goose 0.19.1

use crate::metrics::NullableFloat;
use std::fmt::{Debug, Display, Formatter, Write};

/// A value that can be used to provide a delta
///
/// As the actual value can be an unsigned type, we require an associated type which defines the
/// type of the delta.
pub trait DeltaValue: Copy + Debug + Display {
    type Delta: Copy + Display;

    /// Generate the delta between this and the provided value
    fn delta(self, value: Self) -> Self::Delta;

    /// True if the delta is zero or positive (used for formatting with a `+` prefix)
    fn is_delta_non_negative(value: Self::Delta) -> bool;
}

impl DeltaValue for usize {
    type Delta = isize;

    fn delta(self, value: Self) -> Self::Delta {
        let delta = (self as i128) - (value as i128);
        delta.clamp(isize::MIN as i128, isize::MAX as i128) as isize
    }

    fn is_delta_non_negative(value: Self::Delta) -> bool {
        !value.is_negative()
    }
}

impl DeltaValue for f32 {
    type Delta = f32;

    fn delta(self, value: Self) -> Self::Delta {
        self - value
    }

    fn is_delta_non_negative(value: Self::Delta) -> bool {
        value >= 0.0
    }
}

impl DeltaValue for u64 {
    type Delta = i64;

    fn delta(self, value: Self) -> Self::Delta {
        let delta = (self as i128) - (value as i128);
        delta.clamp(i64::MIN as i128, i64::MAX as i128) as i64
    }

    fn is_delta_non_negative(value: Self::Delta) -> bool {
        !value.is_negative()
    }
}

impl DeltaValue for u16 {
    type Delta = i16;

    fn delta(self, value: Self) -> Self::Delta {
        let delta = self as i32 - value as i32;
        delta.clamp(i16::MIN as i32, i16::MAX as i32) as i16
    }

    fn is_delta_non_negative(value: Self::Delta) -> bool {
        !value.is_negative()
    }
}

impl DeltaValue for f64 {
    type Delta = f64;

    fn delta(self, value: Self) -> Self::Delta {
        self - value
    }

    fn is_delta_non_negative(value: Self::Delta) -> bool {
        value >= 0.0
    }
}

/// A value, being either a plain value or a value with delta to a baseline.
///
/// Serialization always writes just the inner value (stripping deltas), so JSON
/// reports have the same format regardless of whether `--baseline-file` was used.
/// This ensures reports can always be loaded as baselines for future runs.
#[derive(Copy, Clone, Debug, serde::Deserialize, PartialEq)]
#[serde(untagged)]
pub enum Value<T: DeltaValue> {
    Plain(T),
    Delta { value: T, delta: T::Delta },
}

impl<T: DeltaValue + serde::Serialize> serde::Serialize for Value<T> {
    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        self.value().serialize(serializer)
    }
}

impl<T: DeltaValue> From<T> for Value<T> {
    fn from(value: T) -> Self {
        Self::Plain(value)
    }
}

impl From<f32> for Value<NullableFloat> {
    fn from(value: f32) -> Self {
        Self::Plain(NullableFloat::from(value))
    }
}

impl From<f64> for Value<NullableFloat> {
    fn from(value: f64) -> Self {
        Self::Plain(NullableFloat(value))
    }
}

impl<T: DeltaValue> Value<T> {
    pub fn value(&self) -> T {
        match self {
            Self::Plain(value) | Self::Delta { value, .. } => *value,
        }
    }

    pub fn diff(&mut self, other: T) {
        let value = self.value();
        *self = Self::Delta {
            value,
            delta: value.delta(other),
        };
    }
}

pub trait ApplyBaseline<T: DeltaValue> {
    fn eval(&mut self, other: Self);
}

impl<T: DeltaValue> ApplyBaseline<T> for Value<T> {
    fn eval(&mut self, other: Self) {
        self.diff(other.value())
    }
}

impl<T: DeltaValue> ApplyBaseline<T> for Option<Value<T>> {
    fn eval(&mut self, other: Self) {
        if let (Some(value), Some(other)) = (self, other) {
            value.eval(other);
        }
    }
}

impl<T: DeltaValue> Display for Value<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Plain(value) => Display::fmt(value, f),
            Self::Delta { value, delta } => {
                // we can pass on the actual value
                Display::fmt(value, f)?;

                // format delta as `({delta:+})`, keeping the actual format options
                f.write_str(" (")?;

