-- | This module provides 'Context's which are used to expand expressions in
-- templates and allow for arbitrary customisation.
--
-- 'Template's define a small expression DSL which consists of strings,
-- identifiers and function application. There is no type system, every value is
-- a string and on the top level they get substituted verbatim into the page.
--
-- For example, you can build a context that contains
--
-- > … <> functionField "concat" (const . concat) <> …
--
-- which will allow you to use the @concat@ identifier as a function that takes
-- arbitrarily many strings and concatenates them to a new string:
--
-- > $partial(concat("templates/categories/", category))$
--
-- This will evaluate the @category@ field in the context, then prepend the path,
-- and include the referenced file as a template.


--------------------------------------------------------------------------------
{-# LANGUAGE CPP                       #-}
{-# LANGUAGE ExistentialQuantification #-}
module Hakyll.Web.Template.Context
    ( ContextField (..)
    , Context (..)
    , field
    , boolField
    , constField
    , listField
    , listFieldWith
    , functionField
    , mapContext
    , mapContextBy

    , defaultContext
    , bodyField
    , metadataField
    , urlField
    , pathField
    , titleField
    , snippetField
    , dateField
    , dateFieldWith
    , getItemUTC
    , getItemModificationTime
    , modificationTimeField
    , modificationTimeFieldWith
    , teaserField
    , teaserFieldWithSeparator
    , missingField
    ) where


--------------------------------------------------------------------------------
import           Control.Applicative           (Alternative (..))
import           Control.Monad                 (msum)
#if !MIN_VERSION_base(4,13,0)
import           Control.Monad.Fail            (MonadFail)
#endif
import           Data.List                     (intercalate, tails)
import           Data.Time.Clock               (UTCTime (..))
import           Data.Time.Format              (formatTime, parseTimeM)
import           Data.Time.Locale.Compat       (TimeLocale, defaultTimeLocale)
import           Hakyll.Core.Compiler
import           Hakyll.Core.Compiler.Internal
import           Hakyll.Core.Identifier
import           Hakyll.Core.Item
import           Hakyll.Core.Metadata
import           Hakyll.Core.Provider
import           Hakyll.Core.Util.String       (needlePrefix, splitAll)
import           Hakyll.Web.Html
import           Prelude                       hiding (id)
import           System.FilePath               (dropExtension, splitDirectories,
                                                takeBaseName)


--------------------------------------------------------------------------------
-- | Mostly for internal usage
data ContextField
    = EmptyField
    | StringField String
    | forall a. ListField (Context a) [Item a]


--------------------------------------------------------------------------------
-- | The 'Context' monoid. Please note that the order in which you
-- compose the items is important. For example in
--
-- > field "A" f1 <> field "A" f2
--
-- the first context will overwrite the second. This is especially
-- important when something is being composed with
-- 'metadataField' (or 'defaultContext'). If you want your context to be
-- overwritten by the metadata fields, compose it from the right:
--
-- @
-- 'metadataField' \<\> field \"date\" fDate
-- @
--
newtype Context a = Context
    { forall a.
Context a -> String -> [String] -> Item a -> Compiler ContextField
unContext :: String -> [String] -> Item a -> Compiler ContextField
    }


--------------------------------------------------------------------------------
-- | Tries to find a key in the left context,
-- or when that fails in the right context.
instance Semigroup (Context a) where
    <> :: Context a -> Context a -> Context a
(<>) (Context String -> [String] -> Item a -> Compiler ContextField
f) (Context String -> [String] -> Item a -> Compiler ContextField
g) = forall a.
(String -> [String] -> Item a -> Compiler ContextField)
-> Context a
Context forall a b. (a -> b) -> a -> b
$ \String
k [String]
a Item a
i -> String -> [String] -> Item a -> Compiler ContextField
f String
k [String]
a Item a
i forall (f :: * -> *) a. Alternative f => f a -> f a -> f a
<|> String -> [String] -> Item a -> Compiler ContextField
g String
k [String]
a Item a
i

instance Monoid (Context a) where
    mempty :: Context a
mempty  = forall a. Context a
missingField
    mappend :: Context a -> Context a -> Context a
mappend = forall a. Semigroup a => a -> a -> a
(<>)


