From f3bc0a1d840b4ce51657897c763bf4eca80bfd13 Mon Sep 17 00:00:00 2001
From: Marcel Otto <marcelotto@gmx.de>
Date: Sat, 23 Apr 2022 01:11:09 +0200
Subject: [PATCH] Use base of graph or default_base_iri as default in encoder

---
 CHANGELOG.md               |  2 ++
 lib/json/ld/encoder.ex     | 16 ++++++++++++
 test/unit/encoder_test.exs | 50 +++++++++++++++++++++++++++++++++++++-
 3 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e7850fe..7a1b288 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,8 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 
 - context maps can be given now with atom keys or as `RDF.PropertyMap` to
   `JSON.LD.context/2` and `JSON.LD.compact/3`
+- the base IRI of a `RDF.Graph` or the `RDF.default_base_iri/0` is used as the  
+  default `:base` in the `JSON.LD.Encoder`
 - `RDF.Vocabulary.Namespace` modules can be set as base IRI 
 
 
diff --git a/lib/json/ld/encoder.ex b/lib/json/ld/encoder.ex
index 56e7ab7..6b4c41b 100644
--- a/lib/json/ld/encoder.ex
+++ b/lib/json/ld/encoder.ex
@@ -13,6 +13,8 @@ defmodule JSON.LD.Encoder do
     compaction is performed using this context
   - `:base`: : Allows to specify a base URI to be used during compaction
     (only when `:context` is provided).
+    Default is the base IRI of the encoded graph or if none present or in case of
+    encoded datasets the `RDF.default_base_iri/0`.
   - `:use_native_types`: If this flag is set to `true`, RDF literals with a datatype IRI
     that equals `xsd:integer` or `xsd:double` are converted to a JSON numbers and
     RDF literals with a datatype IRI that equals `xsd:boolean` are converted to `true`
@@ -54,12 +56,26 @@ defmodule JSON.LD.Encoder do
   @impl RDF.Serialization.Encoder
   @spec encode(RDF.Data.t(), keyword) :: {:ok, String.t()} | {:error, any}
   def encode(data, opts \\ []) do
+    opts = set_base_iri(data, opts)
+
     with {:ok, json_ld_object} <- from_rdf(data, opts),
          {:ok, json_ld_object} <- maybe_compact(json_ld_object, opts) do
       encode_json(json_ld_object, opts)
     end
   end
 
+  defp set_base_iri(%Graph{base_iri: base_iri}, opts) when not is_nil(base_iri) do
+    Keyword.put_new(opts, :base, IRI.to_string(base_iri))
+  end
+
+  defp set_base_iri(_, opts) do
+    if base = RDF.default_base_iri() do
+      Keyword.put_new(opts, :base, IRI.to_string(base))
+    else
+      opts
+    end
+  end
+
   # TODO: unless we find a way to allow more optimized encode! versions, remove this since it's never used (see the respective warning)
   @impl RDF.Serialization.Encoder
   @spec encode!(RDF.Data.t(), Options.convertible()) :: String.t()
diff --git a/test/unit/encoder_test.exs b/test/unit/encoder_test.exs
index 0987c94..fa7d8f4 100644
--- a/test/unit/encoder_test.exs
+++ b/test/unit/encoder_test.exs
@@ -3,7 +3,7 @@ defmodule JSON.LD.EncoderTest do
 
   doctest JSON.LD.Encoder
 
-  alias RDF.{Dataset, Graph, Description}
+  alias RDF.{Dataset, Graph, Description, IRI}
   alias RDF.NS
 
   import RDF.Sigils
@@ -720,6 +720,54 @@ defmodule JSON.LD.EncoderTest do
                pretty: true
              ) == expected_result
     end
+
+    test "base_iri of a RDF.Graph is used as the default for :base" do
+      context = %{
+        "p" => %{
+          "@id" => IRI.to_string(EX.p()),
+          "@type" => "@id"
+        }
+      }
+
+      assert JSON.LD.Encoder.encode!(
+               Graph.new({EX.S, EX.p(), EX.O}, base_iri: EX),
+               context: context,
+               pretty: true
+             ) ==
+               """
+               {
+                 "@context": {
+                   "p": {
+                     "@id": "#{EX.p()}",
+                     "@type": "@id"
+                   }
+                 },
+                 "@id": "S",
+                 "p": "O"
+               }
+               """
+               |> String.trim()
+
+      assert JSON.LD.Encoder.encode!(
+               Graph.new({EX.S, EX.p(), S.O}, base_iri: EX),
+               context: context,
+               base: S,
+               pretty: true
+             ) ==
+               """
+               {
+                 "@context": {
+                   "p": {
+                     "@id": "#{EX.p()}",
+                     "@type": "@id"
+                   }
+                 },
+                 "@id": "http://example.com/S",
+                 "p": "O"
+               }
+               """
+               |> String.trim()
+    end
   end
 
   describe "problems" do