oxigraph/lib/src/io/write.rs

//! Utilities to write RDF graphs and datasets.

use crate::io::{DatasetFormat, GraphFormat};
use crate::model::*;
use oxttl::nquads::{NQuadsSerializer, ToWriteNQuadsWriter};
use oxttl::ntriples::{NTriplesSerializer, ToWriteNTriplesWriter};
use oxttl::trig::{ToWriteTriGWriter, TriGSerializer};
use oxttl::turtle::{ToWriteTurtleWriter, TurtleSerializer};
use rio_api::formatter::TriplesFormatter;
use rio_api::model as rio;
use rio_xml::RdfXmlFormatter;
use std::io::{self, Write};

/// A serializer for RDF graph serialization formats.
///
/// It currently supports the following formats:
/// * [N-Triples](https://www.w3.org/TR/n-triples/) ([`GraphFormat::NTriples`])
/// * [Turtle](https://www.w3.org/TR/turtle/) ([`GraphFormat::Turtle`])
/// * [RDF/XML](https://www.w3.org/TR/rdf-syntax-grammar/) ([`GraphFormat::RdfXml`])
///
/// ```
/// use oxigraph::io::{GraphFormat, GraphSerializer};
/// use oxigraph::model::*;
///
/// let mut buffer = Vec::new();
/// let mut writer = GraphSerializer::from_format(GraphFormat::NTriples).triple_writer(&mut buffer)?;
/// writer.write(&Triple {
///    subject: NamedNode::new("http://example.com/s")?.into(),
///    predicate: NamedNode::new("http://example.com/p")?,
///    object: NamedNode::new("http://example.com/o")?.into()
/// })?;
/// writer.finish()?;
///
///assert_eq!(buffer.as_slice(), "<http://example.com/s> <http://example.com/p> <http://example.com/o> .\n".as_bytes());
/// # Result::<_,Box<dyn std::error::Error>>::Ok(())
/// ```
pub struct GraphSerializer {
    format: GraphFormat,
}

impl GraphSerializer {
    /// Builds a serializer for the given format
    #[inline]
    pub fn from_format(format: GraphFormat) -> Self {
        Self { format }
    }

    /// Returns a [`TripleWriter`] allowing writing triples into the given [`Write`] implementation
    pub fn triple_writer<W: Write>(&self, writer: W) -> io::Result<TripleWriter<W>> {
        Ok(TripleWriter {
            formatter: match self.format {
                GraphFormat::NTriples => {
                    TripleWriterKind::NTriples(NTriplesSerializer::new().serialize_to_write(writer))
                }
                GraphFormat::Turtle => {
                    TripleWriterKind::Turtle(TurtleSerializer::new().serialize_to_write(writer))
                }
                GraphFormat::RdfXml => TripleWriterKind::RdfXml(RdfXmlFormatter::new(writer)?),
            },
        })
    }
}

/// Allows writing triples.
/// Could be built using a [`GraphSerializer`].
///
/// Warning: Do not forget to run the [`finish`](TripleWriter::finish()) method to properly write the last bytes of the file.
///
/// ```
/// use oxigraph::io::{GraphFormat, GraphSerializer};
/// use oxigraph::model::*;
///
/// let mut buffer = Vec::new();
/// let mut writer = GraphSerializer::from_format(GraphFormat::NTriples).triple_writer(&mut buffer)?;
/// writer.write(&Triple {
///    subject: NamedNode::new("http://example.com/s")?.into(),
///    predicate: NamedNode::new("http://example.com/p")?,
///    object: NamedNode::new("http://example.com/o")?.into()
/// })?;
/// writer.finish()?;
///
///assert_eq!(buffer.as_slice(), "<http://example.com/s> <http://example.com/p> <http://example.com/o> .\n".as_bytes());
/// # Result::<_,Box<dyn std::error::Error>>::Ok(())
/// ```
#[must_use]
pub struct TripleWriter<W: Write> {
    formatter: TripleWriterKind<W>,
}

enum TripleWriterKind<W: Write> {
    NTriples(ToWriteNTriplesWriter<W>),
    Turtle(ToWriteTurtleWriter<W>),
    RdfXml(RdfXmlFormatter<W>),
}

impl<W: Write> TripleWriter<W> {
    /// Writes a triple
    pub fn write<'a>(&mut self, triple: impl Into<TripleRef<'a>>) -> io::Result<()> {
        match &mut self.formatter {
            TripleWriterKind::NTriples(writer) => writer.write_triple(triple),
            TripleWriterKind::Turtle(writer) => writer.write_triple(triple),
            TripleWriterKind::RdfXml(formatter) => {
                let triple = triple.into();
                formatter.format(&rio::Triple {
                    subject: match triple.subject {
                        SubjectRef::NamedNode(node) => rio::NamedNode { iri: node.as_str() }.into(),
                        SubjectRef::BlankNode(node) => rio::BlankNode { id: node.as_str() }.into(),
                        SubjectRef::Triple(_) => {
                            return Err(io::Error::new(
                                io::ErrorKind::InvalidInput,
                                "RDF/XML does not support RDF-star yet",
                            ))
                        }
                    },
                    predicate: rio::NamedNode {
                        iri: triple.predicate.as_str(),
                    },
                    object: match triple.object {
                        TermRef::NamedNode(node) => rio::NamedNode { iri: node.as_str() }.into(),
                        TermRef::BlankNode(node) => rio::BlankNode { id: node.as_str() }.into(),
                        TermRef::Literal(literal) => if literal.is_plain() {
                            if let Some(language) = literal.language() {
                                rio::Literal::LanguageTaggedString {
                                    value: literal.value(),
                                    language,
                                }
                            } else {
                                rio::Literal::Simple {
                                    value: literal.value(),
                                }
                            }
                        } else {
                            rio::Literal::Typed {
                                value: literal.value(),
                                datatype: rio::NamedNode {
                                    iri: literal.datatype().as_str(),
                                },
                            }
                        }
                        .into(),
                        TermRef::Triple(_) => {
                            return Err(io::Error::new(
                                io::ErrorKind::InvalidInput,
                                "RDF/XML does not support RDF-star yet",
                            ))
                        }
                    },
                })
            }
        }
    }