--------------------------------------------------------------------------------
field' :: String -> (Item a -> Compiler ContextField) -> Context a
field' :: forall a. String -> (Item a -> Compiler ContextField) -> Context a
field' String
key Item a -> Compiler ContextField
value = forall a.
(String -> [String] -> Item a -> Compiler ContextField)
-> Context a
Context forall a b. (a -> b) -> a -> b
$ \String
k [String]
_ Item a
i ->
    if String
k forall a. Eq a => a -> a -> Bool
== String
key
        then Item a -> Compiler ContextField
value Item a
i
        else forall a. String -> Compiler a
noResult forall a b. (a -> b) -> a -> b
$ String
"Tried field " forall a. [a] -> [a] -> [a]
++ String
key


--------------------------------------------------------------------------------
-- | Constructs a new field for a 'Context'.
-- If the key matches, the compiler is run and its result is substituted in the
-- template.
--
-- If the compiler fails, the field will be considered non-existent
-- in an @$if()$@ macro or ultimately break the template application
-- (unless the key is found in another context when using '<>').
-- Use 'empty' or 'noResult' for intentional failures of fields used in
-- @$if()$@, to distinguish them from exceptions thrown with 'fail'.
field
    :: String                      -- ^ Key
    -> (Item a -> Compiler String) -- ^ Function that constructs a value based
                                   -- on the item (e.g. accessing metadata)
    -> Context a
field :: forall a. String -> (Item a -> Compiler String) -> Context a
field String
key Item a -> Compiler String
value = forall a. String -> (Item a -> Compiler ContextField) -> Context a
field' String
key (forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap String -> ContextField
StringField forall b c a. (b -> c) -> (a -> b) -> a -> c
. Item a -> Compiler String
value)


--------------------------------------------------------------------------------
-- | Creates a 'field' to use with the @$if()$@ template macro.
-- Attempting to substitute the field into the template will cause an error.
boolField
    :: String
    -> (Item a -> Bool)
    -> Context a
boolField :: forall a. String -> (Item a -> Bool) -> Context a
boolField String
name Item a -> Bool
f = forall a. String -> (Item a -> Compiler ContextField) -> Context a
field' String
name (\Item a
i -> if Item a -> Bool
f Item a
i
    then forall (m :: * -> *) a. Monad m => a -> m a
return ContextField
EmptyField
    else forall a. String -> Compiler a
noResult forall a b. (a -> b) -> a -> b
$ String
"Field " forall a. [a] -> [a] -> [a]
++ String
name forall a. [a] -> [a] -> [a]
++ String
" is false")


--------------------------------------------------------------------------------
-- | Creates a 'field' that does not depend on the 'Item' but always yields
-- the same string
constField :: String     -- ^ Key
           -> String     -- ^ Value
           -> Context a
constField :: forall a. String -> String -> Context a
constField String
key = forall a. String -> (Item a -> Compiler String) -> Context a
field String
key forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a b. a -> b -> a
const forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall (m :: * -> *) a. Monad m => a -> m a
return


--------------------------------------------------------------------------------
-- | Creates a list field to be consumed by a @$for(…)$@ expression.
-- The compiler returns multiple items which are rendered in the loop body
-- with the supplied context.
listField :: String -> Context a -> Compiler [Item a] -> Context b
listField :: forall a b. String -> Context a -> Compiler [Item a] -> Context b
listField String
key Context a
c Compiler [Item a]
xs = forall a b.
String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
listFieldWith String
key Context a
c (forall a b. a -> b -> a
const Compiler [Item a]
xs)


--------------------------------------------------------------------------------
-- | Creates a list field like 'listField', but supplies the current page
-- to the compiler.
listFieldWith
    :: String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
listFieldWith :: forall a b.
String -> Context a -> (Item b -> Compiler [Item a]) -> Context b
listFieldWith String
key Context a
c Item b -> Compiler [Item a]
f = forall a. String -> (Item a -> Compiler ContextField) -> Context a
field' String
key forall a b. (a -> b) -> a -> b
$ forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (forall a. Context a -> [Item a] -> ContextField
ListField Context a
c) forall b c a. (b -> c) -> (a -> b) -> a -> c
. Item b -> Compiler [Item a]
f


