rdf-ex/lib/rdf/serializations/turtle_encoder.ex
2018-09-17 02:08:16 +02:00

368 lines
11 KiB
Elixir

defmodule RDF.Turtle.Encoder do
@moduledoc false
use RDF.Serialization.Encoder
alias RDF.Turtle.Encoder.State
alias RDF.{IRI, Literal, BlankNode, Description}
@indentation_char " "
@indentation 4
@native_supported_datatypes [
RDF.Datatype.NS.XSD.boolean,
RDF.Datatype.NS.XSD.integer,
RDF.Datatype.NS.XSD.double,
RDF.Datatype.NS.XSD.decimal
]
@rdf_type RDF.type
@rdf_nil RDF.nil
# Defines rdf:type of subjects to be serialized at the beginning of the encoded graph
@top_classes [RDF.NS.RDFS.Class] |> Enum.map(&RDF.iri/1)
# Defines order of predicates at the beginning of a resource description
@predicate_order [RDF.type, RDF.NS.RDFS.label, RDF.iri("http://purl.org/dc/terms/title")]
@ordered_properties MapSet.new(@predicate_order)
@impl RDF.Serialization.Encoder
def encode(data, opts \\ []) do
with base = Keyword.get(opts, :base) |> init_base(),
prefixes = Keyword.get(opts, :prefixes, %{}) |> init_prefixes(),
{:ok, state} = State.start_link(data, base, prefixes) do
try do
State.preprocess(state)
{:ok,
base_directive(base) <>
prefix_directives(prefixes) <>
graph_statements(state)
}
after
State.stop(state)
end
end
end
defp init_base(nil), do: nil
defp init_base(base) do
with base = to_string(base) do
if String.ends_with?(base, ~w[/ #]) do
{:ok, base}
else
IO.warn("invalid base: #{base}")
{:bad, base}
end
end
end
defp init_prefixes(nil), do: %{}
defp init_prefixes(prefixes) do
Enum.reduce prefixes, %{}, fn {prefix, iri}, reverse ->
Map.put(reverse, RDF.iri(iri), to_string(prefix))
end
end
defp base_directive(nil), do: ""
defp base_directive({_, base}), do: "@base <#{base}> .\n"
defp prefix_directive({ns, prefix}), do: "@prefix #{prefix}: <#{to_string(ns)}> .\n"
defp prefix_directives(prefixes) do
case Enum.map(prefixes, &prefix_directive/1) do
[] -> ""
prefixes -> Enum.join(prefixes, "") <> "\n"
end
end
defp graph_statements(state) do
State.data(state)
|> RDF.Data.descriptions
|> order_descriptions(state)
|> Enum.map(&description_statements(&1, state))
|> Enum.reject(&is_nil/1)
|> Enum.join("\n")
end
defp order_descriptions(descriptions, state) do
base_iri = State.base_iri(state)
group =
Enum.group_by descriptions, fn
%Description{subject: ^base_iri} ->
:base
description ->
with types when not is_nil(types) <- description.predications[@rdf_type] do
Enum.find @top_classes, :other, fn top_class ->
Map.has_key?(types, top_class)
end
else
_ -> :other
end
end
ordered_descriptions = (
@top_classes
|> Stream.map(fn top_class -> group[top_class] end)
|> Stream.reject(&is_nil/1)
|> Stream.map(&sort_description_group/1)
|> Enum.reduce([], fn class_group, ordered_descriptions ->
ordered_descriptions ++ class_group
end)
) ++ (group |> Map.get(:other, []) |> sort_description_group())
case group[:base] do
[base] -> [base | ordered_descriptions]
_ -> ordered_descriptions
end
end
defp sort_description_group(descriptions) do
Enum.sort descriptions, fn
%Description{subject: %IRI{}}, %Description{subject: %BlankNode{}} -> true
%Description{subject: %BlankNode{}}, %Description{subject: %IRI{}} -> false
%Description{subject: s1}, %Description{subject: s2} ->
to_string(s1) < to_string(s2)
end
end
defp description_statements(description, state, nesting \\ 0) do
with %BlankNode{} <- description.subject,
ref_count when ref_count < 2 <-
State.bnode_ref_counter(state, description.subject)
do
unrefed_bnode_subject_term(description, ref_count, state, nesting)
else
_ -> full_description_statements(description, state, nesting)
end
end
defp full_description_statements(subject, description, state, nesting) do
with nesting = nesting + @indentation do
subject <> newline_indent(nesting) <> (
predications(description, state, nesting)
) <> " .\n"
end
end
defp full_description_statements(description, state, nesting) do
term(description.subject, state, :subject, nesting)
|> full_description_statements(description, state, nesting)
end
defp blank_node_property_list(description, state, nesting) do
with indented = nesting + @indentation do
"[" <> newline_indent(indented) <>
predications(description, state, indented) <>
newline_indent(nesting) <> "]"
end
end
defp predications(description, state, nesting) do
description.predications
|> order_predications()
|> Enum.map(&predication(&1, state, nesting))
|> Enum.join(" ;" <> newline_indent(nesting))
end
defp order_predications(predications) do
sorted_predications =
@predicate_order
|> Enum.map(fn predicate -> {predicate, predications[predicate]} end)
|> Enum.reject(fn {_, objects} -> is_nil(objects) end)
unsorted_predications =
Enum.reject(predications, fn {predicate, _} ->
MapSet.member?(@ordered_properties, predicate)
end)
sorted_predications ++ unsorted_predications
end
defp predication({predicate, objects}, state, nesting) do
term(predicate, state, :predicate, nesting) <> " " <> (
objects
|> Enum.map(fn {object, _} -> term(object, state, :object, nesting) end)
|> Enum.join(", ") # TODO: split if the line gets too long
)
end
defp unrefed_bnode_subject_term(bnode_description, ref_count, state, nesting) do
if valid_list_node?(bnode_description.subject, state) do
case ref_count do
0 ->
bnode_description.subject
|> list_term(state, nesting)
|> full_description_statements(
list_subject_description(bnode_description), state, nesting)
1 ->
nil
_ ->
raise "Internal error: This shouldn't happen. Please raise an issue in the RDF.ex project with the input document causing this error."
