defmodule Ewebmachine.Core.DSL do
  ## Macros and helpers defining the DSL for the Ewebmachine decision core :
  ## It mainly hides the `conn` and `user_state` rebindings and logic.
  ## The goal of the DSL was to mimic the one from the Basho
  ## implementation which uses the process dictionnary in order to reuse
  ## their decision core implementation.

  ## Usage : 

  ##     decision mydecision(arg1,arg2) do # def mydecision(conn,user_state,arg1,arg2)
  ##       exists? = resource_call(:resource_exists)
  ##       # here : the right module handler in found in the conn
  ##       # then conn and user_state are rebinded according to its return
  ##       d(otherdecision(arg3)) 
  ##       # if conn is halted, then return it, else call otherdecision(conn,user_state,arg3)
  ##       h(anhelper) call anhelper(conn,user_state), same as d() without the halt logic
  ##     end
  ##     helper myhelper(arg2) do :toto end #same as decision myhelper(arg2)
  @moduledoc false

  defmacro __using__(_opts) do quote do
    import Ewebmachine.Core.DSL
    import Ewebmachine.Core.API
    import Ewebmachine.Core.Utils
    @compile :nowarn_unused_vars
  end end

  def sig_to_sigwhen({:when,_,[{name,_,params},guard]}), do: {name,params,guard}
  def sig_to_sigwhen({name,_,params}) when is_list(params), do: {name,params,true}
  def sig_to_sigwhen({name,_,_}), do: {name,[],true}

  defmacro resource_call(fun) do quote do
    handler = var!(conn).private[:resource_handlers][unquote(fun)] || Ewebmachine.Handlers
    args = [var!(conn),var!(user_state)]
    {reply, myconn, myuser_state} = term = apply(handler,unquote(fun),args)
    if handler !== Ewebmachine.Handlers do 
      myconn = Ewebmachine.Log.debug_call(myconn,handler,unquote(fun),args,term)
    end
    {reply,var!(conn),var!(user_state)} = case reply do
      {:halt,code}-> #if halt, store current conn and fake reply
        {reply,_,_} = if !:erlang.function_exported(Ewebmachine.Handlers,unquote(fun),2), do: {"",[],[]}, #body producing fun
                        else: apply(Ewebmachine.Handlers,unquote(fun),[myconn,myuser_state])
        haltconn = myconn |> Plug.Conn.put_status(code) |> Ewebmachine.Log.debug_enddecision
        if !haltconn.resp_body, do: haltconn = %{haltconn|resp_body: ""}
        haltconn = %{haltconn|state: :set}
        {reply,Plug.Conn.put_private(myconn,:machine_halt_conn,haltconn),myuser_state}
      _ ->{reply,myconn,myuser_state}
    end
    reply
  end end

  defmacro helper(sig, do: body) do
    {name,params,guard} = sig_to_sigwhen(sig)
    params = (quote do: [var!(conn),var!(user_state)]) ++ params
    quote do
      def unquote(name)(unquote_splicing(params)) when unquote(guard) do
        reply = unquote(body)
        {reply,var!(conn),var!(user_state)}
      end
    end
  end

  defmacro decision(sig, do: body) do
    {name,params,guard} = sig_to_sigwhen(sig)
    params = (quote do: [var!(conn),var!(user_state)]) ++ params
    quote do
      def unquote(name)(unquote_splicing(params)) when unquote(guard) do
        var!(conn) = Ewebmachine.Log.debug_decision(var!(conn),unquote(name))
        reply = unquote(body)
        {reply,var!(conn),var!(user_state)}
      end
    end 
  end

  defmacro h(sig) do
    {name,params,_guard} = sig_to_sigwhen(sig)
    params = (quote do: [var!(conn),var!(user_state)]) ++ params
    quote do
      {reply,var!(conn),var!(user_state)} = unquote(name)(unquote_splicing(params))
      reply
    end
  end

  defmacro d(sig) when is_integer(sig) do 
    quote do d(respond(unquote(sig))) end
  end
  defmacro d(sig) do quote do
    case var!(conn) do
      %{private: %{machine_halt_conn: nil}}->var!(conn)
      %{private: %{machine_halt_conn: halt_conn}}-> var!(conn) = halt_conn
      %{halted: true}->var!(conn)
      _ -> h(unquote(sig)) ; var!(conn)
    end
  end end
end