--------------------------------------------------------------------------------
-- | Creates a variadic function field.
--
-- The function will be called with the dynamically evaluated string arguments
-- from the template as well as the page that is currently rendered.
functionField :: String                                  -- ^ Key
              -> ([String] -> Item a -> Compiler String) -- ^ Function
              -> Context a
functionField :: forall a.
String -> ([String] -> Item a -> Compiler String) -> Context a
functionField String
name [String] -> Item a -> Compiler String
value = forall a.
(String -> [String] -> Item a -> Compiler ContextField)
-> Context a
Context forall a b. (a -> b) -> a -> b
$ \String
k [String]
args Item a
i ->
    if String
k forall a. Eq a => a -> a -> Bool
== String
name
        then String -> ContextField
StringField forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> [String] -> Item a -> Compiler String
value [String]
args Item a
i
        else forall a. String -> Compiler a
noResult forall a b. (a -> b) -> a -> b
$ String
"Tried function field " forall a. [a] -> [a] -> [a]
++ String
name


--------------------------------------------------------------------------------
-- | Transform the respective string results of all fields in a context.
-- For example,
--
-- > mapContext (++"c") (constField "x" "a" <> constField "y" "b")
--
-- is equivalent to
--
-- > constField "x" "ac" <> constField "y" "bc"
--
mapContext :: (String -> String) -> Context a -> Context a
mapContext :: forall a. (String -> String) -> Context a -> Context a
mapContext = forall a.
(String -> Bool) -> (String -> String) -> Context a -> Context a
mapContextBy (forall a b. a -> b -> a
const Bool
True)


--------------------------------------------------------------------------------
-- | Transform the respective string results of all fields in a context
-- satisfying a predicate. For example,
--
-- > mapContextBy (=="y") (++"c") (constField "x" "a" <> constField "y" "b")
--
-- is equivalent to
--
-- > constField "x" "a" <> constField "y" "bc"
--
mapContextBy :: (String -> Bool) -> (String -> String) -> Context a -> Context a
mapContextBy :: forall a.
(String -> Bool) -> (String -> String) -> Context a -> Context a
mapContextBy String -> Bool
p String -> String
f (Context String -> [String] -> Item a -> Compiler ContextField
c) = forall a.
(String -> [String] -> Item a -> Compiler ContextField)
-> Context a
Context forall a b. (a -> b) -> a -> b
$ \String
k [String]
a Item a
i -> do
    ContextField
fld <- String -> [String] -> Item a -> Compiler ContextField
c String
k [String]
a Item a
i
    case ContextField
fld of
        ContextField
EmptyField      -> forall {m :: * -> *} {a}. MonadFail m => String -> m a
wrongType String
"boolField"
        StringField String
str -> forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ String -> ContextField
StringField forall a b. (a -> b) -> a -> b
$
                             if String -> Bool
p String
k then String -> String
f String
str else String
str
        ContextField
_               -> forall {m :: * -> *} {a}. MonadFail m => String -> m a
wrongType String
"ListField"
  where
    wrongType :: String -> m a
wrongType String
typ = forall (m :: * -> *) a. MonadFail m => String -> m a
fail forall a b. (a -> b) -> a -> b
$ String
"Hakyll.Web.Template.Context.mapContext: " forall a. [a] -> [a] -> [a]
++
        String
"can't map over a " forall a. [a] -> [a] -> [a]
++ String
typ forall a. [a] -> [a] -> [a]
++ String
"!"

--------------------------------------------------------------------------------
-- | A context that allows snippet inclusion. In processed file, use as:
--
-- > ...
-- > $snippet("path/to/snippet/")$
-- > ...
--
-- The contents of the included file will not be interpolated like @partial@
-- does it.
--
snippetField :: Context String
snippetField :: Context String
snippetField = forall a.
String -> ([String] -> Item a -> Compiler String) -> Context a
functionField String
"snippet" forall {a} {p}.
(Binary a, Typeable a) =>
[String] -> p -> Compiler a
f
  where
    f :: [String] -> p -> Compiler a
f [String
contentsPath] p
_ = forall a. (Binary a, Typeable a) => Identifier -> Compiler a
loadBody (String -> Identifier
fromFilePath String
contentsPath)
    f []             p
_ = forall (m :: * -> *) a. MonadFail m => String -> m a
fail String
"No argument to function 'snippet()'"
    f [String]
_              p
_ = forall (m :: * -> *) a. MonadFail m => String -> m a
fail String
"Too many arguments to function 'snippet()'"

