//! The leaf value type flowing through substitution and filters.

use std::fmt;

/// A leaf value: the result of resolving a `{{ path }}` before and after
/// filters run. Callers populate a [`crate::Substituter`] with these and read
/// them back out with `get`.
#[derive(Debug, Clone, PartialEq)]
pub enum Value {
    Int(i64),
    Float(f64),
    String(String),
}

impl Value {
    /// Coerce to `f64` for numeric filters. `Int` is widened; `String` returns `None`.
    pub fn as_f64(&self) -> Option<f64> {
        match self {
            Self::Int(n) => Some(*n as f64),
            Self::Float(x) => Some(*x),
            Self::String(_) => None,
        }
    }
}

impl fmt::Display for Value {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Int(n) => write!(f, "{n}"),
            Self::Float(x) => f.write_str(&format_float(*x)),
            Self::String(s) => f.write_str(s),
        }
    }
}

/// Format a float with up to 4 decimal places, trimming trailing zeros.
///
/// `22.0 -> "22"`, `0.59 -> "0.59"`, `0.0367 -> "0.0367"`, `61960.0 -> "61960"`.
fn format_float(x: f64) -> String {
    let s = format!("{x:.4}");
    let trimmed = s.trim_end_matches('0').trim_end_matches('.');
    trimmed.to_string()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn float_formatting_strips_trailing_zeros() {
        assert_eq!(format_float(22.0), "22");
        assert_eq!(format_float(0.59), "0.59");
        assert_eq!(format_float(61960.0), "61960");
        assert_eq!(format_float(0.5), "0.5");
        assert_eq!(format_float(1.085), "1.085");
    }

    #[test]
    fn as_f64_widens_int_and_rejects_string() {
        assert_eq!(Value::Int(5).as_f64(), Some(5.0));
        assert_eq!(Value::Float(1.5).as_f64(), Some(1.5));
        assert_eq!(Value::String("x".into()).as_f64(), None);
    }

    #[test]
    fn display_matches_format() {
        assert_eq!(Value::Int(580).to_string(), "580");
        assert_eq!(Value::Float(0.5).to_string(), "0.5");
        assert_eq!(Value::String("lifetime".into()).to_string(), "lifetime");
    }
}