defmodule Monet.Reader do
	@moduledoc """
	Reads and parses responses from the server. Should not be called directly from
	outside this library.
	"""
	use Bitwise, only: [bsr: 2, band: 1]

	import NimbleParsec
	import Monet.Connection, only: [connection: 2]

	alias Monet.{Error, Result, Prepared}

	@doc "Reads the result from a query"
	def result(conn) do
		with {:ok, payload} <- message(conn, nil) do
			parse_result(payload, conn)
		end
	end

	@doc "Reads a single message"
	def message(conn, acc \\ nil) do
		conn
		|> read_n(2)
		|> payload(conn, acc)
	end

	defp payload({:ok, <<1, 0>>}, _conn, _acc), do: {:ok, ""}

	defp payload({:ok, <<header::little-16>>}, conn, acc) do
		len = bsr(header, 1)
		fin = band(header, 1)

		case read_n(conn, len) do
			{:ok, <<"!", rest::binary>>} -> monet_error(rest)
			{:ok, data} ->
				cond do
					fin == 0 -> message(conn, [acc || [], data])
					acc == nil -> {:ok, data}
					true -> {:ok, :erlang.iolist_to_binary([acc, data])}
				end
			err -> err
		end
	end

	defp payload({:error, err}, _conn, _acc) do
		{:error, Error.new(:network, err)}
	end

	defp monet_error(<<err::binary>>) do
		{message, code} = case Integer.parse(err) do
			{code, <<?!, message::binary>>} -> {message, code}
			_ -> {err, nil}
		end
		{:error, %Error{source: :monetd, message: message, code: code}}
	end

	defp read_n(conn, n) do
		socket = connection(conn, :socket)
		timeout = connection(conn, :read_timeout)
		:gen_tcp.recv(socket, n, timeout)
	end

	# result from a select
	defp parse_result(<<"&1 ", data::binary>>, _conn) do
		case String.split(data, "\n", parts: 6) do
			[header, _tables, columns, types, _length, rows] ->
				with {:ok, types} <- parse_result_types(types),
						 {:ok, row_count, header} <- parse_result_header(header),
						 {:ok, columns} <- parse_result_columns(columns),
						 {:ok, rows} <- parse_result_rows(row_count, types, rows)
				do
					{:ok, Result.new(header, columns, rows, row_count)}
				end
			_ -> {:error, Error.new(:driver, "invalid query response", data)}
		end
	end

	# result from an insert or update
	defp parse_result(<<"&2 ", data::binary>>, _conn) do
		with {row_count, <<" ", rest::binary>>} <- Integer.parse(data),
				 {last_id, _} <- Integer.parse(rest)
		do
			{:ok, Result.upsert(data, row_count, last_id)}
		else
			_ -> {:error, Error.new(:driver, "invalid insert/update result", data)}
		end
	end

	# result from a create or drop
	defp parse_result(<<"&3 ", data::binary>>, _conn) do
		case :binary.split(data, "\n") do
			[_, <<"!", rest::binary>>] -> monet_error(rest)
			_ -> {:ok, Result.meta(String.trim_trailing(data))}
		end
	end

	# Result from a transaction. We expect it to be in auto-commit false (hence the f)
	defp parse_result("&4 f\n", _conn) do
		{:ok, Result.meta("&4 f")}
	end

	# result from a prepared request
	defp parse_result(<<"&5 ", _::binary>> = data, conn) do
		Prepared.build(conn, data)
	end

	# result from a QBLOCK ??
	defp parse_result(<<"&6 ", _data::binary>>, _conn) do
		raise "QBLOCK result parsing not implemented"
	end

	defp parse_result(unknown, _conn) do
		{:error, Error.new(:driver, "unknown query result", unknown)}
	end

	defp parse_result_types(types) do
		l = byte_size(types) - 9
		case types do
			<<"% ", types::bytes-size(l), " # type">> -> {:ok, types |> String.split(",\t") |> Enum.map(&String.to_atom/1)}
			_ -> {:error, Error.new(:driver, "invalid result type header", types)}
		end
	end

	defp parse_result_header(header) do
		with [_query_id, rest] <- :binary.split(header, " "),
				 {row_count, _} <- Integer.parse(rest)
		do
			{:ok, row_count, header}
		else
			_ -> {:error, Error.new(:driver, "invalid result header", header)}
		end
	end

	defp parse_result_columns(columns) do
		l = byte_size(columns) - 9
		case columns do
			<<"% ", columns::bytes-size(l), " # name">> -> {:ok, String.split(columns, ",\t")}
			_ -> {:error, Error.new(:driver, "invalid result columns header", columns)}
		end
	end

	defp parse_result_rows(0, _types, _data), do: {:ok, []}

	defp parse_result_rows(_row_count, types, data) do
		do_parse_result_rows(types, data, [])
	end

	defp do_parse_result_rows(types, data, acc) do
		case parse_row(types, data) do
			{:ok, "", row} -> {:ok, Enum.reverse([row | acc])}
			{:ok, rest, row} -> do_parse_result_rows(types, rest, [row | acc])
			err -> err
		end
	end

