/// Functionality to limit HTTP requests based on header and body information.
[<AutoOpen>]
module Limit =
  /// Limits to only requests with one of the specified `Content-Type` headers,
  /// returning `406 NotAcceptable` when the request header doesn't exists in the set of specified types.
  let contentTypes contentTypes =
    fun next (ctx : HttpContext) ->
      match Option.ofObj ctx.Request.ContentType with
      | Some t when Seq.contains t contentTypes -> next ctx
      | Some _ -> RequestErrors.notAcceptable (text "request header 'Content-Type' doesn't had expected value") earlyReturn ctx
      | None -> RequestErrors.notAcceptable (text "expected to have request header 'Content-Type'") earlyReturn ctx

  /// Limits to only requests with a specific `Content-Type` header, 
  /// returning `406 NotAcceptable` when the request header value doesn't match the specified type.
  let contentType contentType = contentTypes [ contentType ]

  /// Limits request `Content-Length` header to a specified length, 
  /// returning `406 NotAcceptable` when no such header is present or the value exceeds the maximum specified length.
  let contentLength l =
    fun next (ctx : HttpContext) ->
      match Option.ofNullable (ctx.Request.GetTypedHeaders().ContentLength) with
      | Some v when v <= l ->  next ctx
      | Some _ -> RequestErrors.notAcceptable (text "request header 'Content-Length' is too large") earlyReturn ctx
      | None -> RequestErrors.notAcceptable (text "request doesn't contain 'Content-Length' header") earlyReturn ctx

  /// Limits the request body size to a specified length, returing `413 Payload Too Large` if the body size exceeds the specified maximum.
  let maxBodySize l =
    fun next (ctx : HttpContext) ->
      ctx.Features.Get<IHttpMaxRequestBodySizeFeature>().MaxRequestBodySize <- Nullable<_> l
      try next ctx
      with :? BadHttpRequestException as ex when ex.StatusCode = 413 ->
        (clearResponse >=> setStatusCode ex.StatusCode >=> text "request body too large") earlyReturn ctx