
90132
91133--------------------------------------------------------------------------------
92−-- | 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'.
93143field
94144 :: String -- ^ Key
95145 -> (Item a -> Compiler String) -- ^ Function that constructs a value based
96− -- on the item
146+ -- on the item (e.g. accessing metadata)
97147 -> Context a
98148field key value = field' key (fmap StringField . value)
99149
100150
101151--------------------------------------------------------------------------------
102152-- | Creates a 'field' to use with the @$if()$@ template macro.
153+-- Attempting to substitute the field into the template will cause an error.
103154boolField
104155 :: String
105156 -> (Item a -> Bool)
106157 -> Context a
107−boolField name f = field name (\i -> if f i
108− then pure (error $ unwords ["no string value for bool field:",name])
109− else empty)
158+boolField name f = field' name (\i -> if f i
159+ then return EmptyField
160+ else noResult $ "Field " ++ name ++ " is false")
110161
111162
112163--------------------------------------------------------------------------------
113−-- | Creates a 'field' that does not depend on the 'Item'
114−constField :: String -> String -> Context a
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
115169constField key = field key . const . return
116170
117171
118172--------------------------------------------------------------------------------
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.
119176listField :: String -> Context a -> Compiler [Item a] -> Context b
120177listField key c xs = listFieldWith key c (const xs)
121178
122179
123180--------------------------------------------------------------------------------
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.
124187listFieldWith
125188 :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
126189listFieldWith key c f = field' key $ fmap (ListField c) . f
127190
128191
129192--------------------------------------------------------------------------------
130−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
131200functionField name value = Context $ \k args i ->
132201 if k == name
133202 then StringField <$> value args i
134− else empty
203+ else noResult $ "Tried function field " ++ name
135204
136205
137206--------------------------------------------------------------------------------
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+--
138216mapContext :: (String -> String) -> Context a -> Context a
139217mapContext f (Context c) = Context $ \k a i -> do
140218 fld <- c k a i
141219 case fld of
220+ EmptyField -> wrongType "boolField"
142221 StringField str -> return $ StringField (f str)
143− ListField _ _ -> fail $
144− "Hakyll.Web.Template.Context.mapContext: " ++
145− "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 ++ "!"
146226
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()'"
147243
148244--------------------------------------------------------------------------------
149245-- | A context that contains (in that order)
@@ -163,8 +259,7 @@ defaultContext =
163259 metadataField `mappend`
164260 urlField "url" `mappend`
165261 pathField "path" `mappend`
166− titleField "title" `mappend`
167− missingField
262+ titleField "title"
168263
169264
170265--------------------------------------------------------------------------------
@@ -182,15 +277,20 @@ bodyField key = field key $ return . itemBody
182277-- | Map any field to its metadata value, if present
183278metadataField :: Context a
184279metadataField = Context $ \k _ i -> do
185− value <- getMetadataField (itemIdentifier i) k
186− 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
187285
188286
189287--------------------------------------------------------------------------------
190288-- | Absolute url to the resulting item
191289urlField :: String -> Context a
192−urlField key = field key $
193− 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
194294
195295
196296--------------------------------------------------------------------------------
@@ -237,10 +337,16 @@ titleField = mapContext takeBaseName . pathField
237337-- Alternatively, when the metadata has a field called @path@ in a
238338-- @folder/yyyy-mm-dd-title.extension@ format (the convention for pages)
239339-- and no @published@ metadata field set, this function can render
240−-- the date. This pattern matches the file name or directory names
340+-- the date. This pattern matches the file name or directory names
241341-- that begins with @yyyy-mm-dd@ . For example:
242342-- @folder//yyyy-mm-dd-title//dist//main.extension@ .
243343-- 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.
244350
245351dateField :: String -- ^ Key in which the rendered date should be placed
246352 -> String -- ^ Format to use on the date
@@ -251,7 +357,7 @@ dateField = dateFieldWith defaultTimeLocale
251357--------------------------------------------------------------------------------
252358-- | This is an extended version of 'dateField' that allows you to
253359-- specify a time locale that is used for outputting the date. For more
254−-- details, see 'dateField'.
360+-- details, see 'dateField' and 'formatTime'.
255361dateFieldWith :: TimeLocale -- ^ Output time locale
256362 -> String -- ^ Destination key
257363 -> String -- ^ Format to use on the date
@@ -271,17 +377,18 @@ getItemUTC :: MonadMetadata m
271377 -> m UTCTime -- ^ Parsed UTCTime
272378getItemUTC locale id' = do
273379 metadata <- getMetadata id'
274− let tryField k fmt = M.lookup k metadata >>= parseTime' fmt
275− paths = splitDirectories $ toFilePath id'
380+ let tryField k fmt = lookupString k metadata >>= parseTime' fmt
381+ paths = splitDirectories $ (dropExtension . toFilePath) id'
276382
277383 maybe empty' return $ msum $
278384 [tryField "published" fmt | fmt <- formats] ++
279385 [tryField "date" fmt | fmt <- formats] ++
280− [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]
281388 where
282389 empty' = fail $ "Hakyll.Web.Template.Context.getItemUTC: " ++
283390 "could not parse time for " ++ show id'
284− parseTime' = parseTime locale
391+ parseTime' = parseTimeM True locale
285392 formats =
286393 [ "%a, %d %b %Y %H:%M:%S %Z"
287394 , "%Y-%m-%dT%H:%M:%S%Z"
@@ -294,20 +401,33 @@ getItemUTC locale id' = do
294401
295402
296403--------------------------------------------------------------------------------
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.
297416modificationTimeField :: String -- ^ Key
298417 -> String -- ^ Format
299− -> Context a -- ^ Resuting context
418+ -> Context a -- ^ Resulting context
300419modificationTimeField = modificationTimeFieldWith defaultTimeLocale
301420
302421
303422--------------------------------------------------------------------------------
423+-- | Creates a field with the last modification date of the underlying item
424+-- in a custom localisation format (see 'formatTime').
304425modificationTimeFieldWith :: TimeLocale -- ^ Time output locale
305426 -> String -- ^ Key
306427 -> String -- ^ Format
307428 -> Context a -- ^ Resulting context
308429modificationTimeFieldWith locale key fmt = field key $ \i -> do
309− provider <- compilerProvider <$> compilerAsk
310− let mtime = resourceModificationTime provider $ itemIdentifier i
430+ mtime <- getItemModificationTime $ itemIdentifier i
311431 return $ formatTime locale fmt mtime
312432
313433
@@ -318,9 +438,21 @@ modificationTimeFieldWith locale key fmt = field key $ \i -> do
318438teaserField :: String -- ^ Key to use
319439 -> Snapshot -- ^ Snapshot to load
320440 -> Context String -- ^ Resulting context
321−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
322454 body <- itemBody <$> loadSnapshot (itemIdentifier item) snapshot
323− case needlePrefix teaserSeparator body of
455+ case needlePrefix separator body of
324456 Nothing -> fail $
325457 "Hakyll.Web.Template.Context: no teaser defined for " ++
326458 show (itemIdentifier item)
@@ -328,7 +460,22 @@ teaserField key snapshot = field key $ \item -> do
328460
329461
330462--------------------------------------------------------------------------------
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.
331465missingField :: Context a
332−missingField = Context $ \k _ i -> fail $
333− "Missing field $" ++ k ++ "$ in context for item " ++
334− 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