                // for the delta, we want a plus sign for non-negative values (including zero)
                if T::is_delta_non_negative(*delta) {
                    f.write_char('+')?;
                }
                Display::fmt(delta, f)?;

                f.write_char(')')?;

                // done
                Ok(())
            }
        }
    }
}

/// A trait for types that can have baseline deltas applied to them.
///
/// This is implemented by metric structs (e.g. `RequestMetric`, `ResponseMetric`)
/// to allow correlating current metrics with baseline metrics and computing deltas.
pub trait DeltaTo {
    fn delta_to(&mut self, other: &Self);
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::metrics::Value;
    #[test]
    fn eval_optional() {
        assert_eq!(
            {
                let mut value = Some(Value::Plain(10usize));
                value.eval(Some(Value::Plain(5usize)));
                value
            },
            Some(Value::Delta {
                value: 10usize,
                delta: 5isize
            })
        );

        assert_eq!(
            {
                let mut value: Option<Value<usize>> = None;
                value.eval(Some(Value::Plain(5usize)));
                value
            },
            None
        );
    }

    #[test]
    fn delta_to_string() {
        assert_eq!(format!("{}", 0usize.delta(10usize)), "-10");
        assert_eq!(format!("{}", 10usize.delta(10usize)), "0");
        assert_eq!(format!("{}", 10usize.delta(0usize)), "10");
    }

    #[test]
    fn value_to_string() {
        fn value<T: DeltaValue>(value: T, baseline: T) -> Value<T> {
            let mut result = Value::from(value);
            result.diff(baseline);
            result
        }

        assert_eq!(format!("{}", value(0usize, 1000usize)), "0 (-1000)");
        assert_eq!(format!("{}", value(1000usize, 1000usize)), "1000 (+0)");
        assert_eq!(format!("{}", value(1000usize, 0usize)), "1000 (+1000)");
    }

    #[test]
    fn delta_value_f32() {
        assert_eq!(100.0f32.delta(50.0f32), 50.0f32);
        assert_eq!(50.0f32.delta(100.0f32), -50.0f32);
        assert_eq!(0.0f32.delta(0.0f32), 0.0f32);
        assert!(f32::is_delta_non_negative(1.0));
        assert!(f32::is_delta_non_negative(0.0));
        assert!(!f32::is_delta_non_negative(-1.0));
    }

    #[test]
    fn delta_value_f64() {
        assert_eq!(100.0f64.delta(50.0f64), 50.0f64);
        assert_eq!(50.0f64.delta(100.0f64), -50.0f64);
    }

    #[test]
    fn delta_value_u64() {
        assert_eq!(100u64.delta(50u64), 50i64);
        assert_eq!(50u64.delta(100u64), -50i64);
        assert_eq!(u64::MAX.delta(0u64), i64::MAX); // clamps
        assert_eq!(0u64.delta(u64::MAX), i64::MIN); // clamps
    }

    #[test]
    fn delta_value_u16() {
        assert_eq!(100u16.delta(50u16), 50i16);
        assert_eq!(50u16.delta(100u16), -50i16);
        assert_eq!(u16::MAX.delta(0u16), i16::MAX); // clamps, not overflow
        assert_eq!(0u16.delta(u16::MAX), i16::MIN); // clamps, not overflow
    }

    #[test]
    fn delta_value_nullable_float() {
        use crate::metrics::NullableFloat;
        let a = NullableFloat(100.0);
        let b = NullableFloat(60.0);
        assert_eq!(a.delta(b), 40.0f64);
        assert_eq!(b.delta(a), -40.0f64);
    }

    #[test]
    fn value_serde_round_trip() {
        // Plain value round-trips as itself
        let plain = Value::Plain(42usize);
        let json = serde_json::to_string(&plain).unwrap();
        assert_eq!(json, "42");
        let deserialized: Value<usize> = serde_json::from_str(&json).unwrap();
        assert_eq!(deserialized, plain);

        // Delta value serializes as just the inner value (deltas are stripped)
        let delta = Value::Delta {
            value: 100usize,
            delta: 50isize,
        };
        let json = serde_json::to_string(&delta).unwrap();
        assert_eq!(json, "100");
        // Deserializes back as Plain since the delta was stripped
        let deserialized: Value<usize> = serde_json::from_str(&json).unwrap();
        assert_eq!(deserialized, Value::Plain(100usize));
    }
}