    /// Writes the last bytes of the file
    pub fn finish(self) -> io::Result<()> {
        match self.formatter {
            TripleWriterKind::NTriples(writer) => writer.finish().flush(),
            TripleWriterKind::Turtle(writer) => writer.finish()?.flush(),
            TripleWriterKind::RdfXml(formatter) => formatter.finish()?.flush(), //TODO: remove flush when the next version of Rio is going to be released
        }
    }
}

/// A serializer for RDF graph serialization formats.
///
/// It currently supports the following formats:
/// * [N-Quads](https://www.w3.org/TR/n-quads/) ([`DatasetFormat::NQuads`])
/// * [TriG](https://www.w3.org/TR/trig/) ([`DatasetFormat::TriG`])
///
/// ```
/// use oxigraph::io::{DatasetFormat, DatasetSerializer};
/// use oxigraph::model::*;
///
/// let mut buffer = Vec::new();
/// let mut writer = DatasetSerializer::from_format(DatasetFormat::NQuads).quad_writer(&mut buffer);
/// writer.write(&Quad {
///    subject: NamedNode::new("http://example.com/s")?.into(),
///    predicate: NamedNode::new("http://example.com/p")?,
///    object: NamedNode::new("http://example.com/o")?.into(),
///    graph_name: NamedNode::new("http://example.com/g")?.into(),
/// })?;
/// writer.finish()?;
///
///assert_eq!(buffer.as_slice(), "<http://example.com/s> <http://example.com/p> <http://example.com/o> <http://example.com/g> .\n".as_bytes());
/// # Result::<_,Box<dyn std::error::Error>>::Ok(())
/// ```
pub struct DatasetSerializer {
    format: DatasetFormat,
}

impl DatasetSerializer {
    /// Builds a serializer for the given format
    #[inline]
    pub fn from_format(format: DatasetFormat) -> Self {
        Self { format }
    }

    /// Returns a [`QuadWriter`] allowing writing triples into the given [`Write`] implementation
    pub fn quad_writer<W: Write>(&self, writer: W) -> QuadWriter<W> {
        QuadWriter {
            formatter: match self.format {
                DatasetFormat::NQuads => {
                    QuadWriterKind::NQuads(NQuadsSerializer::new().serialize_to_write(writer))
                }
                DatasetFormat::TriG => {
                    QuadWriterKind::TriG(TriGSerializer::new().serialize_to_write(writer))
                }
            },
        }
    }
}

/// Allows writing triples.
/// Could be built using a [`DatasetSerializer`].
///
/// Warning: Do not forget to run the [`finish`](QuadWriter::finish()) method to properly write the last bytes of the file.
///
/// ```
/// use oxigraph::io::{DatasetFormat, DatasetSerializer};
/// use oxigraph::model::*;
///
/// let mut buffer = Vec::new();
/// let mut writer = DatasetSerializer::from_format(DatasetFormat::NQuads).quad_writer(&mut buffer);
/// writer.write(&Quad {
///    subject: NamedNode::new("http://example.com/s")?.into(),
///    predicate: NamedNode::new("http://example.com/p")?,
///    object: NamedNode::new("http://example.com/o")?.into(),
///    graph_name: NamedNode::new("http://example.com/g")?.into(),
/// })?;
/// writer.finish()?;
///
///assert_eq!(buffer.as_slice(), "<http://example.com/s> <http://example.com/p> <http://example.com/o> <http://example.com/g> .\n".as_bytes());
/// # Result::<_,Box<dyn std::error::Error>>::Ok(())
/// ```
#[must_use]
pub struct QuadWriter<W: Write> {
    formatter: QuadWriterKind<W>,
}

enum QuadWriterKind<W: Write> {
    NQuads(ToWriteNQuadsWriter<W>),
    TriG(ToWriteTriGWriter<W>),
}

impl<W: Write> QuadWriter<W> {
    /// Writes a quad
    pub fn write<'a>(&mut self, quad: impl Into<QuadRef<'a>>) -> io::Result<()> {
        match &mut self.formatter {
            QuadWriterKind::NQuads(writer) => writer.write_quad(quad),
            QuadWriterKind::TriG(writer) => writer.write_quad(quad),
        }
    }

    /// Writes the last bytes of the file
    pub fn finish(self) -> io::Result<()> {
        match self.formatter {
            QuadWriterKind::NQuads(writer) => writer.finish().flush(),
            QuadWriterKind::TriG(writer) => writer.finish()?.flush(),
        }
    }
}