linked-data-core 0.2.3

Core library for Linked Data crates
Documentation 
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use oxiri::Iri;
use snafu::ResultExt;
use syn::spanned::Spanned;

use crate::attributes::ast::VariantAttribute;
use crate::attributes::parse_ld_attributes;
use crate::prefix_mappings::PrefixMappings;
use crate::{Error, InvalidMappingSnafu};

pub struct RdfVariantAttributes {
  pub predicate_path: PredicatePath,
}

pub enum PredicatePath {
  // Represents a path with an intermediate blank node
  // :s <to_blank> _:blank .
  // _:blank <from_blank> :o .
  ChainedPath {
    to_blank: Iri<String>,
    from_blank: Iri<String>,
  },

  // For the direct case:
  // :s :predicate :o .
  Predicate(Iri<String>),
}

impl RdfVariantAttributes {
  pub fn try_from_attrs(
    variant: &syn::Variant,
    inner_attrs: Vec<syn::Attribute>,
    outer_attrs: Vec<syn::Attribute>,
    prefix_mappings: &PrefixMappings,
  ) -> Result<Self, Error> {
    let inner_attrs: Vec<VariantAttribute> = parse_ld_attributes(&inner_attrs)?;
    let outer_attrs: Vec<VariantAttribute> = parse_ld_attributes(&outer_attrs)?;

    let unpack_variant_attrs = |attrs: &[VariantAttribute]| -> Result<Option<Iri<String>>, Error> {
      if let Some(VariantAttribute::Iri(iri)) = attrs.get(1) {
        Err(Error::MultipleIris { span: iri.span() })
      } else {
        attrs
          .first()
          .map(|variant_attr| match variant_attr {
            VariantAttribute::Iri(lit_str) => lit_str,
          })
          .map(|lit_str| {
            prefix_mappings
              .expand(lit_str.value())
              .context(InvalidMappingSnafu {
                span: lit_str.span(),
              })
          })
          .transpose()
      }
    };

    let inner_attr = unpack_variant_attrs(&inner_attrs)?;
    let outer_attr = unpack_variant_attrs(&outer_attrs)?;

    match (inner_attr, outer_attr) {
      (None, None) => Err(Error::MissingIriAttribute {
        span: variant.span(),
      }),
      (None, Some(outer_iri)) => Ok(RdfVariantAttributes {
        predicate_path: PredicatePath::Predicate(outer_iri),
      }),
      (Some(inner_iri), None) => Ok(RdfVariantAttributes {
        predicate_path: PredicatePath::Predicate(inner_iri),
      }),
      (Some(to_blank), Some(from_blank)) => Ok(RdfVariantAttributes {
        predicate_path: PredicatePath::ChainedPath {
          to_blank,
          from_blank,
        },
      }),
    }
  }
}