end
else
case ref_count do
0 ->
blank_node_property_list(bnode_description, state, nesting) <> " .\n"
1 ->
nil
_ ->
raise "Internal error: This shouldn't happen. Please raise an issue in the RDF.ex project with the input document causing this error."
end
end
end
defp list_subject_description(description) do
with description = Description.delete_predicates(description, [RDF.first, RDF.rest]) do
if Enum.count(description.predications) == 0 do
# since the Turtle grammar doesn't allow bare lists, we add a statement
description |> RDF.type(RDF.List)
else
description
end
end
end
defp unrefed_bnode_object_term(bnode, ref_count, state, nesting) do
if valid_list_node?(bnode, state) do
list_term(bnode, state, nesting)
else
if ref_count == 1 do
State.data(state)
|> RDF.Data.description(bnode)
|> blank_node_property_list(state, nesting)
else
raise "Internal error: This shouldn't happen. Please raise an issue in the RDF.ex project with the input document causing this error."
end
end
end
defp valid_list_node?(bnode, state) do
MapSet.member?(State.list_nodes(state), bnode)
end
defp list_term(head, state, nesting) do
head
|> State.list_values(state)
|> term(state, :list, nesting)
end
defp term(@rdf_type, _, :predicate, _), do: "a"
defp term(@rdf_nil, _, _, _), do: "()"
defp term(%IRI{} = iri, state, _, _) do
based_name(iri, State.base(state)) ||
prefixed_name(iri, State.prefixes(state)) ||
"<#{to_string(iri)}>"
end
defp term(%BlankNode{} = bnode, state, position, nesting)
when position in ~w[object list]a do
if (ref_count = State.bnode_ref_counter(state, bnode)) <= 1 do
unrefed_bnode_object_term(bnode, ref_count, state, nesting)
else
to_string(bnode)
end
end
defp term(%BlankNode{} = bnode, _, _, _),
do: to_string(bnode)
defp term(%Literal{value: value, language: language}, _,_ , _) when not is_nil(language),
do: ~s["#{value}"@#{language}]
defp term(%Literal{value: value, language: language}, _,_ , _) when not is_nil(language),
do: ~s["#{value}"@#{language}]
defp term(%Literal{datatype: datatype} = literal, _, _,_) when is_xsd_string(datatype),
do: literal |> Literal.lexical |> quoted()
defp term(%Literal{datatype: datatype} = literal, state, _, nesting)
when datatype in @native_supported_datatypes do
if Literal.valid?(literal) do
literal |> Literal.canonical |> Literal.lexical
else
typed_literal_term(literal, state, nesting)
end
end
defp term(%Literal{} = literal, state, _, nesting),
do: typed_literal_term(literal, state, nesting)
defp term(list, state, _, nesting) when is_list(list) do
"(" <>
(
list
|> Enum.map(&term(&1, state, :list, nesting))
|> Enum.join(" ")
) <>
")"
end
defp based_name(%IRI{} = iri, base), do: based_name(to_string(iri), base)
defp based_name(iri, {:ok, base}) do
if String.starts_with?(iri, base) do
"<#{String.slice(iri, String.length(base)..-1)}>"
end
end
defp based_name(_, _), do: nil
defp typed_literal_term(%Literal{datatype: datatype} = literal, state, nesting),
do: ~s["#{Literal.lexical(literal)}"^^#{term(datatype, state, :datatype, nesting)}]
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
end
defp quoted(string) do
if String.contains?(string, ["\n", "\r"]) do
~s["""#{string}"""]
else
~s["#{escape(string)}"]
end
end
defp escape(string) do
string
|> String.replace("\\", "\\\\\\\\")
|> String.replace("\b", "\\b")
|> String.replace("\f", "\\f")
|> String.replace("\t", "\\t")
|> String.replace("\n", "\\n")
|> String.replace("\r", "\\r")
|> String.replace("\"", ~S[\"])
end
defp newline_indent(nesting),
do: "\n" <> String.duplicate(@indentation_char, nesting)
end