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diff --git a/src/asciideck_line_reader.erl b/src/asciideck_line_reader.erl
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+++ b/src/asciideck_line_reader.erl
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+%% Copyright (c) 2017-2018, Loïc Hoguin <[email protected]>
+%%
+%% Permission to use, copy, modify, and/or distribute this software for any
+%% purpose with or without fee is hereby granted, provided that the above
+%% copyright notice and this permission notice appear in all copies.
+%%
+%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+-module(asciideck_line_reader).
+-behaviour(gen_server).
+
+%% API.
+-export([start_link/1]).
+-export([read_line/1]).
+-export([get_position/1]).
+-export([set_position/2]).
+
+%% gen_server.
+-export([init/1]).
+-export([handle_call/3]).
+-export([handle_cast/2]).
+-export([handle_info/2]).
+-export([terminate/2]).
+-export([code_change/3]).
+
+-record(state, {
+	lines :: [binary()],
+	length :: non_neg_integer(),
+	pos = 1 :: non_neg_integer()
+}).
+
+%% API.
+
+-spec start_link(binary()) -> {ok, pid()}.
+start_link(Data) ->
+	gen_server:start_link(?MODULE, [Data], []).
+
+-spec read_line(pid()) -> binary() | eof.
+read_line(Pid) ->
+	gen_server:call(Pid, read_line).
+
+%% @todo peek_line
+
+-spec get_position(pid()) -> pos_integer().
+get_position(Pid) ->
+	gen_server:call(Pid, get_position).
+
+-spec set_position(pid(), pos_integer()) -> ok.
+set_position(Pid, Pos) ->
+	gen_server:cast(Pid, {set_position, Pos}).
+
+%% gen_server.
+
+init([Data]) ->
+	Lines0 = binary:split(Data, <<"\n">>, [global]),
+	%% We add an empty line at the end to simplify parsing.
+	%% This has the inconvenient that when parsing blocks
+	%% this empty line will be included in the result if
+	%% the block is not properly closed.
+	Lines = lists:append(Lines0, [<<>>]),
+	{ok, #state{lines=Lines, length=length(Lines)}}.
+
+handle_call(read_line, _From, State=#state{length=Length, pos=Pos})
+		when Pos > Length ->
+	{reply, eof, State};
+%% @todo I know this isn't the most efficient. We could keep
+%% the lines read separately and roll back when set_position
+%% wants us to. But it works fine for now.
+handle_call(read_line, _From, State=#state{lines=Lines, pos=Pos}) ->
+	{reply, lists:nth(Pos, Lines), State#state{pos=Pos + 1}};
+handle_call(get_position, _From, State=#state{pos=Pos}) ->
+	{reply, Pos, State};
+handle_call(_Request, _From, State) ->
+	{reply, ignored, State}.
+
+handle_cast({set_position, Pos}, State) ->
+	{noreply, State#state{pos=Pos}};
+handle_cast(_Msg, State) ->
+	{noreply, State}.
+
+handle_info(_Info, State) ->
+	{noreply, State}.
+
+terminate(_Reason, _State) ->
+	ok.
+
+code_change(_OldVsn, State, _Extra) ->
+	{ok, State}.