defmodule Ewebmachine.Core.API do
  import Ewebmachine.Core.DSL
  alias Plug.Conn
  @moduledoc false

  helper method, do: 
    conn.method

  helper resp_redirect, do: 
    conn.private[:resp_redirect]

  helper get_resp_header(name), do: 
    first_or_nil(Conn.get_resp_header(conn,name))

  helper path, do: 
    conn.path_info

  helper get_header_val(name), do: 
    first_or_nil(Conn.get_req_header(conn,name))

  helper set_response_code(code) do
    conn = conn # halt machine when set response code, on respond
      |> Conn.put_private(:machine_halt_conn,nil)
      |> Conn.put_status(code)
      |> Ewebmachine.Log.debug_enddecision
    if !conn.resp_body, do: conn = %{conn|resp_body: ""}
    conn = %{conn|state: :set}
    :ok
  end

  helper set_resp_header(k,v), do: 
    (conn = Conn.put_resp_header(conn,k,v); :ok)

  helper set_resp_headers(kvs), do:
    (conn = Enum.reduce(kvs,conn,fn {k,v},acc->Conn.put_resp_header(acc,k,v) end); :ok)

  helper remove_resp_header(k), do:
    (conn = Conn.delete_resp_header(conn,k); :ok)

  helper set_disp_path(path), do:
    (conn = %{conn| script_name: String.split("#{path}","/")}; :ok)

  helper resp_body, do:
    (conn.private[:machine_body_stream] || conn.resp_body)

  helper set_resp_body(body) when is_binary(body) or is_list(body), do:
    (conn = %{conn | resp_body: body}; :ok)
  helper set_resp_body(body), do: #if not an IO List, then it should be an enumerable
    (conn = Conn.put_private(conn,:machine_body_stream,body); :ok)

  helper has_resp_body, do:
    (!is_nil(conn.resp_body) or !is_nil(conn.private[:machine_body_stream]))

  helper get_metadata(key), do:
    conn.private[key]

  helper set_metadata(k,v), do:
    (conn = Conn.put_private(conn,k,v); :ok)

  helper compute_body_md5 do
    {:ok, body, conn} = Conn.read_body(conn, length: 1_000_000)
    :crypto.hash(:md5,body)
  end

  def first_or_nil([v|_]), do: v
  def first_or_nil(_), do: nil
end

defmodule Ewebmachine.Core.Utils do
  @moduledoc "HTTP utility module"

  @type norm_content_type :: {type::String.t,subtype::String.t,params::map}

  @doc "convert any content type representation (see spec) into a `norm_content_type`"
  @spec normalize_mtype({type::String.t,params::map} | type::String.t | norm_content_type) :: norm_content_type
  def normalize_mtype({type,params}) do
    case String.split(type) do
      [type,subtype]->{type,subtype,params}
      _->{"application","octet-stream",%{}}
    end
  end
  def normalize_mtype({_,_,%{}}=mtype), do: mtype
  def normalize_mtype(type) do
    case Plug.Conn.Utils.media_type(to_string(type)) do
      {:ok,type,subtype,params}->{type,subtype,params}
      :error-> {"application","octet-stream",%{}}
    end
  end

  @doc "format a `norm_content_type` into an HTTP content type header"
  @spec format_mtype(norm_content_type) :: String.t
  def format_mtype({type,subtype,params}) do
    params = params |> Enum.map(fn {k,v}->"; #{k}=#{v}" end) |> Enum.join
    "#{type}/#{subtype}#{params}"
  end

  @doc """
  HTTP Content negociation, get the content type to send from : 

  - `accept_header`, the HTTP header `Accept`
  - `ct_provided`, the list of provided content types
  """
  @spec choose_media_type([norm_content_type],String.t) :: norm_content_type
  def choose_media_type(ct_provided,accept_header) do
    accepts = accept_header |> Plug.Conn.Utils.list |> Enum.map(fn "*"->"*/*";e->e end) |>  Enum.map(&Plug.Conn.Utils.media_type/1)
    accepts = for {:ok,type,subtype,params}<-accepts do 
      q = case Float.parse(params["q"] || "1") do {q,_}->q ; _ -> 1 end
      {q,type,subtype,Dict.delete(params,"q")}
    end |> Enum.sort |> Enum.reverse
    Enum.find_value(accepts,fn {_,atype,asubtype,aparams}->
      Enum.find(ct_provided, fn {type,subtype,params}->
        (atype=="*" or atype==type) and (asubtype=="*" or asubtype==subtype) and aparams==params
      end)
    end)
  end

