summaryrefslogtreecommitdiff
path: root/lib/Hakyll/Web/Html.hs
blob: fc3deaa2ae70102d0ec53db093929643750cfe14 (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
188
--------------------------------------------------------------------------------
-- | Provides utilities to manipulate HTML pages
module Hakyll.Web.Html
    ( -- * Generic
      withTags
    , withTagList

      -- * Headers
    , demoteHeaders

      -- * Url manipulation
    , getUrls
    , withUrls
    , toUrl
    , toSiteRoot
    , isExternal

      -- * Stripping/escaping
    , stripTags
    , escapeHtml
    ) where


--------------------------------------------------------------------------------
import           Data.Char                       (digitToInt, intToDigit,
                                                  isDigit, toLower)
import           Data.List                       (isPrefixOf)
import qualified Data.Set                        as S
import           System.FilePath.Posix           (joinPath, splitPath,
                                                  takeDirectory)
import           Text.Blaze.Html                 (toHtml)
import           Text.Blaze.Html.Renderer.String (renderHtml)
import qualified Text.HTML.TagSoup               as TS
import           Network.URI                     (isUnreserved, escapeURIString)


--------------------------------------------------------------------------------
-- | Map over all tags in the document
withTags :: (TS.Tag String -> TS.Tag String) -> String -> String
withTags = withTagList . map

-- | Map over all tags (as list) in the document
withTagList :: ([TS.Tag String] -> [TS.Tag String]) -> String -> String
withTagList f = renderTags' . f . parseTags'

--------------------------------------------------------------------------------
-- | Map every @h1@ to an @h2@, @h2@ to @h3@, etc.
demoteHeaders :: String -> String
demoteHeaders = withTags $ \tag -> case tag of
    TS.TagOpen t a -> TS.TagOpen (demote t) a
    TS.TagClose t  -> TS.TagClose (demote t)
    t              -> t
  where
    demote t@['h', n]
        | isDigit n = ['h', intToDigit (min 6 $ digitToInt n + 1)]
        | otherwise = t
    demote t        = t


--------------------------------------------------------------------------------
isUrlAttribute :: String -> Bool
isUrlAttribute = (`elem` ["src", "href", "data", "poster"])


--------------------------------------------------------------------------------
getUrls :: [TS.Tag String] -> [String]
getUrls tags = [v | TS.TagOpen _ as <- tags, (k, v) <- as, isUrlAttribute k]


--------------------------------------------------------------------------------
-- | Apply a function to each URL on a webpage
withUrls :: (String -> String) -> String -> String
withUrls f = withTags tag
  where
    tag (TS.TagOpen s a) = TS.TagOpen s $ map attr a
    tag x                = x
    attr (k, v)          = (k, if isUrlAttribute k then f v else v)


--------------------------------------------------------------------------------
-- | Customized TagSoup renderer. The default TagSoup renderer escape CSS
-- within style tags, and doesn't properly minimize.
renderTags' :: [TS.Tag String] -> String
renderTags' = TS.renderTagsOptions TS.RenderOptions
    { TS.optRawTag   = (`elem` ["script", "style"]) . map toLower
    , TS.optMinimize = (`S.member` minimize) . map toLower
    , TS.optEscape   = id
    }
  where
    -- A list of elements which must be minimized
    minimize = S.fromList
        [ "area", "br", "col", "embed", "hr", "img", "input", "meta", "link"
        , "param"
        ]


--------------------------------------------------------------------------------
-- | Customized TagSoup parser: do not decode any entities.
parseTags' :: String -> [TS.Tag String]
parseTags' = TS.parseTagsOptions (TS.parseOptions :: TS.ParseOptions String)
    { TS.optEntityData   = \(str, b) -> [TS.TagText $ "&" ++ str ++ [';' | b]]
    , TS.optEntityAttrib = \(str, b) -> ("&" ++ str ++ [';' | b], [])
    }


--------------------------------------------------------------------------------
-- | Convert a filepath to an URL starting from the site root
--
-- Example:
--
-- > toUrl "foo/bar.html"
--
-- Result:
--
-- > "/foo/bar.html"
--
-- This also sanitizes the URL, e.g. converting spaces into '%20'
toUrl :: FilePath -> String
toUrl url = case url of
    ('/' : xs) -> '/' : sanitize xs
    xs         -> '/' : sanitize xs
  where
    -- Everything but unreserved characters should be escaped as we are
    -- sanitising the path therefore reserved characters which have a
    -- meaning in URI does not appear. Special casing for `/`, because it has
    -- a special meaning in FilePath as well as in URI.
    sanitize = escapeURIString (\c -> c == '/' || isUnreserved c)


--------------------------------------------------------------------------------
-- | Get the relative url to the site root, for a given (absolute) url
toSiteRoot :: String -> String
toSiteRoot = emptyException . joinPath . map parent
           . filter relevant . splitPath . takeDirectory
  where
    parent            = const ".."
    emptyException [] = "."
    emptyException x  = x
    relevant "."      = False
    relevant "/"      = False
    relevant "./"     = False
    relevant _        = True


--------------------------------------------------------------------------------
-- | Check if an URL links to an external HTTP(S) source
isExternal :: String -> Bool
isExternal url = any (flip isPrefixOf url) ["http://", "https://", "//"]


--------------------------------------------------------------------------------
-- | Strip all HTML tags from a string
--
-- Example:
--
-- > stripTags "<p>foo</p>"
--
-- Result:
--
-- > "foo"
--
-- This also works for incomplete tags
--
-- Example:
--
-- > stripTags "<p>foo</p"
--
-- Result:
--
-- > "foo"
stripTags :: String -> String
stripTags []         = []
stripTags ('<' : xs) = stripTags $ drop 1 $ dropWhile (/= '>') xs
stripTags (x : xs)   = x : stripTags xs


--------------------------------------------------------------------------------
-- | HTML-escape a string
--
-- Example:
--
-- > escapeHtml "Me & Dean"
--
-- Result:
--
-- > "Me &amp; Dean"
escapeHtml :: String -> String
escapeHtml = renderHtml . toHtml