63 lines
2.5 KiB
Haskell
63 lines
2.5 KiB
Haskell
{-# LANGUAGE CPP #-}
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-- | This module provides the function to execute a @GraphQL@ request --
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-- according to a 'Schema'.
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module Data.GraphQL.Execute (execute) where
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#if !MIN_VERSION_base(4,8,0)
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import Control.Applicative ((<$>))
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#endif
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import Control.Applicative (Alternative)
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import Data.Maybe (catMaybes)
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import qualified Data.Aeson as Aeson
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import Data.GraphQL.AST
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import Data.GraphQL.Schema (Schema(..))
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import qualified Data.GraphQL.Schema as Schema
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import Data.GraphQL.Error
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-- | Takes a 'Schema', a variable substitution function ('Schema.Subs'), and a
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-- @GraphQL@ 'document'. The substitution is applied to the document using
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-- 'rootFields', and the 'Schema''s resolvers are applied to the resulting fields.
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--
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-- Returns the result of the query against the 'Schema' wrapped in a /data/ field, or
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-- errors wrapped in an /errors/ field.
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execute :: Alternative f
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=> Schema.Schema f -> Schema.Subs -> Document -> f Aeson.Value
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execute (Schema resolvs) subs doc = runCollectErrs res
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where res = Schema.resolvers resolvs $ rootFields subs doc
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-- | Takes a variable substitution function and a @GraphQL@ document.
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-- If the document contains one query (and no other definitions)
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-- it applies the substitution to the query's set of selections
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-- and then returns their fields.
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rootFields :: Schema.Subs -> Document -> [Field]
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rootFields subs (Document [DefinitionOperation (Query (Node _varDefs _ _ sels))]) =
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Schema.fields $ substitute subs <$> sels
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rootFields _ _ = []
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-- | Takes a variable substitution function and a selection. If the
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-- selection is a field it applies the substitution to the field's
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-- arguments using 'subsArg', and recursively applies the substitution to
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-- the arguments of fields nested in the primary field.
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substitute :: Schema.Subs -> Selection -> Selection
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substitute subs (SelectionField (Field alias name args directives sels)) =
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SelectionField $ Field
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alias
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name
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-- TODO: Get rid of `catMaybes`, invalid arguments should raise an error
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(catMaybes $ subsArg subs <$> args)
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directives
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(substitute subs <$> sels)
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substitute _ sel = sel
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-- TODO: Support different value types
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-- | Takes a variable substitution function and an argument. If the
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-- argument's value is a variable the substitution is applied to the
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-- variable's name.
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subsArg :: Schema.Subs -> Argument -> Maybe Argument
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subsArg subs (Argument n (ValueVariable (Variable v))) =
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Argument n . ValueString <$> subs v
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subsArg _ arg = Just arg
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