From 929e2a8c8186f4876114e806343e86979f542fc5 Mon Sep 17 00:00:00 2001
From: Marcel Otto <marcelotto@gmx.de>
Date: Mon, 2 Nov 2020 02:05:23 +0100
Subject: [PATCH] Use RDF.PrefixMap.prefixed_name/2 in Turtle encoder

---
 CHANGELOG.md                             |  2 ++
 lib/rdf/serializations/turtle_encoder.ex | 32 ++----------------------
 test/unit/turtle_encoder_test.exs        | 19 +++++++-------
 3 files changed, 14 insertions(+), 39 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 91cdae1..ce7d351 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,8 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 
 - more compact Inspect form for `RDF.PrefixMap`
 - the `RDF.Turtle.Encoder` accepts `RDF.Vocabulary.Namespace` modules as `base`
+- the performance of the `RDF.Turtle.Encoder` was improved (by using a more
+  efficient method for resolving IRIs to prefixed names for most use cases)
 - `RDF.BlankNode.new/0` creates integer-based blank nodes, which is much more
   efficient in terms of performance and memory consumption than the previous
   ref-based blank nodes
diff --git a/lib/rdf/serializations/turtle_encoder.ex b/lib/rdf/serializations/turtle_encoder.ex
index df92d73..97bde34 100644
--- a/lib/rdf/serializations/turtle_encoder.ex
+++ b/lib/rdf/serializations/turtle_encoder.ex
@@ -46,7 +46,6 @@ defmodule RDF.Turtle.Encoder do
     prefixes =
       Keyword.get(opts, :prefixes)
       |> prefixes(data)
-      |> init_prefixes()
 
     with {:ok, state} = State.start_link(data, base, prefixes) do
       try do
@@ -111,12 +110,6 @@ defmodule RDF.Turtle.Encoder do
   defp prefixes(nil, _), do: RDF.default_prefixes()
   defp prefixes(prefixes, _), do: PrefixMap.new(prefixes)
 
-  defp init_prefixes(prefixes) do
-    Enum.reduce(prefixes, %{}, fn {prefix, iri}, reverse ->
-      Map.put(reverse, iri, to_string(prefix))
-    end)
-  end
-
   defp base_directive(nil, _), do: ""
 
   defp base_directive({_, base}, opts) do
@@ -126,7 +119,7 @@ defmodule RDF.Turtle.Encoder do
     end <> "\n\n"
   end
 
-  defp prefix_directive({ns, prefix}, opts) do
+  defp prefix_directive({prefix, ns}, opts) do
     case Keyword.get(opts, :directive_style) do
       :sparql -> "PREFIX #{prefix}: <#{to_string(ns)}>\n"
       _ -> "@prefix #{prefix}: <#{to_string(ns)}> .\n"
@@ -390,28 +383,7 @@ defmodule RDF.Turtle.Encoder do
       }]
 
   def prefixed_name(iri, prefixes) do
-    with {ns, name} <- split_iri(iri) do
-      case prefixes[ns] do
-        nil -> nil
-        prefix -> prefix <> ":" <> name
-      end
-    end
-  end
-
-  defp split_iri(%IRI{} = iri),
-    do: iri |> IRI.parse() |> split_iri()
-
-  defp split_iri(%URI{fragment: fragment} = uri) when not is_nil(fragment),
-    do: {RDF.iri(%URI{uri | fragment: ""}), fragment}
-
-  defp split_iri(%URI{path: nil}),
-    do: nil
-
-  defp split_iri(%URI{path: path} = uri) do
-    with [{pos, _}] = Regex.run(~r"[^/]*$"u, path, return: :index),
-         {ns_path, name} = String.split_at(path, pos) do
-      {RDF.iri(%URI{uri | path: ns_path}), name}
-    end
+    PrefixMap.prefixed_name(prefixes, iri)
   end
 
   defp quoted(string) do
diff --git a/test/unit/turtle_encoder_test.exs b/test/unit/turtle_encoder_test.exs
index 95d9d9d..eba2668 100644
--- a/test/unit/turtle_encoder_test.exs
+++ b/test/unit/turtle_encoder_test.exs
@@ -5,7 +5,7 @@ defmodule RDF.Turtle.EncoderTest do
 
   doctest Turtle.Encoder
 
-  alias RDF.Graph
+  alias RDF.{Graph, PrefixMap}
   alias RDF.NS
   alias RDF.NS.{RDFS, OWL}
 
@@ -202,9 +202,9 @@ defmodule RDF.Turtle.EncoderTest do
                """
                @base <#{to_string(EX.__base_iri__())}> .
 
+               @prefix owl: <#{to_string(OWL.__base_iri__())}> .
                @prefix rdf: <#{to_string(RDF.__base_iri__())}> .
                @prefix rdfs: <#{to_string(RDFS.__base_iri__())}> .
-               @prefix owl: <#{to_string(OWL.__base_iri__())}> .
 
                <>
                    a owl:Ontology .
@@ -331,9 +331,9 @@ defmodule RDF.Turtle.EncoderTest do
       assert Turtle.Encoder.encode!(dataset) ==
                """
                @prefix ex: <http://example.org/#> .
+               @prefix owl: <http://www.w3.org/2002/07/owl#> .
                @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
                @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
-               @prefix owl: <http://www.w3.org/2002/07/owl#> .
 
                <http://other.example.com/S2>
                    a rdfs:Class .
@@ -366,10 +366,11 @@ defmodule RDF.Turtle.EncoderTest do
   describe "prefixed_name/2" do
     setup do
       {:ok,
-       prefixes: %{
-         RDF.iri(EX.__base_iri__()) => "ex",
-         ~I<http://example.org/> => "ex2"
-       }}
+       prefixes:
+         PrefixMap.new(
+           ex: EX,
+           ex2: ~I<http://example.org/>
+         )}
     end
 
     test "hash iri with existing prefix", %{prefixes: prefixes} do
@@ -383,7 +384,7 @@ defmodule RDF.Turtle.EncoderTest do
     end
 
     test "hash iri with non-existing prefix" do
-      refute Turtle.Encoder.prefixed_name(EX.foo(), %{})
+      refute Turtle.Encoder.prefixed_name(EX.foo(), PrefixMap.new())
     end
 
     test "slash iri with existing prefix", %{prefixes: prefixes} do
@@ -397,7 +398,7 @@ defmodule RDF.Turtle.EncoderTest do
     end
 
     test "slash iri with non-existing prefix" do
-      refute Turtle.Encoder.prefixed_name(~I<http://example.org/foo>, %{})
+      refute Turtle.Encoder.prefixed_name(~I<http://example.org/foo>, PrefixMap.new())
     end
   end