-- | This module defines an abstract syntax tree for the @GraphQL@ language based on
--   <https://facebook.github.io/graphql/ Facebook's GraphQL Specification>.

module Data.GraphQL.AST where

import Data.Int (Int32)
import Data.String (IsString(fromString))
import Data.Text (Text, pack)

-- * Name

type Name = Text

-- * Document

newtype Document = Document [Definition] deriving (Eq,Show)

data Definition = DefinitionOperation OperationDefinition
                | DefinitionFragment  FragmentDefinition
                  deriving (Eq,Show)

data OperationDefinition = Query    Node
                         | Mutation Node
                           deriving (Eq,Show)

data Node = Node Name [VariableDefinition] [Directive] SelectionSet
            deriving (Eq,Show)

data VariableDefinition = VariableDefinition Variable Type (Maybe DefaultValue)
                          deriving (Eq,Show)

newtype Variable = Variable Name deriving (Eq,Show)

instance IsString Variable where
    fromString = Variable . pack

type SelectionSet = [Selection]

data Selection = SelectionField Field
               | SelectionFragmentSpread FragmentSpread
               | SelectionInlineFragment InlineFragment
                 deriving (Eq,Show)

-- | A 'SelectionSet' is primarily composed of 'Field's. A 'Field' describes one
--   discrete piece of information available to request within a 'SelectionSet'.
--
--   Some 'Field's describe complex data or relationships to other data. In
--   order to further explore this data, a 'Field' may itself contain a
--   'SelectionSet', allowing for deeply nested requests. All @GraphQL@ operations
--   must specify their 'Selection's down to 'Field's which return scalar values to
--   ensure an unambiguously shaped response.
--
--   <https://facebook.github.io/graphql/#sec-Language.Query-Document.Fields Field Specification>
data Field = Field Alias Name [Argument] [Directive] SelectionSet
             deriving (Eq,Show)

type Alias = Name

-- | 'Field's are conceptually functions which return values, and occasionally accept
--   'Argument's which alter their behavior. These 'Argument's often map directly to
--   function arguments within a @GraphQL@ server’s implementation.
--
--   <https://facebook.github.io/graphql/#sec-Language.Query-Document.Arguments Argument Specification>
data Argument = Argument Name Value deriving (Eq,Show)

-- * Fragments

data FragmentSpread = FragmentSpread Name [Directive]
                      deriving (Eq,Show)

data InlineFragment =
    InlineFragment TypeCondition [Directive] SelectionSet
    deriving (Eq,Show)

data FragmentDefinition =
    FragmentDefinition Name TypeCondition [Directive] SelectionSet
    deriving (Eq,Show)

type TypeCondition = NamedType

-- * Values

-- | 'Field' and 'Directive' 'Arguments' accept input values of various literal
--   primitives; input values can be scalars, enumeration values, lists, or input
--   objects.
--
--   If not defined as constant (for example, in 'DefaultValue'), input values
--   can be specified as a 'Variable'. List and inputs objects may also contain
--   'Variable's (unless defined to be constant).
--
--   <https://facebook.github.io/graphql/#sec-Input-Values Input Value Specification>
data Value = ValueVariable Variable
           | ValueInt Int32
           -- GraphQL Float is double precison
           | ValueFloat Double
           | ValueBoolean Bool
           | ValueString Text
           | ValueEnum Name
           | ValueList ListValue
           | ValueObject ObjectValue
             deriving (Eq,Show)

newtype ListValue = ListValue [Value] deriving (Eq,Show)

newtype ObjectValue = ObjectValue [ObjectField] deriving (Eq,Show)

data ObjectField = ObjectField Name Value deriving (Eq,Show)

type DefaultValue = Value

-- * Directives

data Directive = Directive Name [Argument] deriving (Eq,Show)

-- * Type Reference

data Type = TypeNamed NamedType
          | TypeList ListType
          | TypeNonNull NonNullType
            deriving (Eq,Show)

newtype NamedType = NamedType Name deriving (Eq,Show)

newtype ListType = ListType Type deriving (Eq,Show)

data NonNullType = NonNullTypeNamed NamedType
                 | NonNullTypeList  ListType
                   deriving (Eq,Show)