/// The MIT License (MIT)

/// Copyright (c) 2016 Bazinga Technologies Inc

namespace FSharp.Data.GraphQL

open System

open System.Reflection

open System.Collections.Generic

type GraphQLException(msg) =

inherit Exception(msg)

type MalformedQueryException(msg) =

inherit GraphQLException(msg)

/// General helper functions and types.

module Helpers =

/// Executes a function that returns unit, and then return its parameter again.

let tee f x = f x; x

/// Casts a System.Object to an option to a System.Object option.

let optionCast (value: obj) =

let optionDef = typedefof<option<_>>

if isNull value then None

else

let t = value.GetType()

let p = t.GetProperty("Value")

if t.IsGenericType && t.GetGenericTypeDefinition() = optionDef then

Some (p.GetValue(value, [||]))

else None

/// Matches a System.Object with an option.

/// If the object is an Option, returns it as Some, otherwise, return None.

let (|ObjectOption|_|) = optionCast

/// Lifts a System.Object to an option, unless it is already an option.

let toOption x =

match x with

| null -> None

| ObjectOption v

| v -> Some v

module internal Array =

/// <summary>

/// Returns a new array with unique elements. Uniqueness is determined by

/// output of the <paramref name="keyf"/> function.

/// </summary>

/// <param name="keyf">Function, which output is used to determine uniqueness of input elements.</param>

/// <param name="array">Array of elements.</param>

let distinctBy keyf (array:'T[]) =

let temp = Array.zeroCreate array.Length

let mutable i = 0

let hashSet = HashSet<_>(HashIdentity.Structural<_>)

for v in array do

if hashSet.Add(keyf v) then

temp.[i] <- v

i <- i + 1

Array.sub temp 0 i

module internal List =

/// <summary>

/// Merges elements of two lists, returning a new list without duplicates.

/// </summary>

/// <param name="f">Function used to determine if any two given elements are considered equal.</param>

/// <param name="listx">First list with elements to merge.</param>

/// <param name="listy">Second list with elements to merge.</param>

let mergeBy f listx listy =

let uniqx =

listx

|> List.filter (fun x -> not <| List.exists(fun y -> f(x) = f(y)) listy)

uniqx @ listy

module internal Set =

/// <summary>

/// Maps over each of the <paramref name="set"/> elements, applying function

/// over each one of them to generate new Set. Sets generated this way are

/// then flattened into single output set.

/// </summary>

/// <param name="f">Function used to generate Set from each of the input's elements.</param>

/// <param name="set">Input set.</param>

let collect f set = set |> Set.fold (fun acc e -> acc + f e) Set.empty

module internal Map =

/// <summary>

/// Merges the entries of two maps by their key, returning new map in result.

/// </summary>

/// <param name="mergeFn">

/// Function, which takes key shared by entries in both maps, first entry's value,

/// second entry's value to produce a result value used in newly generated map.

/// </param>

/// <param name="mapx">First map with elements to merge.</param>

/// <param name="mapy">Second map with elements to merge.</param>

let merge mergeFn mapx mapy =

mapy

|> Map.fold (fun acc ky vy ->

match Map.tryFind ky acc with

| Some vx -> Map.add ky (mergeFn ky vx vy) acc

| None -> Map.add ky vy acc) mapx

module internal ReflectionHelper =

/// <summary>

/// Returns pair of function constructors for `cons(head,tail)` and `nil`

/// used to create list of type <paramref name="t"/> given at runtime.

/// </summary>

/// <param name="t">Type used for result list constructors as type param</param>

let listOfType t =

let listType = typedefof<_ list>.GetTypeInfo().MakeGenericType([|t|]).GetTypeInfo()

let nil =

let empty = listType.GetDeclaredProperty "Empty"

empty.GetValue (null)

let cons =

let cons = listType.GetDeclaredMethod "Cons"

fun item list -> cons.Invoke (null, [| item; list |])

(cons, nil)

/// <summary>

/// Returns pair of function constructors for `some(value)` and `none`

/// used to create option of type <paramref name="t"/> given at runtime.

/// </summary>

/// <param name="t">Type used for result option constructors as type param</param>

let optionOfType t =

let optionType = typedefof<_ option>.GetTypeInfo().MakeGenericType([|t|]).GetTypeInfo()

let none =

let x = optionType.GetDeclaredProperty "None"

x.GetValue(null)

let some =

let createSome = optionType.GetDeclaredMethod "Some"

fun value ->

if value <> null

then

let valueType = value.GetType().GetTypeInfo()

if valueType = optionType

then value

elif t.GetTypeInfo().IsAssignableFrom(valueType)

then createSome.Invoke(null, [| value |])

else null

else none

(some, none)