numbers-le 0.2.0

//! Numbers in free-form text, for a format nothing here parses.
//!
//! **It has no grammar, and that shows.** `v1.2.3` reads as `1.2` and
//! `0.3`, because a scan with no parser cannot know a version string is
//! one token. That is what the extension does, and it is why this is now
//! reserved for prose: Markdown, a log, a plain-text file. A source
//! language goes to `source.rs`, which does have a grammar, because on a
//! source file this scan does not merely miss literals — it shreds them.

use std::sync::LazyLock;

use regex::Regex;

use super::policy::{Literal, plain_notation};

/// The extension's `TEXT_NUMBER_RE`: optional sign, digits, optional
/// point, optional exponent.
static TEXT_NUMBER: LazyLock<Regex> = LazyLock::new(|| {
    Regex::new(r"[+-]?(?:\d+(?:\.\d*)?|\.\d+)(?:[eE][+-]?\d+)?")
        .expect("a constant pattern compiles")
});

pub(crate) fn extract(text: &str) -> Vec<Literal> {
    spanned(text)
        .into_iter()
        .map(|(literal, _)| literal)
        .collect()
}

/// The numbers, each with the byte offset of the run that produced it.
/// A scan already knows where it matched, so the fallback places its
/// values for free.
pub(crate) fn spanned(text: &str) -> Vec<(Literal, usize)> {
    TEXT_NUMBER
        .find_iter(text)
        .filter_map(|found| {
            found
                .as_str()
                .parse::<f64>()
                .ok()
                .filter(|value| value.is_finite())
                .map(|value| {
                    (
                        Literal {
                            value,
                            notation: plain_notation(found.as_str()),
                        },
                        found.start(),
                    )
                })
        })
        .collect()
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::extract::policy::Notation;

    fn values(text: &str) -> Vec<f64> {
        extract(text)
            .into_iter()
            .map(|literal| literal.value)
            .collect()
    }

    #[test]
    fn plain_numbers_are_found() {
        assert_eq!(values("rate 0.0825 on 1000 units"), [0.0825, 1000.0]);
    }

    #[test]
    fn signs_and_exponents_are_read() {
        assert_eq!(values("offset -7e2 and +3"), [-700.0, 3.0]);
    }

    /// The scan reads its own runs, so it keeps what the text said.
    #[test]
    fn a_run_carries_the_notation_it_was_written_in() {
        let notations: Vec<Notation> = extract("-7e2 and 3")
            .into_iter()
            .map(|literal| literal.notation)
            .collect();
        assert_eq!(notations, [Notation::Scientific, Notation::Decimal]);
    }

    /// Ported behaviour, not an oversight. Written down because it is
    /// the first thing anyone will report as a bug — and the reason a
    /// source file no longer comes here.
    #[test]
    fn a_version_string_has_no_grammar_to_protect_it() {
        assert_eq!(values("v1.2.3"), [1.2, 0.3]);
        assert_eq!(values("3.16.15"), [3.16, 0.15]);
    }

    #[test]
    fn text_without_numbers_yields_nothing() {
        assert!(values("no numbers on this line at all").is_empty());
    }

    #[test]
    fn a_span_points_at_the_run() {
        let text = "rate 0.0825 here";
        let (literal, offset) = spanned(text)[0];
        assert_eq!(literal.value, 0.0825);
        assert_eq!(&text[offset..offset + 6], "0.0825");
    }

    /// An overflowing literal is infinity, and infinity is not a number
    /// this tool emits.
    #[test]
    fn an_overflowing_run_is_dropped() {
        assert!(values("1e400").is_empty());
    }
}