Add Parser concept

[cmdoret]

Currently, we have an Extractor class, whose job is to extract all metadata about a repository.
With #70 and #68, Extractor has the ability to list_files() present in a repository and access their contents.

Ideally, the responsibility of an extractor should stop there. It should not be responsible for extracting metadata from file contents.

The proposal here is to have a separate object responsible for it: Parser. A Parser would take a file as input and extract specific RDF triples from it. The Repo's RDF graph could then be enriched using the Parser graphs.

graph TD;
    repo[Repository URL]-->ext{Extractor};
    ext --> meta[Metadata];
    ext --> files[Files];
    meta --> repograph{Repository};
    repograph --> repo_rdf[Repo RDF];
    files --> parser{Parser};
    parser --> spec_rdf[Specific RDF];
    repo_rdf --> union((Union));
    spec_rdf --> union;
    union --> enhanced[Enhanced RDF];

Loading

Parsers could be added for pyproject.toml, setup.py, licenses, Cargo.toml, R's DESCRIPTION, package.json, etc...

[cmdoret]

A rough example of what the parser interface may look like. Each parser would only need to implement the parsing algorithm and the logic to define compatible resources.

class Parser(ABC):
    def __init__(self, max_size_kb: Optional[int]=2048):
        self.max_size = max_size

    @abstractmethod
    def _parse(self, input: Resource) -> rdflib.Graph:
        """Extract triples"""
        ...

    @abstractmethod
    def can_parse(self, input: Resource) -> bool:
        """Match based on filename (content and size?)"""
        ...

    def parse(self, input: Resource) -> Optional[rdflib.Graph]:
        if self.can_parse(input):
            return self._parse(input)
        return None

# Potentially more helper methods that will be available to all parsers