  @doc "Remove quotes from HTTP quoted string"
  def quoted_string(value), do: 
    Plug.Conn.Utils.token(value)
  @doc "Get the string list from a comma separated list of HTTP quoted strings"
  def split_quoted_strings(str), do:
    (str |> Plug.Conn.Utils.list |> Enum.map(&Plug.Conn.Utils.token/1))

  @doc "Convert a calendar date to a rfc1123 date string"
  @spec rfc1123_date({{year::integer,month::integer,day::integer}, {h::integer, min::integer, sec::integer}}) :: String.t
  def rfc1123_date({{yyyy, mm, dd}, {hour, min, sec}}) do
    day_number = :calendar.day_of_the_week({yyyy, mm, dd})
    :io_lib.format('~s, ~2.2.0w ~3.s ~4.4.0w ~2.2.0w:~2.2.0w:~2.2.0w GMT',
                     [:httpd_util.day(day_number), dd, :httpd_util.month(mm),
                      yyyy, hour, min, sec]) |> IO.iodata_to_binary
  end

  @doc "Convert rfc1123 or rfc850 to :calendar dates"
  @spec convert_request_date(String.t) :: {{year::integer,month::integer,day::integer}, {h::integer, min::integer, sec::integer}}
  def convert_request_date(date) do
    try do :httpd_util.convert_request_date('#{date}') catch _,_ -> :bad_date end
  end

  @doc """
  HTTP Encoding negociation, get the encoding to use from : 

  - `acc_enc_hdr`, the HTTP header `Accept-Encoding`
  - `encs`, the list of supported encoding
  """
  @spec choose_encoding([String.t],String.t) :: String.t
  def choose_encoding(encs,acc_enc_hdr), do:
    choose(encs,acc_enc_hdr,"identity")

  @doc """
  HTTP Charset negociation, get the charset to use from : 

  - `acc_char_hdr`, the HTTP header `Accept-Charset`
  - `charsets`, the list of supported charsets
  """
  @spec choose_charset([String.t],String.t) :: String.t
  def choose_charset(charsets,acc_char_hdr), do:
    choose(charsets,acc_char_hdr,"utf8")

  defp choose(choices,header,default) do
    ## sorted set of {prio,value}
    prios = prioritized_values(header)

    # determine if default is ok or any is ok if no match
    default_prio = Enum.find_value(prios, fn {prio,v}-> v==default && prio end)
    start_prio = Enum.find_value(prios, fn {prio,v}-> v=="*" && prio end)
    default_ok = case default_prio do
      nil -> start_prio !== 0.0
      0.0 -> false
      _ -> true
    end
    any_ok = not start_prio in [nil,0.0]

    # remove choices where prio == 0.0
    {zero_prios,prios} = Enum.partition(prios,fn {prio,_}-> prio == 0.0 end)
    choices_to_remove = Enum.map(zero_prios,&elem(&1,1))
    choices = Enum.filter(choices,&!(String.downcase(&1) in choices_to_remove))

    # find first match, if not found and any_ok, then first choice, else if default_ok, take it
    if choices !== [] do
      Enum.find_value(prios, fn {_,val}->
        Enum.find(choices, &(val == String.downcase(&1)))
      end) ||
        (any_ok && hd(choices) || 
          (default_ok && Enum.find(choices,&(&1 == default)) || 
            nil))
    end
  end

  defp prioritized_values(header) do
    header 
    |> Plug.Conn.Utils.list
    |> Enum.map(fn e->
        {q,v} = case String.split(e,~r"\s;\s", parts: 2) do
          [value,params] ->
             case Float.parse(Plug.Conn.Utils.params(params)["q"] || "1.0") do
               {q,_}->{q,value}
               :error -> {1.0,value}
             end
          [value] -> {1.0,value}
        end
        {q,String.downcase(v)}
      end)
    |> Enum.sort
    |> Enum.reverse
  end
end