--------------------------------------------------------------------------------
-- | A context that contains (in that order)
--
--     1. A @$body$@ field
--
--     2. Metadata fields
--
--     3. A @$url$@ 'urlField'
--
--     4. A @$path$@ 'pathField'
--
--     5. A @$title$@ 'titleField'
defaultContext :: Context String
defaultContext :: Context String
defaultContext =
    String -> Context String
bodyField     String
"body"     forall a. Monoid a => a -> a -> a
`mappend`
    forall a. Context a
metadataField            forall a. Monoid a => a -> a -> a
`mappend`
    forall a. String -> Context a
urlField      String
"url"      forall a. Monoid a => a -> a -> a
`mappend`
    forall a. String -> Context a
pathField     String
"path"     forall a. Monoid a => a -> a -> a
`mappend`
    forall a. String -> Context a
titleField    String
"title"


--------------------------------------------------------------------------------
teaserSeparator :: String
teaserSeparator :: String
teaserSeparator = String
"<!--more-->"


--------------------------------------------------------------------------------
-- | Constructs a 'field' that contains the body of the item.
bodyField :: String -> Context String
bodyField :: String -> Context String
bodyField String
key = forall a. String -> (Item a -> Compiler String) -> Context a
field String
key forall a b. (a -> b) -> a -> b
$ forall (m :: * -> *) a. Monad m => a -> m a
return forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. Item a -> a
itemBody


--------------------------------------------------------------------------------
-- | Map any field to its metadata value, if present
metadataField :: Context a
metadataField :: forall a. Context a
metadataField = forall a.
(String -> [String] -> Item a -> Compiler ContextField)
-> Context a
Context forall a b. (a -> b) -> a -> b
$ \String
k [String]
_ Item a
i -> do
    let id :: Identifier
id = forall a. Item a -> Identifier
itemIdentifier Item a
i
        empty' :: Compiler a
empty' = forall a. String -> Compiler a
noResult forall a b. (a -> b) -> a -> b
$ String
"No '" forall a. [a] -> [a] -> [a]
++ String
k forall a. [a] -> [a] -> [a]
++ String
"' field in metadata " forall a. [a] -> [a] -> [a]
++
            String
"of item " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show Identifier
id
    Maybe String
value <- forall (m :: * -> *).
MonadMetadata m =>
Identifier -> String -> m (Maybe String)
getMetadataField Identifier
id String
k
    forall b a. b -> (a -> b) -> Maybe a -> b
maybe forall {a}. Compiler a
empty' (forall (m :: * -> *) a. Monad m => a -> m a
return forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ContextField
StringField) Maybe String
value


--------------------------------------------------------------------------------
-- | Absolute url to the resulting item
urlField :: String -> Context a
urlField :: forall a. String -> Context a
urlField String
key = forall a. String -> (Item a -> Compiler String) -> Context a
field String
key forall a b. (a -> b) -> a -> b
$ \Item a
i -> do
    let id :: Identifier
id = forall a. Item a -> Identifier
itemIdentifier Item a
i
        empty' :: [a]
empty' = forall (m :: * -> *) a. MonadFail m => String -> m a
fail forall a b. (a -> b) -> a -> b
$ String
"No route url found for item " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show Identifier
id
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (forall b a. b -> (a -> b) -> Maybe a -> b
maybe forall {a}. [a]
empty' String -> String
toUrl) forall a b. (a -> b) -> a -> b
$ Identifier -> Compiler (Maybe String)
getRoute Identifier
id


--------------------------------------------------------------------------------
-- | Filepath of the underlying file of the item
pathField :: String -> Context a
pathField :: forall a. String -> Context a
pathField String
key = forall a. String -> (Item a -> Compiler String) -> Context a
field String
key forall a b. (a -> b) -> a -> b
$ forall (m :: * -> *) a. Monad m => a -> m a
return forall b c a. (b -> c) -> (a -> b) -> a -> c
. Identifier -> String
toFilePath forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. Item a -> Identifier
itemIdentifier


