tools/graph/src/language.rs

use oxigraph::model::{Literal, TermRef};
use oxilangtag::LanguageTag;
use spargebra::algebra::{Expression, Function, GraphPattern};
use spargebra::term::Variable;
use std::sync::LazyLock;

pub static ENGLISH_TAG: LazyLock<LanguageTag<String>> =
    LazyLock::new(|| LanguageTag::parse("en".to_string()).unwrap());

pub static ENGLISH_OR_UNTAGGED: LazyLock<LanguageCondition> =
    LazyLock::new(|| LanguageCondition::ExactMatchOrUntagged(ENGLISH_TAG.clone()));

#[derive(Clone, Debug)]
pub enum LanguageCondition {
    ExactMatchOnly(LanguageTag<String>),
    ExactMatchOrUntagged(LanguageTag<String>),
    UntaggedOnly,
    AnyOrNone,
}

impl LanguageCondition {
    pub fn primary_matches_term<'a>(&self, term: impl Into<TermRef<'a>>) -> bool {
        if let TermRef::Literal(literal) = term.into() {
            let tag = literal
                .language()
                .map(LanguageTag::parse_and_normalize)
                .and_then(Result::ok);

            match (tag, self) {
                (Some(language), LanguageCondition::ExactMatchOnly(expectation))
                | (Some(language), LanguageCondition::ExactMatchOrUntagged(expectation)) => {
                    language.primary_language() == expectation.primary_language()
                }
                (None, LanguageCondition::ExactMatchOrUntagged(_)) => true,
                (None, LanguageCondition::UntaggedOnly) => true,
                (_, LanguageCondition::AnyOrNone) => true,
                _ => false,
            }
        } else {
            false
        }
    }

    pub fn primary_language(&self) -> Option<&str> {
        match self {
            LanguageCondition::ExactMatchOnly(tag) => Some(tag.primary_language()),
            LanguageCondition::ExactMatchOrUntagged(tag) => Some(tag.primary_language()),
            _ => None,
        }
    }

    pub fn filter(&self, variable: impl Into<String>) -> String {
        let variable = variable.into();

        let exact = |language: &LanguageTag<String>| {
            Expression::FunctionCall(
                Function::LangMatches,
                vec![
                    Expression::FunctionCall(
                        Function::Lang,
                        vec![Expression::Variable(Variable::new_unchecked(&variable))],
                    ),
                    Expression::Literal(Literal::new_simple_literal(language.to_string())),
                ],
            )
        };

        let untagged = Expression::Not(Box::new(Expression::FunctionCall(
            Function::HasLang,
            vec![Expression::Variable(Variable::new_unchecked(&variable))],
        )));

        match self {
            Self::ExactMatchOnly(language) => Some(exact(language)),
            Self::ExactMatchOrUntagged(language) => Some(Expression::Or(
                Box::new(exact(language)),
                Box::new(untagged),
            )),
            Self::UntaggedOnly => Some(untagged),
            Self::AnyOrNone => None,
        }
        .map(|expr| {
            GraphPattern::Filter {
                expr,
                inner: Box::new(GraphPattern::Bgp { patterns: vec![] }),
            }
            .to_string()
        })
        .unwrap_or_default()
    }
}