From 426b6d832c0277878f810d3a6e7742f237778988 Mon Sep 17 00:00:00 2001
From: Marcel Otto <marcelotto@gmx.de>
Date: Wed, 4 Nov 2020 20:43:19 +0100
Subject: [PATCH] Add RDF.NTriples.Encoder.stream/2

---
 lib/rdf/serializations/ntriples_encoder.ex | 51 ++++++++++++++++++----
 test/unit/ntriples_encoder_test.exs        | 31 +++++++++++++
 2 files changed, 73 insertions(+), 9 deletions(-)

diff --git a/lib/rdf/serializations/ntriples_encoder.ex b/lib/rdf/serializations/ntriples_encoder.ex
index ef7cff5..5fff37c 100644
--- a/lib/rdf/serializations/ntriples_encoder.ex
+++ b/lib/rdf/serializations/ntriples_encoder.ex
@@ -3,26 +3,33 @@ defmodule RDF.NTriples.Encoder do
 
   use RDF.Serialization.Encoder
 
-  alias RDF.{BlankNode, IRI, XSD, Literal, Statement, Triple, LangString}
+  alias RDF.{Triple, Term, IRI, BlankNode, Literal, LangString, XSD}
 
   @impl RDF.Serialization.Encoder
   @callback encode(RDF.Data.t(), keyword) :: {:ok, String.t()} | {:error, any}
   def encode(data, _opts \\ []) do
-    result =
-      data
-      |> Enum.reduce([], &[statement(&1) | &2])
-      |> Enum.reverse()
-      |> Enum.join("\n")
+    {:ok,
+     data
+     |> Enum.reduce([], &[statement(&1) | &2])
+     |> Enum.reverse()
+     |> Enum.join()}
+  end
 
-    {:ok, if(result == "", do: result, else: result <> "\n")}
+  @impl RDF.Serialization.Encoder
+  @spec stream(RDF.Data.t(), keyword) :: Enumerable.t()
+  def stream(data, opts \\ []) do
+    case Keyword.get(opts, :mode, :string) do
+      :string -> Stream.map(data, &statement(&1))
+      :iodata -> Stream.map(data, &iolist_statement(&1))
+    end
   end
 
   @spec statement(Triple.t()) :: String.t()
   def statement({subject, predicate, object}) do
-    "#{term(subject)} #{term(predicate)} #{term(object)} ."
+    "#{term(subject)} #{term(predicate)} #{term(object)} .\n"
   end
 
-  @spec term(Statement.subject() | Statement.predicate() | Statement.object()) :: String.t()
+  @spec term(Term.t()) :: String.t()
   def term(%IRI{} = iri) do
     "<#{to_string(iri)}>"
   end
@@ -42,4 +49,30 @@ defmodule RDF.NTriples.Encoder do
   def term(%BlankNode{} = bnode) do
     to_string(bnode)
   end
+
+  @spec iolist_statement(Triple.t()) :: iolist
+  def iolist_statement({subject, predicate, object}) do
+    [iolist_term(subject), " ", iolist_term(predicate), " ", iolist_term(object), " .\n"]
+  end
+
+  @spec iolist_term(Term.t()) :: String.t()
+  def iolist_term(%IRI{} = iri) do
+    ["<", iri.value, ">"]
+  end
+
+  def iolist_term(%Literal{literal: %LangString{} = lang_string}) do
+    [~s["], lang_string.value, ~s["@], lang_string.language]
+  end
+
+  def iolist_term(%Literal{literal: %XSD.String{} = xsd_string}) do
+    [~s["], xsd_string.value, ~s["]]
+  end
+
+  def iolist_term(%Literal{} = literal) do
+    [~s["], Literal.lexical(literal), ~s["^^<], to_string(Literal.datatype_id(literal)), ">"]
+  end
+
+  def iolist_term(%BlankNode{} = bnode) do
+    to_string(bnode)
+  end
 end
diff --git a/test/unit/ntriples_encoder_test.exs b/test/unit/ntriples_encoder_test.exs
index cf4850b..c6ff263 100644
--- a/test/unit/ntriples_encoder_test.exs
+++ b/test/unit/ntriples_encoder_test.exs
@@ -14,6 +14,10 @@ defmodule RDF.NTriples.EncoderTest do
 
   defvocab EX, base_iri: "http://example.org/#", terms: [], strict: false
 
+  test "stream_support?/0" do
+    assert NTriples.Encoder.stream_support?()
+  end
+
   describe "serializing a graph" do
     test "an empty graph is serialized to an empty string" do
       assert NTriples.Encoder.encode!(Graph.new()) == ""
@@ -68,4 +72,31 @@ defmodule RDF.NTriples.EncoderTest do
                """
     end
   end
+
+  describe "stream/2" do
+    graph =
+      Graph.new([
+        {EX.S1, EX.p1(), EX.O1},
+        {EX.S2, EX.p2(), RDF.bnode("foo")},
+        {EX.S3, EX.p3(), ~L"foo"},
+        {EX.S3, EX.p3(), ~L"foo"en}
+      ])
+
+    expected_result = """
+    <http://example.org/#S1> <http://example.org/#p1> <http://example.org/#O1> .
+    <http://example.org/#S2> <http://example.org/#p2> _:foo .
+    <http://example.org/#S3> <http://example.org/#p3> "foo"@en .
+    <http://example.org/#S3> <http://example.org/#p3> "foo" .
+    """
+
+    assert NTriples.Encoder.stream(graph, mode: :string)
+           |> Enum.to_list()
+           |> IO.iodata_to_binary() ==
+             expected_result
+
+    assert NTriples.Encoder.stream(graph, mode: :iodata)
+           |> Enum.to_list()
+           |> IO.iodata_to_binary() ==
+             expected_result
+  end
 end