--------------------------------------------------------------------------------
-- | This title 'field' takes the basename of the underlying file by default
titleField :: String -> Context a
titleField :: forall a. String -> Context a
titleField = forall a. (String -> String) -> Context a -> Context a
mapContext String -> String
takeBaseName forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. String -> Context a
pathField


--------------------------------------------------------------------------------
-- | When the metadata has a field called @published@ in one of the
-- following formats then this function can render the date.
--
--   * @Mon, 06 Sep 2010 00:01:00 +0000@
--
--   * @Mon, 06 Sep 2010 00:01:00 UTC@
--
--   * @Mon, 06 Sep 2010 00:01:00@
--
--   * @2010-09-06T00:01:00+0000@
--
--   * @2010-09-06T00:01:00Z@
--
--   * @2010-09-06T00:01:00@
--
--   * @2010-09-06 00:01:00+0000@
--
--   * @2010-09-06 00:01:00@
--
--   * @September 06, 2010 00:01 AM@
--
-- Following date-only formats are supported too (@00:00:00@ for time is
-- assumed)
--
--   * @2010-09-06@
--
--   * @06.09.2010@
--
--   * @September 06, 2010@
--
-- Alternatively, when the metadata has a field called @path@ in a
-- @folder/yyyy-mm-dd-title.extension@ format (the convention for pages)
-- and no @published@ metadata field set, this function can render
-- the date. This pattern matches the file name or directory names
-- that begins with @yyyy-mm-dd@ . For example:
-- @folder//yyyy-mm-dd-title//dist//main.extension@ .
-- In case of multiple matches, the rightmost one is used.
--
-- As another alternative, if none of the above matches, and the file has a
-- path which contains nested directories specifying a date, then that date
-- will be used. In other words, if the path is of the form
-- @**//yyyy//mm//dd//**//main.extension@ .
-- As above, in case of multiple matches, the rightmost one is used.

dateField :: String     -- ^ Key in which the rendered date should be placed
          -> String     -- ^ Format to use on the date
          -> Context a  -- ^ Resulting context
dateField :: forall a. String -> String -> Context a
dateField = forall a. TimeLocale -> String -> String -> Context a
dateFieldWith TimeLocale
defaultTimeLocale


--------------------------------------------------------------------------------
-- | This is an extended version of 'dateField' that allows you to
-- specify a time locale that is used for outputting the date. For more
-- details, see 'dateField' and 'formatTime'.
dateFieldWith :: TimeLocale  -- ^ Output time locale
              -> String      -- ^ Destination key
              -> String      -- ^ Format to use on the date
              -> Context a   -- ^ Resulting context
dateFieldWith :: forall a. TimeLocale -> String -> String -> Context a
dateFieldWith TimeLocale
locale String
key String
format = forall a. String -> (Item a -> Compiler String) -> Context a
field String
key forall a b. (a -> b) -> a -> b
$ \Item a
i -> do
    UTCTime
time <- forall (m :: * -> *).
(MonadMetadata m, MonadFail m) =>
TimeLocale -> Identifier -> m UTCTime
getItemUTC TimeLocale
locale forall a b. (a -> b) -> a -> b
$ forall a. Item a -> Identifier
itemIdentifier Item a
i
    forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ forall t. FormatTime t => TimeLocale -> String -> t -> String
formatTime TimeLocale
locale String
format UTCTime
time


--------------------------------------------------------------------------------
-- | Parser to try to extract and parse the time from the @published@
-- field or from the filename. See 'dateField' for more information.
-- Exported for user convenience.
getItemUTC :: (MonadMetadata m, MonadFail m)
           => TimeLocale        -- ^ Output time locale
           -> Identifier        -- ^ Input page
           -> m UTCTime         -- ^ Parsed UTCTime
getItemUTC :: forall (m :: * -> *).
(MonadMetadata m, MonadFail m) =>
TimeLocale -> Identifier -> m UTCTime
getItemUTC TimeLocale
locale Identifier
id' = do
    Metadata
metadata <- forall (m :: * -> *). MonadMetadata m => Identifier -> m Metadata
getMetadata Identifier
id'
    let tryField :: String -> String -> Maybe UTCTime
tryField String
k String
fmt = String -> Metadata -> Maybe String
lookupString String
k Metadata
metadata forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
>>= String -> String -> Maybe UTCTime
parseTime' String
fmt
        paths :: [String]
paths          = String -> [String]
splitDirectories forall a b. (a -> b) -> a -> b
$ (String -> String
dropExtension forall b c a. (b -> c) -> (a -> b) -> a -> c
. Identifier -> String
toFilePath) Identifier
id'