	# first value in the row, strip out the leading "[ "
	defp parse_row(types, <<"[ ", data::binary>>) do
		parse_row(types, data, [])
	end

	defp parse_row(_types, data) do
		{:error, Error.new(:driver, "invalid row prefix", data)}
	end

	# last value in the row, special handling to strip out the trailing data
	defp parse_row([type], <<data::binary>>, row) do
		case parse_value(type, data) do
			{:ok, <<"\t]\n", rest::binary>>, value} -> {:ok, rest, Enum.reverse([value | row])}
			{:ok, {:text, <<"]\n", rest::binary>>}, value} -> {:ok, rest, Enum.reverse([value | row])}
			{:ok, _, _} -> {:error, Error.new(:driver, "invalid row terminator", data)}
			err -> err
		end
	end

	defp parse_row([type | types], <<data::binary>>, row) do
		case parse_value(type, data) do
			{:ok, <<",\t", rest::binary>>, value} -> parse_row(types, rest, [value | row])
			{:ok, {:text, <<rest::binary>>}, value} -> parse_row(types, rest, [value | row])
			{:ok, _, _value} -> {:error, Error.new(:driver, "invalid value separator", data)}
			err -> err
		end
	end

	defp parse_value(_type, <<"NULL", rest::binary>>), do: {:ok, rest, nil}

	defp parse_value(type, data) when type in [:int, :tinyint, :bigint, :hugeint, :oid, :smallint, :serial] do
		case Integer.parse(data) do
			{value, rest} -> {:ok, rest, value}
			:error -> {:error, Error.new(:driver, "invalid integer", data)}
		end
	end

	defp parse_value(type, data) when type in [:double, :float, :real] do
		case Float.parse(data) do
			{value, rest} -> {:ok, rest, value}
			:error -> {:error, Error.new(:driver, "invalid float", data)}
		end
	end

	defp parse_value(:decimal, data) do
		{value, rest} = extract_token(data)
		case Decimal.parse(value) do
			{:ok, value} -> {:ok, rest, value}
			:error -> {:error, Error.new(:driver, "invalid decimal", data)}
		end
	end

	defp parse_value(:boolean, <<"true", rest::binary>>), do: {:ok, rest, true}
	defp parse_value(:boolean, <<"false", rest::binary>>), do: {:ok, rest, false}
	defp parse_value(:boolean, invalid), do: {:error, Error.new(:driver, "invalid boolean", invalid)}

	@string_types [:char, :varchar, :clob, :text, :json]
	defp parse_value(type, <<?", data::binary>>) when type in @string_types do
		# Unlike the other functions, this actually strips out the trailing delimiter
		# (the "\t" or ",\t" depending on if it's the last column or not).
		# This breaks a lot of our parsing since we expect "rest" to not be consumed.
		# To solve this, and to avoid re-concatenating the separator, we return a special
		# "rest" of {:text, rest} which the other parses can special case.

		[string, rest] = :binary.split(data, "\t")
		{:ok, {:text, rest}, string |> parse_string() |> :erlang.iolist_to_binary()}
	end

	defp parse_value(type, invalid) when type in @string_types do
		{:error, Error.new(:driver, "invalid string prefix", invalid)}
	end

	defp parse_value(:uuid, <<uuid::bytes-size(36), rest::binary>>) do
		{:ok, rest, uuid}
	end

	defp parse_value(:blob, data) do
		{value, rest} = extract_token(data)
		case Base.decode16(value) do
			{:ok, value} -> {:ok, rest, value}
			:error -> {:error, Error.new(:driver, "invalid blob", data)}
		end
	end

	defp parse_value(:time, data) do
		with {:ok, data, rest, _, _, _} <- extract_time(data),
				 {:ok, time} <- build_time(data)
		do
			{:ok, rest, time}
		else
			_ -> {:error, Error.new(:driver, "invalid time", data)}
		end
	end

	# MonetDB strips out any leading zeros from the year, so we can't use Date.from_iso8601
	defp parse_value(:date, data) do
		with {:ok, [year, month, day], rest, _, _, _} <- extract_date(data),
				 {:ok, date} <- Date.new(year, month, day)
		do
			{:ok, rest, date}
		else
			_ -> {:error, Error.new(:driver, "invalid date", data)}
		end
	end

	defp parse_value(:timestamp, data) do
		with {:ok, <<" ", rest::binary>>, date} <- parse_value(:date, data),
				 {:ok, rest, time} <- parse_value(:time, rest),
				 {:ok, datetime} <- NaiveDateTime.new(date, time)
		do
			{:ok, rest, datetime}
		else
			_ -> {:error, Error.new(:driver, "invalid timestamp", data)}
		end
	end

