nom-openmetrics 0.2.0

use crate::{parser::string, Label};
use nom::{
    bytes::complete::{take_while, take_while1},
    character::complete::char,
    combinator::{map, recognize},
    error::context,
    multi::separated_list0,
    sequence::{delimited, preceded, separated_pair},
    IResult, Parser,
};
use nom_language::error::VerboseError;

fn is_metric_label_start(c: char) -> bool {
    c.is_ascii_alphabetic() || c == '_'
}

fn is_metric_label_end(c: char) -> bool {
    c.is_ascii_alphanumeric() || c == '_'
}

/// Parse a `Label` for a metric
pub(crate) fn label(input: &str) -> IResult<&str, Label, VerboseError<&str>> {
    context(
        "label",
        map(
            separated_pair(metric_label, char('='), label_value),
            |(name, value)| Label { name, value },
        ),
    )
    .parse(input)
}

/// Parse `Label`s for a metric
pub(crate) fn labels(input: &str) -> IResult<&str, Vec<Label>, VerboseError<&str>> {
    context(
        "labels",
        delimited(char('{'), separated_list0(char(','), label), char('}')),
    )
    .parse(input)
}

fn label_value(input: &str) -> IResult<&str, String, VerboseError<&str>> {
    string::label(input)
}

/// Matches a metric name `[a-zA-Z_][a-zA-Z0-9_]*`
fn metric_label(input: &str) -> IResult<&str, &str, VerboseError<&str>> {
    context(
        "metric label",
        recognize(preceded(
            take_while1(is_metric_label_start),
            take_while(is_metric_label_end),
        )),
    )
    .parse(input)
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::test::parse;
    use nom_language::error::VerboseErrorKind;
    use rstest::rstest;

    #[rstest]
    #[case(r#"job="prometheus""#, Label::new("job", "prometheus".into()))]
    #[case(r#"job="☃""#, Label::new("job", "☃".into()))]
    fn label(#[case] input: &str, #[case] expected: Label<'_>) {
        use crate::test::parse;

        let (rest, label) = parse(super::label, input);

        assert_eq!(expected, label, "input: {input}");
        assert!(rest.is_empty());
    }

    #[rstest]
    #[case(
        r#"{job="prometheus",instance="scrape.example"}"#,
        vec![
            Label::new("job", "prometheus".into()),
            Label::new("instance", "scrape.example".into())
        ])]
    fn labels(#[case] input: &str, #[case] expected: Vec<Label<'_>>) {
        let (rest, labels) = parse(super::labels, input);

        assert_eq!(expected, labels, "input: {input}");
        assert!(rest.is_empty());
    }

    #[test]
    fn metric_label_error() {
        let input = "0";

        let Err(nom::Err::Error(error)) = metric_label(input) else {
            unreachable!("input {input} must error");
        };

        let (error_input, VerboseErrorKind::Context(kind)) = error.errors.last().unwrap() else {
            unreachable!("error kind mismatch for {error:?}");
        };

        assert_eq!(&"0", error_input);
        assert_eq!(&"metric label", kind);
    }

    #[rstest]
    #[case("A0", "", "A0")]
    #[case("__name__", "", "__name__")]
    #[case("a0", "", "a0")]
    #[case("name_0_more", "", "name_0_more")]
    #[case("rule:name", ":name", "rule")]
    #[case("up", "", "up")]
    #[case("up{", "{", "up")]
    fn metric_label_ok(
        #[case] input: &str,
        #[case] expected_rest: &str,
        #[case] expected_parsed: &str,
    ) {
        let (rest, parsed) = parse(super::metric_label, input);

        assert_eq!(
            expected_parsed, parsed,
            "parsed mismatch, expected {expected_parsed} got {parsed}"
        );
        assert_eq!(
            expected_rest, rest,
            "rest mismatch, expected {expected_rest} got {rest}"
        );
    }
}