    forall b a. b -> (a -> b) -> Maybe a -> b
maybe forall {a}. m a
empty' forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ forall (t :: * -> *) (m :: * -> *) a.
(Foldable t, MonadPlus m) =>
t (m a) -> m a
msum forall a b. (a -> b) -> a -> b
$
        [String -> String -> Maybe UTCTime
tryField String
"published" String
fmt | String
fmt <- [String]
formats] forall a. [a] -> [a] -> [a]
++
        [String -> String -> Maybe UTCTime
tryField String
"date"      String
fmt | String
fmt <- [String]
formats] forall a. [a] -> [a] -> [a]
++
        [String -> String -> Maybe UTCTime
parseTime' String
"%Y-%m-%d" forall a b. (a -> b) -> a -> b
$ forall a. [a] -> [[a]] -> [a]
intercalate String
"-" forall a b. (a -> b) -> a -> b
$ forall a. Int -> [a] -> [a]
take Int
3 forall a b. (a -> b) -> a -> b
$ String -> String -> [String]
splitAll String
"-" String
fnCand | String
fnCand <- forall a. [a] -> [a]
reverse [String]
paths] forall a. [a] -> [a] -> [a]
++
        [String -> String -> Maybe UTCTime
parseTime' String
"%Y-%m-%d" forall a b. (a -> b) -> a -> b
$ forall a. [a] -> [[a]] -> [a]
intercalate String
"-" forall a b. (a -> b) -> a -> b
$ [String]
fnCand | [String]
fnCand <- forall a b. (a -> b) -> [a] -> [b]
map (forall a. Int -> [a] -> [a]
take Int
3) forall a b. (a -> b) -> a -> b
$ forall a. [a] -> [a]
reverse forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. [a] -> [[a]]
tails forall a b. (a -> b) -> a -> b
$ [String]
paths]
  where
    empty' :: m a
empty'     = forall (m :: * -> *) a. MonadFail m => String -> m a
fail forall a b. (a -> b) -> a -> b
$ String
"Hakyll.Web.Template.Context.getItemUTC: " forall a. [a] -> [a] -> [a]
++
        String
"could not parse time for " forall a. [a] -> [a] -> [a]
++ forall a. Show a => a -> String
show Identifier
id'
    parseTime' :: String -> String -> Maybe UTCTime
parseTime' = forall (m :: * -> *) t.
(MonadFail m, ParseTime t) =>
Bool -> TimeLocale -> String -> String -> m t
parseTimeM Bool
True TimeLocale
locale
    formats :: [String]
formats    =
        [ String
"%a, %d %b %Y %H:%M:%S %Z"
        , String
"%a, %d %b %Y %H:%M:%S"
        , String
"%Y-%m-%dT%H:%M:%S%Z"
        , String
"%Y-%m-%dT%H:%M:%S"
        , String
"%Y-%m-%d %H:%M:%S%Z"
        , String
"%Y-%m-%d %H:%M:%S"
        , String
"%Y-%m-%d"
        , String
"%d.%m.%Y"
        , String
"%B %e, %Y %l:%M %p"
        , String
"%B %e, %Y"
        , String
"%b %d, %Y"
        ]


--------------------------------------------------------------------------------
-- | Get the time on which the actual file was last modified. This only works if
-- there actually is an underlying file, of couse.
getItemModificationTime
    :: Identifier
    -> Compiler UTCTime
getItemModificationTime :: Identifier -> Compiler UTCTime
getItemModificationTime Identifier
identifier = do
    Provider
provider <- CompilerRead -> Provider
compilerProvider forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> Compiler CompilerRead
compilerAsk
    forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ Provider -> Identifier -> UTCTime
resourceModificationTime Provider
provider Identifier
identifier