	# I'm pretty this timezone stuff isn't right
	defp parse_value(:timestamptz, data) do
		with {:ok, <<" ", rest::binary>>, date} <- parse_value(:date, data),
				 {:ok, rest, time} <- parse_value(:time, rest),
				 {:ok, time_zone, rest, _, _, _} <- extract_time_zone(rest)
		do
			{timezone, abbreviation, offset} = build_time_zone(time_zone)
			datetime = %DateTime{
				year: date.year,
				month: date.month,
				day: date.day,
				hour: time.hour,
				minute: time.minute,
				second: time.second,
				microsecond: time.microsecond,
				utc_offset: offset,
				std_offset: 0, # ??
				time_zone: timezone,
				zone_abbr: abbreviation,
			}
			{:ok, rest, datetime}
		else
			_ -> {:error, Error.new(:driver, "invalid timestamptz", data)}
		end
	end


	defp parse_value(type, data) do
		{:error, Error.new(:driver, "unsupported type: #{type}", data)}
	end

	# We don't have to do a perfect job here, just need to figure out the boundaries.
	# The problem with :binary.split is that:
	#  a) we want to keep the separator/terminator to keep everything consistent
	#  b) the separator/terminator can be 2 different things
	defp extract_token(<<data::binary>>) do
		len = token_length(data, 0)
		<<value::bytes-size(len), rest::binary>> = data
		{value, rest}
	end
	defp token_length(<<?,, _rest::binary>>, len), do: len
	defp token_length(<<?\t, _rest::binary>>, len), do: len
	defp token_length(<<_, rest::binary>>, len), do: token_length(rest, len + 1)

	defp parse_string(data, acc \\ []) do
		case :binary.split(data, "\\") do
			[text, <<?e, rest::binary>>] -> parse_string(rest, [acc, text, ?\e])
			[text, <<?f, rest::binary>>] -> parse_string(rest, [acc, text, ?\f])
			[text, <<?n, rest::binary>>] -> parse_string(rest, [acc, text, ?\n])
			[text, <<?r, rest::binary>>] -> parse_string(rest, [acc, text, ?\r])
			[text, <<?t, rest::binary>>] -> parse_string(rest, [acc, text, ?\t])
			[text, <<?v, rest::binary>>] -> parse_string(rest, [acc, text, ?\v])
			[text, <<?\\, rest::binary>>] -> parse_string(rest, [acc, text, ?\\])
			[text, <<?', rest::binary>>] -> parse_string(rest, [acc, text, ?'])
			[text, <<?", rest::binary>>] -> parse_string(rest, [acc, text, ?"])
			[text] ->
				# The last chunk can be terminated with either '"' or '",' depending
				# on whether or not it's the last column. Strip it either way.
				len1 = byte_size(text) - 1
				len2 = len1 - 1
				case text do
					<<text::bytes-size(len1), ?">> -> [acc, text]
					<<text::bytes-size(len2), ~s(",)>> -> [acc, text]
				end
		end
	end

	defp build_time([hour, minute, seconds]) do
		Time.new(hour, minute, seconds)
	end

	defp build_time([hour, minute, seconds, milli]) do
		Time.new(hour, minute, seconds, {milli * 1000, 3})
	end

	defp build_time([hour, minute, seconds, milli, micro]) do
		Time.new(hour, minute, seconds, {milli * 1000 + micro, 6})
	end

	@utc {"Etc/UTC", "UTC", 0}
	defp build_time_zone(["z"]), do: @utc
	defp build_time_zone(["Z"]), do: @utc
	defp build_time_zone(["+00:00"]), do: @utc
	defp build_time_zone(["-00:00"]), do: @utc
	defp build_time_zone([sign, hh, mm]) do
		time = "#{sign}#{hh}:#{mm}"
		hours = String.to_integer(hh)
		minutes = String.to_integer(mm)

		offset = hours * 3600 + minutes * 60
		offset = case sign do
			"+" -> offset
			"-" -> -offset
		end

		{"Etc/UTC" <> time, time, offset}
	end

	date =
		integer(min: 1, max: 4)
		|> ignore(string("-"))
		|> integer(2)
		|> ignore(string("-"))
		|> integer(2)

	time =
		integer(2)
		|> ignore(string(":"))
		|> integer(2)
		|> ignore(string(":"))
		|> integer(2)
		|> optional(
			ignore(string("."))
			|> integer(3)
			|> optional(integer(3))
		)

	time_zone =
		choice([
			string("z"),
			string("Z"),
			string("+00:00"),
			string("-00:00"),
			string("+") |> integer(2) |> ignore(string(":")) |> integer(2),
			string("-") |> integer(2) |> ignore(string(":")) |> integer(2)
		])

	defparsec :extract_date, date, inline: true
	defparsec :extract_time, time, inline: true
	defparsec :extract_time_zone, time_zone, inline: true
end