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
|
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE LambdaCase #-}
-- | This module provides a representation of a @GraphQL@ Schema in addition to
-- functions for defining and manipulating Schemas.
module Data.GraphQL.Schema
( Schema(..)
, Resolver
, Subs
, object
, objectA
, scalar
, scalarA
, array
, arrayA
, enum
, enumA
, resolvers
, fields
-- * AST Reexports
, Field
, Argument(..)
, Value(..)
) where
import Data.Bifunctor (first)
import Data.Monoid (Alt(Alt,getAlt))
import Control.Applicative (Alternative((<|>), empty))
import Data.Maybe (catMaybes)
import Data.Foldable (fold)
import qualified Data.Aeson as Aeson
import Data.HashMap.Strict (HashMap)
import qualified Data.HashMap.Strict as HashMap
import Data.Text (Text)
import qualified Data.Text as T (null, unwords)
import Data.GraphQL.AST
import Data.GraphQL.Error
-- | A GraphQL schema.
-- @f@ is usually expected to be an instance of 'Alternative'.
data Schema f = Schema [Resolver f]
-- | Resolves a 'Field' into an @Aeson.@'Aeson.Object' with error information
-- (or 'empty'). @f@ is usually expected to be an instance of 'Alternative'.
type Resolver f = Field -> CollectErrsT f Aeson.Object
-- | Variable substitution function.
type Subs = Text -> Maybe Text
-- | Create a named 'Resolver' from a list of 'Resolver's.
object :: Alternative f => Text -> [Resolver f] -> Resolver f
object name resolvs = objectA name $ \case
[] -> resolvs
_ -> empty
-- | Like 'object' but also taking 'Argument's.
objectA
:: Alternative f
=> Text -> ([Argument] -> [Resolver f]) -> Resolver f
objectA name f fld@(Field _ _ args _ sels) =
withField name (resolvers (f args) $ fields sels) fld
-- | A scalar represents a primitive value, like a string or an integer.
scalar :: (Alternative f, Aeson.ToJSON a) => Text -> a -> Resolver f
scalar name s = scalarA name $ \case
[] -> pure s
_ -> empty
-- | Like 'scalar' but also taking 'Argument's.
scalarA
:: (Alternative f, Aeson.ToJSON a)
=> Text -> ([Argument] -> f a) -> Resolver f
scalarA name f fld@(Field _ _ args _ []) = withField name (errWrap $ f args) fld
scalarA _ _ _ = empty
-- | Like 'object' but taking lists of 'Resolver's instead of a single list.
array :: Alternative f => Text -> [[Resolver f]] -> Resolver f
array name resolvs = arrayA name $ \case
[] -> resolvs
_ -> empty
-- | Like 'array' but also taking 'Argument's.
arrayA
:: Alternative f
=> Text -> ([Argument] -> [[Resolver f]]) -> Resolver f
arrayA name f fld@(Field _ _ args _ sels) =
withField name (joinErrs $ traverse (flip resolvers $ fields sels) $ f args) fld
-- | Represents one of a finite set of possible values.
-- Used in place of a 'scalar' when the possible responses are easily enumerable.
enum :: Alternative f => Text -> f [Text] -> Resolver f
enum name enums = enumA name $ \case
[] -> enums
_ -> empty
-- | Like 'enum' but also taking 'Argument's.
enumA :: Alternative f => Text -> ([Argument] -> f [Text]) -> Resolver f
enumA name f fld@(Field _ _ args _ []) = withField name (errWrap $ f args) fld
enumA _ _ _ = empty
-- | Helper function to facilitate 'Argument' handling.
withField
:: (Alternative f, Aeson.ToJSON a)
=> Text -> CollectErrsT f a -> Field -> CollectErrsT f (HashMap Text Aeson.Value)
withField name f (Field alias name' _ _ _) =
if name == name'
then fmap (first $ HashMap.singleton aliasOrName . Aeson.toJSON) f
else empty
where
aliasOrName = if T.null alias then name' else alias
-- | Takes a list of 'Resolver's and a list of 'Field's and applies each
-- 'Resolver' to each 'Field'. Resolves into a value containing the
-- resolved 'Field', or a null value and error information.
resolvers :: Alternative f => [Resolver f] -> [Field] -> CollectErrsT f Aeson.Value
resolvers resolvs =
fmap (first Aeson.toJSON . fold)
. traverse (\fld -> getAlt (foldMap (Alt . ($ fld)) resolvs) <|> errmsg fld)
where
errmsg (Field alias name _ _ _) = addErrMsg msg $ (errWrap . pure) val
where
val = HashMap.singleton aliasOrName Aeson.Null
msg = T.unwords ["field", name, "not resolved."]
aliasOrName = if T.null alias then name else alias
-- | Checks whether the given 'Selection' contains a 'Field' and
-- returns the 'Field' if so, else returns 'Nothing'.
field :: Selection -> Maybe Field
field (SelectionField x) = Just x
field _ = Nothing
-- | Returns a list of the 'Field's contained in the given 'SelectionSet'.
fields :: SelectionSet -> [Field]
fields = catMaybes . fmap field
|
