feat(cognitarium): add support for triples serialization

contracts/okp4-cognitarium/src/rdf.rs

@@ -1,15 +1,23 @@
 use crate::msg::DataFormat;
 use cosmwasm_std::{StdError, StdResult};
+use rio_api::formatter::TriplesFormatter;
 use rio_api::model::{Quad, Triple};
 use rio_api::parser::{QuadsParser, TriplesParser};
-use rio_turtle::{NQuadsParser, NTriplesParser, TurtleError, TurtleParser};
-use rio_xml::{RdfXmlError, RdfXmlParser};
-use std::io::BufRead;
+use rio_turtle::{
+    NQuadsFormatter, NQuadsParser, NTriplesFormatter, NTriplesParser, TurtleError, TurtleFormatter,
+    TurtleParser,
+};
+use rio_xml::{RdfXmlError, RdfXmlFormatter, RdfXmlParser};
+use std::io::{self, BufRead};
 
 pub struct TripleReader<R: BufRead> {
     parser: TriplesParserKind<R>,
 }
 
+pub struct TripleWriter<W: std::io::Write> {
+    writer: TriplesWriterKind<W>,
+}
+
 #[allow(clippy::large_enum_variant)]
 pub enum TriplesParserKind<R: BufRead> {
     NTriples(NTriplesParser<R>),
@@ -18,6 +26,13 @@ pub enum TriplesParserKind<R: BufRead> {
     NQuads(NQuadsParser<R>),
 }
 
+pub enum TriplesWriterKind<W: std::io::Write> {
+    NTriples(NTriplesFormatter<W>),
+    Turtle(TurtleFormatter<W>),
+    RdfXml(io::Result<RdfXmlFormatter<W>>),
+    NQuads(NQuadsFormatter<W>),
+}
+
 impl<R: BufRead> TripleReader<R> {
     pub fn new(format: DataFormat, src: R) -> Self {
         TripleReader {
@@ -52,6 +67,68 @@ impl<R: BufRead> TripleReader<R> {
     }
 }
 
+impl<W: std::io::Write> TripleWriter<W> {
+    pub fn new(format: DataFormat, dst: W) -> Self {
+        TripleWriter {
+            writer: match format {
+                DataFormat::RDFXml => TriplesWriterKind::RdfXml(RdfXmlFormatter::new(dst)),
+                DataFormat::Turtle => TriplesWriterKind::Turtle(TurtleFormatter::new(dst)),
+                DataFormat::NTriples => TriplesWriterKind::NTriples(NTriplesFormatter::new(dst)),
+                DataFormat::NQuads => TriplesWriterKind::NQuads(NQuadsFormatter::new(dst)),
+            },
+        }
+    }
+
+    pub fn write(&mut self, triple: &Triple<'_>) -> io::Result<()> {
+        match &mut self.writer {
+            TriplesWriterKind::Turtle(formatter) => {
+                formatter.format(triple)
+            },
+            TriplesWriterKind::NTriples(formatter) => {
+                formatter.format(triple)
+            },
+            TriplesWriterKind::NQuads(formatter) => {
+                use rio_api::formatter::QuadsFormatter;
+
+                let quad = &Quad {
+                    subject: triple.subject,
+                    predicate: triple.predicate,
+                    object: triple.object,
+                    graph_name: None,
+                };
+
+                formatter.format(quad)
+            },
+            TriplesWriterKind::RdfXml(format_result) => {
+                match format_result {
+                    Ok(formatter) => formatter.format(triple),
+                    Err(e) => return Err(io::Error::new(io::ErrorKind::Other, e.to_string())),
+                }
+            },
+        }
+    }
+
+    #[allow(dead_code)]
+    pub fn write_all(&mut self, triples: Vec<&Triple<'_>>) -> io::Result<()> {
+        for triple in triples {
+            self.write(triple)?;
+        }
+        Ok(())
+    }
+
+    pub fn finish(self) -> io::Result<()> {
+        match self.writer {
+            TriplesWriterKind::Turtle(formatter) => formatter.finish(),
+            TriplesWriterKind::NTriples(formatter) => formatter.finish(),
+            TriplesWriterKind::NQuads(formatter) => formatter.finish(),
+            TriplesWriterKind::RdfXml(format_result) => match format_result {
+                Ok(formatter) => formatter.finish(),
+                Err(e) => Err(io::Error::new(io::ErrorKind::Other, e.to_string())),
+            },
+        }.map(|_| ())
+    }
+}
+
 pub fn explode_iri(iri: &str) -> StdResult<(String, String)> {
     let mut marker_index: Option<usize> = None;
     for delim in ['#', '/', ':'] {