--------------------------------------------------------------------------------
-- | Creates a field with the last modification date of the underlying item.
modificationTimeField :: String     -- ^ Key
                      -> String     -- ^ Format
                      -> Context  a -- ^ Resulting context
modificationTimeField :: forall a. String -> String -> Context a
modificationTimeField = forall a. TimeLocale -> String -> String -> Context a
modificationTimeFieldWith TimeLocale
defaultTimeLocale


--------------------------------------------------------------------------------
-- | Creates a field with the last modification date of the underlying item
-- in a custom localisation format (see 'formatTime').
modificationTimeFieldWith :: TimeLocale  -- ^ Time output locale
                          -> String      -- ^ Key
                          -> String      -- ^ Format
                          -> Context a   -- ^ Resulting context
modificationTimeFieldWith :: forall a. TimeLocale -> String -> String -> Context a
modificationTimeFieldWith TimeLocale
locale String
key String
fmt = forall a. String -> (Item a -> Compiler String) -> Context a
field String
key forall a b. (a -> b) -> a -> b
$ \Item a
i -> do
    UTCTime
mtime <- Identifier -> Compiler UTCTime
getItemModificationTime forall a b. (a -> b) -> a -> b
$ forall a. Item a -> Identifier
itemIdentifier Item a
i
    forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ forall t. FormatTime t => TimeLocale -> String -> t -> String
formatTime TimeLocale
locale String
fmt UTCTime
mtime


--------------------------------------------------------------------------------
-- | A context with "teaser" key which contain a teaser of the item.
-- The item is loaded from the given snapshot (which should be saved
-- in the user code before any templates are applied).
teaserField :: String           -- ^ Key to use
            -> Snapshot         -- ^ Snapshot to load
            -> Context String   -- ^ Resulting context
teaserField :: String -> String -> Context String
teaserField = String -> String -> String -> Context String
teaserFieldWithSeparator String
teaserSeparator


--------------------------------------------------------------------------------
-- | A context with "teaser" key which contain a teaser of the item, defined as
-- the snapshot content before the teaser separator. The item is loaded from the
-- given snapshot (which should be saved in the user code before any templates
-- are applied).
teaserFieldWithSeparator :: String           -- ^ Separator to use
                         -> String           -- ^ Key to use
                         -> Snapshot         -- ^ Snapshot to load
                         -> Context String   -- ^ Resulting context
teaserFieldWithSeparator :: String -> String -> String -> Context String
teaserFieldWithSeparator String
separator String
key String
snapshot = forall a. String -> (Item a -> Compiler String) -> Context a
field String
key forall a b. (a -> b) -> a -> b
$ \Item String
item -> do
    String
body <- forall a. Item a -> a
itemBody forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> forall a.
(Binary a, Typeable a) =>
Identifier -> String -> Compiler (Item a)
loadSnapshot (forall a. Item a -> Identifier
itemIdentifier Item String
item) String
snapshot
    case String -> String -> Maybe String
needlePrefix String
separator String
body of
        Maybe String
Nothing -> forall (m :: * -> *) a. MonadFail m => String -> m a
fail forall a b. (a -> b) -> a -> b
$
            String
"Hakyll.Web.Template.Context: no teaser defined for " forall a. [a] -> [a] -> [a]
++
            forall a. Show a => a -> String
show (forall a. Item a -> Identifier
itemIdentifier Item String
item)
        Just String
t -> forall (m :: * -> *) a. Monad m => a -> m a
return String
t


--------------------------------------------------------------------------------
-- | Constantly reports any field as missing. Mostly for internal usage,
-- it is the last choice in every context used in a template application.
missingField :: Context a
missingField :: forall a. Context a
missingField = forall a.
(String -> [String] -> Item a -> Compiler ContextField)
-> Context a
Context forall a b. (a -> b) -> a -> b
$ \String
k [String]
_ Item a
_ -> forall a. String -> Compiler a
noResult forall a b. (a -> b) -> a -> b
$
    String
"Missing field '" forall a. [a] -> [a] -> [a]
++ String
k forall a. [a] -> [a] -> [a]
++ String
"' in context"